Genetic exchange of determinants for capsular polysaccharide biosynthesis between Klebsiella pneumoniae strains expressing serotypes K2 and K21a

Hypermucoviscosity Regulator RmpD Interacts with Wzc and Controls Capsular Polysaccharide Chain Length

Klebsiella pneumoniae is a leading cause of nosocomial infections, including pneumonia, bacteremia, and urinary tract infections. Treatment options are increasingly restricted by the high prevalence of resistance to frontline antibiotics, including carbapenems, and the recently identified plasmid-conferred colistin resistance. The classical pathotype (cKp) is responsible for most of the nosocomial infections observed globally, and these isolates are often multidrug resistant. The hypervirulent pathotype (hvKp) is a primary pathogen capable of causing community-acquired infections in immunocompetent hosts. The hypermucoviscosity (HMV) phenotype is strongly associated with the increased virulence of hvKp isolates. Recent studies demonstrated that HMV requires capsule (CPS) synthesis and the small protein RmpD but is not dependent on the increased amount of capsule associated with hvKp. Here, we identified the structure of the capsular and extracellular polysaccharide isolated from hvKp strain KPPR1S (serotype K2) with and without RmpD. We found that the polymer repeat unit structure is the same in both strains and that it is identical to the K2 capsule. However, the chain length of CPS produced by strains expressing rmpD demonstrates more uniform length. This property was reconstituted in CPS from Escherichia coli isolates that possess the same CPS biosynthesis pathway as K. pneumoniae but naturally lack rmpD. Furthermore, we demonstrate that RmpD binds Wzc, a conserved capsule biosynthesis protein required for CPS polymerization and export. Based on these observations, we present a model for how the interaction of RmpD with Wzc could impact CPS chain length and HMV. IMPORTANCE Infections caused by Klebsiella pneumoniae continue to be a global public health threat; the treatment of these infections is complicated by the high frequency of multidrug resistance. K. pneumoniae produces a polysaccharide capsule required for virulence. Hypervirulent isolates also have a hypermucoviscous (HMV) phenotype that increases virulence, and we recently demonstrated that a horizontally acquired gene, rmpD, is required for HMV and hypervirulence but that the identity of the polymeric product(s) in HMV isolates is uncertain. Here, we demonstrate that RmpD regulates capsule chain length and interacts with Wzc, a part of the capsule polymerization and export machinery shared by many pathogens. We further show that RmpD confers HMV and regulates capsule chain length in a heterologous host (E. coli). As Wzc is a conserved protein found in many pathogens, it is possible that RmpD-mediated HMV and increased virulence may not be restricted to K. pneumoniae.

Healthcare Facilities as Potential Reservoirs of Antimicrobial Resistant Klebsiella pneumoniae: An Emerging Concern to Public Health in Bangladesh

The emergence of virulent extended spectrum β-lactamase producing Klebsiella pneumoniae (ESBL-KP) including carbapenem-resistant Klebsiella pneumoniae (CRKP) in hospital-acquired infections has resulted in significant morbidity and mortality worldwide. We investigated the antibiotic resistance and virulence factors associated with ESBL-KP and CRKP in tertiary care hospitals in Bangladesh and explored their ability to form biofilm. A total of 67 ESBL-KP were isolated from 285 Klebsiella pneumoniae isolates from environmental and patient samples from January 2019 to April 2019. For ESBL-KP isolates, molecular typing was carried out using enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR), antibiotic susceptibility testing, PCR for virulence and drug-resistant genes, and biofilm assays were also performed. All 67 isolates were multidrug-resistant (MDR) to different antibiotics at high levels and 42 isolates were also carbapenem-resistant. The most common β-lactam resistance gene was bla_CTX-M-1 (91%), followed by bla_TEM (76.1%), bla_SHV (68.7%), bla_OXA-1 (29.9%), bla_GES (14.9%), bla_CTX-M-9 (11.9%), and bla_CTX-M-2 (4.5%). The carbapenemase genes bla_KPC (55.2%), bla_IMP (28.4%), bla_VIM (14.9%), bla_NDM-1 (13.4%), and bla_OXA-48 (10.4%) and virulence-associated genes such as fimH (71.6%), ugeF (58.2%), wabG (56.7%), ureA (47.8%) and kfuBC (28.4%) were also detected. About 96.2% of the environmental and 100% of the patient isolates were able to form biofilms. ERIC-PCR-based genotyping and hierarchical clustering of K. pneumoniae isolates revealed an association between environmental and patient samples, indicating clonal association with possible transmission of antimicrobial resistance genes. Our findings can help in improving patient care and infection control, and the development of public health policies related to hospital-acquired infections.

Molecular identification of Klebsiella pneumoniae and expression of immune genes in infected spotted gar Lepisosteus oculatus

Spotted gar (Lepisosteus oculatus) is a primitive ray-finned fish which has not undergone the third round whole genome duplication and commonly used as a model to study the evolution of immune genes. In this study, a pathogenic strain of Klebsiella pneumoniae (termed KPY01) was isolated from a diseased spotted gar, based on the Gram-stain and phylogenetic analysis of the 16S rDNA and khe genes. Further, the virulence genes and drug resistance genes were determined and drug sensitivity tests were performed to explore the virulence and drug resistance of the KPY01. Putative biosynthetic gene clusters (BGCs) for the biosynthesis of secondary metabolites were predicted using the anti-SMASH5.0 online genome mining platform. Histopathological analysis revealed that the immune cells were significantly decreased in the white pulp of spleen of fish infected with K. pneumonia and tissue inflammation became apparent. Besides, the expression of cytokines including interleukin (il) -8, il-10, il-12a, il-18 and interferon γ (ifn-γ) were shown to be modulated in the spleen, gills and kidney. Our work provides useful information for further investigation on the virulence of K. pneumoniae and host immune responses to K. pneumoniae infection in fish.

Nutrient conditions are primary drivers of bacterial capsule maintenance in Klebsiella

The fitness cost associated with the production of bacterial capsules is considered to be offset by the protection provided by these extracellular structures against biotic aggressions or abiotic stress. However, it is unknown if the capsule contributes to fitness in the absence of these. Here, we explored conditions favouring the maintenance of the capsule in Klebsiella pneumoniae, where the capsule is known to be a major virulence factor. Using short-term experimental evolution on different Klebsiella strains, we showed that small environmental variations have a strong impact on the maintenance of the capsule. Capsule inactivation is frequent in nutrient-rich, but scarce in nutrient-poor media. Competitions between wild-type and capsule mutants in nine different strains confirmed that the capsule is costly in nutrient-rich media. Surprisingly, these results also showed that the presence of a capsule provides a clear fitness advantage in nutrient-poor conditions by increasing both growth rates and population yields. The comparative analyses of the wild-type and capsule mutants reveal complex interactions between the environment, genetic background and serotype even in relation to traits known to be relevant during pathogenesis. In conclusion, our data suggest there are novel roles for bacterial capsules yet to be discovered and further supports the notion that the capsule's role in virulence may be a by-product of its contribution to bacterial adaptation outside the host.

A Synthetic Carbohydrate-Protein Conjugate Vaccine Candidate against Klebsiella pneumoniae Serotype K2

Klebsiella pneumoniae causes pneumonia and liver abscesses in humans worldwide and contains virulence factor capsular polysaccharides and lipopolysaccharides linked to the cell wall. Although capsular polysaccharides are good antigens for vaccine production and capsular oligosaccharides conjugate vaccines are proven effective against infections caused by encapsulated pathogens, there is still no Klebsiella pneumoniae vaccine available. One obstacle is that the capsular polysaccharide of a dominated Klebsiella pneumoniae serotype K2 is difficult to synthesize chemically due to the three 1,2-cis linkages in its structure. In this study, we successfully synthesized K2 capsular polysaccharides from tetra- to octasaccharides in highly a stereoselective manner. Subsequently, three synthesized glycans were conjugated to DT protein to provide glycoconjugate vaccine candidates (DT-Hexa, DT-Hepta, and DT-Octa) that were used in in vivo immunization experiments in mice. The results of immunized studies showed all three glycoconjugates elicited antibodies that recognized all of the synthetic glycans at 1:200-fold dilution. Particularly, the DT-Hepta conjugate elicited a higher level of antibodies that can recognize longer glycan (octasaccharide) even at 1:12800-fold dilution and exhibited good bactericidal activity. Our results concluded that heptasaccharide is the minimal epitope and a potential candidate for the vaccine against the K2 sero group of Klebsiella pneumoniae.

Hypervirulent Klebsiella pneumoniae - clinical and molecular perspectives

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

Impact of Klebsiella pneumoniae in lower gastrointestinal tract diseases

The 2016 Global Burden of Disease report by WHO revealed that diseases of the gastrointestinal tract (GIT) had one of the highest incidence rates worldwide. The plethora of factors that contribute to the development of GIT-related illnesses can be divided into genetic, environmental and lifestyle factors. Apart from that, the role that infectious agents play in the development of GIT diseases has piqued the interest of researchers worldwide. The human gut harbors approximately 10¹⁴ bacteria in it with increasing concentration toward the lower GIT. Among the various microbiota that colonize the human gut, Gram-negative bacteria have been most notoriously linked to GIT-related diseases such as inflammatory bowel disease (IBD) including Crohn's disease and ulcerative colitis and colorectal cancer (CRC). Some of the notable culprits that have been attributed to these diseases are Bacteroides fragilis, Fusobacterium nucleatum, Escherichia coli and Helicobacter pylori. However, studies in recent years are beginning to recognize a new player, Klebsiella pneumoniae (K. pneumoniae) in the causation and progression of GIT diseases. Once synonymous with infections and diseases of the upper respiratory tract, K. pneumoniae has now emerged as one of the pathogens commonly isolated from patients with GIT diseases. However, extensive studies attributing K. pneumoniae to GIT diseases, particularly that of CRC are scanty. Therefore, this review intends to shed light on the association of K. pneumoniae in gastrointestinal diseases such as Crohn's disease, ulcerative colitis as well as CRC.

Rhinoscleroma pathogenesis: The type K3 capsule of Klebsiella rhinoscleromatis is a virulence factor not involved in Mikulicz cells formation

Rhinoscleroma is a human specific chronic granulomatous infection of the nose and upper airways caused by the Gram-negative bacterium Klebsiella pneumoniae subsp. rhinoscleromatis. Although considered a rare disease, it is endemic in low-income countries where hygienic conditions are poor. A hallmark of this pathology is the appearance of atypical foamy monocytes called Mikulicz cells. However, the pathogenesis of rhinoscleroma remains poorly investigated. Capsule polysaccharide (CPS) is a prominent virulence factor in bacteria. All K. rhinoscleromatis strains are of K3 serotype, suggesting that CPS can be an important driver of rhinoscleroma disease. In this study, we describe the creation of the first mutant of K. rhinoscleromatis, inactivated in its capsule export machinery. Using a murine model recapitulating the formation of Mikulicz cells in lungs, we observed that a K. rhinoscleromatis CPS mutant (KR cps-) is strongly attenuated and that mice infected with a high dose of KR cps- are still able to induce Mikulicz cells formation, unlike a K. pneumoniae capsule mutant, and to partially recapitulate the characteristic strong production of IL-10. Altogether, the results of this study show that CPS is a virulence factor of K. rhinoscleromatis not involved in the specific appearance of Mikulicz cells.

Epidemiology and Virulence of Klebsiella pneumoniae

Strains of Klebsiella pneumoniae are frequently opportunistic pathogens implicated in urinary tract and catheter-associated urinary-tract infections of hospitalized patients and compromised individuals. Infections are particularly difficult to treat since most clinical isolates exhibit resistance to several antibiotics leading to treatment failure and the possibility of systemic dissemination. Infections of medical devices such as urinary catheters is a major site of K. pneumoniae infections and has been suggested to involve the formation of biofilms on these surfaces. Over the last decade there has been an increase in research activity designed to investigate the pathogenesis of K. pneumoniae in the urinary tract. These investigations have begun to define the bacterial factors that contribute to growth and biofilm formation. Several virulence factors have been demonstrated to mediate K. pneumoniae infectivity and include, but are most likely not limited to, adherence factors, capsule production, lipopolysaccharide presence, and siderophore activity. The development of both in vitro and in vivo models of infection will lead to further elucidation of the molecular pathogenesis of K. pneumoniae. As for most opportunistic infections, the role of host factors as well as bacterial traits are crucial in determining the outcome of infections. In addition, multidrug-resistant strains of these bacteria have become a serious problem in the treatment of Klebsiella infections and novel strategies to prevent and inhibit bacterial growth need to be developed. Overall, the frequency, significance, and morbidity associated with K. pneumoniae urinary tract infections have increased over many years. The emergence of these bacteria as sources of antibiotic resistance and pathogens of the urinary tract present a challenging problem for the clinician in terms of management and treatment of individuals.

Effect in virulence of switching conserved homologous capsular polysaccharide genes from Klebsiella pneumoniae serotype K1 into K20

The capsular polysaccharides in different serotypes of Klebsiella pneumoniae (KP) coded by the (CPS) gene cluster are characterized by a conserved and a hyper-variable region. We performed a virulence study by switching genes in the highly conserved region of the CPS cluster between strains. Six genes in the CPS conserved region in serotype K20, including galF, acidPPc, wzi, wza, wzb and wzc, were knocked out and replaced by the homologous genes from serotype K1. Compared to the parental K20 strain, the mutants showed a decline in lethality (LD₅₀) in mice from 10-fold to > 10⁵-fold and were categorized in terms of the effect on virulence as low (L) for galF and acidPPC, moderate (M) for wzi, and high (H) for wza, wzb and wzc. Although substituting the acidPPC gene from K1 for acidPPC in the K20 strain fully restored virulence, substitution with the wzi, wza, wzb or wzc homologs from K1 did not. The restoration with wzi from K1 led to a partial restoration of virulence, with the LD₅₀ in mice changing from 10⁴ to 10³ CFU_. For the wza, wzb and wzc genes, Complementation of K20 wza, wzb and wzc from K1 resulted in varied degrees of lethality in mice. Variable improvement in serum killing and phagocytosis was observed when the knockout mutants were compared with the gene-switched strains. In conclusion, homologous genes for capsule synthesis failed to exhibit the same functionality when switched between serotypes and virulence was decreased in different degree in according to the genes' homology.

Genomic epidemiology and global diversity of the emerging bacterial pathogen Elizabethkingia anophelis

Elizabethkingia anophelis is an emerging pathogen involved in human infections and outbreaks in distinct world regions. We investigated the phylogenetic relationships and pathogenesis-associated genomic features of two neonatal meningitis isolates isolated 5 years apart from one hospital in Central African Republic and compared them with Elizabethkingia from other regions and sources. Average nucleotide identity firmly confirmed that E. anophelis, E. meningoseptica and E. miricola represent demarcated genomic species. A core genome multilocus sequence typing scheme, broadly applicable to Elizabethkingia species, was developed and made publicly available (http://bigsdb.pasteur.fr/elizabethkingia). Phylogenetic analysis revealed distinct E. anophelis sublineages and demonstrated high genetic relatedness between the African isolates, compatible with persistence of the strain in the hospital environment. CRISPR spacer variation between the African isolates was mirrored by the presence of a large mobile genetic element. The pan-genome of E. anophelis comprised 6,880 gene families, underlining genomic heterogeneity of this species. African isolates carried unique resistance genes acquired by horizontal transfer. We demonstrated the presence of extensive variation of the capsular polysaccharide synthesis gene cluster in E. anophelis. Our results demonstrate the dynamic evolution of this emerging pathogen and the power of genomic approaches for Elizabethkingia identification, population biology and epidemiology.

Low molecular weight protein tyrosine phosphatase: Multifaceted functions of an evolutionarily conserved enzyme

Originally identified as a low molecular weight acid phosphatase, LMW-PTP is actually a protein tyrosine phosphatase that acts on many phosphotyrosine-containing cellular proteins that are primarily involved in signal transduction. Differences in sequence, structure, and substrate recognition as well as in subcellular localization in different organisms enable LMW-PTP to exert many different functions. In fact, during evolution, the LMW-PTP structure adapted to perform different catalytic actions depending on the organism type. In bacteria, this enzyme is involved in the biosynthesis of group 1 and 4 capsules, but it is also a virulence factor in pathogenic strains. In yeast, LMW-PTPs dephosphorylate immunophilin Fpr3, a peptidyl-prolyl-cis-trans isomerase member of the protein chaperone family. In humans, LMW-PTP is encoded by the ACP1 gene, which is composed of three different alleles, each encoding two active enzymes produced by alternative RNA splicing. In animals, LMW-PTP dephosphorylates a number of growth factor receptors and modulates their signalling processes. The involvement of LMW-PTP in cancer progression and in insulin receptor regulation as well as its actions as a virulence factor in a number of pathogenic bacterial strains may promote the search for potent, selective and bioavailable LMW-PTP inhibitors.

Susceptibility to Klebsiella pneumonaie infection in collaborative cross mice is a complex trait controlled by at least three loci acting at different time points

BACKGROUND

Klebsiella pneumoniae (Kp) is a bacterium causing severe pneumonia in immunocompromised hosts and is often associated with sepsis. With the rise of antibiotic resistant bacteria, there is a need for new effective and affordable control methods; understanding the genetic architecture of susceptibility to Kp will help in their development. We performed the first quantitative trait locus (QTL) mapping study of host susceptibility to Kp infection in immunocompetent Collaborative Cross mice (CC). We challenged 328 mice from 73 CC lines intraperitoneally with 104 colony forming units of Kp strain K2. Survival and body weight were monitored for 15 days post challenge. 48 of the CC lines were genotyped with 170,000 SNPs, with which we mapped QTLs.

RESULTS

CC lines differed significantly (P < 0.05) in mean survival time, between 1 to 15 days post infection, and broad sense heritability was 0.45. Distinct QTL were mapped at specific time points during the challenge. A QTL on chromosome 4 was found only on day 2 post infection, and QTL on chromosomes 8 and 18, only on day 8. By using the sequence variations of the eight inbred strain founders of the CC to refine QTL localization we identify several candidate genes.

CONCLUSION

Host susceptibility to Kp is a complex trait, controlled by multiple genetic factors that act sequentially during the course of infection.

Phenotypic, antimicrobial susceptibility profile and virulence factors of Klebsiella pneumoniae isolated from buffalo and cow mastitic milk

Studies on the prevalence and virulence genes of Klebsiella mastitis pathogens in a buffalo population are undocumented. Also, the association of rmpA kfu, uge, magA, Aerobactin, K1 and K2 virulent factors with K. pneumoniae buffalo, and cow mastitis is unreported. The virulence of K. pneumoniae was evaluated through both phenotypic and molecular assays. In vivo virulence was assessed by the Vero cell cytotoxicity, suckling mouse assay and mice lethality test. Antimicrobial susceptibility was tested by disk diffusion method. The 45 K. pneumoniae isolates from buffalo (n = 10/232) and cow (n = 35/293) milk were isolated (45/525; 8.6%) and screened via PCR for seven virulence genes encoding uridine diphosphate galactose 4 epimerase encoding gene responsible for capsule and smooth lipopolysaccharide synthesis (uge), siderophores (kfu and aerobactin), protectines or invasins (rmpA and magA), and the capsule and hypermucoviscosity (K1 and K2). The most common virulence genes were rmpA, kfu, uge, and magA (77.8% each). Aerobactin and K1 genes were found at medium rates of 66.7% each and K2 (55.6%). The Vero cell cytotoxicity and LD (50) in mice were found in 100% of isolates. A multidrug resistance pattern was observed for 40% of the antimicrobials. The distribution of virulence profiles indicate a role of rmpA, kfu, uge, magA, Aerobactin, and K1 and K2 in pathogenicity of K. pneumoniae in udder infections and invasiveness, and constitutes a threat for vulnerable animals, even more if they are in combination with antibiotic resistance.

Pushing the Bacterial Envelope

Over the past three decades, a powerful array of techniques has been developed for expressing heterologous proteins and saccharides on the surface of bacteria. Surface-engineered bacteria, in turn, have proven useful in a variety of settings, including high-throughput screening, biofuel production, and vaccinology. In this chapter, we provide a comprehensive review of methods for displaying polypeptides and sugars on the bacterial cell surface, and discuss the many innovative applications these methods have found to date. While already an important biotechnological tool, we believe bacterial surface display may be further improved through integration with emerging methodology in other fields, such as protein engineering and synthetic chemistry. Ultimately, we envision bacterial display becoming a multidisciplinary platform with the potential to transform basic and applied research in bacteriology, biotechnology, and biomedicine.

Inhibition of Klebsiella pneumoniae Growth and Capsular Polysaccharide Biosynthesis by Fructus mume

Klebsiella pneumoniae is the predominant pathogen isolated from liver abscess of diabetic patients in Asian countries. With the spread of multiple-drug-resistant K. pneumoniae, there is an increasing need for the development of alternative bactericides and approaches to block the production of bacterial virulence factors. Capsular polysaccharide (CPS), especially from the K1 and K2 serotypes, is considered the major determinant for K. pneumoniae virulence. We found that extracts of the traditional Chinese medicine Fructus mume inhibited the growth of K. pneumoniae strains of both serotypes. Furthermore, Fructus mume decreased the mucoviscosity, and the CPS produced in a dose-dependent manner, thus reducing bacterial resistance to serum killing. Quantitative reverse transcription polymerase chain reaction analyses showed that Fructus mume downregulated the mRNA levels of cps biosynthesis genes in both serotypes, possibly by increasing the intracellular iron concentration in K. pneumoniae. Moreover, citric acid, a major organic acid in Fructus mume extracts, was found to have an inhibitory effect on growth and CPS biosynthesis in K. pneumoniae. Taken together, our results indicate that Fructus mume not only possesses antibacterial activity against highly virulent K. pneumoniae strains but also inhibits bacterial CPS biosynthesis, thereby facilitating pathogen clearance by the host immune system.

Virulent clones of Klebsiella pneumoniae: identification and evolutionary scenario based on genomic and phenotypic characterization

Klebsiella pneumoniae is found in the environment and as a harmless commensal, but is also a frequent nosocomial pathogen (causing urinary, respiratory and blood infections) and the agent of specific human infections including Friedländer's pneumonia, rhinoscleroma and the emerging disease pyogenic liver abscess (PLA). The identification and precise definition of virulent clones, i.e. groups of strains with a single ancestor that are associated with particular infections, is critical to understand the evolution of pathogenicity from commensalism and for a better control of infections. We analyzed 235 K. pneumoniae isolates of diverse environmental and clinical origins by multilocus sequence typing, virulence gene content, biochemical and capsular profiling and virulence to mice. Phylogenetic analysis of housekeeping genes clearly defined clones that differ sharply by their clinical source and biological features. First, two clones comprising isolates of capsular type K1, clone CC23^K1 and clone CC82^K1, were strongly associated with PLA and respiratory infection, respectively. Second, only one of the two major disclosed K2 clones was highly virulent to mice. Third, strains associated with the human infections ozena and rhinoscleroma each corresponded to one monomorphic clone. Therefore, K. pneumoniae subsp. ozaenae and K. pneumoniae subsp. rhinoscleromatis should be regarded as virulent clones derived from K. pneumoniae. The lack of strict association of virulent capsular types with clones was explained by horizontal transfer of the cps operon, responsible for the synthesis of the capsular polysaccharide. Finally, the reduction of metabolic versatility observed in clones Rhinoscleromatis, Ozaenae and CC82^K1 indicates an evolutionary process of specialization to a pathogenic lifestyle. In contrast, clone CC23^K1 remains metabolically versatile, suggesting recent acquisition of invasive potential. In conclusion, our results reveal the existence of important virulent clones associated with specific infections and provide an evolutionary framework for research into the links between clones, virulence and other genomic features in K. pneumoniae.

Topo-optical investigations on the surface of bacterial cells during the phagocytosis of Klebsiella pneumoniae in mouse

Polarisation optical methods provide the means to perform sub-microscopic investigations on structures containing spatially highly ordered molecules, for example the cell envelope of prokaryotic cells. Such structures can evoke birefringence, which can be enhanced or modified by different dyes or reagents, thus providing the possibility of a more specific investigation of the composition and structure of bacterial surface compounds. Klebsiella pneumoniae synthesises sterically different carbohydrate-rich structures, including those of the outermost capsular polysaccharide, the polysaccharide somatic antigen of the lipopolysaccharide molecule and the peptidoglycan layer of the cell wall. In the study reported here, the nature and intensity of topo-optical activity of these structures was analysed using the aldehyde-bisulphite-toluidine blue reaction, sialic acid topo-optical reactions and chlorpromazine-eosin charge transfer reactions. Furthermore, a mouse intraperitoneal model was used to analyse alterations in topo-optical characteristics of bacteria during phagocytosis. Both encapsulated and non-encapsulated bacterial cells changed their original pattern and orientation of birefringence after being phagocytosed.

Manno(rhamno)biose-containing capsular polysaccharides of Klebsiella pneumoniae enhance opsono-stimulation of human polymorphonuclear leukocytes

We tested the relationship between the capsular and the O-antigen structures and the ability of bacteria to trigger respiratory burst in human polymorphonuclear leukocytes (PMNL). Capsulated and non-capsulated variants as well as capsule-switched derivatives of Klebsiella serotypes bearing or lacking manno(rhamno)biose repeats in their capsular polysaccharides and expressing either mannose-rich or mannose-poor O antigens were tested for their ability to induce respiratory burst and survive in human PMNL. Luminol-enhanced chemiluminescence (CL) was measured to quantify respiratory burst. Intracellular survival was quantified by determining the viable counts of intracellular bacteria. K serotypes and the capsule-switched derivative lacking manno(rhamno)biose induced significantly lower CL than those expressing manno(rhamno)biose. Manno(rhamno)biose-lacking serotypes survived in the cells significantly better than serotypes expressing these repeats. C1q depletion did not affect CL induced by the manno(rhamno)biose-containing serotype, whereas factor B depletion revealed a significantly reduced CL. Likewise, EGTA in the presence of Mg(2+) significantly decreased CL, but the values were higher than those induced by the bacterium opsonized with factor B-depleted serum. In the presence of EGTA, Mg(2+)-treated factor B-depleted serum revealed a significant reduction in the CL response compared with the responses induced by opsonization with factor B-depleted serum alone. These results indicate, in addition to the alternative pathway, a manno(rhamno)biose pattern recognition of Klebsiella by PMNL probably by the complement lectin pathway.

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.

Klebsiella pneumoniae genotype K1: an emerging pathogen that causes septic ocular or central nervous system complications from pyogenic liver abscess

BACKGROUND

Since 1986, researchers have noted a syndrome of Klebsiella pneumoniae pyogenic liver abscess that is complicated by endophthalmitis or central nervous system infections. There are limited data regarding the role of bacterial genotype in the pathogenesis of this syndrome.

METHODS

We conducted a retrospective cohort study involving 177 cases of K. pneumoniae pyogenic liver abscess treated during 1997-2005 at a tertiary university hospital in Taiwan. We performed bacterial cps genotyping by polymerase chain reaction detection of serotype-specific alleles at wzy and wzx loci and used an in vitro serum assay to evaluate the virulence of bacterial strains.

RESULTS

Septic ocular or central nervous system complications developed in 23 patients (13%). Logistic regression analysis showed that genotype K1 was the only significant risk factor (adjusted odds ratio, 4.8; 95% confidence interval, 1.5-15.7, P=.009). The serum resistance assay indicated that, on average, K1 strains (n=100) were significantly more virulent than were strains of K2 (n=36), K20/K5/K54 (n=21), or other genotypes (n=20) (P<.001 for each comparison). In addition to the serotype-specific cps region, the genomic background of K1 strains also differed significantly from that of non-K1 strains (20-kb kfu/PTS region, 97/100 vs. 13/77; P<.001). Of the 19 cases in which genotype K1 strains caused complications, 8 patients (42%) did not have identifiable underlying medical diseases.

CONCLUSIONS

K. pneumoniae genotype K1 is an emerging pathogen capable of causing catastrophic septic ocular or central nervous system complications from pyogenic liver abscess independent of underlying diseases in the host.

Identification of Klebsiella pneumoniae genes uniquely expressed in a strain virulent using a murine model of bacterial pneumonia

Klebsiella pneumoniae is a gram-negative bacterium of significant clinical importance. This study examines the differential pulmonary host anti-bacterial responses towards two clinical isolates of K. pneumoniae. Intratracheal inoculation with 7 x 10(4)CFU of strain 43816 induced 100% mortality in C57BL/6J mice within 5 days post infection, whereas infection with 5 x 10(5)CFU of strain IA565 resulted in 100% survival. Infection with strain 43816 resulted in significant pulmonary and peripheral blood bacterial burden and induction of the chemokines MIP-2, KC and MCP-1 by 24h post infection. In contrast, IA565-infected mice displayed basal chemokine levels and no detectable bacteria by 24h post inoculation were isolated from lungs or peripheral blood. These data indicate an apparent lack of pathogenicity of strain IA565. Since little is known about Klebsiella-specific virulence genes, we have utilized PCR-based genomic DNA and cDNA suppressive subtractive hybridization and identified nine DNA sequences unique to the pathogenic strain of K. pneumoniae 43816. These sequences were highly homologous to enteric bacterial genes regulating iron uptake, fimbrial-mediated adhesion, energy production and conversion, transcriptional regulation, signal transduction, restriction endonuclease activity, and membrane transport.

Signature-tagged mutagenesis of Klebsiella pneumoniae to identify genes that influence biofilm formation on extracellular matrix material

Klebsiella pneumoniae causes urinary tract infections, respiratory tract infections, and septicemia in susceptible individuals. Strains of Klebsiella frequently produce extended-spectrum beta-lactamases, and infections with these strains can lead to relatively high mortality rates (approximately 15%). Other virulence factors include production of an antiphagocytic capsule and outer membrane lipopolysaccharide (LPS), which mediates serum resistance, as well as fimbriae on the surface of the bacteria. Type 1 fimbriae mediate adherence to many types of epithelial cells and may facilitate adherence of the bacteria to the bladder epithelium. Type 3 fimbriae can bind in vitro to the extracellular matrix of urinary and respiratory tissues, suggesting that they mediate binding to damaged epithelial surfaces. In addition, type 3 fimbriae are required for biofilm formation by Klebsiella pneumoniae on plastics and human extracellular matrix; thus, they may facilitate the formation of treatment-resistant biofilm on indwelling plastic devices, such as catheters and endotracheal tubing. The presence of these devices may cause tissue damage, allowing Klebsiella to grow as a biofilm on exposed tissue basement membrane components. Though in vivo biofilm growth may be an important step in the infection process, little is known about the genetic factors required for biofilm formation by Klebsiella pneumoniae. Thus, we performed signature-tagged mutagenesis to identify factors produced by K. pneumoniae strain 43816 that are required for biofilm formation. We identified mutations in the cps capsule gene cluster, previously unidentified transcriptional regulators, fimbrial, and sugar phosphotransferase homologues, as well as genetic loci of unknown function, that affect biofilm formation.

Molecular serotyping of Klebsiella species isolates by restriction of the amplified capsular antigen gene cluster

The objective of the present work was to develop a molecular method that would enable determination of the capsular serotypes of Klebsiella isolates without the use of antiserum. PCR amplification of the capsular antigen gene cluster (cps) was followed by digestion with the restriction enzyme HincII (cps PCR-restriction fragment length polymorphism [RFLP] analysis). The profiles (C patterns) obtained for 224 strains representing the 77 known K serotypes showed 3 to 13 fragments ranging in size from 0.2 to 4.4 kb. A total of 97 distinct C patterns were obtained; 100% of 61 pairs of samples tested twice showed reproducible C patterns. The C patterns were K-type specific; i.e., the C pattern(s) of any K serotype was distinct from the C patterns of all other K serotypes, with the only exceptions being serotypes K22 and K37, which are known to cross-react. For 12 of 17 K types for which at least two strains were included, C-pattern variations were found among strains with the same K serotype. Therefore, cps PCR-RFLP analysis has a higher discriminatory power than classical K serotyping. C-pattern identity was observed among strains with a given K type that were collected many years apart and from distinct sources, indicating C-pattern stability. Only 4.5% of the strains were nontypeable, because of unsuccessful PCR amplification (whereas 8 to 23% are nontypeable by classical K serotyping). Three of four noncapsulated strains analyzed showed recognizable C patterns. The K serotypes of 18 (82%) of 22 recent Klebsiella pneumoniae clinical isolates could be deduced from their C patterns. In conclusion, cps PCR-RFLP analysis allows determination of the K serotype, while it is easier to perform and more discriminatory than classical serotyping.

A global emerging disease of Klebsiella pneumoniae liver abscess: is serotype K1 an important factor for complicated endophthalmitis?

BACKGROUND AND AIMS

Over the past two decades in Taiwan, pyogenic liver abscess has usually been caused by a single microorganism, Klebsiella pneumoniae, and is frequently associated with the serious complication of endophthalmitis, especially in diabetic patients. However, the relationship between the clinical presentation and bacterial factors remains unclear. The aim of this study was to investigate the clinical features of patients and the serotype and ribotype of K pneumoniae liver abscess.

METHODS

From July 1991 to June 1998, a total of 134 cases of K pneumoniae liver abscess with 248 K pneumoniae isolates from the same patients were collected from two large medical centres in northern Taiwan. Clinical data were collected from medical records. Serotyping and ribotyping were performed using the countercurrent immunoelectrophoresis method and automated Riboprinter.

RESULTS

Serotyping revealed that the most common serotypes were K1 (63.4%) and K2 (14.2%). K1 isolates occurred at a significantly higher frequency (p<0.01) than all other serotypes. Among 134 patients, 105 (78.4%) had suffered from diabetes mellitus for 3-15 years. Fourteen patients (10.4%) had metastatic infection to the eye causing septic endophthalmitis. Liver aspirates, and blood and vitreous pus cultures yielded the same serotype of K pneumoniae in all patients. Among patients with septic endophthalmitis, 92.3% (13/14) were diabetic, and 85.7% (12/14) of the isolates belonged to serotype K1. For molecular typing, different degrees of genetic polymorphism among isolates with the same K1 serotype suggested no particular prevalence of any one strain in K pneumoniae liver abscess.

CONCLUSION

K pneumoniae serotype K1 was significantly associated with liver abscess and the complication of endophthalmitis, especially in diabetic patients. Physicians should request an immediate report of serotyping and susceptibility test results simultaneously if a diagnosis of pyogenic liver abscess has been made so that early and appropriate management for possible complications will not be delayed. The use of ceftriaxone because of its higher concentration in the aqueous humor is suggested to decrease the chance of septic endophthalmitis.

Capsule impedes adhesion to and invasion of epithelial cells by Klebsiella pneumoniae

The adhesion of K21a, K26, K36, and K50 capsulated Klebsiella strains to ileocecal (HCT-8) and bladder (T24) epithelial cell lines was significantly lower than that of their corresponding spontaneous noncapsulated variants K21a/3, K26/1, K36/3, and K50/3, respectively. Internalization of the bacteria by both epithelial cell lines was also significantly reduced. Similarly, a capsule-switched derivative, K2(K36), that exhibited a morphologically larger K36 capsule and formed more capsular material invaded the ileocecal epithelial cell line poorly compared to the corresponding K2 parent strain. None of the capsulated strains exhibited significant mannose-sensitive type 1 fimbriae, whereas two of the noncapsulated variants K21a/3 and K50/3 exhibited potent mannose-sensitive hemagglutinating activity. Although hemagglutinating activity that could be attributed to mannose-resistant Klebsiella type 3 fimbriae was weak in all strains, in several cases the encapsulated parent strains exhibited lower titers than their corresponding noncapsulated variants. Although the level of adhesion to the ileocecal cells is not different from adhesion to bladder cells, bacterial internalization by bladder cells was significantly lower than internalization by ileocecal cells, suggesting that bladder cells lack components required for the internalization of Klebsiella.

Inability of encapsulated Klebsiella pneumoniae to assemble functional type 1 fimbriae on their surface

We screened phase variants of Klebsiella pneumoniae isolates for the expression of capsule and type 1 fimbriae and found that all of the 22 blood isolates were encapsulated and did not express type 1 fimbriae while 10 of 11 urinary tract isolates expressed type 1 fimbriae but were unencapsulated. Phase variants from selected isolates were found to be either unencapsulated and fimbriated or lacked both structures. Variants expressing both structures were not detected. Fimbrial subunits FimH and FimA were localized in the periplasmic space of the parent strain and on the surface of the unencapsulated variants. The results suggest that capsule formation impedes assembly of pre-formed fimbrial subunits on the bacterial surface.

Protein tyrosine kinases in bacterial pathogens are associated with virulence and production of exopolysaccharide

In eukaryotes, tyrosine protein phosphorylation has been studied extensively, while in bacteria, it is considered rare and is poorly defined. We demonstrate that Escherichia coli possesses a gene, etk, encoding an inner membrane protein that catalyses tyrosine autophosphorylation and phosphorylation of a synthetic co-polymer poly(Glu:Tyr). This protein tyrosine kinase (PTK) was termed Ep85 or Etk. All the E.coli strains examined possessed etk; however, only a subset of pathogenic strains expressed it. Etk is homologous to several bacterial proteins including the Ptk protein of Acinetobacter johnsonii, which is the only other known prokaryotic PTK. Other Etk homologues are AmsA of the plant pathogen Erwinia amylovora and Orf6 of the human pathogen Klebsiella pneumoniae. These proteins are involved in the production of exopolysaccharide (EPS) required for virulence. We demonstrated that like Etk, AmsA and probably also Orf6 are PTKs. Taken together, these findings suggest that tyrosine protein phosphorylation in prokaryotes is more common than was appreciated previously, and that Etk and its homologues define a distinct protein family of prokaryotic membrane-associated PTKs involved in EPS production and virulence. These prokaryotic PTKs may serve as a new target for the development of new antibiotics.

Klebsiella spp. as nosocomial pathogens: epidemiology, taxonomy, typing methods, and pathogenicity factors

Bacteria belonging to the genus Klebsiella frequently cause human nosocomial infections. In particular, the medically most important Klebsiella species, Klebsiella pneumoniae, accounts for a significant proportion of hospital-acquired urinary tract infections, pneumonia, septicemias, and soft tissue infections. The principal pathogenic reservoirs for transmission of Klebsiella are the gastrointestinal tract and the hands of hospital personnel. Because of their ability to spread rapidly in the hospital environment, these bacteria tend to cause nosocomial outbreaks. Hospital outbreaks of multidrug-resistant Klebsiella spp., especially those in neonatal wards, are often caused by new types of strains, the so-called extended-spectrum-beta-lactamase (ESBL) producers. The incidence of ESBL-producing strains among clinical Klebsiella isolates has been steadily increasing over the past years. The resulting limitations on the therapeutic options demand new measures for the management of Klebsiella hospital infections. While the different typing methods are useful epidemiological tools for infection control, recent findings about Klebsiella virulence factors have provided new insights into the pathogenic strategies of these bacteria. Klebsiella pathogenicity factors such as capsules or lipopolysaccharides are presently considered to be promising candidates for vaccination efforts that may serve as immunological infection control measures.

Phagocyte-bacteria interactions

Recognition and phagocytosis of micro-organisms in a serum-poor environment represent innate immunity against many extracellular pathogens. As a paradigm for such processes, we discuss the recognition of Klebsiella pneumoniae by alveolar macrophages and monocyte-derived macrophages in the absence of serum. Macrophages recognize and subsequently kill Klebsiella expressing Man-alpha 2/3-Man or Rha-alpha 2/3-Rha sequences in their capsular polysaccharides by two mechanisms: (a) recognition of the capsular structures by macrophage mannose receptors, and (b) opsonization by the lung surfactant protein A (SP-A), which binds to the capsular polysaccharides of Klebsiella and to SP-A receptors on the macrophages. Sp-A may also enhance phagocytosis by increasing the activity of macrophage mannose receptors. We conclude that a specific microbial surface structure may be a target for recognition by macrophages via several mechanisms, as exemplified in the case of Klebsiella capsular polysaccharides. Multiple recognition mechanisms of pathogens by macrophages may be essential to provide innate immunity to reduce the frequency of infections caused by a relatively less virulent bacterium in the immuno-compromised host.

Mast cell modulation of neutrophil influx and bacterial clearance at sites of infection through TNF-alpha

Although mast cells have been implicated in a variety of inflammatory conditions including immediate hypersensitivity and interstitial cystitis, their physiological role in the body is unknown. We investigated the role of mast cells in host defence against bacterial infections using a well characterized mast-cell-deficiency mouse model. We report here that mast cells, which are selectively located at portals of bacterial entry, are important to host defence. Mast-cell-deficient WBB6F1-W/Wv mice (W/Wv) were up to 20-fold less efficient in clearing enterobacteria than control WBB6F1 +/+ (+/+) mice or mast-cell-reconstituted W/Wv (W/Wv+MC) mice. With higher bacteria inocula, only W/Wv mice died (80%). The limited bacterial clearance in W/Wv mice directly correlated with impaired neutrophil influx. The mast-cell chemoattractant TNF-alpha was implicated in the neutrophil response because TNF-alpha was locally released only in +/+ and W/Wv+MC mice, TNF-alpha-specific antibodies blocked over 70% of the neutrophil influx, and purified mast cells released TNF-alpha upon incubation with bacteria. Additionally, the type-1 fimbrial subunit, FimH, was the necessary enterobacterial component for mast-cell activation and neutrophil influx because an isogenic FimH- mutant evoked a limited neutrophil response in +/+ mice compared to wild-type bacteria.

Regulation of expression of group IA capsular polysaccharides in Escherichia coli and related extracellular polysaccharides in other bacteria

Bacterial surface polysaccharides fulfill a number of important roles in cell-cell interactions, survival in natural environments, and formation of biofilms. Consequently, the mechanisms involved in regulation of extracellular polysaccharides are predicted to have a significant impact on microbial adaptation. Strains of Escherichia coli, Klebsiella spp, and Erwinia spp produce extracellular polysaccharides which share structural features. There are also similarities in the organization of genes required for synthesis of these cell surface polymers and, in some cases, the mechanism of synthesis may be related. Despite the diverse habitats of these bacteria, the systems which regulate expression of their extracellular polysaccharides appear to share components and mechanisms. Understanding these regulatory processes may lead to novel therapeutic approaches for pathogens, or for control of unwanted biofilm formation in industrial settings.

Relationships among capsular structure, phagocytosis, and mouse virulence in Klebsiella pneumoniae

Klebsiella pneumoniae strains of the K2 capsular serotype are usually highly virulent in mice, which is in contrast to the low virulence of most other serotypes. Here we used a genetic approach to examine the relative contribution of capsule type to the virulence of K. pneumoniae in mice. We used wild-type strains expressing capsular polysaccharide (CPS) serotypes K2 (strain KPA1) and K21a (strains KPB1 and KPC1), which were then used to construct capsule-switched derivatives. The close proximity of the cps gene cluster to selectable his markers made it possible to mobilize the cps genes by conjugation from one serotype (donor) to another (recipient) and to obtain recombinants in which interserotype switching had occurred by reciprocal recombination. Each capsule-switched derivative examined of the KPA and KPC strain backgrounds produced a CPS that was immunologically and structurally identical to that of the donor. Strain background was confirmed by demonstrating restriction fragment length polymorphism patterns identical to those of the respective recipients. The parent strains were then compared with capsule-switched recombinants for phenotypic properties associated with virulence. Clearance from the bloodstreams of mice was rapid in serotype K21a strains of either wild-type or recombinant origin, whereas K2 strains remained viable in the blood during the period examined. These differences appeared to be dependent upon the CPS type but independent of strain background. Binding to macrophages was higher in K21a strains than in those with the K2 capsule and was also independent of the strain background. Both blood clearance and macrophage-binding activities were completely inhibited by yeast mannan, suggesting that they were mediated via the macrophage mannose receptor. The K2 parent strain was highly virulent to mice (50% lethal dose [LD50], 3 x 10(3)), while the K21a parent strains demonstrated low virulence (LD50, > 2 x 10(8)). Interestingly, the virulence of recombinant KPC10(cpsK2), originally of the KPC1(cpsK21a) background, was intermediate (LD50, 4 x 10(5)). In contrast, both cpsK21a recombinants of the originally virulent KPA1 (cpsK2) background became nearly avirulent (LD50, > 2 x 10(8)). Six additional serotypes (K12, K24, K32, K55, K62, and K67) were examined, and all showed a positive correlation between the ability of the Klebsiella serotype to interact with a human mannose receptor, as expressed by Cos I cell recombinants, and the LD50 of the serotype. These results suggest that expression of a capsule which is recognized by the mannose receptor markedly affects the interaction with macrophages and blood clearance.(ABSTRACT TRUNCATED AT 400 WORDS)