Hypervirulent Klebsiella pneumoniae

Fecal Klebsiella pneumoniae Carriage Is Intermittent and of High Clonal Diversity

The Klebsiella pneumoniae complex comprises several closely related entities, which are ubiquitous in the natural environment, including in plants, animals, and humans. K. pneumoniae is the major species within this complex. K. pneumoniae strains are opportunistic pathogens and a common cause of healthcare-associated infections. K. pneumoniae can colonize the human gastrointestinal tract, which may become a reservoir for infection. The aim of this study was to investigate the fecal K. pneumoniae carriage in six healthy individuals during a 1 year period. Stool samples were obtained once a week. Using direct and pre-enriched cultures streaked on ampicillin-supplemented agar plates, up to eight individual colonies per positive sample were selected for further characterization. Whole genome sequencing (WGS) was performed for strain characterization. Sequence type (ST), core genome complex type (CT), K and O serotypes, virulence traits, antibiotic resistance profiles, and plasmids were extracted from WGS data. In total, 80 K. pneumoniae isolates were obtained from 48 positive cultures of 278 stool samples from five of the six test subjects. The samples of the five colonized volunteers yielded at most two, three, four (two persons), and five different strains, respectively. These 80 K. pneumoniae isolates belonged to 60 STs, including nine new STs; they were of 70 CTs, yielded 48 K serotypes, 11 O serotypes, and 39 wzc and 51 wzi alleles. Four of the five subjects harbored serotypes K20 and K47, as well as STs ST37, ST101, ST1265, and ST20, which had previously been linked to high-risk K. pneumoniae clones. In total, 25 genes conferring antibiotic resistance and 42 virulence genes were detected among all 80 isolates. Plasmids of 15 different types were found among 65 of the isolates. Fecal carriage of individual strains was of short duration: 70 strains were found on a single sampling day only, and 5 strains were isolated in samples collected over two consecutive weeks. Two of the five colonized individuals—working colleagues having meals together—shared identical K. pneumoniae types four times during the study period. Our findings point toward the potential role of food as a reservoir for K. pneumoniae in humans.

Co-occurrence of Rapid Gene Gain and Loss in an Interhospital Outbreak of Carbapenem-Resistant Hypervirulent ST11-K64 Klebsiella pneumoniae

We report an outbreak of carbapenemase-producing hypervirulent Klebsiella pneumoniae in two hospitals that undergo frequent patient transfers. Analysis of 11 completely assembled genomes showed that the bacteria were ST11-K64 strains. Moreover, 12 single nucleotide polymorphisms (SNPs) identified the strains as having originated from the same cluster, and were also indicative of the interhospital transmission of infection. Five plasmids were assembled in each of the strains. One plasmid carried several virulence genes, including the capsular polysaccharide regulators rmpA and rmpA2. Two others carried antimicrobial-resistance genes, including one for carbapenem resistance, bla_KPC–2. Comparative genomic analysis indicated the occurrence of frequent and rapid gain and loss of genomic content along transmissions and the co-existence of progeny strains in the same ward. A 10-kbp fragment harboring antimicrobial resistance-conferring genes flanked by insert sequences was missing in a plasmid from strain KP20194c in patient 3, and this strain also likely subsequently infected patient 4. However, strains containing the 10-kbp fragment were also isolated from the ward environment at approximately the same time, and harbored different chromosome indels. Tn1721 and multiple additional insert sequence-mediated transpositions were also seen. These results indicated that there is a rapid reshaping and diversification of the genomic pool of K. pneumoniae facilitated by mobile genetic elements, even a short time after outbreak onset. ST11-K64 CR-hvKP strains have the potential to become new significant superbugs and a threat to public health.

Clinical Observation and Prognostic Analysis of Patients With Klebsiella pneumoniae Bloodstream Infection

Background and purpose

The clinical prognosis of Klebsiella pneumoniae(K. pneumoniae) bloodstream infection is poor, and the prevalence of drug-resistant bacteria makes clinical anti-infective treatment more challenging. This retrospective study evaluated the epidemiological characteristics of patients with K. pneumoniae, the risk factors for drug-resistant bacterial infection and death, and analyzed treatment options.

Methods

Clinical data of 297 patients diagnosed with K. pneumoniae bacteremia between June 2014 and June 2019 were collected.

Results

Intensive care unit hospitalization history, operation history, recent antibiotic use history, mechanical ventilation, and number of days hospitalized before bloodstream infection were found to be independent risk factors for drug-resistant bacterial infection. The risk of death for carbapenem-resistant K. pneumoniae infection was 2.942 times higher than that for carbapenem-sensitive K. pneumoniae infection. For extensively drug-resistant K. pneumoniae bacteremia patients, the mortality rate of combined anti-infective therapy was lower.

Conclusions

Clinicians should pay attention to patients with high-risk drug-resistant bacteria infection and administer timely anti-infection treatment. The findings of this study may provide some suggestions for early identification and standardized treatment of patients with K. pneumoniae bacteremia.

Epidemiology, mortality and risk factors for patients with K. pneumoniae bloodstream infections: Clinical impact of carbapenem resistance in a tertiary university teaching hospital of Beijing

BACKGROUND

This study compared the epidemiology of carbapenem-resistant (CRKP) and carbapenem-sensitive (CSKP) K. pneumoniae bloodstream infections (BSIs), and assessed risk factors for 28-day mortality of patients with K. pneumoniae BSIs.

METHODS

A retrospective cohort study was conducted in a 2000-bed tertiary teaching hospital of Beijing between Jan 1st 2013 to Dec 31st, 2019. All patients with K. pneumoniae BSI were identified through the Hospital Information System. The endpoints included incidence rate, mortality and risk factors for mortality of patients with K. pneumoniae BSIs.

RESULTS

496 patients with K. pneumoniae BSIs were included in the analysis, with 108 CRKP BSIs. The incidence rate of K. pneumoniae BSI was 10.6 (CI: 9.7, 11.6) per 100 000 patient-days, with the rate for CRKP BSI was 2.3 (95% CI: 1.9, 2.8). The 28-day mortality was 38.0% for CRKP BSI and 8.8% for CSKP BSI, respectively. Logistic analysis showed, higher Charlson Comorbidity Index score (OR = 1.26, 95%CI 1.12-1.43, p < 0.001), respiratory failure (OR = 2.73, 95%CI1.28-5.84, p = 0.010), renal failure (OR = 4.13, 95%CI1.93-8.83, p < 0.001), septic shock (OR = 8.77, 95%CI3.60-21.32, p < 0.001), mechanical ventilation (OR = 4.41, 95%CI1.59-12.25, p = 0.004) and CRKP infection (OR = 3.04, 95%CI1.28-7.22, p = 0.012) were independently associated with 28-day mortality.

CONCLUSIONS

Considerable incidence rate and remarkable mortality of patients with K. pneumoniae (especially CRKP) BSI was declared in the study. Patient conditions before (higher CCI) and after presentation (respiratory failure, renal failure, septic shock), and healthcare factors (mechanical ventilation and CRKP infection) were independently associated with 28-day mortality. Understanding these risks helps better establishment of infection control strategies.

Draft Genome Sequences of Klebsiella Species Isolated from the International Space Station

Isolated across four locations aboard the International Space Station (ISS), 10 bacterial strains were compared using whole-genome sequencing analysis and were phylogenetically identified as Klebsiella The whole-genome sequences will aid in comparative genomic studies of ISS Klebsiella strains with Earth counterparts to gain insight into their adaptation to space conditions.

The New Klebsiella pneumoniae ST152 Variants with Hypermucoviscous Phenotype Isolated from Renal Transplant Recipients with Asymptomatic Bacteriuria-Genetic Characteristics by WGS

Klebsiella pneumoniae (Kp) is one of the most important etiological factors of urinary tract infections in renal transplant (RTx) recipients. We described the antimicrobial susceptibility phenotypes and genomic features of two hypermucoviscous (HM) Kp isolates recovered from RTx recipients with asymptomatic bacteriuria (ABU). Using whole genome sequencing (WGS) data, we showed that the strains belong to the ST152 lineage with the KL149 capsular serotype, but without rmpA/magA genes, which is typical for HM+ hypervirulent Kp. These new strains carried virulence-associated genes that predispose for urinary tract infections (UTIs). Likewise, both strains carried the ecp gene encoding pilus common for extended-spectrum β-lactamase (ESBL) Escherichia coli. Although the two ST152 isolates were closely related and differed by only nine single nucleotide polymorphisms (SNPs) in their chromosomes, they had different plasmid compositions and chromosomal elements, with isolate KP28872 carrying an ESBL plasmid and an integrative conjugative element. These two isolates are an example of the high plasticity of the K. pneumoniae accessory genome. The identification of patients with ABU matched with the correct epidemiological profiling of isolates could facilitate interventions to prevent or rapidly treat K. pneumoniae infections.

Plasmid diversity among genetically related Klebsiella pneumoniae blaKPC-2 and blaKPC-3 isolates collected in the Dutch national surveillance

Carbapenemase-producing Klebsiella pneumoniae emerged as a nosocomial pathogen causing morbidity and mortality in patients. For infection prevention it is important to track the spread of K. pneumoniae and its plasmids between patients. Therefore, the major aim was to recapitulate the contents and diversity of the plasmids of genetically related K. pneumoniae strains harboring the beta-lactamase gene bla_KPC-2 or bla_KPC-3 to determine their dissemination in the Netherlands and the former Dutch Caribbean islands from 2014 to 2019. Next-generation sequencing was combined with long-read third-generation sequencing to reconstruct 22 plasmids. wgMLST revealed five genetic clusters comprised of K. pneumoniae bla_KPC-2 isolates and four clusters consisted of bla_KPC-3 isolates. KpnCluster-019 bla_KPC-2 isolates were found both in the Netherlands and the Caribbean islands, while bla_KPC-3 cluster isolates only in the Netherlands. Each K. pneumoniae bla_KPC-2 or bla_KPC-3 cluster was characterized by a distinct resistome and plasmidome. However, the large and medium plasmids contained a variety of antibiotic resistance genes, conjugation machinery, cation transport systems, transposons, toxin/antitoxins, insertion sequences and prophage-related elements. The small plasmids carried genes implicated in virulence. Thus, implementing long-read plasmid sequencing analysis for K. pneumoniae surveillance provided important insights in the transmission of a KpnCluster-019 bla_KPC-2 strain between the Netherlands and the Caribbean.

K-PAM: a unified platform to distinguish Klebsiella species K- and O-antigen types, model antigen structures and identify hypervirulent strains

A computational method has been developed to distinguish the Klebsiella species serotypes to aid in outbreak surveillance. A reliability score (estimated based on the accuracy of a specific K-type prediction against the dataset of 141 distinct K-types) average (ARS) that reflects the specificity between the Klebsiella species capsular polysaccharide biosynthesis and surface expression proteins, and their K-types has been established. ARS indicates the following order of potency in accurate serotyping: Wzx (ARS = 98.5%),Wzy (ARS = 97.5%),WbaP (ARS = 97.2%),Wzc (ARS = 96.4%),Wzb (ARS = 94.3%),WcaJ (ARS = 93.8%),Wza (ARS = 79.9%) and Wzi (ARS = 37.1%). Thus, Wzx, Wzy and WbaP can give more reliable K-typing compared with other proteins. A fragment-based approach has further increased the Wzi ARS from 37.1% to 80.8%. The efficacy of these 8 proteins in accurate K-typing has been confirmed by a rigorous testing and the method has been automated as K-PAM (www.iith.ac.in/K-PAM/). Testing also indicates that the use of multiple genes/proteins helps in reducing the K-type multiplicity, distinguishing the K-types that have identical K-locus (like KN3 and K35) and identifying the ancestral serotypes of Klebsiella spp. K-PAM has the facilities to O-type using Wzm (ARS = 85.7%) and Wzt (ARS = 85.7%) and identifies the hypervirulent Klebsiella species by the use of rmpA, rmpA2, iucA, iroB and peg-344 marker genes. Yet another highlight of the server is the repository of the modeled 11 O- and 79 K- antigen 3D structures.

AmpR Increases the Virulence of Carbapenem-Resistant Klebsiella pneumoniae by Regulating the Initial Step of Capsule Synthesis

Background

Non-hypermucoviscous carbapenem-resistant Klebsiella pneumoniae with enhanced virulence lacking hvKP-specific virulence factors is uncommon, and the virulence mechanisms of this organism are not understood.

Methods

Following a retrospective study of carbapenem-resistant K. pneumoniae based on core genome multilocus sequence typing (cgMLST), isolates that caused high mortality were investigated with a genome-wide association study (GWAS), proteome analysis and an animal model.

Results

The subclone of sequence type 11 (ST11) K. pneumoniae, which belongs to complex type 3176 (CT3176) and K-locus 47 (KL47), was highlighted due to the high mortality of infected patients. GWAS analysis showed that transcriptional regulatory gene ampR was associated with the CT3176 isolates. In a mouse model, the mortality, bacterial load and pathological changes of mice infected with ampR-carrying isolates were distinct from those infected with ampR-null isolates. The ampR gene that enhances the virulence of the non-hypermucoviscous KL47 strain was unable to enhance the virulence of hypermucoviscous KL1 strain. Proteome analysis showed that the expression of WcaJ in the ampR⁺ isolates was significantly higher than that in the ampR⁻ isolates. Quantification of capsular polysaccharide confirmed that more capsule polysaccharide was produced by ampR⁺ and ampR-complementary strains compared to ampR⁻ strains. It is suggested that the enhancement of the initial stage of capsule synthesis may be the cause of the enhanced virulence of these non-hypermucoviscous ST11 carbapenem-resistant K. pneumoniae isolates.

Conclusion

Non-hypermucoviscous ST11 carbapenem-resistant K. pneumoniae with enhanced virulence warrants continued surveillance and investigation.

Pyogenic liver abscess and endogenous endophthalmitis secondary toKlebsiella pneumoniae

Invasive Liver Abscess Syndrome is a manifestation of systemic infection caused by Klebsiella pneumoniae. This constellation of symptoms has been well-reported throughout Southeast Asia though it is uncommon in the United States. This article reports the identification of a pyogenic liver abscess and associated endogenous endophthalmitis in a patient presenting to the emergency department.

The Small Protein RmpD Drives Hypermucoviscosity in Klebsiella pneumoniae

Klebsiella pneumoniae has a remarkable ability to cause a wide range of human diseases. It is divided into two broad classes: classical strains that are a notable problem in health care settings due to multidrug resistance, and hypervirulent (hv) strains that are historically drug sensitive but able to establish disease in immunocompetent hosts. Alarmingly, there has been an increased frequency of clinical isolates that have both drug resistance and hv-associated genes. One such gene, rmpA, encodes a transcriptional regulator required for maximal capsule (cps) gene expression and confers hypermucoviscosity (HMV). This link has resulted in the assumption that HMV is caused by elevated capsule production. However, we recently reported a new cps regulator, RmpC, and ΔrmpC mutants have reduced cps expression but retain HMV, suggesting that capsule production and HMV may be separable traits. Here, we report the identification of a small protein, RmpD, that is essential for HMV but does not impact capsule. RmpD is 58 residues with a putative N-terminal transmembrane domain and highly positively charged C-terminal half, and it is conserved among other hv K. pneumoniae strains. Expression of rmpD in trans complements both ΔrmpD and ΔrmpA mutants for HMV, suggesting that RmpD is the key driver of this phenotype. The rmpD gene is located between rmpA and rmpC, within an operon regulated by RmpA. These data, combined with our previous work, suggest a model in which the RmpA-associated phenotypes are largely due to RmpA activating the expression of rmpD to produce HMV and rmpC to stimulate cps expression.IMPORTANCE Capsule is a critical virulence factor in Klebsiella pneumoniae, in both antibiotic-resistant classical strains and hypervirulent strains. Hypervirulent strains usually have a hypermucoviscosity (HMV) phenotype that contributes to their heightened virulence capacity, but the production of HMV is not understood. The transcriptional regulator RmpA is required for HMV and also activates capsule gene expression, leading to the assumption that HMV is caused by hyperproduction of capsule. We have identified a new gene (rmpD) required for HMV but not for capsule production. This distinction between HMV and capsule production will promote a better understanding of the mechanisms of hypervirulence, which is in great need given the alarming increase in clinical isolates with both drug resistance and hypervirulence traits.

Genomic insights into multidrug-resistant and hypervirulent Klebsiella pneumoniae co-harboring metal resistance genes in aquatic environments

Klebsiella pneumoniae is one of the most important pathogens related to hospital-acquired infections. The incidence of infections by hypervirulent K. pneumoniae (hvKp), especially community-acquired infections, has been increasing in recent decades. The occurrence of multidrug-resistant (MDR) hvKp has been increasingly reported worldwide decreasing the treatment options, which is a concern. Aquatic environments have been considered a reservoir of MDR pathogens, which contribute to the spread of MDR pathogens. Therefore, this study aimed to characterize MDR-hvKp strains obtained from public aquatic environments using whole genome sequencing in Brazil. Resistome analysis showed ARGs to β-lactams, quinolones, tetracyclines, sulfonamides, and fosfomycin as well as several metal resistance genes. Virulome analysis showed several virulence genes. Besides, genomic islands, CRISPR and prophage-related sequences were also detected. MLST analysis revealed the presence of two novel sequences types (STs) belonging to different clonal complexes (CCs) [ST4415 (CC515) and ST4416 (CC2654)], and one already described [ST661 (CC661)]. The presence of MDR-hvKp lineages in water sources belonging to STs and CCs associated with humans and animals shows the ability of these pathogens to spread to different aquatic environments. This study reports for the first time two novel STs of MDR-hvKp as well as the presence of a rare ST661 closely related to outbreaks in aquatic environments, and contributes to surveillance studies and MDR-hvKp monitoring worldwide.

Spread of ST348 Klebsiella pneumoniae Producing NDM-1 in a Peruvian Hospital

The aim of this study was to characterize carbapenem-resistant Klebsiella pneumoniae (CR-Kp) isolates recovered from adults and children with severe bacteremia in a Peruvian Hospital in June 2018. Antimicrobial susceptibility was determined by disc/gradient diffusion and broth microdilution when necessary. Antibiotic resistance mechanisms were evaluated by PCR and DNA sequencing. Clonal relatedness was assessed using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Plasmid typing was performed with a PCR-based method. Thirty CR-Kp isolates were recovered in June 2018. All isolates were non-susceptible to all β-lactams, ciprofloxacin, gentamicin and trimethoprim-sulfamethoxazole, while mostly remaining susceptible to colistin, tigecycline, levofloxacin and amikacin. All isolates carried the bla_NDM-1 gene and were extended spectrum β-lactamase (ESBL) producers. PFGE showed four different pulsotypes although all isolates but two belonged to the ST348 sequence type, previously reported in Portugal. bla_NDM-1 was located in an IncFIB-M conjugative plasmid. To our knowledge, this is the first report of an New Delhi metallo-β-lactamase (NDM)-producing K. pneumoniae recovered from both children and adults in Lima, Peru, as well as the first time that the outbreak strain ST348 is reported in Peru and is associated with NDM. Studies providing epidemiological and molecular data on CR-Kp in Peru are essential to monitor their dissemination and prevent further spread.

The Characteristic of Virulence, Biofilm and Antibiotic Resistance of Klebsiella pneumoniae

Klebsiella pneumoniae is an important gram-negative opportunistic pathogen that causes a variety of infectious diseases, including urinary tract infections, bacteremia, pneumonia, and liver abscesses. With the emergence of multidrug-resistant (MDR) and hypervirulent K. pneumoniae (hvKP) strains, the rapid spread of these clinical strains in geography is particularly worrying. However, the detailed mechanisms of virulence and antibiotic resistance in K. pneumoniae are still not very clear. Therefore, studying and elucidating the pathogenic mechanisms and drug resistance mechanism of K. pneumoniae infection are important parts of current medical research. In this paper, we systematically summarized the virulence, biofilm, and antibiotic tolerance mechanisms of K. pneumoniae, and explored the application of whole genome sequencing and global proteomics, which will provide new clues for clinical treatment of K. pneumoniae.

Klebsiella pneumoniae bacteremia revisited: Comparison between 2007 and 2017 prospective cohorts at a medical center in Taiwan

BACKGROUND

Community onset K. pneumoniae bacteremia (KPB) is a major problem in Taiwan for decades. We aimed to revisit the role of virulent genotype K1/K2 and possible predisposing factors, compared to our published 2007 cohort.

METHODS

All adult patients with monomicrobial KPB during 2017 at a medical center in Taiwan were prospectively enrolled. We genotyped the major K types of K. pneumoniae strains, and analyzed the role of prior use of antibiotic or proton pump inhibitor (PPI).

RESULTS

A total of 213 cases were enrolled. Compared to our previous 2007 study (n = 231), there was a higher percentage of patients with community onset bacteremia (75% vs. 60%, p = 0.003). The overall mortality rate was lower in 2017 (23% vs. 32%, p = 0.02), while the rates of antimicrobial resistance (all classes) were higher in 2017. There were 40 cases of liver abscesses in 2017 (19%), with an overall mortality rate of 7.5%. The prevalence of K1 was similar (16% in 2017 vs. 19% in 2007), but the prevalence of K2 decreased significantly (7% in 2017 vs. 17% in 2007, p = 0.001). After excluding 39 cases without data of recent medication use, 48 of 174 (28%) of patients had received a PPI within 90 days. Patients with recent PPI use had more complicated underlying illnesses, higher antimicrobial resistance, and higher in-hospital mortality, but was negatively associated with liver abscess (4% vs. 24%, p = 0.002). Of patients with community-acquired bacteremia, 51% used antibiotics within 90 days. After excluding 37 patients received antibiotics within 14 days before the detection of bacteremia, patient with antibiotic use within 15-90 days had higher Pittsburgh bacteremia scores (4.5 vs. 2.7, p = 0.04), creatinine levels, and frequency of recent surgery, but was not associated with liver abscess (21% vs. 31%, p = 0.33).

DISCUSSION

In summary, after a decade, community onset KPB is still prevalent (1.3 case per 1000 emergency department visit). K1 remains to be the dominant genotype. The association of prior ampicillin/amoxicillin or PPIs use for liver abscess is not confirmed.

Capsular polysaccharide and lipopolysaccharide O type analysis of Klebsiella pneumoniae isolates by genotype in China

Klebsiella pneumoniae is a common pathogen associated with nosocomial infections and is characterised serologically by capsular polysaccharide (K) and lipopolysaccharide O antigens. We surveyed a total of 348 non-duplicate K. pneumoniae clinical isolates collected over a 1-year period in a tertiary care hospital, and determined their O and K serotypes by sequencing of the wbb Y and wzi gene loci, respectively. Isolates were also screened for antimicrobial resistance and hypervirulent phenotypes; 94 (27.0%) were identified as carbapenem-resistant (CRKP) and 110 (31.6%) as hypervirulent (hvKP). isolates fell into 58 K, and six O types, with 92.0% and 94.2% typeability, respectively. The predominant K types were K14K64 (16.38%), K1 (14.66%), K2 (8.05%) and K57 (5.46%), while O1 (46%), O2a (27.9%) and O3 (11.8%) were the most common. CRKP and hvKP strains had different serotype distributions with O2a:K14K64 (41.0%) being the most frequent among CRKP, and O1:K1 (26.4%) and O1:K2 (17.3%) among hvKP strains. Serotyping by gene sequencing proved to be a useful tool to inform the clinical epidemiology of K. pneumoniae infections and provides valuable data relevant to vaccine design.

Community-acquired infection caused by the uncommon hypervirulent Klebsiella pneumoniae ST66-K2 lineage

Klebsiella pneumoniae (Kp) reference strain Kp52.145 is widely used in experimental Klebsiella pathophysiology. Since 1935, only one other strain of the same sublineage (sequence type ST66, capsular serotype K2) was isolated (AJ210, Australia). Here, we describe a community-acquired invasive infection caused by a ST66-K2 Kp strain in France. Four hypermucoviscous Kp isolates responsible for acute otitis media, meningitis, bacteraemia and bacteriuria, respectively, were obtained from a patient with a history of chronic alcoholism and diabetes mellitus, and infected with HIV. The isolates were characterized by phenotypic and genomic methods. The four genetically identical ST66-K2 isolates presented a full antimicrobial susceptibility profile, including to ampicillin, corresponding to a single strain (SB5881), which was more closely related to AJ210 (135 SNPs) than to Kp52.145 (388 SNPs). Colibactin and yersiniabactin gene clusters were present on the integrative and conjugative element ICEKp10 in the chromosome. The two plasmids from Kp52.145 were detected in SB5881. In addition to carrying genes for virulence factors RmpA, aerobactin and salmochelin, plasmid II has acquired in SB5881, the conjugation machinery gene cluster from plasmid I. We report the first case of community-acquired infection caused by a hypervirulent ST66-K2 Kp strain in Europe. This demonstrates the long-term persistence of the high-virulence and laboratory model ST66-K2 sublineage. The combination of a conjugative apparatus and major virulence genes on a single plasmid may contribute to the co-occurrence of hypervirulence and multidrug resistance in single Kp strains.

Fluoroquinolones as an alternative treatment for Klebsiella pneumoniae liver abscess and impact on hospital length of stay

Klebsiella pneumoniae liver abscess (KPLA) is an endemic disease in East Asia. Patients with KPLA usually require prolonged intravenous (i.v.) β-lactam therapy and hospitalisation. Fluoroquinolones have high oral bioavailability and the potential to shorten the duration of i.v. therapy. The aim of this study was to investigate the feasibility of fluoroquinolones as an alternative treatment for KPLA in Taiwan. Consecutive patients with KPLA in a medical centre in Taiwan between July 2012 and August 2019 were retrospectively enrolled. Clinical characteristics and outcomes were compared between cases treated with β-lactams and fluoroquinolones. A multivariate logistic regression model and propensity-score adjusted analysis were performed to identify independent risk factors for prolonged hospitalisation. A total of 234 patients with KPLA were identified during the study period. Most patients received β-lactams (n = 199; 85.0%), whilst only 35 (15.0%) received fluoroquinolones as the major therapy. Fluoroquinolones had similar clinical efficacy to β-lactams even in critically ill patients. Patients treated with fluoroquinolones had a shorter i.v. antibiotics duration (18.9 ± 7.6 days vs. 28.5 ± 14.7 days; P < 0.001) and hospital length of stay (LOS) (20.9 ± 8.3 days vs. 29.5 ± 16.2 days; P < 0.001) than patients treated with β-lactams. Major therapy with fluoroquinolones was an independent protective factor for hospital LOS > 14 days in all patients and for hospital LOS > 21 days in critically ill patients. In conclusion, fluoroquinolones were an effective alternative treatment for KPLA that resulted in a shorter duration of i.v. therapy and hospital LOS.

Genomic Profiling Reveals Distinct Routes To Complement Resistance in Klebsiella pneumoniae

The serum complement system is a first line of defense against bacterial invaders. Resistance to killing by serum enhances the capacity of Klebsiella pneumoniae to cause infection, but it is an incompletely understood virulence trait. Identifying and characterizing the factors responsible for preventing activation of, and killing by, serum complement could inform new approaches to treatment of K. pneumoniae infections. Here, we used functional genomic profiling to define the genetic basis of complement resistance in four diverse serum-resistant K. pneumoniae strains (NTUH-K2044, B5055, ATCC 43816, and RH201207), and explored their recognition by key complement components.

The serum complement system is a first line of defense against bacterial invaders. Resistance to killing by serum enhances the capacity of Klebsiella pneumoniae to cause infection, but it is an incompletely understood virulence trait. Identifying and characterizing the factors responsible for preventing activation of, and killing by, serum complement could inform new approaches to treatment of K. pneumoniae infections. Here, we used functional genomic profiling to define the genetic basis of complement resistance in four diverse serum-resistant K. pneumoniae strains (NTUH-K2044, B5055, ATCC 43816, and RH201207), and explored their recognition by key complement components. More than 90 genes contributed to resistance in one or more strains, but only three, rfaH, lpp, and arnD, were common to all four strains. Deletion of the antiterminator rfaH, which controls the expression of capsule and O side chains, resulted in dramatic complement resistance reductions in all strains. The murein lipoprotein gene lpp promoted capsule retention through a mechanism dependent on its C-terminal lysine residue; its deletion led to modest reductions in complement resistance. Binding experiments with the complement components C3b and C5b-9 showed that the underlying mechanism of evasion varied in the four strains: B5055 and NTUH-K2044 appeared to bypass recognition by complement entirely, while ATCC 43816 and RH201207 were able to resist killing despite being associated with substantial levels of C5b-9. All rfaH and lpp mutants bound C3b and C5b-9 in large quantities. Our findings show that, even among this small selection of isolates, K. pneumoniae adopts differing mechanisms and utilizes distinct gene sets to avoid complement attack.

First description of antimicrobial resistance in carbapenem-susceptible Klebsiella pneumoniae after imipenem treatment, driven by outer membrane remodeling

BACKGROUND

The emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a looming threat to human health. Although there are numerous studies regarding porin alteration in association with the production of ESBLs and/or AmpC β-lactamase, a systematic study on the treatment-emergence of porins alteration in antibiotic resistance does not yet exist. The aim of this study was to investigate the underlying mechanism of resistance of K. pneumoniae during carbapenem treatment.

RESULTS

Here, we report three strains (FK-2624, FK-2723 and FK-2820) isolated from one patient before and after imipenem treatment during hospitalization. Antibiotic susceptibility testing indicated that that the first isolate, FK-2624, was susceptible to almost all tested antimicrobials, being resistant only to fosfomycin. The subsequent isolates FK-2723 and FK-2820 were multidrug resistant (MDR). After imipenem therapy, FK-2820 was found to be carbapenem-resistant. PCR and Genome Sequencing analysis indicated that oqxA, and fosA5, were identified in all three strains. In addition, FK-2624 also harbored bla_SHV-187 and bla_TEM-116. The bla_SHV-187 and bla_TEM-116 genes were not detected in FK-2723 and FK-2820. bla_DHA-1, qnrB4, aac (6')-IIc, and bla_SHV-12, EreA2, CatA2, SulI, and tetD, were identified in both FK-2723 and FK-2820. Moreover, the genes bla_DHA-1, qnrB4, aac (6')-IIc were co-harbored on a plasmid. Of the virulence factors found in this study, ybtA, ICEKp6, mrkD, entB, iroN, rmpA2-6, wzi16 and capsular serotype K57 were found in the three isolates. The results of pairwise comparisons, multi-locus sequencing typing (MLST) and pulsed-field gel electrophoresis (PFGE) revealed high homology among the isolates. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results showed that isolate FK-2820 lacked OmpK36, with genome sequence data validating that there was a premature stop codon in the ompK36 gene and real-time RT-PCR suggesting high turnover of the ompK36 non-sense transcript in FK-2820, with the steady-state mRNA level 0.007 relative to the initial isolate.

CONCLUSION

This study in China highlight that the alteration of outer membrane porins due to the 14-day use of imipenem play a potential role in leading to clinical presentation of carbapenem-resistance. This is the first description of increased resistance developing from a carbapenem-susceptible K. pneumoniae with imipenem treatment driven by outer membrane remodeling.

Percutaneous fine-needle aspiration for pyogenic liver abscess (3-6 cm): a two-center retrospective study

BACKGROUND

The role of ultrasonography-guided percutaneous fine-needle aspiration (PNA) for pyogenic liver abscess (PLA) remains without consensus, especially in abscesses 3 to 6 cm in diameter. The objective of this study was to evaluate the comparative effectiveness and safety of PNA combined with antibiotics.

METHODS

This was a retrospective study of patients with PLA that were from 3 to 6 cm in diameter who treated at two medical centers in Shanghai, China, from January 2014 to March 2019. Patients were divided into groups treated by PNA plus antibiotics or antibiotics alone. Patients demographics and clinical data related diagnosis, antibiotic treatment, and patient outcomes were analyzed.

RESULTS

Out of a total of 94 PLA patients, 42 (44.7%) patients received PNA combined with antibiotics, and 52 (55.3%) received antibiotics alone. There were no complications related to PNA. In the PNA group, 13 (31.7%) patients with negative blood culture and 8 (19.5%) patients without blood culture were microbiologically confirmed via aspiration. The time for temperature normalization (P < 0.001) and the reduction rate of C-reactive protein within the first week (P = 0.031) were significantly lower in the PNA group. In the multivariate analysis, treatment with PNA was more likely to result in clinical improvement of PLA (odds ratio = 0.33, 95% confidence intervals (CI): 0.11-0.96, P = 0.043).

CONCLUSIONS

PNA combined with antibiotics appears to be a safe, effective, and promising treatment for PLA of 3-6 cm in size. Furthermore, the technique allows for direct microbial sample, which can improve the selection of antibiotics.

Molecular characteristics of extended-spectrum β-lactamase-producing Klebsiella pneumoniae in Japan: Predominance of CTX-M-15 and emergence of hypervirulent clones

OBJECTIVE

To provide data on the molecular characteristics of extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae clinical isolates in Japan.

METHODS

A total of 100 clinical isolates of ESBL-producing K. pneumoniae collected throughout Japan between June and July 2018 were studied. ESBL genes were analyzed using PCR and DNA sequencing. Transferability of ESBL genes was investigated by conjugation experiments. Plasmid replicon types, virulence genes (rmpA, rmpA2, iucA, iroB, and peg-344) associated with hypervirulent K. pneumoniae (hvKp), and capsule types were detected using PCR. Genotyping was performed using multilocus sequence typing.

RESULTS

All ESBL-producing isolates carried bla_CTX-M genes. The most predominant CTX-M-type identified was CTX-M-15 (n=55). We identified 24 sequence types (STs) among the CTX-M-15 producers, with ST25 (n=8) being the most common. Most of the transconjugants carrying bla_CTX-M-15 contained the FIIk replicon. Of the 100 ESBL-producing isolates, 31 were hvKp defined by the presence of the virulence genes. These ESBL-producing hvKp isolates belonged to eight STs (STs 23, 25, 36, 65, 86, 268, 412, and 4492), with five capsule types (K1, K2, K20, K57, and undefined).

CONCLUSIONS

CTX-M-15 was the predominant ESBL among K. pneumoniae isolates from Japan. This study shows that ESBL-producing hvKp strains comprising various clones are emerging in Japan.

Conserved G-Quadruplex Motifs in Gene Promoter Region Reveals a Novel Therapeutic Approach to Target Multi-Drug Resistance Klebsiella pneumoniae

An opportunistic pathogen, Klebsiella pneumoniae is known to cause life-threating nosocomial infection with a high rate of morbidity and mortality. Evolutions of multi-drug-resistant and hyper-virulent strains of K. pneumoniae make the situation worse. Currently, there is no incisive drug molecule available for drug-resistant hyper-virulent K. pneumoniae infection that emphasizes the need for identification of novel and more promising drug targets in K. pneumoniae. Recently, various non-canonical structures of nucleic acids especially G-quadruplex (G4) motifs have been identified as potential therapeutic targets against several human pathogenic bacteria and viruses including Mycobacterium tuberculosis, Streptococcus pneumoniae, human immunodeficiency virus (HIV), Ebola, and Nipah. Therefore, in present study we screened the K. pneumoniae genomes for identification of evolutionary conserved G4 structure-forming motifs as promising anti-bacterial drug targets. Bioinformatics analysis revealed the presence of six highly conserved G4 motifs in the promoter region of five essential genes that play a critical role in nutrient transport and metabolism. Biophysical studies showed the formation of G4 structure by these conserved motifs. Circular Dichroism melting analysis showed the stabilization of these G4 motifs by a well-known G4-stabilizing agent, BRACO-19. The stabilization of these motifs by BRACO-19 was also able to stop the primer extension process, which is an essential phenomenon for expression of the G4-harboring gene. The addition of G4-specific ligand at low micromolar range was observed to be lethal for the growth of this bacteria and negatively controlled the expression of the G4-harboring genes via G4 structure stabilization. These observations strengthen the formation of G4 structures by the predicted G4 motif in vivo, which can be stabilized by G4 ligands like BRACO-19. This stabilization of G4 structures can attenuate the expression of G4-harboring essential genes and thus play a critical role in the regulation of gene expression. Thus, taking all given result in consideration, for the first time, this study showed the new therapeutic avenue for combating K. pneumoniae infection by characterizing the conserved G4 motifs as promising therapeutic targets.

Cohorting KPC+ Klebsiella pneumoniae (KPC-Kp)-positive patients: A genomic exposé of cross-colonization hazards in a long-term acute-care hospital (LTACH)

OBJECTIVE

Cohorting patients who are colonized or infected with multidrug-resistant organisms (MDROs) protects uncolonized patients from acquiring MDROs in healthcare settings. The potential for cross transmission within the cohort and the possibility of colonized patients acquiring secondary isolates with additional antibiotic resistance traits is often neglected. We searched for evidence of cross transmission of KPC+ Klebsiella pneumoniae (KPC-Kp) colonization among cohorted patients in a long-term acute-care hospital (LTACH), and we evaluated the impact of secondary acquisitions on resistance potential.

DESIGN

Genomic epidemiological investigation.

SETTING

A high-prevalence LTACH during a bundled intervention that included cohorting KPC-Kp-positive patients.

METHODS

Whole-genome sequencing (WGS) and location data were analyzed to identify potential cases of cross transmission between cohorted patients.

RESULTS

Secondary KPC-Kp isolates from 19 of 28 admission-positive patients were more closely related to another patient's isolate than to their own admission isolate. Of these 19 cases, 14 showed strong genomic evidence for cross transmission (<10 single nucleotide variants or SNVs), and most of these patients occupied shared cohort floors (12 patients) or rooms (4 patients) at the same time. Of the 14 patients with strong genomic evidence of acquisition, 12 acquired antibiotic resistance genes not found in their primary isolates.

CONCLUSIONS

Acquisition of secondary KPC-Kp isolates carrying distinct antibiotic resistance genes was detected in nearly half of cohorted patients. These results highlight the importance of healthcare provider adherence to infection prevention protocols within cohort locations, and they indicate the need for future studies to assess whether multiple-strain acquisition increases risk of adverse patient outcomes.

Stool Samples of Acute Diarrhea Inpatients as a Reservoir of ST11 Hypervirulent KPC-2-Producing Klebsiella pneumoniae

China has been experiencing a rapid increase in the number of nosocomial infections caused by carbapenem-resistant Klebsiella pneumoniae ST11 (ST11-CRKP) for decades. The emergence of hypervirulent ST11-CRKP (ST11-CR-HvKP) strains is expected to become a serious public health issue in China, considering that carbapenem resistance and virulence have converged in an epidemic clone. K. pneumoniae strains that colonize the human intestinal tract may become a reservoir of virulence and carbapenemase-encoding genes. Here, we first characterized the genotypes and antimicrobial phenotypes of ST11-CR-HvKP strains isolated from diarrheal stool samples of inpatients in Zhejiang Province, China. Active surveillance approaches based on the findings of the present study should be implemented, particularly in intensive care units, to combat the spread of ST11-CR-HvKP and to improve treatment.

The emergence and spread of carbapenem-resistant hypervirulent Klebsiella pneumoniae sequence type 11 (ST11-CR-HvKP) in China are a great concern in the public health community. However, the underlying mechanism that enables its wide dissemination in China remains unclear. Here, we investigated the prevalence of carriage of carbapenemase-producing Enterobacteriaceae (CPE) among inpatients with diarrhea in a teaching hospital over 1 year to identify ST11-CR-HvKP reservoirs and to understand the genetic background and plasmid profiles of these pathogens. As assessed by stool analysis, the CPE colonization rate (12.4%) among the inpatients with diarrhea was high (12.4%). Antibiotic exposure, surgical history, and CPE positivity were correlated. Genomic investigation of 65 carbapenem-resistant K. pneumoniae isolates indicated a shared bacterial population in various wards. According to maximum likelihood phylogenetic tree analysis, these isolates were partitioned into three major clades. Analysis of the wzi locus revealed three different K types (KL105, KL47, and K64) among the ST11 isolates, indicating the genetic diversity of these isolates. Genetic and sequence mapping revealed the complexity of virulence and resistance plasmid sets harbored by the isolates. These observations indicate that the dissemination of resistant bacteria is more complex than initially anticipated and possibly involves multiple K. pneumoniae ST11 lineages and a variety of virulence plasmids. Collectively, we show for the first time that stool may be a source of ST11-CR-HvKP isolates. Furthermore, the findings reveal the silent dissemination of ST11-CR-HvKP bacteria in Zhejiang Province, China. Future investigations are warranted to determine the association between rectal colonization by ST11-CR-HvKP and clinical infections.

IMPORTANCE China has been experiencing a rapid increase in the number of nosocomial infections caused by carbapenem-resistant Klebsiella pneumoniae ST11 (ST11-CRKP) for decades. The emergence of hypervirulent ST11-CRKP (ST11-CR-HvKP) strains is expected to become a serious public health issue in China, considering that carbapenem resistance and virulence have converged in an epidemic clone. K. pneumoniae strains that colonize the human intestinal tract may become a reservoir of virulence and carbapenemase-encoding genes. Here, we first characterized the genotypes and antimicrobial phenotypes of ST11-CR-HvKP strains isolated from diarrheal stool samples of inpatients in Zhejiang Province, China. Active surveillance approaches based on the findings of the present study should be implemented, particularly in intensive care units, to combat the spread of ST11-CR-HvKP and to improve treatment.

Clinical Features and Risk Factors Associated With 30-Day Mortality in Patients With Pneumonia Caused by Hypervirulent Klebsiella pneumoniae (hvKP)

Background

Reports on metastatic or invasive infections by hypervirulent Klebsiella pneumoniae (hvKP) have increased recently. However, the effects of its virulence on clinical course and outcomes in pneumonia patients have rarely been addressed. We assessed and compared the clinical features of hvKp and classic K. pneumoniae (cKP) strains isolated from patients with pneumonia caused by K. pneumoniae. We also investigated the effects of virulence factors and the K. pneumoniae capsular serotypes K1 and K2 on mortality.

Methods

In this retrospective study, we enrolled 91 patients diagnosed as having pneumonia caused by K. pneumoniae and obtained their demographic and clinical data from medical records. We evaluated genes for K1 and K2, antimicrobial susceptibility, and the virulence genes rmpA, iutA, entB, ybtS, kfu, mrkD, and allS. Strains that possessed rmpA and iutA were defined as hvKP (N=39), while the remaining were classified as cKP (N=52). Odds ratio (OR) for the risk factors associated with 30-day mortality was calculated using the binary logistic regression model.

Results

The 30-day mortality in all patients was 23.1%; it was 17.9% (7/39) in the hvKP group and 26.9% (14/52) in the cKP group (P=0.315). Bacteremia (OR=38.1; 95% confidence interval [CI], 2.5–570.2), altered mental status (OR=8.8; 95% CI, 1.7–45.0), and respiratory rate >30 breaths/min (OR=4.8; 95% CI, 1.2–20.0) were independent risk factors for 30-day mortality in all patients.

Conclusions

Our results suggest that hypervirulence determinants do not have a significant effect on 30-day mortality in patients with pneumonia caused by K. pneumoniae.

Phenotypic and Genomic Characterization of Virulence Heterogeneity in Multidrug-Resistant ST11 Klebsiella pneumoniae During Inter-Host Transmission and Evolution

Background

Multidrug-resistant (MDR) ST11 hypervirulent Klebsiella pneumoniae (hvKp) is emerging in China.

Purpose

The aim of this study was to track the transmission and evolution of hvKp.

Materials and Methods

A retrospective study focused on Kp infection was conducted. Clinical data were collected from electronic medical records. Whole-genome sequencing of Kp strains was performed. Single-nucleotide polymorphisms (SNPs) were analyzed and a transmission map was constructed. Sequence type, and antimicrobial and virulence-associated genes were characterized. Strains with some combination of the virulence genes, _prmpA, _prmpA2, iucA, iroB, and peg-344, were defined as hvKp. Kp virulence phenotypes were evaluated using the Galleria mellonella model.

Results

All 33 Kp strains were MDR-Kp and 13 (39.4%) were hvKp. Most hvKp strains (84.6%, 11/13) were hospital-acquired infections (HAIs). Two unique combinations of virulence-associated genes were detected among hvKp strains. Eleven cases were associated with _prmpA2+iucA and two strains presented with peg-344+_prmpA+_prmpA2+iucA. Surprisingly, two community-acquired MDR-hvKp infection cases were identified. Eight hvKp strains (61.5%, 8/13) exhibited a hypervirulent phenotype in the G. mellonella model. Five MDR-hvKp strains with the hypervirulence phenotype originated from a single cluster. Additionally, nine clones were identified among the two clades, six of which were hvKp. Moreover, the hvKp in clade 1 carried the IncHI1B plasmid replicon, whereas none of the hvKp strains in clade 2 harbored IncHI1B. These data, showing that different hvKp clones distributed into separate clades, indicate that transmission and evolution occurred within the hospital.

Conclusion

During inter-host evolution and transmission, various virulence clusters of the epidemic clone, MDR-ST11, converged, conferring phenotypic virulence heterogeneity and spread within the hospital and possibly the community. Mobile/conjugative genetic elements associated with virulence-encoding gene clusters might emerge and have been transmitted within the hospital, suggesting that enhanced ongoing surveillance is essential.

RcsAB and Fur Coregulate the Iron-Acquisition System via entC in Klebsiella pneumoniae NTUH-K2044 in Response to Iron Availability

The iron acquisition system is an essential virulence factor for human infection and is under tight regulatory control in a variety of pathogens. Ferric-uptake regulator (Fur) is one of Fe²⁺-responsive transcription factor that maintains iron homeostasis, and the regulator of capsule synthesis (Rcs) is known to regulate exopolysaccharide biosynthesis. We speculate the Rcs may involve in iron-acquisition given the identified regulator box in the upstream of entC that participated in the biosynthesis of enterobactin. To study the coregulation by RcsAB and Fur of entC, we measured the β-galactosidase activity and relative mRNA expression of entC in WT and mutant strains. The RcsAB- and Fur-protected regions were identified by an electrophoretic mobility shift assay (EMSA) and a DNase I footprinting assay. A regulatory cascade was identified with which Fur repressed rcsA expression and reduced RcsAB and entC expression. Our study demonstrated that entC was coregulated by two different transcriptional regulators, namely, RcsAB and Fur, in response to iron availability in Klebsiella pneumoniae.

Rapid Detection to Differentiate Hypervirulent Klebsiella pneumoniae (hvKp) From Classical K. pneumoniae by Identifying peg-344 With Loop-Mediated Isothermal Amplication (LAMP)

Objectives

To establish a rapid molecular diagnostics of hvKp using the peg-344 loop-mediated isothermal amplification technique (LAMP).

Methods

In all, 28 K. pneumoniae strains isolated from the blood of patients were used for the peg-344 LAMP. K. pneumoniae NTUH-K2044 and K. pneumoniae ATCC700603 were used as positive control and negative control, respectively. For comparison, all the results were detected in a polymerase chain reaction (PCR), which was considered the gold standard for the detection of the gene. Mouse lethality assay, and Serum killing assay were also used to determine the virulence phenotype of K. pneumoniae.

Results

We determined the specificity and sensitivity of the primers for peg-344 detection in the LAMP reactions. This LAMP assay was able to specifically differentiate hvKp from classical K. pneumoniae (cKp) at 65°C, which was 100-fold more sensitive than a PCR assay for peg-344 detection. The virulence phenotype of K. pneumoniae detected by LAMP was as precise as by Mouse lethality assay and Serum killing assay.

Conclusion

The LAMP assay is easy to perform and rapid. Therefore, it can be routinely applied to differentiate hvKp from cKp in the clinical laboratory.

Pharmacokinetics-Pharmacodynamics of Enmetazobactam Combined with Cefepime in a Neutropenic Murine Thigh Infection Model

Third-generation cephalosporin (3GC)-resistant Enterobacteriaceae are classified as critical priority pathogens, with extended-spectrum β-lactamases (ESBLs) as principal resistance determinants. Enmetazobactam (formerly AAI101) is a novel ESBL inhibitor developed in combination with cefepime for empirical treatment of serious Gram-negative infections in settings where ESBLs are prevalent. Cefepime-enmetazobactam has been investigated in a phase 3 trial in patients with complicated urinary tract infections or acute pyelonephritis. This study examined pharmacokinetic-pharmacodynamic (PK-PD) relationships of enmetazobactam, in combination with cefepime, for ESBL-producing isolates of Klebsiella pneumoniae in 26-h murine neutropenic thigh infection models. Enmetazobactam dose fractionation identified the time above a free threshold concentration (fT > C_T ) as the PK-PD index predictive of efficacy. Nine ESBL-producing isolates of K. pneumoniae, resistant to cefepime and piperacillin-tazobactam, were included in enmetazobactam dose-ranging studies. The isolates encoded CTX-M-type, SHV-12, DHA-1, and OXA-48 β-lactamases and covered a cefepime-enmetazobactam MIC range from 0.06 to 2 μg/ml. Enmetazobactam restored the efficacy of cefepime against all isolates tested. Sigmoid curve fitting across the combined set of isolates identified enmetazobactam PK-PD targets for stasis and for a 1-log₁₀ bioburden reduction of 8% and 44% fT > 2 μg/ml, respectively, with a concomitant cefepime PK-PD target of 40 to 60% fT > cefepime-enmetazobactam MIC. These findings support clinical dose selection and breakpoint setting for cefepime-enmetazobactam.

High Prevalence of 16s rRNA Methylase Genes Among Carbapenem-Resistant Hypervirulent Klebsiella pneumoniae Isolates in a Chinese Tertiary Hospital

Thirty-nine carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP) isolates collected from a Chinese tertiary hospital were used in the characterization of the prevalence of 16S rRNA methylase genes. In total, 66.7% (26/39) of the CR-hvKP isolates were found to carry 16S rRNA methylase genes. The most frequently detected 16S rRNA methylase gene was armA (11/26, 42.3%), followed by rmtB (8/26, 30.8%), and coexistence of both armA and rmtB (7/26, 26.9%). All the clinical isolates were found to carry at least one carbapenemase gene, with blaKPC-2 (79.5%, 31/39), blaNDM-1 (10.3%, 4/39), and cocarrying blaKPC-2 and blaNDM-1 (10.3%, 4/39). A total of 89.7% (35/39) isolates carried extended-spectrum β-lactamase (ESBL) genes, including 61.5% (24/39) blaSHV-1, 71.8% (28/39) blaTEM-1, and 89.7% (35/39) blaCTX-M-14. All except four isolates (89.7%, 35/39) harbored quinolone resistance genes, with qnrS (82.1%, 32/39), aac(6')-Ib-cr (79.5%, 31/39), and qnrB (2.6%, 1/39). Twenty-six hvKP strains in this study were first reported to cocarry carbapenemase genes, ESBL genes, quinolone resistance genes, and 16S rRNA methylase genes simultaneously. Multilocus sequence typing (MLST) analysis assigned the 39 CR-hvKP isolates into 4 sequence types (STs), with ST11 encompassing 79.5% of the strains. Pulsed field gel electrophoresis (PFGE) typing showed that strains closely related by MLST clustered in major PFGE clusters, of which cluster A accounts for 31 ST11 isolates. Cumulatively, 16S rRNA methylase genes are highly prevalent in CR-hvKP clinical isolates especially for ST11; it is, therefore, critical to continuously monitor the epidemiology of these 16S rRNA methylase-producing CR-hvKP while simultaneously minimizing potential risks from aminoglycoside-resistant CR-hvKP.

Adaptive evolution of virulence and persistence in carbapenem-resistant Klebsiella pneumoniae

Among the most urgent public health threats is the worldwide emergence of carbapenem-resistant Enterobacteriaceae1-4, which are resistant to the antibiotic class of 'last resort'. In the United States and Europe, carbapenem-resistant strains of the Klebsiella pneumoniae ST258 (ref. 5) sequence type are dominant, endemic6-8 and associated with high mortality6,9,10. We report the global evolution of pathogenicity in carbapenem-resistant K. pneumoniae, resulting in the repeated convergence of virulence and carbapenem resistance in the United States and Europe, dating back to as early as 2009. We demonstrate that K. pneumoniae can enhance its pathogenicity by adopting two opposing infection programs through easily acquired gain- and loss-of-function mutations. Single-nucleotide polymorphisms in the capsule biosynthesis gene wzc lead to hypercapsule production, which confers phagocytosis resistance, enhanced dissemination and increased mortality in animal models. In contrast, mutations disrupting capsule biosynthesis genes impair capsule production, which enhances epithelial cell invasion, in vitro biofilm formation and persistence in urinary tract infections. These two types of capsule mutants have emerged repeatedly and independently in Europe and the United States, with hypercapsule mutants associated with bloodstream infections and capsule-deficient mutants associated with urinary tract infections. In the latter case, drug-tolerant K. pneumoniae can persist to yield potentially untreatable, persistent infection.

Molecular and Clinical Characterization of Multidrug-Resistant and Hypervirulent Klebsiella pneumoniae Strains from Liver Abscess in Taiwan

Hypervirulent Klebsiella pneumoniae strains are the major cause of liver abscesses throughout East Asia, and these strains are usually antibiotic susceptible. Recently, multidrug-resistant and hypervirulent (MDR-HV) K. pneumoniae strains have emerged due to hypervirulent strains acquiring antimicrobial resistance determinants or the transfer of a virulence plasmid into a classic MDR strain. In this study, we characterized the clinical and microbiological properties of K. pneumoniae liver abscess (KPLA) caused by MDR-HV strains in Taiwan. Patients with community onset KPLA were retrospectively identified at Taipei Veterans General Hospital during January 2013 to May 2018. Antimicrobial resistance mechanisms, capsular types, and sequence types were determined. MDR-HV strains and their parental antimicrobial-susceptible strains further underwent whole-genome sequencing (WGS) and in vivo mice lethality tests. Thirteen MDR-HV strains were identified from a total of 218 KPLA episodes. MDR-HV strains resulted in similar outcomes to antimicrobial-susceptible strains. All MDR-HV strains were traditional hypervirulent clones carrying virulence capsular types. The major resistance mechanisms were the overexpression of efflux pumps and/or the acquisition of ESBL or AmpC β-lactamase genes. WGS revealed that two hypervirulent strains had evolved to an MDR phenotype due to mutation in the ramR gene and the acquisition of an SHV-12-bearing plasmid, respectively. Both these MDR-HV strains retained high virulence compared to their parental strains. The spread of MDR-HV K. pneumoniae strains in the community raises significant public concerns, and measures should be taken to prevent the further acquisition of carbapenemase and other resistance genes among these strains in order to avoid the occurrence of untreatable KPLA.

Identification of hypervirulent Klebsiella pneumoniae isolates using the string test in combination with Galleria mellonella infectivity

Distinguishing between hypervirulent Klebsiella pneumoniae (hvKp) and classical Klebsiella pneumoniae (cKp) is a challenge to clinical laboratories. The aim of this study was to determine the practicability of combining the G. mellonella killing assay with a string test to differentiate hvKp from cKp. One hundred and three clinical K. pneumoniae isolates were collected. PCR amplification and wzi sequencing were used to determine the capsular serotype. Virulence genes allS, iro, iuc, and rmpA2, used frequently to identify hvKp, were detected by PCR. The virulence of K. pneumoniae isolates was evaluated using the following assays in parallel: molecular markers detection, G. mellonella killing assay alone, G. mellonella killing assay combined with the string test, and mouse infection. The results showed that the sensitivity, specificity, positive predictive value, and negative predictive value of combining the G. mellonella killing assay with a string test were 95.56%, 94.83%, 93.48%, and 96.49%, respectively, compared with mouse infection used as a positive reference. These values were significantly greater than those obtained using the G. mellonella killing assay only. The sensitivity, specificity, positive predictive value, and negative predictive value of allS, iro, iuc, and rmpA2 were greater than 77.78%, but less than combining the G. mellonella killing assay and string test. G. mellonella killing assay used in conjugation with the string test is a relatively simple and accurate method to assess K. pneumoniae virulence and differentiate between hvKp and cKp.

Human host-defense peptide LL-37 targets stealth siderophores

A growing number of evidence shows that human-associated microbiota is an important contributor in health and disease. However, much of the complexity of host-microbiota interaction remains to be elucidated both at cellular and molecular levels. Siderophores are chemically diverse, ferric-specific chelators synthesized and secreted by microbes to secure their iron acquisition. The host defense peptide LL-37 is ubiquitously produced at epithelial surfaces modulating microbial communities and suppressing pathogenic strains. The present work demonstrates that LL-37 binds tightly siderocalin-resistant stealth siderophores which are important contributors to the virulence of several pathogens. As indicated by circular dichroism spectroscopic experiments, addition of aerobactin and rhizoferrin increases the membrane active α-helical conformation of the partially folded peptide. The cationic nature of LL-37 (+6 net charge at pH 7.4) and the multiple carboxylate groups present in siderophores refer to the dominant contribution of electrostatic interactions in the stabilization of peptide-chelator adducts. It is proposed that aside siderocalin proteins, LL-37 may be a complementary, less specific component of the siderophore scavenging repertoire of the innate immune system.

The emergence of the hypervirulent Klebsiella pneumoniae (hvKp) strains among circulating clonal complex 147 (CC147) harbouring blaNDM/OXA-48 carbapenemases in a tertiary care center of Iran

Background

Klebsiella pneumoniae is a public health concern because of its ability to develop multidrug resistance and hypervirulent genotypes, of those capsular types K1 and K2 cause community and nosocomial life-threatening infections. This study aimed to determine the antibiotic susceptibility patterns and genotypic traits of a collection of Klebsiella spp. isolates. Furthermore, the clonal relatedness of bla_NDM producing strains was investigated.

Methods

During a 19-months  surveillance study, 122 Klebsiella spp. isolates were cultured from extraintestinal specimens of patients admitted to the tertiary referral hospital in Semnan, Iran. Isolates were identified using biochemical tests and subjected to determination of phylogroups, capsular types and virulence/resistance genes content. Hypervirulent K. pneumoniae (hvKp) strains were detected genotypically, and Enterobacterial Repetitive Intergenic Consensus (ERIC)-PCR fingerprinting was used to determine the clonality of bla_NDM producing strains.

Results

Multidrug resistant phenotype was detected in 75 (61.5%) isolates and amikacin was found as the most potent antibiotic with the susceptibility rate of 85.2%. The carbapenemase genes were detected in 45 (36.8%) strains, including 21 (17.2%) bla_OXA-48, 7 (5.6%) bla_NDM-1, 14 (11.4%) bla_NDM-1/OXA-48 and 3 (2.4%) bla_IMP- carrying strains, while 55 (45.08%) isolates showed carbapenem resistant phenotype. The first bla_NDM-1 carrying strain was cultured from a sputum specimen on March 2015, while the last positive one was recovered from blood culture on September 2016. Most of the isolates (80.3%) belonged to phylogroup I, and bla_NDM-1 was identified among all three phylogroups. The ERIC-PCR clustered the 101 bla_NDM negative and 21 bla_NDM-1 positive isolates into 25 and five clusters, respectively, and the latter group belonged to clonal complex 147 (CC147). One K1 and 15 K2 bla_NDM-1 negative isolates were detected, of those three strains were identified as hvKp. Five K2 positive strains, including four bla_OXA-48 producer and one hvKp sequence type 86 (ST86) were carbapenem resistant. Among carbapenem resistant isolates, CC147 strains harboured higher rates of siderophores iutA and ybtS.

Conclusion

The present findings showed a hospital circulation of CC147 bla_NDM-1 or bla_NDM-1/OXA-48 producing strains, disseminated in different wards. The hvKp/ST86 strain expressing K2 capsular type and carbapenem resistant phenotype wasn’t reported from Iran so far. So, it seems that we must be aware of the emergence and spread of new K. pneumoniae clones associated with resistant and hypermucoviscous phenotypes.

Prevalence and characteristics of pks gene cluster harbouring Klebsiella pneumoniae from bloodstream infection in China

Bloodstream infection (BSI), caused by Klebsiella pneumoniae, is associated with high morbidity and mortality, where the pks gene cluster plays a major role in their occurrence and prevalence. Information on the prevalence and characteristics of this gene cluster in K. pneumoniae is currently limited in mainland China. We therefore undertook a multicentre longitudinal study which revealed the prevalence, overall, community-onset and hospital-acquired BSI to be 20.5%, 28.3% and 13.0%, respectively. Compared to pks-negative, pks-positive isolates were significantly more susceptible to antimicrobial agents with a low incidence (5.1%) of multidrug-resistance and with infrequent extended-spectrum beta-lactamase (ESBL) production. Among pks-positive isolates, ST23 (78/117) and ST65 (20/117) were the dominant sequence types, and the majority harboured virulence genes. Community-onset BSI patients infected with pks-positive isolates had a higher proportion of liver abscesses and a lower proportion of biliary obstructions (P < 0.05). The pks-positive isolates were mostly sporadic in the phylogenetic tree, with a 65.8 and 47.0 average allele difference between Clade 1 and Clade 2, respectively. We concluded that although pks-positive K. pneumoniae were generally susceptible to antimicrobials, the high prevalence of such isolates in community cases and the genotoxicity, merits further investigation.

Hypervirulent Klebsiella pneumoniae - clinical and molecular perspectives

Hypervirulent Klebsiella pneumoniae (hvKp) has emerged as a concerning global pathogen. hvKp is more virulent than classical K. pneumoniae (cKp) and capable of causing community-acquired infections, often in healthy individuals. hvKp is carried in the gastrointestinal tract, which contributes to its spread in the community and healthcare settings. First recognized in Asia, hvKp arose as a leading cause of pyogenic liver abscesses. In the decades since, hvKp has spread globally and causes a variety of infections. In addition to liver abscesses, hvKp is distinct from cKp in its ability to metastasize to distant sites, including most commonly the eye, lung and central nervous system (CNS). hvKp has also been implicated in primary extrahepatic infections including bacteremia, pneumonia and soft tissue infections. The genetic determinants of hypervirulence are often found on large virulence plasmids as well as chromosomal mobile genetic elements which can be used as biomarkers to distinguish hvKp from cKp clinical isolates. These distinct virulence determinants of hvKp include up to four siderophore systems for iron acquisition, increased capsule production, K1 and K2 capsule types, and the colibactin toxin. Additionally, hvKp strains demonstrate hypermucoviscosity, a phenotypic description of hvKp in laboratory conditions that has become a distinguishing feature of many hypervirulent isolates. Alarmingly, multidrug-resistant hypervirulent strains have emerged, creating a new challenge in combating this already dangerous pathogen.

Population genomics of Klebsiella pneumoniae

Klebsiella pneumoniae is a common cause of antimicrobial-resistant opportunistic infections in hospitalized patients. The species is naturally resistant to penicillins, and members of the population often carry acquired resistance to multiple antimicrobials. However, knowledge of K. pneumoniae ecology, population structure or pathogenicity is relatively limited. Over the past decade, K. pneumoniae has emerged as a major clinical and public health threat owing to increasing prevalence of healthcare-associated infections caused by multidrug-resistant strains producing extended-spectrum β-lactamases and/or carbapenemases. A parallel phenomenon of severe community-acquired infections caused by 'hypervirulent' K. pneumoniae has also emerged, associated with strains expressing acquired virulence factors. These distinct clinical concerns have stimulated renewed interest in K. pneumoniae research and particularly the application of genomics. In this Review, we discuss how genomics approaches have advanced our understanding of K. pneumoniae taxonomy, ecology and evolution as well as the diversity and distribution of clinically relevant determinants of pathogenicity and antimicrobial resistance. A deeper understanding of K. pneumoniae population structure and diversity will be important for the proper design and interpretation of experimental studies, for interpreting clinical and public health surveillance data and for the design and implementation of novel control strategies against this important pathogen.

The intersection of capsule gene expression, hypermucoviscosity and hypervirulence in Klebsiella pneumoniae

For ∼30 years, two distinct groups of clinical isolates of Klebsiella pneumoniae have been recognized. Classical strains (cKp) are typically isolated from patients with some degree of immunocompromise and are not virulent in mouse models of infection whereas hypervirulent strains (hvKp) are associated with community acquired invasive infections and are highly virulent in mouse models of infection. Hyperproduction of capsule and a hypermucoviscous colony phenotype have been strongly associated with the hypervirulence of hvKp strains. Recent studies have begun to elucidate the relationship between capsule gene expression, hypermucoviscosity and hypervirulence. Additionally, genes associated with hyperproduction of capsule and hypermucoviscosity in hvKp strains have been identified in a few cKp isolates. However, it is not clear how the acquisition of these genes impacts the virulence of cKp isolates. A better understanding of the potential risks of these strains is particularly important given that many of them are resistant to multiple antibiotics, including carbapenems.

Emergence of ST11-K47 and ST11-K64 hypervirulent carbapenem-resistant Klebsiella pneumoniae in bacterial liver abscesses from China: a molecular, biological, and epidemiological study

Background: Multidrug-resistant bacteria, especially those with high virulence, are an emerging problem in clinical settings.

Methods: We conducted a multicentre epidemiological and comparative genomic analysis on the evolution, virulence and antimicrobial resistance of carbapenem-resistant Enterobacteriaceae in patients with bacterial liver abscesses from 2012 to 2016.

Results: A total of 477 bacterial isolates were collected. Enterobacteriaceae were the main pathogen (89.3%) with K. pneumoniae (52.4%) predominating followed by Escherichia coli (26.8%). All CRKps (3.2%) were of sequence type (ST) 11 and serotypes K47 or K64, and simultaneously possessed acquired bla_KPC-2/bla_KPC-5 and bla_CTX-M-65 together with the multidrug transporter EmrE. Seven Hv-CRKps (five ST11-K47, two ST11-K64) were confirmed by bacteriological test, neutrophil killing assay and Galleria mellonella infection model. Genomic analysis indicated that the emergence of one ST11-K64 Hv-CRKp strain was related to the acquisition of rmpA/rmpA2 genes and siderophore gene clusters, while ST11-K47 Hv-CRKp lacked these traditional virulence genes. Further complete genome analysis of one ST11-K47 Hv-CRKp strain, R16, showed that it acquired a rare plasmid (pR16-Hv-CRKp1) carrying bla_KPC-2, bla_SHV-12, bla_TEM-1, bla_CTX-M-65, rmtB and a predicted virulence gene R16_5486 simultaneously.

Conclusion: The emergence of the ST11-K47/K64 Hv-CRKps, which are simultaneously multidrug-resistant and hypervirulent, requires urgent control measures to be implemented.

Genomic surveillance for hypervirulence and multi-drug resistance in invasive Klebsiella pneumoniae from South and Southeast Asia

BACKGROUND

Klebsiella pneumoniae is a leading cause of bloodstream infection (BSI). Strains producing extended-spectrum beta-lactamases (ESBLs) or carbapenemases are considered global priority pathogens for which new treatment and prevention strategies are urgently required, due to severely limited therapeutic options. South and Southeast Asia are major hubs for antimicrobial-resistant (AMR) K. pneumoniae and also for the characteristically antimicrobial-sensitive, community-acquired "hypervirulent" strains. The emergence of hypervirulent AMR strains and lack of data on exopolysaccharide diversity pose a challenge for K. pneumoniae BSI control strategies worldwide.

METHODS

We conducted a retrospective genomic epidemiology study of 365 BSI K. pneumoniae from seven major healthcare facilities across South and Southeast Asia, extracting clinically relevant information (AMR, virulence, K and O antigen loci) using Kleborate, a K. pneumoniae-specific genomic typing tool.

RESULTS

K. pneumoniae BSI isolates were highly diverse, comprising 120 multi-locus sequence types (STs) and 63 K-loci. ESBL and carbapenemase gene frequencies were 47% and 17%, respectively. The aerobactin synthesis locus (iuc), associated with hypervirulence, was detected in 28% of isolates. Importantly, 7% of isolates harboured iuc plus ESBL and/or carbapenemase genes. The latter represent genotypic AMR-virulence convergence, which is generally considered a rare phenomenon but was particularly common among South Asian BSI (17%). Of greatest concern, we identified seven novel plasmids carrying both iuc and AMR genes, raising the prospect of co-transfer of these phenotypes among K. pneumoniae.

CONCLUSIONS

K. pneumoniae BSI in South and Southeast Asia are caused by different STs from those predominating in other regions, and with higher frequency of acquired virulence determinants. K. pneumoniae carrying both iuc and AMR genes were also detected at higher rates than have been reported elsewhere. The study demonstrates how genomics-based surveillance-reporting full molecular profiles including STs, AMR, virulence and serotype locus information-can help standardise comparisons between sites and identify regional differences in pathogen populations.

Genomic surveillance for hypervirulence and multi-drug resistance in invasive Klebsiella pneumoniae from South and Southeast Asia

BACKGROUND

Klebsiella pneumoniae is a leading cause of bloodstream infection (BSI). Strains producing extended-spectrum beta-lactamases (ESBLs) or carbapenemases are considered global priority pathogens for which new treatment and prevention strategies are urgently required, due to severely limited therapeutic options. South and Southeast Asia are major hubs for antimicrobial-resistant (AMR) K. pneumoniae and also for the characteristically antimicrobial-sensitive, community-acquired "hypervirulent" strains. The emergence of hypervirulent AMR strains and lack of data on exopolysaccharide diversity pose a challenge for K. pneumoniae BSI control strategies worldwide.

METHODS

We conducted a retrospective genomic epidemiology study of 365 BSI K. pneumoniae from seven major healthcare facilities across South and Southeast Asia, extracting clinically relevant information (AMR, virulence, K and O antigen loci) using Kleborate, a K. pneumoniae-specific genomic typing tool.

RESULTS

K. pneumoniae BSI isolates were highly diverse, comprising 120 multi-locus sequence types (STs) and 63 K-loci. ESBL and carbapenemase gene frequencies were 47% and 17%, respectively. The aerobactin synthesis locus (iuc), associated with hypervirulence, was detected in 28% of isolates. Importantly, 7% of isolates harboured iuc plus ESBL and/or carbapenemase genes. The latter represent genotypic AMR-virulence convergence, which is generally considered a rare phenomenon but was particularly common among South Asian BSI (17%). Of greatest concern, we identified seven novel plasmids carrying both iuc and AMR genes, raising the prospect of co-transfer of these phenotypes among K. pneumoniae.

CONCLUSIONS

K. pneumoniae BSI in South and Southeast Asia are caused by different STs from those predominating in other regions, and with higher frequency of acquired virulence determinants. K. pneumoniae carrying both iuc and AMR genes were also detected at higher rates than have been reported elsewhere. The study demonstrates how genomics-based surveillance-reporting full molecular profiles including STs, AMR, virulence and serotype locus information-can help standardise comparisons between sites and identify regional differences in pathogen populations.

The Galleria mellonella Infection Model Does Not Accurately Differentiate between Hypervirulent and Classical Klebsiella pneumoniae

Hypervirulent Klebsiella pneumoniae (hvKp) is of increasing concern because it can infect individuals in community and health care settings and because such infections are becoming difficult to treat. Identification of hvKp is important for patient care and to track its global spread. The genetic definition of hvKp, which can be used for its identification and the development of diagnostic tests, has not been optimized. Determination of possession of 4 of 5 genes that are present on the hvKp-specific virulence plasmid is highly accurate for identifying hvKp. However, an ongoing issue is whether strains that possess only some of these markers are still hypervirulent. The Galleria mellonella model and, less commonly, the murine infection model have been used to assess the virulence of these ambiguously identifiable strains. This report demonstrates that the murine model but not the G. mellonella model accurately identifies suspected hvKp strains. This information is critical for the development of diagnostics for patient care and for future research studies.

Hypervirulent Klebsiella pneumoniae (hvKp) is an emerging pathogen of increasing concern due to its ability to cause serious organ and life-threatening infections in healthy individuals and its increasing acquisition of antimicrobial resistance determinants. Identification of hvKp is critical for patient care and epidemiologic and research studies. Five genotypic markers on the hvKp-specific virulence plasmid can accurately differentiate hvKp from the less virulent classical K. pneumoniae (cKp) strain, but it is unclear whether the possession of fewer markers accurately predicts the hvKp pathotype. Likewise, the effect, if any, of various antimicrobial resistance factors on the pathogenic potential of hvKp has been incompletely explored. The Galleria mellonella infection model is often used to assess virulence, but this tool has not been validated. Therefore, levels of lethality of defined hvKp and cKp strain cohorts were compared in Galleria and outbred mouse models. The murine model, but not the G. mellonella model, accurately differentiated hvKp from cKp strains. Therefore, isolates in which the pathogenic potential is ambiguous due to an incomplete hvKp biomarker profile, an incomplete pLVPK-like hvKp-specific virulence plasmid, antimicrobial resistance that could decrease biofitness, and/or the lack of a characteristic clinical presentation should be validated in an outbred murine model. These data will assist in determining the minimal genomic content needed for full expression of the hypervirulence phenotype. This information, in turn, is critical for the development of the pragmatic point-of-care testing requisite for patient care and for the performance of epidemiologic and research studies going forward.

IMPORTANCE Hypervirulent Klebsiella pneumoniae (hvKp) is of increasing concern because it can infect individuals in community and health care settings and because such infections are becoming difficult to treat. Identification of hvKp is important for patient care and to track its global spread. The genetic definition of hvKp, which can be used for its identification and the development of diagnostic tests, has not been optimized. Determination of possession of 4 of 5 genes that are present on the hvKp-specific virulence plasmid is highly accurate for identifying hvKp. However, an ongoing issue is whether strains that possess only some of these markers are still hypervirulent. The Galleria mellonella model and, less commonly, the murine infection model have been used to assess the virulence of these ambiguously identifiable strains. This report demonstrates that the murine model but not the G. mellonella model accurately identifies suspected hvKp strains. This information is critical for the development of diagnostics for patient care and for future research studies.

Vaccine Protection against Multidrug-Resistant Klebsiella pneumoniae in a Nonhuman Primate Model of Severe Lower Respiratory Tract Infection

Klebsiella pneumoniae is a human gut communal organism and notorious opportunistic pathogen. The relative high burden of asymptomatic colonization by K. pneumoniae is often compounded by multidrug resistance-a potential problem for individuals with significant comorbidities or other risk factors for infection. A carbapenem-resistant K. pneumoniae strain classified as multilocus sequence type 258 (ST258) is widespread in the United States and is usually multidrug resistant. Thus, treatment of ST258 infections is often difficult. Inasmuch as new preventive and/or therapeutic measures are needed for treatment of such infections, we developed an ST258 pneumonia model in cynomolgus macaques and tested the ability of an ST258 capsule polysaccharide type 2 (CPS2) vaccine to moderate disease severity. Compared with sham-vaccinated animals, those vaccinated with ST258 CPS2 had significantly less disease as assessed by radiography 24 h after intrabronchial installation of 108 CFU of ST258. All macaques vaccinated with CPS2 ultimately developed ST258-specific antibodies that significantly enhanced serum bactericidal activity and killing of ST258 by macaque neutrophils ex vivo Consistent with a protective immune response to CPS2, transcripts encoding inflammatory mediators were increased in infected lung tissues obtained from CPS-vaccinated animals compared with control, sham-vaccinated macaques. Taken together, our data provide support for the idea that vaccination with ST258 CPS can be used to prevent or moderate infections caused by ST258. As with studies performed decades earlier, we propose that this prime-boost vaccination approach can be extended to include multiple capsule types.IMPORTANCE Multidrug-resistant bacteria continue to be a major problem worldwide, especially among individuals with significant comorbidities and other risk factors for infection. K. pneumoniae is among the leading causes of health care-associated infections, and the organism is often resistant to multiple classes of antibiotics. A carbapenem-resistant K. pneumoniae strain known as multilocus sequence type 258 (ST258) is the predominant carbapenem-resistant Enterobacteriaceae in the health care setting in the United States. Infections caused by ST258 are often difficult to treat and new prophylactic measures and therapeutic approaches are needed. To that end, we developed a lower respiratory tract infection model in cynomolgus macaques in which to test the ability of ST258 CPS to protect against severe ST258 infection.

Pup mortality in New Zealand sea lions (Phocarctos hookeri) at Enderby Island, Auckland Islands, 2013-18

New Zealand sea lions (Phocarctos hookeri) are an endemic and endangered species. Pup mortality at Enderby Island (50.5°S, 166.28°E) in the New Zealand sub-Antarctic has been well studied, with subsequent investigations yielding more intricate detail of the causes of mortality, as new diagnostic methods become available. Klebsiella pneumoniae was first reported in 2001-02 at this site, causing a pup mortality epizootic and is now known to be present at several colonies. This bacterium is a common mucosal commensal of humans and animals, however the agent found in pups at necropsy is a hypervirulent strain, readily recognised in microbial culture as being hypermucoviscous. Infection causes septicaemia with a common syndrome of subsequent meningitis and polyarthritis. This investigation uses histopathology and microbiology, with new modalities such as matrix assisted laser desorption/ionisation-time of flight mass spectrometry to show that Klebsiella septicaemia could have historically been, and continues to be, the most important cause of pup mortality, but has been previously underrepresented due to the often cryptic presentation and sometimes peracute course of disease. Hypermucoviscous K. pneumoniae should be considered a serious threat to pup survival in the species, causing on average 60.2% of pup deaths annually at Enderby Island between 2013 and 2018, with likely more continuing mortality following pup dispersal and the cessation of the summer monitoring season. Less common causes of death included starvation (14.8%), trauma/asphyxiation (9.9%) and other infections (7%). This study forms the basis for further evaluation of risk factors for pup mortality in the species, with a view to developing active mitigation.

Burden of bacterial bloodstream infection-a brief update on epidemiology and significance of multidrug-resistant pathogens

BACKGROUND

Bloodstream infections comprise a wide variety of pathogens and clinical syndromes with considerable overlap with similar syndromes of non-bacteraemic infections and diverse risk factors, therapeutic implications and outcomes. Yet, this heterogeneous 'entity' has the advantage to be pathogen-defined compared with the broad and even more heterogeneous entity 'sepsis', and so has become helpful for clinicians and epidemiologists for research and surveillance purposes. The increasing availability of population-based and large multicentre well-defined cohort studies should allow us to assess with much confidence and in detail its burden, the significance of antimicrobial resistance, and areas of uncertainty regarding further epidemiological evolution and optimized treatment regimens.

AIM

To review key aspects of bloodstream infection epidemiology and burden, and summarize recent news and questions concerning critical developments.

SOURCES

Peer-reviewed articles based on the search terms 'bloodstream infection' and 'bacteremia' combined with the terms 'epidemiology' and 'burden'. The emphasis was on new information from studies in adult patients and on the added burden due to pathogen resistance to first- and second-line antimicrobial agents.

CONTENT

Topics covered include recent developments in the epidemiology of bloodstream infection due to key pathogens and published information about the relevance of resistance for patient outcomes.

IMPLICATIONS

Despite the availability of population-based studies and an increasing number of large well-defined multicentre cohort studies, more surveillance and systematic data on bloodstream infection epidemiology at regional level and in resource-limited settings may be needed to better design new methods for prevention and define the need for and further develop optimized therapeutic strategies.

Targeting the Sugary Armor of Klebsiella Species

The emergence of multidrug-resistant strains of Gram-negative Klebsiella species is an urgent global threat. The World Health Organization has listed Klebsiella pneumoniae as one of the global priority pathogens in critical need of next-generation antibiotics. Compared to other Gram-negative pathogens, K. pneumoniae accumulates a greater diversity of antimicrobial-resistant genes at a higher frequency. The evolution of a hypervirulent phenotype of K. pneumoniae is yet another concern. It has a broad ecological distribution affecting humans, agricultural animals, plants, and aquatic animals. Extracellular polysaccharides of Klebsiella, such as lipopolysaccharides, capsular polysaccharides, and exopolysaccharides, play crucial roles in conferring resistance against the host immune response, as well as in colonization, surface adhesion, and for protection against antibiotics and bacteriophages. These extracellular polysaccharides are major virulent determinants and are highly divergent with respect to their antigenic properties. Wzx/Wzy-, ABC-, and synthase-dependent proteinaceous nano-machineries are involved in the biosynthesis, transport, and cell surface expression of these sugar molecules. Although the proteins involved in the biosynthesis and surface expression of these sugar molecules represent potential drug targets, variation in the amino acid sequences of some of these proteins, in combination with diversity in their sugar composition, poses a major challenge to the design of a universal drug for Klebsiella infections. This review discusses the challenges in universal Klebsiella vaccine and drug development from the perspective of antigen sugar compositions and the proteins involved in extracellular antigen transport.