Hypervirulent Klebsiella pneumoniae

Antimicrobial resistance in hypermucoviscous and non-hypermucoviscous Klebsiella pneumoniae: a systematic review and meta-analysis

Antimicrobial resistance has recently increased due to emerging carbapenem-resistant Klebsiella pneumoniae and extended-spectrum β-lactamase (ESBL)-producing strains of K. pneumoniae, especially among hypermucoviscous K. pneumoniae (hmKp) strains. To evaluate the prevalence of ESBL-producing and carbapenem-resistant strains in hmKp and non-hmKp clinical isolates through a systematic review and meta-analysis. We searched PubMed, Scopus, and Cochrane Library databases from January 2000 to June 2023. Clinical and in vivo/in vitro studies involving confirmed K. pneumoniae clinical isolates differentiated into hmKP and non-hmKP strains based on string test results. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated based on the number of individuals in each target group. Forest plots were used to visualize the effect sizes and 95% CIs of individual studies estimated using the inverse variance and DerSimonian - Laird methods with fixed - and random-effects models, respectively. Heterogeneity was assessed using Cochran's Q test (I2 ≥ 50%). Fifteen studies comprising 2049 clinical isolates of K. pneumoniae met the inclusion criteria. Meta-analysis revealed that hmKp strains were associated with a significantly lower prevalence of ESBL-producing strains (pooled OR: 0.26, 95% CI: 0.11-0.63, P = 0.003) and a slightly lower prevalence of carbapenem-resistant strains than non-hmKp strains (pooled OR: 0.63, 95% CI: 0.40-0.97, P = 0.038). hmKp strains exhibited lower and slightly lower prevalence of ESBL production and carbapenem resistance, respectively, than non-hmKp strains. However, given the rising prevalence of ESBL-producing and carbapenem-resistant hmKp strains, patients infected by string-test-positive K. pneumoniae must be managed prudently, considering the potential for highly resistant strains.

A study of clinical and bacteriological characteristics of Klebsiella pneumoniae isolates in Birjand, South-East Iran: Hypervirulent phenotype, biofilm formation, virulence factors, and antibiotic resistance

This study assessed antimicrobial susceptibility, biofilm formation, hypervirulence traits, and virulence-related genes in K. pneumoniae. 119 isolates underwent antibiotic susceptibility testing using the Kirby-Bauer method, biofilm assessment through Congo red agar and Microtiter plate assays, PCR for various genes, and the String test for hypermucoviscosity. Clinical characteristics and virulence factors of hypervirulent (hvKP) were compared to classic K. pneumoniae (cKP) strains. Among the isolates, 77.3% were multi-drug resistant (MDR), and 83.2% showed biofilm-forming ability, with a higher MDR incidence in biofilm producers. A significant correlation was found between biofilm formation and the presence of the blaCTX-M15 gene. Genes luxS, mrkA, pgaA, and wzm were significantly related to biofilm production. Three K. pneumoniae (2.5%) were identified as hvKP, with higher prevalence of capsular serotypes K1/K2 and virulence-related genes iuc, rmpA, and rmpA2 than cKP. The study underscores the importance of surveillance and stewardship in combating MDR, biofilm-forming, highly virulent K. pneumoniae.

Diverse polysaccharide production and biofilm formation abilities of clinical Klebsiella pneumoniae

Klebsiella pneumoniae infections have become a growing threat for human health. The lack of understanding of the relationship between antibiotic resistance, mucoviscosity, and biofilm formation impedes our abilities to effectively predict K. pneumoniae infection outcomes. The Multidrug-Resistant Organism Repository and Surveillance Network offers a unique opportunity into the genetic and phenotypic variabilities in the K. pneumoniae isolates. To this end, we compared the genetic profiles of these isolates with the phenotypic biofilm formation, percent mucoviscosity, and growth rates. There was a significant phenotype-genotype correlation with decreased biofilm formation and an insertion sequence in the transcriptional activator of the type III fimbrial system. Interestingly, the most mucoid strains in the populations were lacking the genetic element regulating the mucoid phenotype and three of these isolates were able to form robust biofilms. The combination of phenotypic, genomic, and image analyses revealed an intricate relation between growth, mucoviscosity and specific virulence-associated genetic determinants.

Phenotypic and genomic characterization of ST11-K1 CR-hvKP with highly homologous blaKPC-2-bearing plasmids in China

Carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP) strains present a significant global public health threat due to their high mortality rates. This study investigated the genomic characteristics of seven ST11-K1 CR-hvKP isolates harboring highly homologous KPC-2-encoding multidrug-resistance plasmids. The strains were isolated from a Chinese tertiary hospital between 2017 and 2020. Whole-genome sequencing and bioinformatic analysis revealed various antibiotic resistance genes (ARGs) and virulence determinants. The blaKPC-2-bearing plasmids that contain multiple antibiotic-resistance genes were also identified in these strains. ISfinder and Orifinder were applied to identify insertion sequences (IS) and conjugation-related factors among these blaKPC-2-bearing plasmids. The blaKPC-2 was highly consistent in seven blaKPC-2-bearing plasmids (ISKpn6-blaKPC-2-ISKpn27-ISYps3-IS26). In addition, we found a region composed of ISIR, Tn5393, and IS26. It was located upstream of the blaCTX-M-15 gene and presented in six blaKPC-2-bearing plasmids, with pCR-hvKP221-KPC-P3 as an exception. Conjugation experiments demonstrated the horizontal transfer of resistance plasmids pCR-hvKP128-KPC-P1 and pCR-hvKP132-KPC-P1 across species. Notably, pLVPK-like virulence plasmids carrying virulence gene clusters pCR-hvKP173-Vir-P1, and pCR-hvKP221-Vir-P1 were also detected. A fusional plasmid pCR-hvKP221-Vir-P2, which carries virulence gene clusters and ARGs, was also identified. Five CR-hvKP strains displayed enhanced biofilm formation and high virulence in vivo infection models. Phylogenetic and single nucleotide polymorphism (SNP) analyses indicated a close genetic relationship among the isolates, suggesting a subclade. These findings highlight the complex genetic profiles and potential transmission mechanisms of CR-hvKP strains.

IMPORTANCE

We reported seven CR-hvKP strains all carried a highly homologous blaKPC-2 integrated IncFⅡ-resistant plasmid, and two strains harbored virulence plasmids. Conjugation experiments confirmed the transferability of these plasmids, indicating a potential for resistance spread. Phylogenetic analysis clarified the relationship among the CR-hvKP isolates. This study provides insights into the phenotypic and genomic characteristics of seven ST11-K1 CR-hvKP strains. The high prevalence and potential for local outbreaks emphasize the need for effective control measures.

Emergence of mcr-8.1-bearing MDR-hypervirulent Klebsiella pneumoniae ST307

We report for the first time whole-genome sequencing of four multidrug-resistant sequence type (ST) 307 Klebsiella pneumoniae recovered from patients in two hospitals in Armenia. Comparative genomic analysis revealed that the isolates were closely related, with a maximum of 39 single nucleotide polymorphism (SNP) differences in the core genome. All Armenian isolates carried the integrative and conjugative element ICEKp4, which bears the yersiniabactin locus, and shared a common evolutionary origin, diverging around 2005 (95% CI: 1999 to 2011). Antibiotic susceptibility testing showed resistance to several antibiotics, including ampicillin, amoxicillin-clavulanic acid, cefepime, ceftazidime, norfloxacin, levofloxacin, and chloramphenicol. Specifically, isolates designated as ARM03 and ARM06 were resistant to piperacillin-tazobactam, ARM04 and ARM05 had intermediate resistance to both piperacillin-tazobactam and imipenem, and ARM03 showed intermediate resistance to amikacin. We further identified antimicrobial resistance (AMR) genes in four Armenian isolates, including blaOXA-1, blaTEM-1D, blaSHV-28, dfrA14, tet(A), sul2, qnrB1, aac(6´)-Ib-cr, strA, strB and the extended-spectrum β-lactamase gene blaCTX-M-15. Additionally, ARM03 and ARM06 also obtained dfrA5, sul1, sul3, cmlA1, mphA, aph3-Ia and the unique colistin resistance gene mcr-8.1, which was absent in all other publicly available ST307 isolates. These two isolates also acquired aerobactin siderophore-encoding gene clusters (iucABCD-iutA) and the hypermucoidy locus rmpADC (ARM06 had rmpA fragment). ARM04 and ARM05, as well as ARM03 and ARM06, had nearly identical AMR and virulence genes, along with similar plasmid replicon profiles, respectively. Our findings suggest that a transmission event occurred between the two hospitals in Armenia, likely facilitated by patients or community members, during which K. pneumoniae ST307 isolates acquired plasmids carrying AMR and virulence genes.IMPORTANCEMultidrug-resistant (MDR) Klebsiella pneumoniae sequence type (ST) 307 has emerged as a high-risk clone associated with hospital- and community-acquired infections, posing a major threat to global public health. We report in-depth comparative genomics analyses of K. pneumoniae ST307 isolates recovered from patients in Armenia. The unique colistin resistance gene mcr-8.1 identified in ARM03 and ARM06 was absent in all other ST307 isolates obtained from the publicly available data sets. ARM03 and ARM06 also acquired aerobactin siderophore-encoding gene clusters (iucABCD-iutA) and the hypermucoidy locus rmpADC (ARM06 possessed incomplete rmpA fragment). Our findings suggest that a transmission event has occurred between two hospitals in Armenia either through patients or community members. In addition, the Armenian isolates obtained plasmids carrying virulence and AMR genes during the transmission event. Our study emphasises the importance of genomic surveillance of this emerging MDR-hypervirulent pathogen to provide early interventions.

Deep phosphoproteomics of Klebsiella pneumoniae reveals HipA-mediated tolerance to ciprofloxacin

Klebsiella pneumoniae belongs to the group of bacterial pathogens causing the majority of antibiotic-resistant nosocomial infections worldwide; however, the molecular mechanisms underlying post-translational regulation of its physiology are poorly understood. Here we perform a comprehensive analysis of Klebsiella phosphoproteome, focusing on HipA, a Ser/Thr kinase involved in antibiotic tolerance in Escherichia coli. We show that overproduced K. pneumoniae HipA (HipAkp) is toxic to both E. coli and K. pneumoniae and its toxicity can be rescued by overproduction of the antitoxin HipBkp. Importantly, HipAkp overproduction leads to increased tolerance against ciprofloxacin, a commonly used antibiotic in the treatment of K. pneumoniae infections. Proteome and phosphoproteome analyses in the absence and presence of ciprofloxacin confirm that HipAkp has Ser/Thr kinase activity, auto-phosphorylates at S150, and shares multiple substrates with HipAec, thereby providing a valuable resource to clarify the molecular basis of tolerance and the role of Ser/Thr phosphorylation in this human pathogen.

Prevalence and features of hypervirulent Klebsiella pneumoniae in respiratory specimens at a US hospital system

Hypervirulent Klebsiella pneumoniae (hvKp) strains are considered to be relatively rare in the United States, but cases are increasingly reported. We prospectively and serially collected K. pneumoniae clinical isolates identified in respiratory specimens at a health system in Western Pennsylvania between 2020 and 2022. A total of 273 K. pneumoniae isolates from 216 unique patients were analyzed for markers of hypervirulence by both string test for a hypermucoid phenotype and multiplex PCR to detect isolates carrying cardinal virulence genes rmpA, rmpA2, iutA, and iro. Of the 273 isolates, 13 (4.8%) tested positive by string test including 11 nonduplicate K. pneumoniae isolates, and two of these (0.7%) were positive by PCR for virulence genes rmpA, rmpA2, iutA, and iro. The latter two putative hvKp strains, belonging to sequence types ST23-K1 and ST86-SLV-K2, possessed pLVPK-like plasmids, and were collected from community-associated infections in individuals without known travel histories. Both putative hvKp strains and two additional string test-positive strains were resistant to killing by human serum. The hvKp strains caused significant pneumonia in mice infected by oropharyngeal aspiration, with significantly higher weight loss and increased bacterial burden in the lungs of mice infected with the KL1 (ST23) strain compared to the KL2 (ST86-SLV) strain. We also observed decreased survival of mice infected with the KL1 strain compared to the KL2 strain. These findings add to the growing body of evidence suggesting that hvKp strains, once considered endemic to Asia, may now be circulating in North America.IMPORTANCECertain lineages of Klebsiella pneumoniae are increasingly recognized to cause severe community-associated infection, but information on their prevalence in the United States is limited. In a prospective, sequential cohort of 273 K. pneumoniae respiratory isolates, we identified two of them as genetically defined hypervirulent K. pneumoniae. The isolates were from local residents who developed community-onset pneumonia, suggesting that hypervirulent K. pneumoniae may already be present in the community.

Effects of different carbapenemase and siderophore production on cefiderocol susceptibility in Klebsiella pneumoniae

The resistance mechanism of Gram-negative bacteria to the siderophore antibiotic cefiderocol is primarily attributed to carbapenemase and siderophore uptake pathways; however, specific factors and their relationships remain to be fully elucidated. Here, we constructed cefiderocol-resistant Klebsiella pneumoniae (CRKP) strains carrying different carbapenemases and knocked out siderophore genes to investigate the roles of various carbapenemases and siderophores in the development of cefiderocol resistance. Antimicrobial susceptibility testing revealed that both blaNDM and blaKPC significantly increased the minimum inhibitory concentration (MIC) of Klebsiella pneumoniae (KP) to cefiderocol, while blaOXA-48 showed a modest increase. Notably, KP expressing NDM exhibited a higher cefiderocol MIC compared to KP expressing KPC, although expression of NDM alone did not induce cefiderocol resistance. Laboratory evolutionary experiments demonstrated that combining pNDM with mutations in the siderophore uptake receptor gene cirA and pKPC with a mutation in the two-component system gene envZ led to KP reaching a high level of cefiderocol resistance. Although combining pOXA with mutations in the two-component system gene baeS did not induce cefiderocol resistance, it significantly reduced susceptibility. Moreover, siderophores could influence the development of cefiderocol resistance. Strains deficient in enterobactin exhibited increased susceptibility to cefiderocol, while deficiencies in yersiniabactin and salmochelin showed no significant alterations. In conclusion, carbapenemase gene expression facilitates cefiderocol resistance, but its presence alone is insufficient. Cefiderocol resistance in CRKP typically involves abnormal expression of certain genes and other factors, such as mutations in siderophore uptake receptor genes and two-component system genes. The enterobactin siderophore synthesis gene entB may also contribute to resistance.

Two outbreak cases involving ST65-KL2 and ST11-KL64 hypervirulent carbapenem-resistant Klebsiella pneumoniae: similarity and diversity analysis

The rise of the convergence of hypervirulence and carbapenem resistance in Klebsiella pneumoniae has been increasingly reported in recent years, however, there are few outbreak cases for these producing NDM carbapenemase. In this study, ST65-KL2 and ST11-KL64 hypervirulent and carbapenem-resistant K. pneumoniae (hvCRKP) were identified from two different outbreak cases: (1) clonal spreading of ST65-KL2 in five patients within transplantation wards spanning three months; and (2) clonal transmission of ST11-KL64 in ten patients across 10 months. The representative strains of ST65-KL2 and ST11-KL64 hvCRKP, K22877 and K56649, produced carbapenemase NDM-5 and dual carbapenemases KPC-2 and NDM-13, respectively, and both exhibited high-level carbapenem resistance. Moreover, virulent analysis showed that K22877 and K56649 were hypervirulent and the former possessed stronger virulence. Evolutionary pathways suggested ST65-KL2 and ST11-KL64 hvCRKP could be classified as CR-hvKP (hvKP acquiring carbapenem resistance) and hv-CRKP (CRKP acquiring hypervirulence), respectively. Unexpectedly, ST65-KL2 CR-hvKP showed resistance to ciprofloxacin mediated by plasmid acquisition as its spread, and ST11-KL64 hv-CRKP developed into enhanced virulence and macrophage resistance. Furthermore, compared to the ST65-KL2 CR-hvKP, the ST11-KL64 hv-CRKP tends to cause occult and persistent infection. Global genome analysis revealed ST11-KL64 hv-CRKP and ST65-KL2 CR-hvKP mainly carried blaKPC-2 and had significant differences in Ompk35/36, ybt, resistance and virulence. Effective surveillance should be implemented and novel therapeutic strategies are urgently needed to deal with refractory infections.

Molecular characterization of ST15 carbapenem-resistant Klebsiella pneumoniae isolated in a single patient

BACKGROUND

The carbapenem-resistant K. pneumoniae (CRKP) poses a serious threat to antibiotic applicability and public health. During treatment, K. pneumoniae (KP) frequently exhibits shifts in drug-resistant phenotypes, complicating clinical treatment as it transitions from sensitivity to resistance. In this study, we analyzed the clinical and molecular characteristics of drug resistance changes in KP strains isolated from a single patient, and the potential mechanisms underlying these resistance changes.

METHODS

Antimicrobial susceptibility test and string test were conducted to evaluate the resistant and virulent characterization of the strains. Pulsed field gel electrophoresis (PFGE) was used to investigate the homology relationship between the strains. The whole genome sequencing and phylogenetic analysis of 9 representative isolates was also performed. The transfer ability of the drug-resistant plasmid was studied by plasmid conjugation experiment. The transconjugants were verified by PCR amplification of specific genes, antimicrobial susceptibility test and PFGE.

RESULTS

Our results revealed that 9 KP strains, isolated from the same patient, exhibited 'resistance-sensitivity-resistance-sensitivity' alternately to carbapenems. The differences in DNA fingerprint bands among the nine KP isolates were ≤ 3, which can be classified as the same PFGE type. Phylogenetic analysis showed that these 9 strains constituted a distinct branch within the phylogenetic tree. All nine KP strains belonged to the ST15-KL19 clone. Six of the strains were classified as CRKP, all of which carried eleven drug resistance genes: oqxB, oqxA, fosA6, aac(3)-lld, blaSHV-28, blaKPC-2, blaOXA-1, mph(A), tet(A), catB3 and aac(6')-lb-cr, mediating drug resistance to quinolones, fosfomycin, aminoglycosides, β-lactam, carbapenems, macrolides and chloramphenicol, belonging to multi-drug resistant bacteria. The carbapenem-resistant plasmid p2-KP3762-1 was found to transfer within species, from CRKP to hypervirulent K. pneumoniae (hvKP) RJF293HA, carbapenem-sensitive K. pneumoniae (CSKP) KP3657 and E. coli C600 at a frequency of (1.19±1.58) ×10-6, (1.09±1.38) ×10-7 and (10.9±9.53) ×10-6 respectively, resulting in the dissemination of carbapenem resistance genes.

CONCLUSIONS

In this study, KP strains isolated from a single patient exhibited an alternating phenotype of resistant-sensitive-resistant-sensitive to carbapenems. The 9 KP isolates share a high degree of genetic similarity. The plasmid p2-KP3762-1, harboring the carbapenem resistance gene blaKPC-2, may undergo inter-strain and inter-clone transfer via conjugation in the patient during treatment. Furthermore, our findings suggest that the pathogens in this patient are likely to have a common ancestral origin.

Antimicrobial resistance in Klebsiella pneumoniae: an overview of common mechanisms and a current Canadian perspective

Klebsiella pneumoniae is a ubiquitous opportunistic pathogen of the family Enterobacteriaceae. K. pneumoniae is a member of the ESKAPEE pathogens (Enterococcus faecium, Staphylococcus aureus, K. pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp., and Escherichia coli), a group of bacteria that cause nosocomial infections and are able to resist killing by commonly relied upon antimicrobial agents. The acquisition of antimicrobial resistance (AMR) genes is increasing among community and clinical isolates of K. pneumoniae, making K. pneumoniae a rising threat to human health. In addition to the increase in AMR, K. pneumoniae is also thought to disseminate AMR genes to other bacterial species. In this review, the known mechanisms of K. pneumoniae AMR will be described and the current state of AMR K. pneumoniae within Canada will be discussed, including the impact of the coronavirus disease-2019 pandemic, current perspectives, and outlook for the future.

RES-Xre toxin-antitoxin locus knaAT maintains the stability of the virulence plasmid in Klebsiella pneumoniae

Hypervirulent Klebsiella pneumoniae isolates have been increasingly reported worldwide, especially hypervirulent drug-resistant variants owing to the acquisition of a mobilizable virulence plasmid by a carbapenem-resistant strain. This pLVPK-like mobilizable plasmid encodes various virulence factors; however, information about its genetic stability is lacking. This study aimed to investigate the type II toxin-antitoxin (TA) modules that facilitate the virulence plasmid to remain stable in K. pneumoniae. More than 3,000 TA loci in 2,000 K. pneumoniae plasmids were examined for their relationship with plasmid cargo genes. TA loci from the RES-Xre family were highly correlated with virulence plasmids of hypervirulent K. pneumoniae. Overexpression of the RES toxin KnaT, encoded by the virulence plasmid-carrying RES-Xre locus knaAT, halts the cell growth of K. pneumoniae and E. coli, whereas co-expression of the cognate Xre antitoxin KnaA neutralizes the toxicity of KnaT. knaA and knaT were co-transcribed, representing the characteristics of a type II TA module. The knaAT deletion mutation gradually lost its virulence plasmid in K. pneumoniae, whereas the stability of the plasmid in E. coli was enhanced by adding knaAT, which revealed that the knaAT operon maintained the genetic stability of the large virulence plasmid in K. pneumoniae. String tests and mouse lethality assays subsequently confirmed that a loss of the virulence plasmid resulted in reduced pathogenicity of K. pneumoniae. These findings provide important insights into the role of the RES-Xre TA pair in stabilizing virulence plasmids and disseminating virulence genes in K. pneumoniae.

Integrative and conjugative elements of Pasteurella multocida: Prevalence and signatures in population evolution

Pasteurella multocida (P. multocida) is a bacterial pathogen responsible for a range of infections in humans and various animal hosts, causing significant economic losses in farming. Integrative and conjugative elements (ICEs) are important horizontal gene transfer elements, potentially enabling host bacteria to enhance adaptability by acquiring multiple functional genes. However, the understanding of ICEs in P. multocida and their impact on the transmission of this pathogen remains limited. In this study, 42 poultry-sourced P. multocida genomes obtained by high-throughput sequencing together with 393 publicly available P. multocida genomes were used to analyse the horizontal transfer of ICEs. Eighty-two ICEs were identified in P. multocida, including SXT/R391 and Tn916 subtypes, as well as three subtypes of ICEHin1056 family, with the latter being widely prevalent in P. multocida and carrying multiple resistance genes. The correlations between insertion sequences and resistant genes in ICEs were also identified, and some ICEs introduced the carbapenem gene blaOXA-2 and the bleomycin gene bleO to P. multocida. Phylogenetic and collinearity analyses of these bioinformatics found that ICEs in P. multocida were transmitted vertically and horizontally and have evolved with host specialization. These findings provide insight into the transmission and evolution mode of ICEs in P. multocida and highlight the importance of understanding these elements for controlling the spread of antibiotic resistance.

Hypervirulent carbapenem-susceptible klebsiella pneumoniae ST412/K57 with strong biofilm formation: association with gas gangrene and sepsis

Hypervirulent Klebsiella pneumoniae (hvKp) poses a serious public health threat. Gas gangrene caused by hvKp is rarely reported and potentially results in a poor prognosis. This study describes the case of a hospitalised patient with gas gangrene and sepsis caused by hvKP. Carbapenem-susceptible hypervirulent Klebsiella pneumoniae (CS-hvKp) strains KPLSN and KPLSX were isolated from the knee joint pus and blood specimens of the patient for further investigations. Whole genome sequencing revealed that KPLSN and KPLSX were highly homologous (single nucleotide polymorphisms [SNPs]<10) and belonged to ST412/K57. The minimum inhibitory concentration and minimum bactericidal concentration under biofilm values of meropenem in KPLSN and KPLSX were significantly higher than in the planktonic state (>128 mg/L vs. 0.25 mg/L, P<0.0001). These two strains had high biofilm formation ability, and the results from fluorescence staining experiments showed that they were not easily killed by meropenem in the biofilm state. KPLSN and KPLSX showed high capsule production and were confirmed to have high virulence through experiments with the Galleria mellonella infection model and the BALB/c mice abdominal infection model. The persistent symptoms may be due to enhanced biofilm and capsule formation. Phylogenetic analysis of global ST412 strains showed their evolution towards higher virulence and resistance. These results emphasise the critical need for judicious antibiotic use and novel therapeutic approaches to combat special infections caused by these pathogens.

Overexpression of blaSHV-12 caused by tandem amplification contributed to ceftazidime/avibactam resistance in hypervirulent and carbapenem-resistant Klebsiella pneumoniae

We identified a novel ceftazidime/avibactam (CAZ/AVI) resistance mechanism in endemic sequence type 11 hypervirulent and carbapenem-resistant Klebsiella pneumoniae isolated from a patient who had not been exposed CAZ/AVI. Overexpression of blaSHV-12 caused by tandem gene amplification contributed to CAZ/AVI resistance instead of the carriage of blaKPC-2. Enhanced genomic surveillance is essential to identify emerging variants.

Klebsiella pneumoniae capsular polysaccharide: Mechanism in regulation of synthesis, virulence, and pathogenicity

Hypervirulent Klebsiella pneumoniae exhibits strong pathogenicity and can cause severe invasive infections but is historically recognized as antibiotic-susceptible. In recent years, the escalating global prevalence of antibiotic-resistant hypervirulent K. pneumoniae has raised substantial concerns and created an urgent demand for effective treatment options. Capsular polysaccharide (CPS) is one of the main virulence determinants contributing to the hypervirulent phenotype. The structure of CPS varies widely among strains, and both the structure and composition of CPS can influence the virulence of K. pneumoniae. CPS possesses various immune evasion mechanisms that promote the survival of K. pneumoniae, as well as its colonization and dissemination. Given the proven viability of therapies that target the capsule, improving our understanding of the CPS structure is critical to effectively directing treatment strategies. In this review, the structure and typing of CPS are addressed as well as genes related to synthesis and regulation, relationships with virulence, and pathogenic mechanisms. We aim to provide a reference for research on the pathogenesis of K. pneumoniae.

Arginine Regulates the Mucoid Phenotype of Hypervirulent Klebsiella pneumoniae

Hypervirulent Klebsiella pneumoniae is associated with severe community-acquired infections. Hypervirulent K. pneumoniae colonies typically exhibit a mucoid phenotype. K. pneumoniae mucoidy is influenced by a complex combination of environmental factors and genetic mechanisms. Mucoidy results from altered capsular polysaccharide chain length, yet the specific environmental cues regulating this phenotype and their impact on pathogenesis remain unclear. This study demonstrates that casamino acids enhance the mucoidy phenotype but do not affect total capsular polysaccharide levels. Through targeted screening of each amino acid present in casamino acids, we identified that arginine is necessary and sufficient to stimulate the mucoid phenotype without altering capsule abundance. Furthermore, arginine activates the rmpADC promoter, increasing rmpD transcript levels, which in turn modulates capsular polysaccharide chain length and diversity. The arginine regulator, ArgR, plays a pivotal role in this regulatory cascade since deleting argR decreases mucoidy and increases capsular polysaccharide chain length diversity. Additionally, the ∆argR mutant displays increased macrophage association and has a substantial competitive defect in the lungs of mice, suggesting a link between arginine-dependent gene regulation, immune evasion and in vivo fitness. We discovered that arginine-dependent regulation of mucoidy is conserved in four additional hypervirulent K. pneumoniae isolates likely via a conserved ARG binding box present in rmp promoters. Our findings support a model in which arginine activates ArgR and increases mucoidy in hypervirulent K. pneumoniae. As a result, it is possible that arginine-dependent regulation of mucoidy allows hypervirulent K. pneumoniae to adapt the cell surface across different niches. This study underscores the significance of arginine as a regulatory signal in bacterial virulence.

Molecular characterization of Klebsiella pneumoniae in clinical bovine mastitis in 14 provinces in China

The mastitis caused by Klebsiella pneumoniae (K. pneumoniae) is increasing in the dairy cows. To investigate the epidemic of K. pneumoniae of China, 131 strains were isolated from 495 clinical mastitis milk samples (26.5%) from 14 provinces in China. Among the isolates, K57 was the dominant serotype (45.0%) and 19 (14.5%) isolates were identified as hypervirulent K. pneumoniae (hvKP). The mrkA, entB, wabG and fimH genes were prevalent virulence genes while rmpA, magA, and ycf were not found in K. pneumoniae. Furthermore, K. pneumoniae had serious antibiotic resistance and multiple β-lactamase genes, including blaTEM, blaSHV, blaNDM, blaCTX-M, blaDHA, and blaKPC. Biofilm was an important factor in bacterial resistance and persistent infection, and 77.1% isolates could form biofilm. Although acylated homoserine lactone (AHL, a Gram-negative bacterial quorum sensing signal molecule) was not confirmed among the K. pneumoniae isolates, exogenous AHLs could reduce the biofilm formation ability of the K. pneumoniae strains. Three new ST types (ST6781, ST6782, and ST6783) were first identified in this study. The MLST phylogenetic tree showed the distribution of mastitis associated K. pneumoniae strains had no regular pattern, which confirmed high genomic diversity of mastitis associated K. pneumoniae. In conclusion, the high rate of isolation and serious antibiotic resistance of K. pneumonia were found in this study and indicated a potential threat to public health from the food chain.

Hypervirulent Klebsiella pneumoniae with a hypermucoviscosity phenotype challenges strategies of water disinfection for its capsular polysaccharides

Due to the strong pathogenicity of hypervirulent Klebsiella pneumoniae (hvKP), its performance against disinfectants in water should be understood to protect public health and ecological environment. Unfortunately, the disinfectant tolerance of hvKP with a hypermucoviscosity (HMV) phenotype is a critical underexplored area. Here, the tolerance of K. pneumoniae isolates to common disinfectants was evaluated, and its underlying mechanisms were clarified. Results showed that hvKP strains with HMV exhibited remarkable tolerance to triclosan (TCS), sodium hypochlorite (NaClO), and benzalkonium bromide (BB), surpassing that of low-virulent K. pneumoniae (lvKP) and Escherichia coli, which is the microbial indicator of drinking water quality. Ct value of NaClO reached 4.41 mg/L·min to kill 4-log hvKP, while the values were 2.52 and 2.28 mg/L·min to achieve 4-log killing of lvKP and E. coli, respectively. The curing of the virulence plasmid from hvKP strain K2044 revealed that capsular polysaccharide (CPS) synthesis, driven by the virulence plasmids, helped mitigate cell membrane injury and bacterial inactivation under NaClO stress; consequently, it provided a protective advantage to hvKP. Enhancing the antioxidative stress system to reduce ROS production and mitigate oxidative stress caused by NaClO further improved the disinfectant resistance of hvKP strains with HMV. This study emphasized that hvKP strains with HMV posed a considerable challenge to disinfection procedure of water treatment. It also revealed that an improved dosage of NaClO ensures bacteria killing, indicating the optimization of the design of water treatment processes involving disinfection strategies and technical parameters should be considered.

Inhibiting lipid droplet biogenesis enhances host protection against hypervirulent Klebsiella pneumoniae infections

Hypervirulent Klebsiella pneumoniae (hvKp), an emerging Kp subtype, has become a serious global pathogen. However, the information regarding host interactions and innate immune responses during hvKp infection is limited. Here, we found that hvKp clinical strains increased triacylglycerol synthesis, resulting in lipid droplets (LDs) formation via the mammalian target of rapamycin signaling pathway in RAW264.7 cells. Treatment with rapamycin, an inhibitor of this pathway, affected LDs formation and antimicrobial responses against clinical hvKp infections. In accordance with the role of LDs in modulating inflammation, the pharmacological inhibition of lipogenesis reduced proinflammatory cytokine expression during hvKp infections. In addition, inhibition of LDs formation using pharmacological inhibitors and knockdown of lipogenesis regulators decreased the intracellular survival of hvKp in macrophages. Moreover, inhibiting LDs biogenesis reduced mortality, weight loss, and bacterial loads in hvKp-infected mice. Collectively, these data suggest that LDs biogenesis is crucial in linking host immune responses to clinical hvKp infections.

The draft genome sequence of a carbapenem-resistant Klebsiella pneumoniae strain belonging to sequence type 11 and capsular type 62

Carbapenem-resistant Klebsiella pneumoniae (CRKP) of sequence type 11 (ST11) and capsular type KL47 or KL64 are dominant in China. We report the draft genome sequence of an ST11 blaKPC-2-carrying CRKP strain belonging to uncommon capsular type KL62. This strain carries virulence factors encoding multiple iron acquisition systems and mucoid regulators.

Emergence of hypervirulent and carbapenem-resistant Klebsiella pneumoniae from 2014 - 2021 in Central and Eastern China: a molecular, biological, and epidemiological study

BACKGROUND

In recent years, the hypervirulent and carbapenem-resistant Klebsiella pneumoniae has been increasingly reported worldwide. The objective of this study was to compare the antibiotic resistance and virulence profiles of carbapenem-resistant hypervirulent K.pneumoniae (CR-hvKP) and hypervirulent carbapenem-resistant K.pneumoniae (hv-CRKP) and identify the prevailing strain in clinical settings.

METHODS

In this study, hv-CRKP or CR-hvKP were identified based on the results of whole-genome analysis (WGS), multilocus sequence typing (MLST) and the antimicrobial susceptibility testing. We then compared antibiotic resistance and virulence profiles between CR-hvKP and hv-CRKP through the antimicrobial susceptibility testing and a series of virulence experiments including biofilm formation ability detection method, the resistance test against human serum, siderophore production test, neutrophil phagocytosis assay and Galleria mellonella infection model. Additionally, pathway enrichment analysis was conducted to assess the effect of SNPs on the phenotype.

RESULTS

In this study, we categorized 17.4% of hypervirulent and carbapenem-resistant K. pneumoniae strains as CR-hvKP and 82.6% as hv-CRKP. Among them, 84.2% (16/19) of CR-hvKP strains harboring carbapenemase genes exhibited lower imipenem and meropenem MIC values compared to hv-CRKP strains. The virulence potential of hv-CRKP and CR-hvKP was confirmed by using virulence experiments in vitro and in vivo, showing that virulence of the CR-hvKP strains was comparable to that of hv-CRKP strains. Notably, the 90 hv-CRKP strains were classified into 3 different ST types and 8 capsule types, each showing varying degrees of resistance and virulence. We observed that subclonal replacement was within the predominant hv-CRKP clone, with the ST11-KL64 strain, characterized by high-level resistance and virulence emerging as the currently prevailing subclone, replacing ST11-KL47. KEGG enrichment analysis showed that pathways associated with the citrate cycle (TCA cycle), glycolysis/gluconeogenesis, glutathione metabolism, two-component regulatory system, and folate metabolism were significantly enriched among the group expressing different levels of capsular polysaccharides.

CONCLUSIONS

The hv-CRKP strains exhibited a greater survival advantage in the hospital environment than CR-hvKP strains. Notably, the ST11-KL64 hv-CRKP strain which displayed a high level of resistance and hypervirulence, warrants the most clinical vigilance.

CLINICAL TRIAL NUMBER

Not applicable.

Molecular epidemiology of carbapenemase-producing Klebsiella pneumoniae in Gauteng South Africa

Klebsiella pneumoniae multidrug-resistant (MDR) high-risk clones drive the spread of antimicrobial resistance (AMR) associated infections, resulting in limited therapeutic options. This study described the genomic characteristics of K. pneumoniae MDR high-risk clones in Gauteng, South Africa. Representative carbapenem-resistant [K. pneumoniae carbapenemase (KPC)-2, New-Delhi metallo-beta (β)-lactamase (NDM)-1, oxacillinase (OXA)-181, OXA-232, OXA-48, Verona integron-encoded metallo-β-lactamase (VIM)-1] K. pneumoniae isolates (n = 22) obtained from inpatient and outpatient's urine (n = 9) and inpatients rectal carriage (n = 13) were selected for short-read whole genome sequencing. Klebsiella pneumoniae population include sequence type (ST)-307 (n = 3), ST2497 (n = 5) and ST17 (n = 4). The ST17 strains were exclusively obtained from rectal screening. Ten isolates co-harboured carbapenemase genes including β-lactamase gene encoding KPC-2 + OXA-181, NDM-1 + OXA-48 and NDM-1 + OXA-181. One ST307 isolate (UP-KT-73CKP) co-harboured three carbapenemase genes (blaNDM-1 + blaOXA-48 + blaOXA-181), while all the ST2497 strains co-harboured (blaNDM-1 + blaOXA-232). Phenotypically, hypermucoviscosity was observed in a single ST307 isolate. The ST307 isolate UP-KT-151UKP harboured colibactin genotoxins. The following mobile genetic elements were detected: plasmids [incompatibility group (Inc)-FIB(K), IncX3], and bacteriophages [e.g. Klebsi_ST16_OXA48phi5.4_NC_049450, Klebsi_3LV2017_NC_047817(36)]. The study highlights the importance of local genomic surveillance systems to characterise K. pneumoniae MDR high-risk clones. This data will aid in designing infection and prevention measures for limiting the spread of carbapenemase-producing K. pneumoniae in Gauteng, South Africa.

Epidemiological and molecular characteristics of carbapenem-resistant Klebsiella pneumoniae from pediatric patients in Henan, China

PURPOSE

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is an emerging global threat, whereas its epidemiological characteristics in children are rarely reported. This study aims to analyze clinical and epidemiological characteristics of CRKP from children in Henan, China.

METHODS

CRKP strains were isolated from pediatric patients, and the antimicrobial susceptibility of CRKP was determined using broth microdilution methods. The epidemiological characteristics of CRKP, including specimen sources, clinical data, carbapenemase types, virulence factors, MLST and PBRT typing were analyzed.

RESULTS

In total, 108 CRKP isolates were isolated from specimens including sputum, blood and urine, mainly from preterm pediatric department and internal medical intensive care unit (ICU). Newborns and staying in the ICU were risk factors for crude mortality. 107 isolates exhibited a multi-drug resistant (MDR) phenotype, and one isolate was extensively drug-resistant (XDR). Bacterial susceptibility to colistin, tigecycline and trimethoprim/sulfamethoxazole was 98.10%, 78.50% and 91.43%, respectively. Carbapenemase blaKPC (86.11%) was predominant, followed by blaNDM (5.56%) and blaIMP (2.78%). Two strains co-harbored blaKPC-blaNDM, one had blaKPC-blaIMP, whereas three isolates did not carry any of the analyzed carbapenemase genes. All strains possessed fimH, and 98% of the isolates possessed mrkD. Hypervirulent factors rmpA2 and iucA showed high positive rates (71.30% and 49.07%), with 48.15% of strains containing both genes. MLST analysis identified nine distinct sequence types (STs), with ST11 (82.41%) being the most common, followed by ST2154 (4.63%) and ST307 (3.70%). PBRT analysis revealed IncFII (85.19%) as the most prevalent plasmid.

CONCLUSION

In summary, this study reported the epidemiological features of CRKP in pediatric patients in Henan, China, highlighting the high prevalence of multi-drug-resistant and hypervirulent strains, and underscoring the significance of continuous surveillance.

Antimicrobial Resistance Trends and Epidemiological Characteristics of Isolates from Intra-Abdominal Infections in China: A 6-Year Retrospective Study (2017-2022)

Background: Antimicrobial resistance represents a continuing threat to the health of patients with intra-abdominal infections (IAIs). This study aimed to provide clinicians with guidance to optimize antibiotic therapy. Methods: The clinical data and antibiotic susceptibility results of pathogens from patients with IAIs from 2017 to 2022 were retrospectively collected. The 6-year period was segmented into two stages, namely, the early (2017-2020) and recent stages (2021-2022). The distribution and antibiotic resistance of pathogens were compared between the stages. Results: In total, 5,795 pathogens were isolated from 2,283 patients diagnosed with IAIs. Gram-negative bacteria, Gram-positive bacteria, and fungi accounted for 71.0%, 21.4%, and 7.5% of the isolates, respectively. Klebsiella pneumoniae (1,037, 17.9%) was the primary isolate. The proportion of extended-spectrum β-lactamase-producing Enterobacteriaceae was 89.8% (2,028/2,259), with extended-spectrum β-lactamase-producing Escherichia coli and K. pneumoniae accounting for 27.4% and 43.2%, respectively, of all such isolates. The carbapenem resistance rates of E. coli and K. pneumoniae were 17.1% and 75.9%, respectively. Compared with that in the early stage, the imipenem resistance rate of E. coli was significantly higher in the recent stage (13.8% vs. 25.1%, p < 0.001). Among Gram-positive bacteria, 88 strains of vancomycin-resistant Enterococcus were detected, giving a resistance rate of 10.3%, and the detection rate of methicillin-resistant Staphylococcus aureus was 65.7%. Conclusions: Enterobacteriales and non-fermentative bacteria from IAIs remain highly resistant to carbapenems. The epidemiological characteristics and antibiotic resistance profiles of pathogens in various regions should be closely monitored to mitigate the appearance of drug-resistant bacteria in clinical settings.

Overexpression of β-lactamase genes (blaKPC, blaSHV) and novel CirA deficiencies contribute to decreased cefiderocol susceptibility in carbapenem-resistant Klebsiella pneumoniae before its approval in China

Cefiderocol (FDC) is an effective antibiotic that is used to treat severe infections caused by carbapenem-resistant Klebsiella pneumoniae (CRKP). The mechanisms underlying FDC resistance and molecular epidemiology in China remain unclear. We collected 477 non-duplicate CRKP clinical isolates in central China and characterized their susceptibility to FDC, virulence genes, and sequence typing. The overall FDC susceptibility rate of CRKP was 99.2% in central China, which was higher than that in North America and Europe (96.1%), with MIC50/90 values of 1/2 mg/L. The decrease in FDC susceptibility in central China was concentrated in the ST11 CRKP-carrying virulence plasmids. Whole-genome sequencing (WGS) and quantitative reverse transcription PCR (qRT-PCR) experiments showed that serine β-lactamases, especially highly expressed KPC and SHV, substantially decreased FDC susceptibility in four FDC non-susceptible isolates (two resistant and two intermediate isolates). Notably, different CirA deficiencies, p.E450GfsTer16 and p.E133Ter, were found in both of the resistant isolates. In contrast, global WGS data indicate that the resistance mechanisms in North America and Europe were primarily associated with NDM and KPC variants, predominantly found in ST307 and ST147. Overall, FDC exhibits excellent activity against CRKP in central China, with resistance mechanisms primarily related to high KPC and SHV expression, along with deficiencies in CirA, frequently observed in ST11. This is remarkably different from the situation in North America and Europe and will directly impact the choice of clinical interventions. Additionally, the surveillance of FDC resistance in China is imperative.

Peritonsillar abscess caused by hypervirulent Klebsiella pneumoniae: A case report and literature review

Klebsiella pneumoniae is a pathogenic bacterium responsible for otorhinolaryngology-head and neck infections. Hypervirulent K. pneumoniae (hvKp), an alarming subtype of K. pneumoniae, causes life-threatening hematogenous infection. However, there are few reports on the character of hvKp strain in the field of otorhinolaryngology-head and neck surgery. We report the case of a 60-year-old Japanese man with a peritonsillar abscess caused by hvKp. K. pneumoniae isolated from pus was positive in a string test. Genetic analysis revealed that the strain had K2, rmpA and aerobactin genes. There was no evidence of hematogenous infections such as bacteremia and liver abscess, and there was improvement by surgical drainage and intravenous antimicrobial treatment. To the best of our knowledge, this is the first reported case of peritonsillar abscess caused by hvKp that did not have hematogenous infections. The string test is a simple and inexpensive method for screening hvKp. This case highlights the need for strategies to inhibit the spread of these highly virulent strains by early drainage and appropriate antimicrobial treatment.

Computational strategies in Klebsiella pneumoniae vaccine design: navigating the landscape of in silico insights

The emergence of multidrug-resistant Klebsiella pneumoniae poses a grave threat to global public health, necessitating urgent strategies for vaccine development. In this context, computational tools have emerged as indispensable assets, offering unprecedented insights into klebsiellal biology and facilitating the design of effective vaccines. Here, a review of the application of computational methods in the development of K. pneumoniae vaccines is presented, elucidating the transformative impact of in silico approaches. Through a systematic exploration of bioinformatics, structural biology, and immunoinformatics techniques, the complex landscape of K. pneumoniae pathogenesis and antigenicity was unravelled. Key insights into virulence factors, antigen discovery, and immune response mechanisms are discussed, highlighting the pivotal role of computational tools in accelerating vaccine development efforts. Advancements in epitope prediction, antigen selection, and vaccine design optimisation are examined, highlighting the potential of in silico approaches to update vaccine development pipelines. Furthermore, challenges and future directions in leveraging computational tools to combat K. pneumoniae are discussed, emphasizing the importance of multidisciplinary collaboration and data integration. This review provides a comprehensive overview of the current state of computational contributions to K. pneumoniae vaccine development, offering insights into innovative strategies for addressing this urgent global health challenge.

Impact of nitric oxide donors on capsule, biofilm and resistance profiles of Klebsiella pneumoniae

Klebsiella pneumoniae is considered to be a critical public health threat due to its ability to cause fatal, multi-drug-resistant infections in the bloodstream and key organs. The polysaccharide-based capsule layer that shields K. pneumoniae from clearance via innate immunity is a prominent virulence factor. K. pneumoniae also forms biofilms on biotic and abiotic surfaces. These biofilms significantly reduce penetration by, and antibacterial activity from, traditional antibiotics. Nitric oxide (NO), an endogenous molecule involved in the innate immune system, is equally effective at eradicating bacteria but without engendering resistance. This study investigated the effects of NO-releasing small molecules capable of diverse release kinetics on the capsule and biofilm formation characteristics of multiple K. pneumoniae strains. The use of NO donors with moderate and extended NO-release properties (i.e., half-life >1.8 h) inhibited bacterial growth. Additionally, treatment with NO decreased capsule mucoviscosity in K. pneumoniae strains that normally exhibit hypermucoviscosity. The NO donors were also effective against K. pneumoniae biofilms at the same minimum biocidal concentrations that eliminated planktonic bacteria, while meropenem showed little antibacterial action in the same experiments. These results represent the first account of exogenous NO affecting biomarkers involved in K. pneumoniae infections, and may therefore inform future development of NO-based therapeutics for treating such infections.

An increased prevalence of carbapenem-resistant hypervirulent Klebsiella pneumoniae associated with the COVID-19 pandemic

BACKGROUND

Klebsiella pneumoniae (Kp) is a common community-acquired and nosocomial pathogen. Carbapenem-resistant and hypervirulent (CR-hvKp) variants can emerge rapidly within healthcare facilities and impacted by other infectious agents such as COVID-19 virus.

METHODS

To understand the impact of COVID-19 virus on the prevalence of CR-hvKp, we accessed Kp genomes with corresponding metadata from GenBank. Sequence types (STs), antimicrobial resistance genes, and virulence genes, and those scores and CR-hvKp were identified. We analyzed population diversity and phylogenetic characteristics of five most common STs, measured the prevalence of CR-hvKp, identified CR-hvKp subtypes, and determined associations between carbapenem resistance gene subtypes with STs and plasmid types. These variables were compared pre- and during the COVID-19 pandemic.

FINDINGS

The proportion of CR-hvKp isolates increased within multiple STs in different continents during the COVID-19 pandemic and persistent CR-hvKp subtypes were found in common STs. blaKPC was dominant in CG258, blaKPC-2 was detected in 97 % of the ST11 CR-hvKp, blaNDM subtypes were prominent in ST147 (87.4 %) and ST307 (70.8 %); blaOXA-48 and its subtypes were prevalent in ST15 (80.5 %). The possession of carbapenemase genes was different among subclades from different origins in different periods of time within each ST. IncFIB/IncHI1B hybrid plasmids contained virulence genes and carbapenemase genes and were predominant in ST147 (67.37 %) and ST307 (56.25 %).

INTERPRETATION

The prevalence of CR-hvKp increased during the COVID-19 pandemic, which was evident by an increase in local endemic clones. This process was facilitated by the convergence of plasmids containing carbapenemase genes and virulence genes. These findings have implications for the appropriate use of antimicrobials and infection prevention and control during outbreaks of respiratory viruses and pandemic management.

Macrophage-depleted young mice are beneficial in vivo models to assess the translocation of Klebsiella pneumonia from the gastrointestinal tract to the liver in the elderly

Pathobionts are commensal intestinal microbiota capable of causing systemic infections under specific conditions, such as environmental changes or aging. However, it is unclear how pathobionts are recognized by the intestinal mucosal immune system under physiological conditions. This study demonstrates that the gut pathobiont Klebsiella pneumoniae causes injury to the epithelium and translocates to the liver in specific pathogen-free mice treated with clodronate-liposomes that depleted macrophages. In the clodronate-liposome-treated mice, indigenous classical K. pneumoniae (cKp) with non-K1/K2 capsular serotypes were isolated from the liver, indicating that gut commensal cKp translocated from the gastrointestinal tract to the liver due to the depletion of intestinal macrophages. Oral inoculation of isolated cKp to clodronate-liposome-treated mice significantly reduced the survival rates compared to that of non-treated mice. Our findings demonstrate that intestinal mucosal macrophages play a pivotal role in sensing commensal cKp and suppressing their translocation to the liver. This study demonstrates that clodronate-liposome-treated mouse models are effective for screening and evaluating drugs that prevent the translocation of cKp to the liver, providing new insights into the development of preventive protocols against K. pneumoniae infection.

Identification of hypermucoviscous Klebsiella pneumoniae strains via untargeted surface-enhanced Raman spectroscopy

Klebsiella pneumoniae is one of the most common causes of hospital-acquired infections, especially due to the emergence of the hypervirulent K. pneumoniae (hvKp) strains. Multiple methods have been developed to discriminate hvKp strains from classical K. pneumoniae (cKp) strains, such as the presence of candidate genes (e.g., peg-344, iroB, and iucA), high level of siderophore production, hypermucoviscosity phenotype, etc. Although the string test is commonly used to confirm the hypermucoviscosity of K. pneumoniae strains, it is a method lacking rigidity and accuracy. Surface-enhanced Raman spectroscopy (SERS) coupled with machine learning algorithms has been widely used in discriminating bacterial pathogens with different phenotypes. However, the technique has not be applied to identify hypermucoviscous K. pneumoniae (hmvKp) strains. In this study, we isolated a set of K. pneumoniae strains from clinical samples, among which hmvKp strains (N = 10) and cKP strains (N = 10) were randomly selected to collect SESR spectra. Eight machine learning algorithms were recruited for model construction and spectral prediction in this study, among which support vector machine (SVM) outperforms all other algorithms with the highest prediction accuracy of hmvKp strains (5-fold cross validation = 99.07%). Taken together, this pilot study confirms that SERS, combined with machine learning algorithms, can accurately identify hmvKp strains, which can facilitate the fast recognition of hvKP strains when combined with relevant methods and biomarkers in clinical settings in the near future.

Otitis Media Progressing to Community-Acquired Meningitis in Diabetic Patients: A Case Report of K2-ST375 hypervirulent Klebsiella pneumoniae and Literature Review

Community-acquired Klebsiella pneumoniae meningitis (CA-KPM) can rapidly progress to invasive infection in healthy individuals. We present the case of a 54-year-old man with a history of acute suppurative otitis media and uncontrolled type 2 diabetes mellitus (T2DM), who had been treated with oral antibiotics intermittently and irregularly for one month. His symptoms did not improve and continued to worsen, leading to fever and coma. Metagenomic next-generation sequencing (mNGS) of cerebrospinal fluid (CSF) identified Klebsiella pneumoniae (KP) after 24 hours in the intensive care unit (ICU). Subsequent CSF culture confirmed a hypervirulent KP (hvKp) strain with capsular genotype K2 and sequence type (ST) 375. Fortunately, the patient made a full recovery with targeted antimicrobial therapy and was discharged. Despite the delayed diagnosis, the outcome was favorable. This case highlights the importance of clinicians, particularly otolaryngologists, maintaining a high index of suspicion for CA-KPM in patients with both otitis media and T2DM, emphasizing the need for timely multidisciplinary consultation.

Challenges and opportunities of phage therapy for Klebsiella pneumoniae infections

Traditional antibiotics have been effective in many cases. However, the rise in multidrug-resistant bacteria has diminished their therapeutic efficacy, signaling the dawn of an era beyond antibiotics. The challenge of multidrug resistance in Klebsiella pneumoniae is particularly critical, with increasing global mortality and resistance rates. Therefore, the development of alternative therapies to antibiotics is urgently needed. Phages, which are natural predators of bacteria, have inherent advantages. However, comprehensive information on K. pneumoniae phages is lacking in current literature. This review aims to analyze and summarize relevant studies, focusing on the present state of phage therapy for K. pneumoniae infections. This includes an examination of treatment methodologies, associated challenges, strategies, new phage technologies, clinical trial safety and efficacy, regulatory issues, and future directions for phage therapy development. Enhancing phage technology is crucial for addressing the evolving threat of multidrug-resistant K. pneumoniae.

Liver abscess induced by intestinal hypervirulent Klebsiella pneumoniae through down-regulation of tryptophan-IPA-IL22 axis

Hypervirulent Klebsiella pneumoniae (hvKp) is a significant causative agent of invasive hepatic abscess syndrome in Asia, presenting substantial clinical challenges due to its intricate pathogenesis. This study revealed the crucial role of the gut microbiota in fortifying the host's defense against hvKp infection by enhancing interleukin-22 (IL-22), probably through regulating downstream antimicrobial peptides such as Reg3β. In antibiotic-treated mice, we observed that gut microbiota disruption impaired the transformation of tryptophan to indole, a key ligand for the aryl hydrocarbon receptor (AhR), consequently affecting the regulatory functions of IL-22. Our experimental findings revealed that administering rIL-22 or indole propionic acid notably diminished the translocation of hvKp from the intestine to the liver. This research not only underscores the pivotal role of the gut microbiome in modulating tryptophan metabolism and the IL-22 pathway but also highlights its critical function in preventing hvKp migration from the colon to the liver.

Klebsiella pneumoniae Lipopolysaccharide as a Vaccine Target and the Role of Antibodies in Protection from Disease

Klebsiella pneumoniae is well recognized as a serious cause of infection in healthcare-associated settings and immunocompromised individuals; however, accumulating evidence from resource-limited nations documents an alarming rise in community-acquired K. pneumoniae infections, manifesting as bacteremia and pneumonia as well as neonatal sepsis. The emergence of hypervirulent and antibiotic-resistant K. pneumoniae strains threatens treatment options for clinicians. Effective vaccination strategies could represent a viable alternative that would both preempt the need for antibiotics to treat K. pneumoniae infections and reduce the burden of K. pneumoniae disease globally. There are currently no approved K. pneumoniae vaccines. We review the evidence for K. pneumoniae lipopolysaccharide (LPS) as a vaccine and immunotherapeutic target and discuss the role of antibodies specific for the core or O-antigen determinants within LPS in protection against Klebsiella spp. disease. We expand on the known role of the Klebsiella spp. capsule and O-antigen modifications in antibody surface accessibility to LPS as well as the in vitro and in vivo effector functions reported for LPS-specific antibodies. We summarize key hypotheses stemming from these studies, review the role of humoral immunity against K. pneumoniae O-antigen for protection, and identify areas requiring further research.

Bloodstream infections: mechanisms of pathogenesis and opportunities for intervention

Bloodstream infections (BSIs) are common in hospitals, often life-threatening and increasing in prevalence. Microorganisms in the blood are usually rapidly cleared by the immune system and filtering organs but, in some cases, they can cause an acute infection and trigger sepsis, a systemic response to infection that leads to circulatory collapse, multiorgan dysfunction and death. Most BSIs are caused by bacteria, although fungi also contribute to a substantial portion of cases. Escherichia coli, Staphylococcus aureus, coagulase-negative Staphylococcus, Klebsiella pneumoniae and Candida albicans are leading causes of BSIs, although their prevalence depends on patient demographics and geographical region. Each species is equipped with unique factors that aid in the colonization of initial sites and dissemination and survival in the blood, and these factors represent potential opportunities for interventions. As many pathogens become increasingly resistant to antimicrobials, new approaches to diagnose and treat BSIs at all stages of infection are urgently needed. In this Review, we explore the prevalence of major BSI pathogens, prominent mechanisms of BSI pathogenesis, opportunities for prevention and diagnosis, and treatment options.

Identification of hypermucoviscous Klebsiella pneumoniae K1, K2, K54 and K57 capsular serotypes by Raman spectroscopy

Antimicrobial resistance poses a significant challenge in modern medicine, affecting public health. Klebsiella pneumoniae infections compound this issue due to their broad range of infections and the emergence of multiple antibiotic resistance mechanisms. Efficient detection of its capsular serotypes is crucial for immediate patient treatment, epidemiological tracking and outbreak containment. Current methods have limitations that can delay interventions and increase the risk of morbidity and mortality. Raman spectroscopy is a promising alternative to identify capsular serotypes in hypermucoviscous K. pneumoniae isolates. It provides rapid and in situ measurements with minimal sample preparation. Moreover, its combination with machine learning tools demonstrates high accuracy and reproducibility. This study analyzed the viability of combining Raman spectroscopy with one-dimensional convolutional neural networks (1-D CNN) to classify four capsular serotypes of hypermucoviscous K. pneumoniae: K1, K2, K54 and K57. Our approach involved identifying the most relevant Raman features for classification to prevent overfitting in the training models. Simplifying the dataset to essential information maintains accuracy and reduces computational costs and training time. Capsular serotypes were classified with 96 % accuracy using less than 30 Raman features out of 2400 contained in each spectrum. To validate our methodology, we expanded the dataset to include both hypermucoviscous and non-mucoid isolates and distinguished between them. This resulted in an accuracy rate of 94 %. The results obtained have significant potential for practical healthcare applications, especially for enabling the prompt prescription of the appropriate antibiotic treatment against infections.

Temporal Shifts in Etiological Agents and Antibiotic Resistance Patterns of Biliary Tract Infections in Sichuan Province, China (2017-2023)

Purpose

We analyzed the pathogenic bacteria and antibiotic resistance distributions in patients with biliary tract infections (BTI) using samples from the Antimicrobial Resistant Investigation Network of Sichuan Province (ARINSP) to promote the rational use of antibiotics to reduce multidrug resistance.

Patients and Methods

Participating hospitals identified isolates between 2017 and 2023 and conducted antimicrobial susceptibility tests. Isolated bacteria were identified and tested for drug sensitivity using MOLDI-TOF mass spectrometry system, VITEK automated drug sensitivity system and paper diffusion method, and the results were interpreted with reference to CLSI M100 30th edition standards. WHONET 5.6 was used to analyze the results.

Results

In total, 25,573 bacterial isolates were collected; 18,134 were Gram-negative (70.9%). The top five most frequently isolated bacteria were Escherichia coli (8,181/25,573; 32.0%), Klebsiella pneumoniae (3,247/25,573; 12.7%), Enterococcus faecium (2,331/25,573; 9.1%), Enterococcus faecalis (1,714/25,573; 6.7%), and Enterobacter cloacae (1,429/25,573; 5.6%). E. coli and E. faecalis slowly declined over time, while K. pneumoniae slowly increased; E. faecium frequency was stable; E. coli resistance to ampicillin was the highest among all antibiotics tested; resistance rates decreased with the addition of sulbactam. K. pneumoniae resistance to aztreonam, imipenem, meropenem, ertapenem, and chloramphenicol remained low. E. cloacae was highly resistant to cephalosporins, especially cefoxitin and cefazolin. E. faecalis' resistance to teicoplanin remained low, decreasing from 6.9% in 2017 to 0.0% in 2019 before stabilizing.

Conclusion

The most frequently isolated bacteria from patients with BTIs were Enterobacteriaceae, including E. coli and K. pneumoniae, followed by E. faecium and E. faecalis. Isolates exhibited high resistance to routinely used antibiotics (cephalosporins) and were highly sensitive to tigecycline, carbapenem, amikacin, and vancomycin. The results guide the rational use and continual revision of antibiotic regimens for BTIs to reduce antibiotic resistance.

Virulence plasmid with IroBCDN deletion promoted cross-regional transmission of ST11-KL64 carbapenem-resistant hypervirulent Klebsiella pneumoniae in central China

BACKGROUND

Carbapenem-resistant and hypervirulent Klebsiella pneumoniae (CR-hvKP) caused infections of high mortality and brought a serious impact on public health. This study aims to evaluate the epidemiology, resistance and virulence characteristics of CR-hvKP and to identify potential drivers of cross-regional transmission in different regions of China, in order to provide a basis for developing targeted prevention measures.

METHODS

Clinical K. pneumoniae strains were collected from Jiujiang and Nanchang in Jiangxi province between November 2021 to June 2022. Clinical data of patients (age, sex, source of infection, and diagnosis) were also gathered. We characterized these strains for their genetic relatedness using PFGE, antimicrobial and virulence plasmid structures using whole-genome sequencing, and toxicity using Galleria mellonella infection model.

RESULTS

Among 609 strains, 45 (7.4%) CR-hvKP were identified, while the strains. isolated from Nanchang and Jiujiang accounted for 10.05% (36/358) and 3.59% (9/251). We observed that ST11-KL64 CR-hvKP had an overwhelming epidemic dominance in these two regions. Significant genetic diversity was identified among all ST11-KL64 CR-hvKP cross-regional transmission between Nanchang and Jiujiang and this diversity served as the primary driver of the dissemination of clonal groups. Virulence genes profile revealed that ST11-KL64 CR-hvKP might harbour incomplete pLVPK-like plasmids and primarily evolved from CRKP by acquiring the hypervirulence plasmid. We found the predominance of truncated-IncFIB/IncHI1B type virulence plasmids with a 25 kb fragment deletion that encoded iroBCDN clusters.

CONCLUSION

ST11-KL64 is the most cross-regional prevalent type CR-hvKPs in Jiangxi province, which mainly evolved from CRKPs by acquiring a truncated-IncHI1B/IncFIB virulence plasmid with the deletion of iroBCDN. Stricter surveillance and control measures are urgently needed to prevent the epidemic transmission of ST11-KL64 CR-hvKP.

Whole-genome sequencing of Klebsiella pneumoniae MDR circulating in a pediatric hospital setting: a comprehensive genome analysis of isolates from Guayaquil, Ecuador

BACKGROUND

Klebsiella pneumoniae is the major cause of nosocomial infections worldwide and is related to a worsening increase in Multidrug-Resistant Bacteria (MDR) and virulence genes that seriously affect immunosuppressed patients, long-stay intensive care patients, elderly individuals, and children. Whole-Genome Sequencing (WGS) has resulted in a useful strategy for characterizing the genomic components of clinically important bacteria, such as K. pneumoniae, enabling them to monitor genetic changes and understand transmission, highlighting the risk of dissemination of resistance and virulence associated genes in hospitals. In this study, we report on WGS 14 clinical isolates of K. pneumoniae from a pediatric hospital biobank of Guayaquil, Ecuador.

RESULTS

The main findings revealed pronounced genetic heterogeneity among the isolates. Multilocus sequencing type ST45 was the predominant lineage among non-KPC isolates, whereas ST629 was found more frequently among KPC isolates. Phylogenetic analysis suggested local transmission dynamics. Comparative genomic analysis revealed a core set of 3511 conserved genes and an open pangenome in neonatal isolates. The diversity of MLSTs and capsular types, and the high genetic diversity among these isolates indicate high intraspecific variability. In terms of virulence factors, we identified genes associated with adherence, biofilm formation, immune evasion, secretion systems, multidrug efflux pump transporters, and a notably high number of genes related to iron uptake. A large number of these genes were detected in the ST45 isolate, whereas iron uptake yersiniabactin genes were found exclusively in the non-KPC isolates. We observed high resistance to commonly used antibiotics and determined that these isolates exhibited multidrug resistance including β-lactams, aminoglycosides, fluoroquinolones, quinolones, trimetropins, fosfomycin and macrolides; additionally, resistance-associated point mutations and cross-resistance genes were identified in all the isolates. We also report the first K. pneumoniae KPC-3 gene producers in Ecuador.

CONCLUSIONS

Our WGS results for clinical isolates highlight the importance of MDR in neonatal K. pneumoniae infections and their genetic diversity. WGS will be an imperative strategy for the surveillance of K. pneumoniae in Ecuador, and will contribute to identifying effective treatment strategies for K. pneumoniae infections in critical units in patients at stratified risk.

Emergence of a novel sequence type carbapenem-resistant hypervirulent Klebsiella pneumoniae ST6417 harboring blaNDM-5 on the lncX3 plasmid

Carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP) is a significant pathogen causing major public health problems worldwide. This study characterized a novel sequence type 6417 (ST6471) CR-hvKP strain recovered from the blood of a male patient with septicemia. Strain CR2021 is not susceptible to carbapenems, cephalosporin, sulfonamides, quinolones, or levofloxacin and is susceptible to amikacin and tigecycline. Molecular typing indicated that ST6417 is derived from the most dominant hypervirulent K. pneumoniae (hvKP) clone in China, ST23, with a single-locus variation in tonB. The genomic characterization of CR2021, which contains three plasmids, was performed through whole-genome sequencing. The plasmid pCR2021_IncFII contains 12 antibiotic resistance genes [blaCTX-M-3, blaTEM-1B, blaDHA-1, aac (3)-Ild, aadA16, sul1, sul2, qnrB4, ARR-3, dfrA27, qacE, merACDE], all of which are associated with genetic elements. The plasmid pCR2021_IncFIB carries crucial virulence-related genes, while the plasmid pCR2021_IncX3 only harbors the blaNDM-5 resistance gene and exhibits 99% similarity with two other blaNDM-5-carrying IncX3 plasmids (pSHX180-NDM5, pNDM-K725), with coverage of 87% and 100%, respectively. The blaNDM-5 genetic region contains an additional IS26-Tn3 genetic module. Serum killing and anti-human neutrophil phagocytosis tests indicated that CR2021 exhibits high virulence, which was further confirmed in a Galleria mellonella larvae infection model. CR-hvKP is becoming more prevalent in China; however, the majority have evolved from the multidrug resistance clone ST11 and its variants by acquiring virulence factors. Conversely, CR-hvKP derived from hvKP, such as the clone ST23, remains relatively rare. Therefore, the discovery of ST6417 underscores the need for further research into the genetic characteristics and evolution of bacteria.

IMPORTANCE

ST11 and its variants, which often exhibit drug resistance, represent popular clones of carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP) in China, often leading to high morbidity and mortality rates owing to their high virulence and robust drug resistance. Conversely, CR-hvKP, originating from the high-virulence sequence type ST23, remains rarely reported. In this study, we identified a novel ST6417 CR-hvKP strain derived from ST23, carrying blaNDM-5 on an IncX3 plasmid conferring resistance to carbapenems. In addition, we elucidate its virulence, resistance to drugs, and genetic characteristics. The discovery of ST6417 highlights the diverse pathways in the evolution of CR-hvKP, warranting increased attention.

Invasive Klebsiella pneumoniae Syndrome: A Case Report From Malaysia

Invasive Klebsiella syndrome is a potentially life-threatening condition primarily caused by hypervirulent strains of Klebsiella pneumoniae. It is characterized by severe infections that metastasize to various organs, including the liver, lungs, eyes, and brain. We present a case of invasive K. pneumoniae syndrome in Malaysia, highlighting the aggressiveness of the disease. The case involves a 44-year-old woman with diabetes mellitus who developed cavitary pneumonia, pulmonary embolism, and pleural effusion, requiring prolonged antibiotic treatment and drainage. This case highlights the need for early diagnosis and extended antibiotic therapy to improve patient outcomes.

Clinical Characteristics and Molecular Insights of Carbapenem-Resistant Klebsiella pneumoniae Isolates from Patients in Intensive Care Units

Background: Carbapenem-resistant Klebsiella pneumoniae (CRKP), a significant worldwide public health threat, is common in patients in intensive care units. Methods: A retrospective study was conducted over a period of 22 months to assess the risk factors associated with infection caused by CRKP isolates. Strain identification was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and antimicrobial sensitivity was assessed using the micro broth dilution method and Kirby-Bauer test. The genes blaKPC, blaOXA-48, blaNDM, blaVIM, and blaGES were amplified using polymerase chain reaction (PCR), followed by sequencing of the PCR products. The polymerase hypermucoviscosity phenotype was determined using the string test. Capsular serotypes (K1, K2) and presence of the virulence gene (rmpA) in positive isolates were investigated using phenotypic tests followed by PCR. Results: Length of hospitalization and use of carbapenems were associated with CRKP infection. CRKP isolates exhibited extensive drug resistance, but retained sensitivity to colistin and ceftazidime-avibactam (CZA). The main gene detected in 35 CRKP isolates was blaKPC-2. In addition, 11 strains were positive in the string test, and two of these strains carried rmpA. Conclusions: Prolonged hospitalization and carbapenem exposure increased the risk of CRKP infection in intensive care unit (ICU) patients. The prevalence of CRKP carrying the blaKPC-2 gene was high, and suspected hypervirulent carbapenem-resistant K. pneumoniae isolates were scattered.

Molecular Surveillance of Multidrug-Resistant Bacteria among Refugees from Afghanistan in 2 US Military Hospitals during Operation Allies Refuge, 2021

In 2021, two US military hospitals, Landstuhl Regional Medical Center in Landstuhl, Germany, and Walter Reed National Military Medical Center (WRNMMC) in Bethesda, Maryland, USA, observed a high prevalence of multidrug-resistant bacteria among refugees evacuated from Afghanistan during Operation Allies Refuge. Multidrug-resistant isolates collected from 80 patients carried an array of antimicrobial resistance genes, including carbapenemases (blaNDM-1, blaNDM-5, and blaOXA-23) and 16S methyltransferases (rmtC and rmtF). Considering the rising transmission of antimicrobial resistance and unprecedented population displacement globally, these data are a reminder of the need for robust infection control measures and surveillance.

A Case of Malignant Pleural Effusion Complicated by Klebsiella rhinoscleromatis

This case report describes an elderly man with a history of alcohol use disorder and primary malignant liver neoplasm who presented to the emergency department with dyspnea, asthenia, fever, and signs of respiratory distress. Diagnostic tests, including a chest radiograph and computed tomography, revealed a large left-sided exudative pleural effusion with regular and diffuse pleural enhancement, a large tumor lesion in the left lobe with diaphragmatic and pleural invasion, and a liver with features suggestive of cirrhosis. Laboratory data showed increased inflammatory markers and hyperlactacidemia. Following thoracentesis, pleural fluid culture revealed the growth of Klebsiella rhinoscleromatis. Despite targeted antibiotic therapy with the resolution of the infectious condition, the patient's clinical condition worsened, resulting in multiorgan failure, and the patient ultimately died in this context.

The Association between Resistance and Virulence of Klebsiella pneumoniae in High-Risk Clonal Lineages ST86 and ST101

Klebsiella pneumoniae is an opportunistic pathogen known for two main pathotypes: classical K. pneumoniae (cKp), often multidrug-resistant and common in hospitals, and hypervirulent K. pneumoniae (hvKp), associated with severe community-acquired infections. The recent emergence of strains combining hypervirulence and resistance is alarming. This study investigates the distribution of sequence types (STs), resistance, and virulence factors in K. pneumoniae strains causing bloodstream and urinary tract infections in Croatia. In 2022, 200 consecutive K. pneumoniae isolates were collected from blood and urine samples across several Croatian hospitals. Whole genome sequencing was performed on 194 isolates. Within the analyzed K. pneumoniae population, the distribution of sequence types was determined with multi-locus sequence typing (MLST) and capsule loci, resistance, and virulence determinants were assessed with the bioinformatics tool Kleborate. The analysis identified 77 different STs, with ST101 (24.6%) being the most prevalent, predominantly linked to the K17 capsular type (CT), invasive device usage, high antimicrobial resistance, and low virulence scores. The highest virulence scores were recorded in ST86 isolates, which were predominantly linked to the K2 CT and included some strains with medium resistance scores. String tests were positive in 19 strains, but only four of those harbored hypermucoviscous genetic determinants. The most prevalent ST101 clone in Croatia demonstrated a diverging association between resistance and virulence. An alarming co-existence of resistance and virulence was recorded in the ST86 strains.

Case Study and Genomic Analysis of a Hypervirulent ST25 Klebsiella pneumoniae Strain in a Liver Cirrhosis Patient

Bloodstream infections (BSIs) caused by Klebsiella pneumoniae (K. pneumoniae) are associated with high morbidity and mortality rates. This study presents a sequence type 25 (ST25) strain of hypermucoid K. pneumoniae A1 isolated from the blood of a patient with liver cirrhosis (LC) who succumbed to severe infections. We performed whole-genome sequencing of K. pneumoniae A1, which revealed virulence factors and antibiotic resistance genes. The strain harbors virulence genes encoding aerobactin, salmochelin, yersiniabactin, enterobactin, and rmpA. Additionally, the strain possessed five drug resistance genes: blaSHV-110, blaSHV-81, fosA6, OqxA, and OqxB. We further constructed a phylogenetic tree using 98 ST25 K. pneumoniae strains downloaded from NCBI together with K. pneumoniae A1. Phylogenetic analysis revealed that our isolated strain was closely related to a highly virulent strain isolated from a neonate in our region, differing by only 123 single nucleotide polymorphisms (SNPs). K. pneumoniae A1 is highly suspected to be Hypervirulent Klebsiella pneumoniae (hvKp). This study provided the first in-depth genomic analysis of ST25 K. pneumoniae in a patient with LC in China, highlighting the urgent need for early identification and diagnosis to combat this emerging threat.

Evaluation of an optimal agar medium for detecting hypervirulent Klebsiella pneumoniae using string test

The string test is a screening method for detecting hypervirulent Klebsiella pneumoniae (hvKp). Agar media are used for string tests; however, the effect of the type of media on the test results remains unclear. We aimed to determine the optimal agar medium and cutoff value for the string test. We performed the string test on 99 Klebsiella strains using different agar media: sheep blood, chocolate, Drigalski's and MacConkey. The diagnostic accuracy was calculated in concordance with the rmpA, rmpA2 or iucA gene levels. The diagnostic accuracy rates for sheep blood, chocolate, Drigalski's and MacConkey agar were 0.79, 0.75, 0.73 and 0.64, respectively. When the cutoff was changed from 5 to 10 mm, the diagnostic accuracy rate for sheep blood agar decreased from 0.79 to 0.65. Our findings suggest that the type of agar medium impacts the string test results and sheep blood agar with a 5-mm cutoff is the optimal condition for detecting hvKp.

Development and evaluation of a duplex real-time multienzyme isothermal rapid amplification assay for the detection of hypervirulent Klebsiella pneumoniae in clinical spiked blood specimens

Objectives

Our objective was to establish a rapid and precise method for detecting hypervirulent Klebsiella pneumoniae (hvKP) by utilizing a duplex real-time multienzyme isothermal rapid amplification (real-time MIRA) and to evaluate its performance in clinical spiked blood specimens.

Methods

The research comprised two phases: an initial pilot study to establish the methodology and a clinical validation study to assess its effectiveness. In the pilot phase, we designed specific primers and probes targeting the hvKP pg344 and incA genes and subsequently developed a duplex real-time MIRA assay to evaluate its detection limits, specificity, and efficiency. In the clinical validation phase, we analyzed thirty-three spiked blood specimens using the duplex real-time MIRA assay.

Results

The duplex real-time MIRA assay demonstrated no cross-reactivity with other strains. Sensitivity experiments confirmed that the assay had a detection limit as low as 8 × 102 CFU per reaction for hvKP. The analysis of clinical spiked blood specimens indicated that the sensitivity and specificity of the duplex real-time MIRA assay were on par with those of duplex real-time PCR.

Conclusions

These findings confirm that the duplex real-time MIRA assay is a fast, straightforward, and dependable method for detecting hvKP.