Enhancement of extracapsular polysaccharide synthesis in Klebsiella pneumoniae by RmpA2, which shows homology to NtrC and FixJ

Coexistence of c-rmpA with p-rmpA and p-rmpA2 rather than excessive siderophores confers higher virulence in K1 Klebsiella pneumoniae

Pyogenic liver abscess (PLA), which is particularly endemic in East Asia, is a relatively common and fatal infectious disease. Over the last 30-40 years, Klebsiella pneumoniae has replaced Escherichia coli as the dominant and overwhelming pathogen. To investigate the survival advantage of serotype K1 K. pneumoniae, we determined sequence types (STs), serotypes, and 11 virulence genes (allS, entB, irp2, iroN, iucA, fimH, mrkD, p-rmpA2, c-rmpA, p-rmpA, and peg-344). Virulence genes c-rmpA, p-rmpA, and p-rmpA2 in K. pneumoniae NTUH-K2044, which all confer hypercapsule and consequent hypervirulence, were deleted individually, and the consequent effects were evaluated. The lethality of various K1 K. pneumoniae strains was compared by using the Galleria mellonella model. In total, 31 K1 K. pneumoniae strains causing PLA and 30 causing non-PLA were identified. A significantly higher rate of c-rmpA was presented in PLA-derived K. pneumoniae strains than in non-PLA-derived strains. Similar ST23 (which dominates K1 strains) and string test-positive rates were observed in the two groups. Deletion of c-rmpA, p-rmpA, and p-rmpA2 individually did not confer significant effects on morphologies, such as positive string test, hypercapsule, and growth speed. Δc-rmpA presented weaker expressions of p-rmpA/p-rmpA2 than NTUH-K2044 and showed a higher expression of manC than Δp-rmpA and Δp-rmpA2. Three rmpAs conferred more virulence than one or two rmpAs, which presented an equally lethal effect in K1 K. pneumoniae. Klebsiella pneumoniae strains (H19 and H34) with the same genetic backgrounds except for siderophores showed equal virulence, but were less virulent than strain NTUH-K2044. Thus, the coexistence of c-rmpA with p-rmpA and p-rmpA2 enhances the lethality of K1 K. pneumoniae strains and the development of PLA. Excessive siderophores are not vital for the hypervirulence of K1 K. pneumoniae strains, although K1 strains usually harbour them on a molecular basis.

Interaction of multidrug-resistant hypervirulent Klebsiella pneumoniae with components of human innate host defense

IMPORTANCE

Klebsiella pneumoniae strains with a combination of multidrug resistance and hypervirulence genotypes (MDR hvKp) have emerged as a cause of human infections. The ability of these microbes to avoid killing by the innate immune system remains to be tested fully. To that end, we compared the ability of a global collection of hvKp and MDR hvKp clinical isolates to survive in human blood and resist phagocytic killing by human neutrophils. The two MDR hvKp clinical isolates tested (ST11 and ST147) were killed in human blood and by human neutrophils in vitro, whereas phagocytic killing of hvKp clinical isolates (ST23 and ST86) required specific antisera. Although the data were varied and often isolate specific, they are an important first step toward gaining an enhanced understanding of host defense against MDR hvKp.

Epidemicity and clonal replacement of hypervirulent carbapenem-resistant Klebsiella pneumoniae with diverse pathotypes and resistance profiles in a hospital

OBJECTIVES

The emergence of carbapenem-resistant and hypervirulent Klebsiella pneumoniae (CR-hvKP) poses a great threat to public health. There is a paramount need to increase awareness of the epidemiology, evolution, and pathogenesis of CR-hvKP.

METHODS

We collected strains of K. pneumoniae for over two years in a hospital. CR-hvKP strains were screened by polymerase chain reaction (PCR) with primers targeting the virulence genes. Genome sequencing was used to determine phylogenetic relationships and genetic characterization of virulence elements. The population dynamics within these strains were analyzed through epidemiological data. The string test, siderophore secretion, and murine infection experiments were performed to investigate virulence potential of different clones.

RESULTS

A total of 1172 K. pneumoniae strains were isolated from 817 patients, and 125 isolates were identified as CR-hvKP. In all, 102 CR-hvKP strains belonged to sequence type (ST) 11. Genomic analysis demonstrated that three clones of ST11 successively replaced each other in the hospital. Among them, the strains of clade A and clade B acquired virulence plasmids and the strains of clade C acquired a new integrating conjugative element (ICE). Phenotypic experiments revealed enhanced virulence potential of the recent epidemic clone from clade B. Sequence type 11 strains were favorable hosts for the convergence of virulence and resistance, indicated by clonal replacement and acquisition patterns of virulence elements.

CONCLUSION

The emergence of the enhanced virulence potential of ST11 CR-hvKP suggests that coevolution between hosts and exogenous factors can produce super-virulent CR-hvKP strains, highlighting the need to closely monitor changes in the virulence characteristics of CR-hvKP.

The making of hypervirulent Klebsiella pneumoniae

Klebsiella pneumoniae is a notorious bacterium in clinical practice. Virulence, carbapenem-resistance and their convergence among K. pneumoniae are extensively discussed in this article. Hypervirulent K. pneumoniae (HvKP) has spread from the Asian Pacific Rim to the world, inducing various invasive infections, such as pyogenic liver abscess, endophthalmitis, and meningitis. Furthermore, HvKP has acquired more and more drug resistance. Among multidrug-resistant HvKP, hypervirulent carbapenem-resistant K. pneumoniae (Hv-CRKP), and carbapenem-resistant hypervirulent K. pneumoniae (CR-HvKP) are both devastating for their extreme drug resistance and virulence. The hypervirulence of HvKP is primarily attributed to hypercapsule, macromolecular exopolysaccharides, or excessive siderophores, although it has many other factors, for example, lipopolysaccharides, fimbriae, and porins. In contrast with classical determination of HvKP, that is, animal lethality test, molecular determination could be an optional and practical method after improvement. HvKP, including Hv-CRKP and CR-HvKP, has been progressing. R-M and CRISPR-Cas systems may play pivotal roles in such evolutions. Hv-CRKP and CR-HvKP, in particular the former, should be of severe concern due to their being more and more prevalent.

An outbreak of extensively drug-resistant and hypervirulent Klebsiella pneumoniae in an intensive care unit of a teaching hospital in Southwest China

Extensively drug-resistant and hypervirulent Klebsiella pneumoniae (XDR-hvKp) is a new problem for patients in Intensive Care Unit (ICU) and can become an even more severe threat if resistant to tigecycline, considered one of the ‘last lines of defense’ drugs. This study collected seven non-replicated tigecycline-resistant XDR-hvKp from seven patients and performed genome analysis and epidemiological investigation using whole genome equencing (WGS) and other methods. All strains in this study were identified as ST11-KL64 and showed high resistance to antibiotics such as β-lactams, aminoglycosides, quinolones, and tigecycline, and one strain was also resistant to colistin. All strains were determined to be hvKp by the results of serum resistance assay and Galleria mellonella infection models. All strains had resistance genes bla_CTX-M-65,bla_KPC-2,bla_LAP-2,bla_TEM-1B, rmtB, and qnrS1 and virulence factors such as rmpA, rmpA2, and aerobactin (iucABCD, iutA). The expression of the AcrAB-TolC efflux pump was upregulated in all strains, and the expression levels of the gene pmrK was significantly upregulated in colistin-resistant strain DP compared to colistin-sensitive strain WT in this study. In conclusion, we described an outbreak caused by tigecycline-resistant XDR-hvKp in the ICU of a teaching hospital in southwest China. The spread of these superbugs poses a great threat to patients and therefore requires us to closely monitor these XDR-hvKp and develop relevant strategies to combat them.

The Anti-Virulence Effect of Sub-Minimal Inhibitory Concentrations of Levofloxacin on Hypervirulent Klebsiella pneumoniae

Background

Hypervirulent Klebsiella pneumoniae (hvKp) is best described as a virulent pathogen and generally associated with the hypermucoviscosity phenotype. Increased capsule and aerobactin production are established important hvKp-specific virulence factors. Although hvKp strains have been relatively susceptible to antimicrobials, given the high morbidity and mortality, there is a critical need for alternative strategies for the treatment of hvKp infections. Thus, the anti-virulence therapy has been targeted for the hvKp development of therapeutics.

Materials and Methods

Four hvKp isolates with hypermucoviscous phenotype were used in our experiments. Mucoviscosity of the capsule can be assessed by low-speed centrifugation of cultures. CPS amount was determined by glucuronic acid content. The capsule thickness was measured under microscope after ink staining. The transcriptions of gene were measured by quantitative real-time PCR (qRT-PCR). The effect of levofloxacin on the resistance of K. pneumoniae to phagocytosis by macrophages and mouse lethality assay was observed.

Results

Our data revealed that sub-Minimal Inhibitory Concentrations (sub-MIC) of LVX reduce mucoviscosity and CPS production of hvKp. Microscopic observations demonstrated that the capsule of hvkp bacteria became thinned after treatment with LVX. qRT-PCR showed decreased transcript levels of rmpA, wzi, magA, iroN and icuA genes. Down-regulation of these virulence genes occurred leading to increased susceptibility to phagocytosis by macrophages. Mouse lethality assay revealed that the wild strain had the LD50 of 10³ CFU, while the sub-MIC LVX-treated bacteria had the LD50 of 10⁵ CFU.

Conclusion

Our data suggested that LVX may serve as a potential anti-virulence agent for refractory infection by hvKp.

Recurrent bacteremia with a hypermucoviscous Escherichia coli isolated from a patient with perihilar cholangiocarcinoma: insights from a comprehensive genome-based analysis

Background

Escherichia coli (E. coli) is a common human pathogen, responsible for a broad spectrum of infections. Sites of infection can vary, but the hepato-biliary system is of particular concern due to the infection-associated formation of gallstones and the spread of pathogens from the bile ducts into the bloodstream.

Case presentation

The presented case is striking, as the detected isolate showed a positive string test. This hypermucoviscous phenotype is atypical for E. coli and a particular feature of hypervirulent Klebsiella pneumoniae (K. pneumoniae) variants.

Objectives

To provide new insights into the genomic background of an E. coli strain with an unusual hypermucoviscous phenotype using hybrid short- and long-read sequencing approaches.

Results

Complete hybrid assemblies of the E. coli genome and plasmids were done and used for genome based typing. Isolate 537–20 was assigned to the multilocus sequence type ST88 and serotype O8:H4. The strain showed a close relationship to avian pathogenic strains. Analysis of the chromosome and plasmids revealed the presence of several virulence factors, such as the Conserved Virulence Plasmidic (CVP) region on plasmid 537-20_1, including several iron acquisition genes (sitABCD, iroABCDEN, iucABCD, hbd) and the iutA gene encoding the receptor of the siderophore aerobactin. The hypermucoviscous phenotype could be caused by encapsulation of putative K. pneumoniae origin.

Conclusions

Hybrid sequencing enabled detailed genomic characterization of the hypermucoviscous E. coli strain, revealing virulence factors that have their putative origin in K. pneumoniae.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12941-022-00521-7.

Genomic epidemiology and temperature dependency of hypermucoviscous Klebsiella pneumoniae in Japan

Klebsiella pneumoniae (Kp) has emerged as a global life-threatening pathogen owing to its multidrug resistance and hypervirulence phenotype. Several fatal outbreaks of carbapenem-resistant hypervirulent Kp have been reported recently. Hypermucoviscosity (HMV) is a phenotype commonly associated with hypervirulence of Kp, which is usually regulated by rmpA or rmpA2 (regulators of the mucoid phenotype). Here, we found that temperature was important in the HMV phenotype of Kp, and the impact of temperature on HMV was not uniform among strains. We investigated the HMV phenotype at 37 °C and room temperature (20–25 °C) in 170 clinically isolated hypermucoviscous Kp strains in Japan and analysed the association between the HMV phenotype, virulence genes and antimicrobial resistance (AMR) genes. String length distribution at different temperatures was correlated with the genomic population of Kp. The strains carrying rmpA/rmpA2 frequently showed the HMV phenotype at 37 °C, while the strains negative for these genes tended to show the HMV phenotype at room temperature. Hypervirulent Kp clusters carrying rmpA/rmpA2 without extended-spectrum beta-lactamases (ESBL)/carbapenemases produced higher string lengths at 37 °C than at room temperature, and were mostly isolated from the respiratory tract. Other HMV strains showed distinct characteristics of not carrying rmpA/rmpA2 but were positive for ESBL/carbapenemases, with a higher string length at room temperature than at 37 °C, and were frequently isolated from bloodstream infections. In total, 21 (13.5 %) HMV isolates carried ESBL and carbapenemases, among which five isolates were carbapenem-resistant hypervirulent Kp with a pLVPK-like plasmid (an epidemic virulence plasmid) and a pKPI-6-like plasmid (an epidemic bla_IMP-6-bearing plasmid in Japan), suggesting the convergence of worldwide hypervirulence and epidemic AMR in Japan.

Molecular Epidemiology of Hypervirulent K. pneumoniae and Problems of Health-Care Associated Infections

The review describes virulence factors of hypervirulent K. pneumoniae (hvKp) including genes determining its virulence and discusses their role in the development of health-care associated infections. The contribution of individual virulence factors and their combination to the development of the hypervirulence and the prospects of using these factors as biomarkers and therapeutic targets are described. Virulence factors of hvKp and "classical" K. pneumoniae strains (cKp) with no hypervirulence genes were compared. The mechanisms of biofilm formation by hvKp and high incidence of its antibiotic resistance are of particular importance for in health care institutions. Therefore, the development of methods for hvKp identification allowing early prevention of severe hvKp infection and novel approaches to abrogate its spreading are new challenges for epidemiology, infection diseases, and critical care medicine. New technologies including bacteriological and molecular studies make it possible to develop innovative strategies to diagnose and treat infection caused by hvKp. These include monitoring of both genetic biomarkers of hvKp and resistance plasmid that carry of virulence genes and antibiotic resistance genes, creation of immunological agents for the prevention and therapy of hvKp (vaccines, monoclonal antibodies) as well as personalized hvKp-specific phage therapies and pharmaceuticals enhancing the effect of antibiotics. A variety of approaches can reliably prepare our medicine for a new challenge: spreading of life-threatening health-care associated infections caused by antibiotic-resistant hvKp strains.

Genetic Background and Antibiotic Resistance Profiles of K. pneumoniae NDM-1 Strains Isolated from UTI, ABU, and the GI Tract, from One Hospital in Poland, in Relation to Strains Nationally and Worldwide

In recent years, there has been an observed increase in infections caused by carbapenem-resistant Klebsiella pneumonia (Kp) strains. The aim of this study was the phenotypic and genotypic analysis of eight K. pneumoniae NDM (Kp NDM) isolates, recovered in Poland during the years 2016 and 2018 from seven patients with urinary tract infections (UTIs), asymptomatic bacteriuria (ABU), or colonization of the gut. PCR melting profile genotyping indicated a close relationship between the strains derived from 2018, which were not related to the strain isolated in 2016. WGS results were analyzed in relation to international Kp isolates. Clonal and phylogenetic analyses were performed based on multilocus sequence typing (MLST) and single nucleotide polymorphisms (SNPs) of the core genome. The metallo-β-lactamase was assigned to the NDM-1 type and the sequence was identified as ST11. Eleven antimicrobial resistance genes were detected, mostly from plasmid contigs. Unprecedented profiles of plasmid replicons were described with the IncFII/pKPX-1 dominant replicon. In terms of the KL24 and O2v1 capsular antigen profiles, these isolates corresponded to Greek strains. Strains isolated from UTI, ABU, and colonization GI tract patients were not carrying environment-specific virulence genes. Based on the assessment of strain relationships at the genome level and their direction of evolution, the international character of the sublines was demonstrated, with a documented epidemic potential in Poland and Greece. In conclusion, some groups of patients, e.g., renal transplant recipients or those with complicated UTIs, who are frequently hospitalized and undergoing antibiotic therapy, should be monitored not only for the risk of UTI, but also for colonization by Kp NDM strains.

Virulence Factors in Hypervirulent Klebsiella pneumoniae

Hypervirulent Klebsiella pneumoniae (hvKP) has spread globally since first described in the Asian Pacific Rim. It is an invasive variant that differs from the classical K. pneumoniae (cKP), with hypermucoviscosity and hypervirulence, causing community-acquired infections, including pyogenic liver abscess, pneumonia, meningitis, and endophthalmitis. It utilizes a battery of virulence factors for survival and pathogenesis, such as capsule, siderophores, lipopolysaccharide, fimbriae, outer membrane proteins, and type 6 secretion system, of which the former two are dominant. This review summarizes these hvKP-associated virulence factors in order to understand its molecular pathogenesis and shed light on new strategies to improve the prevention, diagnosis, and treatment of hvKP-causing infection.

Molecular Investigation of Klebsiella pneumoniae from Clinical Companion Animals in Beijing, China, 2017-2019

This work is aimed to elucidate the prevalence and characteristics of antimicrobial resistance, virulence, and molecular typing in Klebsiella pneumoniae from clinical companion animals in Beijing, China. In total, 105 K. pneumoniae (2.0%) isolates were recovered from 5359 samples (dogs, n = 3356; cats, n = 2003). All tested isolates exhibited high resistance to amoxicillin-clavulanate (74.3%). Moreover, resistance rates in dog isolates (2.1%) were significantly higher than in cat isolates (0.9%); however, the rate of multidrug-resistance (MDR) was 57.1% and the MDR prevalence in cats was significantly higher than dogs. Whole-genome sequencing demonstrated plasmids IncX4 and IncFIA (HI1)/FII(K) carried mcr-1 (n = 1) and mcr-8 (n = 1), but bla_OXA-181 (n = 1) and bla_NDM-5 (n = 4) were harbored in IncX3-type plasmids, and the above genes were in different isolates. The most prevalent sequence types (STs) in companion animals were ST1 (n = 9) and ST37 (n = 9). Compared to National Center for Biotechnology Information (NCBI) data on human K. pneumoniae, resistance genes bla_CTX-M and bla_TEM were more prevalent in human isolates; however, aac(6′)-Ib-cr and oqxAB showed a higher prevalence in companion animals. Hypermucoviscosity was reported in 9 (8.6%) isolates, whereas 64 isolates (61.0%) were hypervirulent K. pneumoniae (hvKP) via the Galleria mellonella. These findings validate the high risk of K. pneumonia and necessitate its relevant control in pet clinics.

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.

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.

Small Klebsiella pneumoniae Plasmids: Neglected Contributors to Antibiotic Resistance

Klebsiella pneumoniae is the causative agent of community- and, more commonly, hospital-acquired infections. Infections caused by this bacterium have recently become more dangerous due to the acquisition of multiresistance to antibiotics and the rise of hypervirulent variants. Plasmids usually carry genes coding for resistance to antibiotics or virulence factors, and the recent sequence of complete K. pneumoniae genomes showed that most strains harbor many of them. Unlike large plasmids, small, usually high copy number plasmids, did not attract much attention. However, these plasmids may include genes coding for specialized functions, such as antibiotic resistance, that can be expressed at high levels due to gene dosage effect. These genes may be part of mobile elements that not only facilitate their dissemination but also participate in plasmid evolution. Furthermore, high copy number plasmids may also play a role in evolution by allowing coexistence of mutated and non-mutated versions of a gene, which helps to circumvent the constraints imposed by trade-offs after certain genes mutate. Most K. pneumoniae plasmids 25-kb or smaller replicate by the ColE1-type mechanism and many of them are mobilizable. The transposon Tn1331 and derivatives were found in a high percentage of these plasmids. Another transposon that was found in representatives of this group is the bla KPC-containing Tn4401. Common resistance determinants found in these plasmids were aac(6')-Ib and genes coding for β-lactamases including carbapenemases.

Antibiotic resistance, virulence and genetic diversity of Klebsiella pneumoniae in community- and hospital-acquired urinary tract infections in Iran

Klebsiella pneumoniae is among the most important causes of urinary tract infection (UTI). The aim of this study was to investigate the prevalence and correlation of antibiotic resistance with virulence characteristics and genetic diversity in K. pneumoniae isolated from UTIs in Iran. Phenotypic tests and antibiotic susceptibility were carried out on the isolates. Detection of the virulence and extended-spectrum β-lactamase (ESBL) genes was performed by polymerase chain reaction. Pulsed-field gel electrophoresis (PFGE) was used for exploring the genomic relatedness. Hemolysin, biofilm, and hypermucoviscosity formation were observed in 87.1%, 86.4%, and 12.1% of isolates, respectively. The antibiotic resistance rate of K. pneumoniae isolates ranged from 12.1% for meropenem to 100% for amoxicillin. The prevalence of virulence genes ranged from 1.4% for cnf-1 to 100% for mrkD, fimH, kpn, and entB genes. In this study, 91.7%, 33.3%, and 4.2% of phenotypically ESBL-producers were positive for bla_CTX-M, bla_TEM, and bla_SHV genes, respectively. An association was observed between the presence of traT, fyuA, or cnf-1 genes with antibiotic resistance. Two clone types were obtained by PFGE that indicate different K. pneumoniae clones in community- and hospital-acquired UTIs. The findings of this study are valuable in development of treatment strategies against UTIs in Iran.

The Determination and Correlation of Various Virulence Genes, ESBL, Serum Bactericidal Effect and Biofilm Formation of Clinical Isolated Classical Klebsiella pneumoniae and Hypervirulent Klebsiella pneumoniae from Respiratory Tract Infected Patients

Klebsiella pneumoniae strains that are commonly recognized by clinicians and microbiologists are termed as classical K. pneumoniae (cKP). A strain with capsule-associated mucopolysaccharide web is known as hypervirulent K. pneumoniae (hvKP) as it enhances the serum resistant and biofilm production. Aim is to determine and correlate various virulence genes, ESBL, serum bactericidal effect and biofilm formation of clinical isolated cKP and hvKP from respiratory tract infected patients. A total of 96 K. pneumoniae strains were isolated from sputum of respiratory tract infected patients. The isolates were performed string test, AST, ESBL virulence gene, serum bactericidal and biofilm assays. Out of 96 isolates, 39 isolates (40.6%) were identified with hypervirulent phenotypes. The number of cKP exhibiting resistance to the tested antimicrobials and ESBLs were significantly higher than that of the hvKP strains. The virulence genes of K. pneumoniae such as K1, K2, rmpA, uge, kfu and aerobactin were strongly associated with hvKP than cKP. However, no significant difference was found in FIM-1 and MrKD3 genes. ESBL producing cKP and hvKP were significantly associated with strong biofilm formation (both P < 0.05) and highly associated with bactericidal effect of serum (both P < 0.05) than cKP strains. However, neither biofilm formation nor bactericidal effect of serum was found with significant difference in between ESBL producing cKP and ESBL producing hvKP strains (both P > 0.05). Although the hvKP possess more virulence gene, but they didn't show any significant difference between biofilm formation and bactericidal effect of serum compared with ESBL producing cKP strains.

Rapid phenotypic evolution in multidrug-resistant Klebsiella pneumoniae hospital outbreak strains

Carbapenem-resistant Klebsiella pneumoniae (CRKP) increasingly cause high-mortality outbreaks in hospital settings globally. Following a patient fatality at a hospital in Beijing due to a blaKPC-2-positive CRKP infection, close monitoring was put in place over the course of 14 months to characterize all blaKPC-2-positive CRKP in circulation in the hospital. Whole genome sequences were generated for 100 isolates from blaKPC-2-positive isolates from infected patients, carriers and the hospital environment. Phylogenetic analyses identified a closely related cluster of 82 sequence type 11 (ST11) isolates circulating in the hospital for at least a year prior to admission of the index patient. The majority of inferred transmissions for these isolates involved patients in intensive care units. Whilst the 82 ST11 isolates collected during the surveillance effort all had closely related chromosomes, we observed extensive diversity in their antimicrobial resistance (AMR) phenotypes. We were able to reconstruct the major genomic changes underpinning this variation in AMR profiles, including multiple gains and losses of entire plasmids and recombination events between plasmids, including transposition of blaKPC-2. We also identified specific cases where variation in plasmid copy number correlated with the level of phenotypic resistance to drugs, suggesting that the number of resistance elements carried by a strain may play a role in determining the level of AMR. Our findings highlight the epidemiological value of whole genome sequencing for investigating multi-drug-resistant hospital infections and illustrate that standard typing schemes cannot capture the extraordinarily fast genome evolution of CRKP isolates.

Distinct evolutionary dynamics of horizontal gene transfer in drug resistant and virulent clones of Klebsiella pneumoniae

Klebsiella pneumoniae has emerged as an important cause of two distinct public health threats: multi-drug resistant (MDR) healthcare-associated infections and drug susceptible community-acquired invasive infections. These pathotypes are generally associated with two distinct subsets of K. pneumoniae lineages or 'clones' that are distinguished by the presence of acquired resistance genes and several key virulence loci. Genomic evolutionary analyses of the most notorious MDR and invasive community-associated ('hypervirulent') clones indicate differences in terms of chromosomal recombination dynamics and capsule polysaccharide diversity, but it remains unclear if these differences represent generalised trends. Here we leverage a collection of >2200 K. pneumoniae genomes to identify 28 common clones (n ≥ 10 genomes each), and perform the first genomic evolutionary comparison. Eight MDR and 6 hypervirulent clones were identified on the basis of acquired resistance and virulence gene prevalence. Chromosomal recombination, surface polysaccharide locus diversity, pan-genome, plasmid and phage dynamics were characterised and compared. The data showed that MDR clones were highly diverse, with frequent chromosomal recombination generating extensive surface polysaccharide locus diversity. Additional pan-genome diversity was driven by frequent acquisition/loss of both plasmids and phage. In contrast, chromosomal recombination was rare in the hypervirulent clones, which also showed a significant reduction in pan-genome diversity, largely driven by a reduction in plasmid diversity. Hence the data indicate that hypervirulent clones may be subject to some sort of constraint for horizontal gene transfer that does not apply to the MDR clones. Our findings are relevant for understanding the risk of emergence of individual K. pneumoniae strains carrying both virulence and acquired resistance genes, which have been increasingly reported and cause highly virulent infections that are extremely difficult to treat. Specifically, our data indicate that MDR clones pose the greatest risk, because they are more likely to acquire virulence genes than hypervirulent clones are to acquire resistance genes.

The Complex Rcs Regulatory Cascade

RcsB, a response regulator of the FixJ/NarL family, is at the center of a complex network of regulatory inputs and outputs. Cell surface stress is sensed by an outer membrane lipoprotein, RcsF, which regulates interactions of the inner membrane protein IgaA, lifting negative regulation of a phosphorelay. In vivo evidence supports a pathway in which histidine kinase RcsC transfers phosphate to phosphotransfer protein RcsD, resulting in phosphorylation of RcsB. RcsB acts either alone or in combination with RcsA to positively regulate capsule synthesis and synthesis of small RNA (sRNA) RprA as well as other genes, and to negatively regulate motility. RcsB in combination with other FixJ/NarL auxiliary proteins regulates yet other functions, independent of RcsB phosphorylation. Proper expression of Rcs and its targets is critical for success of Escherichia coli commensal strains, for proper development of biofilm, and for virulence in some pathogens. New understanding of how the Rcs phosphorelay works provides insight into the flexibility of the two-component system paradigm.

Whole genome analysis of hypervirulent Klebsiella pneumoniae isolates from community and hospital acquired bloodstream infection

BACKGROUND

Hypervirulent K. pneumoniae (hvKp) causes severe community acquired infections, predominantly in Asia. Though initially isolated from liver abscesses, they are now prevalent among invasive infections such as bacteraemia. There have been no studies reported till date on the prevalence and characterisation of hvKp in India. The objective of this study is to characterise the hypervirulent strains isolated from bacteraemic patients for determination of various virulence genes and resistance genes and also to investigate the difference between healthcare associated and community acquired hvKp with respect to clinical profile, antibiogram, clinical outcome and molecular epidemiology.

RESULTS

Seven isolates that were susceptible to all of the first and second line antimicrobials and phenotypically identified by positive string test were included in the study. They were then confirmed genotypically by presence of rmpA and rmpA2 by PCR. Among the study isolates, four were from patients with healthcare associated infections; none were fatal. All patients with community acquired infection possessed chronic liver disease with fatal outcome. Genes encoding for siderophores such as aerobactin, enterobactin, yersiniabactin, allantoin metabolism and iron uptake were identified by whole genome sequencing. Five isolates belonged to K1 capsular type including one K. quasipneumoniae. None belonged to K2 capsular type. Four isolates belonged to the international clone ST23 among which three were health-care associated and possessed increased virulence genes. Two novel sequence types were identified in the study; K. pneumoniae belonging to ST2319 and K. quasipneumoniae belonging to ST2320. Seventh isolate belonged to ST420.

CONCLUSION

This is the first report on whole genome analysis of hypervirulent K. pneumoniae from India. The novel sequence types described in this study indicate that these strains are evolving and hvKp is now spread across various clonal types. Studies to monitor the prevalence of hvKp is needed since there is a potential for the community acquired isolates to develop multidrug resistance in hospital environment and may pose a major challenge for clinical management.

Antimicrobial Resistance of Hypervirulent Klebsiella pneumoniae: Epidemiology, Hypervirulence-Associated Determinants, and Resistance Mechanisms

Klebsiella pneumoniae is one of the most clinically relevant species in immunocompromised individuals responsible for community-acquired and nosocomial infections, including pneumonias, urinary tract infections, bacteremias, and liver abscesses. Since the mid-1980s, hypervirulent K. pneumoniae, generally associated with the hypermucoviscosity phenotype, has emerged as a clinically significant pathogen responsible for serious disseminated infections, such as pyogenic liver abscesses, osteomyelitis, and endophthalmitis, in a generally younger and healthier population. Hypervirulent K. pneumoniae infections were primarily found in East Asia and now are increasingly being reported worldwide. Although most hypervirulent K. pneumoniae isolates are antibiotic-susceptible, some isolates with combined virulence and resistance, such as the carbapenem-resistant hypervirulent K. pneumoniae isolates, are increasingly being detected. The combination of multidrug resistance and enhanced virulence has the potential to cause the next clinical crisis. To better understand the basic biology of hypervirulent K. pneumoniae, this review will provide a summarization and discussion focused on epidemiology, hypervirulence-associated factors, and antibiotic resistance mechanisms of such hypervirulent strains. Epidemiological analysis of recent clinical isolates in China warns the global dissemination of hypervirulent K. pneumoniae strains with extensive antibiotic resistance in the near future. Therefore, an immediate response to recognize the global dissemination of this hypervirulent strain with resistance determinants is an urgent priority.

Impacts of Hypervirulence Determinants on Clinical Features and Outcomes of Bacteremia Caused by Extended-Spectrum β-Lactamase-Producing Klebsiella pneumoniae

We investigated the implications of hypervirulence determinants on clinical features of 48 adult patients with bacteremia caused by extended-spectrum β-lactamase-producing Klebsiella pneumoniae. Isolates in the hypervirulence group included any of the following virulence determinants: K1/K2 capsule serotypes, hypermucoviscosity phenotype, rmpA gene, or rmpA2 gene. Nonhypervirulence group isolates were negative for all of the above virulence factors. In this study, all isolates used were non-K1/K2 strains. Statistically significant differences were observed in clinical features of patients between the two groups. The hypervirulent isolates (n = 19), including 11 isolates with the hypermucoviscosity phenotype, 15 with the rmpA gene, and 16 with the rmpA2 gene, were more commonly recovered from diabetic patients and mainly manifested as secondary bacteremia (such as pneumonia, urinary tract infections, or other localized infections). The nonhypervirulent isolates (n = 29) were more commonly recovered from patients after prolonged hospital stays (>30 days) and mostly manifested as primary bacteremia. The overall in-hospital mortality was 56.3%. Hazard ratio (HR) analysis revealed the following positive predictors for mortality: nosocomial infection, stay in an intensive care unit, no removal of the central venous catheter, Charlson comorbidity score, and APACHE II score (≧15). The negative predictors were initial appropriate antibiotic therapy (HR 0.42) and urinary tract infection (HR 0.19). Charlson score was an independent confounder based on multivariate analysis (HR 1.43, 95% confidence interval 1.04-1.99). In conclusion, hypervirulence determinants played a role in causing secondary infections in diabetic patients; however, the presence of morbidity cofactors could themselves influence mortality, despite the absence of hypervirulence determinants.

Klebsiella pneumoniae: Going on the Offense with a Strong Defense

Klebsiella pneumoniae causes a wide range of infections, including pneumonias, urinary tract infections, bacteremias, and liver abscesses. Historically, K. pneumoniae has caused serious infection primarily in immunocompromised individuals, but the recent emergence and spread of hypervirulent strains have broadened the number of people susceptible to infections to include those who are healthy and immunosufficient. Furthermore, K. pneumoniae strains have become increasingly resistant to antibiotics, rendering infection by these strains very challenging to treat. The emergence of hypervirulent and antibiotic-resistant strains has driven a number of recent studies. Work has described the worldwide spread of one drug-resistant strain and a host defense axis, interleukin-17 (IL-17), that is important for controlling infection. Four factors, capsule, lipopolysaccharide, fimbriae, and siderophores, have been well studied and are important for virulence in at least one infection model. Several other factors have been less well characterized but are also important in at least one infection model. However, there is a significant amount of heterogeneity in K. pneumoniae strains, and not every factor plays the same critical role in all virulent Klebsiella strains. Recent studies have identified additional K. pneumoniae virulence factors and led to more insights about factors important for the growth of this pathogen at a variety of tissue sites. Many of these genes encode proteins that function in metabolism and the regulation of transcription. However, much work is left to be done in characterizing these newly discovered factors, understanding how infections differ between healthy and immunocompromised patients, and identifying attractive bacterial or host targets for treating these infections.

Low prevalence of rmpA and high tendency of rmpA mutation correspond to low virulence of extended spectrum β-lactamase-producing Klebsiella pneumoniae isolates

Invasive syndrome caused by Klebsiella pneumoniae (KP), including liver abscess, is mainly caused by community-acquired strains with characteristics of positive hypermucoviscosity (HV) phenotype and regulator of mucoid phenotype A (rmpA) and transcriptional activator (rmpA2) genes. Extended- spectrum β-lactamase-producing KP (ESBL-KP) is commonly nosocomial and rarely HV-positive. We aimed to explore the reasons of the rarer prevalence of HV phenotype, rmpA and rmpA2 as well as the virulence phenotype among the ESBL-KP isolates from clinical specimens than those non-ESBL isolates. The β-lactamase genes, rmpA, rmpA2 and genes for K capsule serotype of 440 KP isolates were analyzed. The virulence of the isolates was characterized by the mouse lethality experiments. The prevalence rates of HV phenotype (∼ 50% vs. < 10%) as well as rmpA and rmpA2 genes (∼ 50-60% vs. < 20-30%) were significantly higher in non-ESBL group than in the ESBL group (p < 0.0001). Expression of HV phenotype in the rmpA-positive KP isolates was significantly rarer in the ESBL group than in non-ESBL group (33.3% vs. 91.9%, p < 0.0001). The frameshift mutations of rmpA and/or rmpA2 corresponded to negative HV phenotype of KP isolates that harbored the rmpA and/or rmpA2, resulting in variable mouse lethality (LD50, ∼ 10(3) - >5 × 10(7) CFU). The mutation rates might significantly differ among KP isolates from various sources. Virulence was dependent on rmpA-related HV phenotype. In conclusion, ESBL-KP isolates were less hypermucoviscous and less virulent than non-ESBL KP isolates, mostly due to concurrently lower carriage and higher mutation rates of the rmpA and rmpA2 genes.

Complete genome sequence of novel T7-like virus vB_KpnP_KpV289 with lytic activity against Klebsiella pneumoniae

A novel bacteriophage, vB_KpnP_KpV289, lytic for hypermucoviscous strains of Klebsiella pneumoniae, was attributed to the family Podoviridae, subfamily Autographivirinae, genus T7likevirus based on transmission electron microscopy and genome analysis. The complete genome of the bacteriophage vB_KpnP_KpV289 consists of a linear double-stranded DNA of 41,054 bp including 179-bp direct-repeat sequences at the ends and 51 open reading frames (ORFs). The G+C content is 52.56 %. The phage was shown to lyse 15 out of 140 (10.7 %) K. pneumoniae strains belonged to the capsular types K-1, K-2, and K-57 and strains without a determined capsular type, including a hypermucoviscous strain of the novel sequence type ST-1554.

Aerobactin, but not yersiniabactin, salmochelin, or enterobactin, enables the growth/survival of hypervirulent (hypermucoviscous) Klebsiella pneumoniae ex vivo and in vivo

The siderophore aerobactin is the dominant siderophore produced by hypervirulent Klebsiella pneumoniae (hvKP) and was previously shown to be a major virulence factor in systemic infection. However, strains of hvKP commonly produce the additional siderophores yersiniabactin, salmochelin, and enterobactin. The roles of these siderophores in hvKP infection have not been optimally defined. To that end, site-specific gene disruptions were created in hvKP1 (wild type), resulting in the generation of hvKP1ΔiucA (aerobactin deficient), hvKP1ΔiroB (salmochelin deficient), hvKP1ΔentB (enterobactin and salmochelin deficient), hvKP1Δirp2 (yersiniabactin deficient), and hvKP1ΔentBΔirp2 (enterobactin, salmochelin, and yersiniabactin deficient). The growth/survival of these constructs was compared to that of their wild-type parent hvKP1 ex vivo in human ascites fluid, human serum, and human urine and in vivo in mouse systemic infection and pulmonary challenge models. Interestingly, in contrast to aerobactin, the inability to produce enterobactin, salmochelin, or yersiniabactin individually or in combination did not decrease the ex vivo growth/survival in human ascites or serum or decrease virulence in the in vivo infection models. Surprisingly, none of the siderophores increased growth in human urine. In human ascites fluid supplemented with exogenous siderophores, siderophores increased the growth of hvKP1ΔiucA, with the relative activity being enterobactin > aerobactin > yersiniabactin > salmochelin, suggesting that the contribution of aerobactin to virulence is dependent on both innate biologic activity and quantity produced. Taken together, these data confirm and extend a role for aerobactin as a critical virulence factor for hvKP. Since it appears that aerobactin production is a defining trait of hvKP strains, this factor is a potential antivirulence target.

Influence of the bacterial phenotypes on the clinical manifestations in Klebsiella pneumoniae bacteremia patients: A retrospective cohort study

Ninety-four episodes of Klebsiella pneumoniae bloodstream infection were identified at a university hospital in Japan. After excluding extended-spectrum beta lactamase-producing strains, 83 blood isolates from these patients were assayed in terms of their bacterial phenotypes such as the mucoid and hypermucoviscosity phenotypes. Bacterial phenotypes were correlated with the patients' clinical manifestations. The hypermucoviscosity phenotype was significantly associated with septic shock at the onset of infections (odds ratio, 15.92; 95% confidence interval, 1.27-468.12), but was not associated with liver abscess formation. Mortality was determined by the presence of septic shock. RmpA gene was associated with the induction of the hypermucoviscosity phenotype. These results reveal unique roles of bacterial phenotypes on the patient's clinical condition in K. pneumoniae bacteremia.

The role of pgaC in Klebsiella pneumoniae virulence and biofilm formation

BACKGROUND

Klebsiella pneumoniae has emerged as one of the major pathogens for community-acquired and nosocomial infections. A four-gene locus that had a high degree similarity with Escherichia coli pgaABCD and Yersinia pestis hmsHFRS was identified in K. pneumoniae genomes. The pgaABCD in E. coli encodes the envelope-spanning Pga machinery for the synthesis and secretion of poly-β-linked N-acetylglucosamine (PNAG). In a limited number of phylogenetically diverse bacteria, PNAG was demonstrated to mediate biofilm formation and had a role in the host-bacteria interactions. The presence of conserved pgaABCD locus among various K. pneumoniae strains suggested a putative requirement of PNAG for this bacterium.

RESULTS

In this study, an in-frame deletion of pgaC was generated in K. pneumoniae CG43 and named ΔpgaC. The loss of pgaC affected the production of PNAG and attenuated the enhancement of in vitro biofilm formation upon the addition of bile salts mixture. In mouse models, ΔpgaC exhibited a weakened ability to colonize the intestine, to disseminate extraintestinally, and to induce a systemic infection when compared to K. pneumoniae CG43.

CONCLUSIONS

Our study demonstrated that pgaC participated in the bile salts induced biofilm formation and was required for K. pneumoniae virulence in vivo.

Plasmid-Mediated Antibiotic Resistance and Virulence in Gram-negatives: the Klebsiella pneumoniae Paradigm

Plasmids harbor genes coding for specific functions including virulence factors and antibiotic resistance that permit bacteria to survive the hostile environment found in the host and resist treatment. Together with other genetic elements such as integrons and transposons, and using a variety of mechanisms, plasmids participate in the dissemination of these traits resulting in the virtual elimination of barriers among different kinds of bacteria. In this article we review the current information about physiology and role in virulence and antibiotic resistance of plasmids from the gram-negative opportunistic pathogen Klebsiella pneumoniae. This bacterium has acquired multidrug resistance and is the causative agent of serious communityand hospital-acquired infections. It is also included in the recently defined ESKAPE group of bacteria that cause most of US hospital infections.

Comparative analysis of Klebsiella pneumoniae genomes identifies a phospholipase D family protein as a novel virulence factor

Background

Klebsiella pneumoniae strains are pathogenic to animals and humans, in which they are both a frequent cause of nosocomial infections and a re-emerging cause of severe community-acquired infections. K. pneumoniae isolates of the capsular serotype K2 are among the most virulent. In order to identify novel putative virulence factors that may account for the severity of K2 infections, the genome sequence of the K2 reference strain Kp52.145 was determined and compared to two K1 and K2 strains of low virulence and to the reference strains MGH 78578 and NTUH-K2044.

Results

In addition to diverse functions related to host colonization and virulence encoded in genomic regions common to the four strains, four genomic islands specific for Kp52.145 were identified. These regions encoded genes for the synthesis of colibactin toxin, a putative cytotoxin outer membrane protein, secretion systems, nucleases and eukaryotic-like proteins. In addition, an insertion within a type VI secretion system locus included sel1 domain containing proteins and a phospholipase D family protein (PLD1). The pld1 mutant was avirulent in a pneumonia model in mouse. The pld1 mRNA was expressed in vivo and the pld1 gene was associated with K. pneumoniae isolates from severe infections. Analysis of lipid composition of a defective E. coli strain complemented with pld1 suggests an involvement of PLD1 in cardiolipin metabolism.

Conclusions

Determination of the complete genome of the K2 reference strain identified several genomic islands comprising putative elements of pathogenicity. The role of PLD1 in pathogenesis was demonstrated for the first time and suggests that lipid metabolism is a novel virulence mechanism of K. pneumoniae.

Hypervirulent (hypermucoviscous) Klebsiella pneumoniae: a new and dangerous breed

A new hypervirulent (hypermucoviscous) variant of Klebsiella pneumoniae has emerged. First described in the Asian Pacific Rim, it now increasingly recognized in Western countries. Defining clinical features are the ability to cause serious, life-threatening community-acquired infection in younger healthy hosts, including liver abscess, pneumonia, meningitis and endophthalmitis and the ability to metastatically spread, an unusual feature for enteric Gram-negative bacilli in the non-immunocompromised. Despite infecting a healthier population, significant morbidity and mortality occurs. Although epidemiologic features are still being defined, colonization, particularly intestinal colonization, appears to be a critical step leading to infection. However the route of entry remains unclear. The majority of cases described to date are in Asians, raising the issue of a genetic predisposition vs. geospecific strain acquisition. The traits that enhance its virulence when compared with “classical” K. pneumoniae are the ability to more efficiently acquire iron and perhaps an increase in capsule production, which confers the hypermucoviscous phenotype. An objective diagnostic test suitable for routine use in the clinical microbiology laboratory is needed. If/when these strains become increasingly resistant to antimicrobials, we will be faced with a frightening clinical scenario.

Microbiological and clinical characteristics of bacteraemia caused by the hypermucoviscosity phenotype of Klebsiella pneumoniae in Korea

Hypermucoviscous (HV) isolates of Klebsiella pneumoniae have been linked to virulence potential in experimental infections. We examined 33 isolates of K. pneumoniae from patients with bacteraemia for the HV phenotype on agar culture, and determined their virulence potential by screening for capsular (K) serotype by polymerase chain reaction and the presence of seven virulence factor genes. Fourteen (42·4%) isolates expressed the HV phenotype and 11 of these were serotype K1 or K2; these serotypes were not identified in HV-negative isolates. The genes rmpA, rmpA2, aerobactin, wabG and allS were significantly more frequent in HV than non-HV isolates. Multilocus sequence typing identified 21 sequence types (ST), eight of which were found in HV-positive isolates and the clonal relatedness of isolates of the most frequent types (ST23 and ST11) from different hospitals was confirmed by pulsed-field gel electrophoresis. The HV phenotype was more associated with community-acquired infection with a lower frequency of fatal underlying illness, but with significantly more focal infections, notably liver abscesses. Clinicians should be aware of such clinical impacts of the HV phenotype.

Characterization of a DHA-1-producing Klebsiella pneumoniae strain involved in an outbreak and role of the AmpR regulator in virulence

A clonal strain of Klebsiella pneumoniae producing the plasmid-encoded cephalosporinase DHA-1 was isolated from four patients admitted to the teaching hospital of Clermont-Ferrand, France, in 2006. It was responsible for severe infections in three of the patients; the fourth was colonized only in the gastrointestinal tract. The strain had at least two plasmids encoding resistance to antibiotics (quinolones, aminoglycosides, chloramphenicol, sulfonamides, and trimethoprim), as shown by disk diffusion assay, and harbored only a few genes for virulence factors (wabG and mrkD), as shown by PCRs. DHA-1 synthesis is regulated by an upstream, divergently transcribed gene, ampR, which is also involved in the expression of virulence factors in Pseudomonas aeruginosa. To investigate the role of AmpR in K. pneumoniae, we cloned the wild-type ampR gene from the DHA-1 clonal isolate into a previously characterized K. pneumoniae background plasmid-cured strain, CH608. ampR was also introduced into a CH608 isogenic mutant deleted of ampD, in which AmpR is present only in its activator form, resulting in constitutive hyperproduction of the β-lactamase. We showed that ampR was involved in the upregulation of capsule synthesis and therefore in resistance to killing by serum. AmpR also modulated biofilm formation and type 3 fimbrial gene expression, as well as colonization of the murine gastrointestinal tract and adhesion to HT-29 intestinal epithelial cells. These results show the pleiotropic role of ampR in the pathogenesis process of K. pneumoniae.

The role of Klebsiella pneumoniae rmpA in capsular polysaccharide synthesis and virulence revisited

Klebsiella pneumoniae community-acquired pyogenic liver abscess (PLA) is an emerging infectious disease. The rmpA gene (for regulator of mucoid phenotype A) has been reported to be associated with PLA in prevalence studies. NTUH-K2044, a K1 PLA isolate, carries three rmpA/A2 genes: two large-plasmid-carried genes (p-rmpA and p-rmpA2) and one chromosomal gene (c-rmpA). In this study, we re-examined the role of rmpA/A2 in PLA pathogenesis to clarify the relationship of rmpA/A2 and capsular serotype to virulence. Using isogenic gene deletion strains and complemented strains of NTUH-K2044, we demonstrated that only p-rmpA enhanced expression of capsular polysaccharide synthesis (cps) genes and capsule production. Nevertheless, the lethal dose and in vivo competitive index indicated that p-rmpA does not promote virulence in mice. The prevalence of these three rmpA/A2 and capsular types in 206 strains was investigated. This revealed a correlation of rmpA/A2 with six PLA-related capsular types (K1, K2, K5, K54, K57 and KN1). However, the correlation of rmpA/A2 with K1 strains from the West was less obvious than with the strains from Asia (17/22 vs 39/39, P = 0.0019). Among the three rmpA/A2 genes, p-rmpA was the most prevalent. Due to the strong correlation with PLA-related capsular types, p-rmpA could serve as a surrogate marker for PLA. We found an association of p-rmpA with three widely spaced loci in a large plasmid (30/32). Therefore, rmpA could be co-inherited together with virulence genes carried by this plasmid.

Appearance of Klebsiella pneumoniae liver abscess syndrome in Argentina: case report and review of molecular mechanisms of pathogenesis

Klebsiella pneumoniae liver abscess syndrome (KLAS) is an emerging invasive infection caused by highly virulent community-acquired strains of K. pneumoniae displaying hypermucoviscosity. The salient features of this syndrome include the presence of bacteremia, primary monomicrobial liver abscess, and metastatic complications. A previously healthy Argentinean man presented with fever and found to have liver abscess caused by K. pneumoniae with metastatic seeding of gastric wall. Cultures from blood and liver abscess grew hypermucoviscous K1 K. pneumoniae with sequence type (ST) 23 by multilocus sequence typing (MLST), positive for rmpA (regulator of mucoid phenotype A), wzy_KpK1 (capsular polymerase) and aerobactin genes. The hypermucoviscous phenotype of this K. pneumoniae isolate was readily identified by the "string test" (colonies formed a long string when touched with a loop). The patient responded favourably to percutaneous drainage of the abscess and antibiotics. This is the first documented report of KLAS described in Argentina, and may signal the emergence of this syndrome in South America.

Hypermucoviscosity associated with Klebsiella pneumoniae-mediated invasive syndrome: a prospective cross-sectional study in Taiwan

OBJECTIVES

To investigate the association between Klebsiella pneumoniae-mediated invasive syndrome and underlying diseases in patients and/or K. pneumoniae characteristics, including the rmpA, rmpA2, and magA genes, capsular polysaccharide (cps) K(1) or K(2) serotypes, hypermucoviscosity (HV) phenotype, and extended-spectrum beta-lactamase (ESBL) production.

METHODS

This was a prospective cross-sectional study.

RESULTS

The invasive syndrome was detected in 19 of 91 patients (20.9%) with K. pneumoniae infections, and diabetes mellitus was the most common underlying disease (9 of 19). The presence of rmpA or rmpA2 was found in 91.4% of the 35 isolates with the HV phenotype, while in only 17.9% of the 56 isolates without HV phenotype. Multivariate logistic regression analysis showed that the HV phenotype was an independent risk factor for K. pneumoniae-mediated invasive syndrome (odds ratio (OR) 58.24, 95% confidence interval (CI) 7.23-468.87; p < 0.001) and was negatively associated with ESBL production (OR 0.042, 95% CI 0.005-0.331; p=0.003). Binary logistic regression analysis revealed that the invasive syndrome was not influenced by the presence of diabetes mellitus among patients infected with K. pneumoniae positive for the rmpA or rmpA2 gene, HV phenotype, or cps K(1)/K(2) serotype.

CONCLUSIONS

The HV phenotype of K. pneumoniae contributes to invasive syndrome and is a negative predictor for K. pneumoniae acquisition of ESBLs.

RmpA regulation of capsular polysaccharide biosynthesis in Klebsiella pneumoniae CG43

Sequence analysis of the large virulence plasmid pLVPK in Klebsiella pneumoniae CG43 revealed the presence of another mucoid factor encoding gene rmpA besides rmpA2. Promoter activity measurement indicated that the deletion of rmpA reduced K2 capsular polysaccharide (CPS) biosynthesis, resulting in decreased colony mucoidy and virulence in mice. Introduction of a multicopy plasmid carrying rmpA restored CPS production in the rmpA or rmpA2 mutant but not in the rcsB mutant. Transformation of the rmpA deletion mutant with an rcsB-carrying plasmid also failed to enhance CPS production, suggesting that a cooperation of RmpA with RcsB is required for regulatory activity. This was further corroborated by the demonstration of in vivo interaction between RmpA and RcsB using two-hybrid analysis and coimmunoprecipitation analysis. A putative Fur binding box was only found at the 5' noncoding region of rmpA. The promoter activity analysis indicated that the deletion of fur increased the rmpA promoter activity. Using electrophoretic mobility shift assay, we further demonstrated that Fur exerts its regulatory activity by binding directly to the promoter. As a result, the fur deletion mutant exhibited an increase in colony mucoidy, CPS production, and virulence in mice. In summary, our results suggested that RmpA activates CPS biosynthesis in K. pneumoniae CG43 via an RcsB-dependent manner. The expression of rmpA is regulated by the availability of iron and is negatively controlled by Fur.

Rapid real-time PCR assays for detection of Klebsiella pneumoniae with the rmpA or magA genes associated with the hypermucoviscosity phenotype: screening of nonhuman primates

The relationship of mucoviscosity-associated (magA) and/or regulator of mucoid phenotype (rmpA) genes to the Klebsiella pneumoniae hypermucoviscosity (HMV) phenotype has been reported. We previously demonstrated that rmpA+ K. pneumoniae can cause serious disease in African green monkeys and isolated rmpA+ and magA+ HMV K. pneumoniae from other species of non-human primates. To rapidly screen African green monkeys/non-human primates for these infections, we developed three real-time PCR assays. The first was K. pneumoniae-specific, targeting the khe gene, while the others targeted rmpA and magA. Primer Express 2 was used with the three K. pneumoniae genes to generate sequence-specific TaqMan/TaqMan-Minor Groove Binder assays. Oral/rectal swabs and necropsy samples were collected; swabs were used for routine culture and DNA extraction. K. pneumoniae colonies were identified on the Vitek 2 with DNA tested using the K. pneumoniae-specific assays. Testing of 45 African green monkeys resulted in 19 khe+ samples from 14 animals with none positive for either rmpA or magA. Of these 19 khe+ samples, five were culture-positive, but none were HMV "string test"-positive. Subsequent testing of 307 non-human primates resulted in 64 HMV K. pneumoniae isolates of which 42 were rmpA+ and 15 were magA+. Non-human primate testing at the U.S. Army Medical Research Institute of Infectious Diseases demonstrated the ability to screen both live and necropsied animals for K. pneumoniae by culture and real-time PCR to determine HMV genotype.

Genome sequencing and comparative analysis of Klebsiella pneumoniae NTUH-K2044, a strain causing liver abscess and meningitis

Nosocomial infections caused by antibiotic-resistant Klebsiella pneumoniae are emerging as a major health problem worldwide, while community-acquired K. pneumoniae infections present with a range of diverse clinical pictures in different geographic areas. In particular, an invasive form of K. pneumoniae that causes liver abscesses was first observed in Asia and then was found worldwide. We are interested in how differences in gene content of the same species result in different diseases. Thus, we sequenced the whole genome of K. pneumoniae NTUH-K2044, which was isolated from a patient with liver abscess and meningitis, and analyzed differences compared to strain MGH 78578, which was isolated from a patient with pneumonia. Six major types of differences were found in gene clusters that included an integrative and conjugative element, clusters involved in citrate fermentation, lipopolysaccharide synthesis, and capsular polysaccharide synthesis, phage-related insertions, and a cluster containing fimbria-related genes. We also conducted comparative genomic hybridization with 15 K. pneumoniae isolates obtained from community-acquired or nosocomial infections using tiling probes for the NTUH-K2044 genome. Hierarchical clustering revealed three major groups of genomic insertion-deletion patterns that correlate with the strains' clinical features, antimicrobial susceptibilities, and virulence phenotypes with mice. Here we report the whole-genome sequence of K. pneumoniae NTUH-K2044 and describe evidence showing significant genomic diversity and sequence acquisition among K. pneumoniae pathogenic strains. Our findings support the hypothesis that these factors are responsible for the changes that have occurred in the disease profile over time.

Serum-induced iron-acquisition systems and TonB contribute to virulence in Klebsiella pneumoniae causing primary pyogenic liver abscess

BACKGROUND

Klebsiella pneumoniae has become the predominant pathogen causing primary pyogenic liver abscess (PLA).

METHODS

K. pneumoniae was stimulated by human serum, and gene expression was analyzed by microarray.

RESULTS

Three putative iron acquisition systems, Yersinia high-pathogenicity island (HPI), iucABCDiutA, and iroA(iroNDCB), that increased in expression and predominated in PLA-associated K. pneumoniae strains were identified. By use of siderophore uptake assays, these 3 systems were confirmed to be siderophore-dependent iron acquisition systems. Only the irp2-iuc-iroA triple mutant showed decreased virulence in mice. Full-genome analysis of K. pneumoniae strain NTUH-K2044 identified 10 putative iron uptake systems. Seven of these 10 systems were TonB dependent, including Yersinia HPI, iucABCDiutA, and iroA. A tonB deletion mutant was demonstrated to have profound attenuation of virulence. Immunization with the tonB mutant resulted in seroconversion of extracellular polysaccharide antibodies and protective efficacy against subsequent exposure to the parental strain.

CONCLUSIONS

Iron uptake systems were the genes in K. pneumoniae that were highly up-regulated in response to sera. Although there are multiple iron transporter systems in NTUH-K2044, a mutation in all 3 loci (irp2, iuc, and iroA) is necessary to decrease virulence. The tonB mutant is a potential vaccine candidate because it can induce a significant protective immune response against challenge with a wild-type strain.

Comparison of prevalence of virulence factors for Klebsiella pneumoniae liver abscesses between isolates with capsular K1/K2 and non-K1/K2 serotypes

Hypermucoviscosity, rmpA (regulator of mucoid phenotype), aerobactin (an iron siderophore), kfu (an iron uptake system), allS (associated with allantoin metabolism), and K1/K2 capsules are important virulence determinants in Klebsiella pneumoniae for liver abscesses. We determined the prevalence of these virulence factors of 50 nonrepeat K. pneumoniae isolates recovered from patients with primary liver abscesses who were treated at 2 medical centers in Taiwan. Virulence genes were surveyed by polymerase chain reaction analysis. The prevalence of hypermucoviscosity phenotype, plasmid-born rmpA, aerobactin, kfu, and allS genes revealed 96%, 100%, 100%, 100%, and 100% in 26 capsular K1 isolates; 90%, 100%, 100%, 0%, and 0% in 10 K2 isolates; and 79%, 86%, 93%, 50%, and 0% in 14 non-K1/K2 isolates; respectively. When injected into mice intraperitoneally, regardless of any capsule K serotype, K. pneumoniae isolates with hypermucoviscosity phenotype as well as presence of rmpA and aerobactin genes exhibited high virulence for mouse lethality (LD(50), <10(2) CFU). Without significant difference in the prevalence of expressing hypermucoviscosity phenotype and carriage of rmpA and aerobactin genes, these virulent non-K1/K2 isolates are as capable as K1/K2 isolates of causing primary liver abscesses.

Contribution of fucose-containing capsules in Klebsiella pneumoniae to bacterial virulence in mice

Bacterium Klebsiella pneumoniae (KP) contains a prominent capsule. Clinical infections usually are associated with pneumonia or urinary tract infection (UTI). Emerging evidence implicates KP in severe liver abscess especially in diabetic patients. The goal of this study was to investigate the capsular polysaccharides from KP of liver abscess (hepatic-KP) and of UTI-KP. The composition of capsular polysaccharides was analyzed by capillary high-performance liquid chromatography (HPLC, Dionex system). The terminal sugars were assayed by binding ability to lectins. The results showed that the capsule of a hepatic KP (KpL1) from a diabetic patient contained fucose, while the capsule from UTI-KP (KpU1) did not. The absence of fucose was verified by the absence of detectable polymerase chain reaction (PCR) fragment for fucose synthesis genes, gmd and wcaG in KpU1. Mice infected with the KpL1 showed high fatality, whereas those infected with the KpU1 showed high survival rate. The KpL1 capsule was reactive to lectins AAA and AAL, which detect fucose, while the KpU1 capsule was reactive to lectin GNA, which detects mannose. Phagocytosis experiment in mouse peritoneal cavity indicated that the peritoneal macrophages could interact with KpU1, while rare association of KpL1 with macrophages was observed. This study revealed that different polysaccharides were displayed on the bacterial capsules of virulent KpL1 as compared with the less virulent KpU1. Interaction of KpU1 with mice peritoneal macrophages was more prominent than that of KpL1. The possession of fucose might contribute to KpL1 virulence by avoiding phagocytosis since fucose on bacteria had been implicated in immune evasion.

Virulence characteristics of Klebsiella and clinical manifestations of K. pneumoniae bloodstream infections

Differences in clinical manifestations are due to virulence factors expressed by the organism.

We studied 455 consecutive episodes of Klebsiella pneumoniae bacteremia occurring in 7 countries. Community-acquired pneumonia and an invasive syndrome of liver abscess, meningitis, or endophthalmitis occurred only in Taiwan and South Africa. Infections by K1 and K2 capsular serotype, the mucoid phenotype, and aerobactin production were important determinants of virulence. The mucoid phenotype was seen in 94% of isolates in patients with community-acquired pneumonia and in 100% of isolates that caused the invasive syndrome in Taiwan and South Africa, compared with only 2% of isolates elsewhere. Mortality of mice injected with mucoid strains (69%) was strikingly higher than that occurring in mice injected with nonmucoid strains (3%, p<0.001). Differences in clinical features of bacteremic infection with K. pneumoniae are due to the virulence factors expressed by the organism.