A gene, uge, is essential for Klebsiella pneumoniae virulence

Isolation and Characterization of Aquatic-Borne Klebsiella pneumoniae from Tropical Estuaries in Malaysia

Klebsiella pneumoniae is an opportunistic pathogen that is responsible for causing nosocomial and community-acquired infections. Despite its common presence in soil and aquatic environments, the virulence potential of K. pneumoniae isolates of environmental origin is largely unknown. Hence, in this study, K. pneumoniae isolated from the estuarine waters and sediments of the Matang mangrove estuary were screened for potential virulence characteristics: antibiotic susceptibility, morphotype on Congo red agar, biofilm formation, presence of exopolysaccharide and capsule, possession of virulence genes (fimH, magA, ugE, wabG and rmpA) and their genomic fingerprints. A total of 55 strains of K. pneumoniae were isolated from both human-distributed sites (located along Sangga Besar River) and control sites (located along Selinsing River) where less human activity was observed, indicated that K. pneumoniae is ubiquitous in the environment. However, the detection of potentially virulent strains at the downstream of Kuala Sepetang village has suggested an anthropogenic contamination source. In conclusion, the findings from this study indicate that the Matang mangrove estuary could harbor potentially pathogenic K. pneumoniae with risk to public health. More studies are required to compare the environmental K. pneumoniae strains with the community-acquired K. pneumoniae strains.

Suppurative peritonitis by Klebsiella pneumoniae in captive gold-handed tamarin (Saguinus midas midas)

This report describes an outbreak of suppurative peritonitis caused by Klebsiella pneumoniae in an adult female of captive golden-handed tamarin (Saguinus midas midas). Two virulent and multidrug-resistant strains were isolated and classified through MLST as ST60 and ST1263. The microbiological diagnosis works as a support tool for preventive measures.

Quantification and comparison of virulence and characteristics of different variants of carbapenemase-producing Klebsiella pneumoniae clinical isolates from Taiwan and the United States

BACKGROUND/PURPOSE

The emergence of Klebsiella pneumoniae carbapenemase (KPC)-producing strains is a challenge for clinicians. The characteristics and virulence of variants of KPC-producing K. pneumoniae isolates were evaluated.

METHODS

Five clinical isolates-three KPC subtypes from Taiwan (KPC2-TW, KPC3-TW, and KPC17-TW) and two clinical strains from the United States (US; KPC2-US, KPC3-US)-were included. Virulent traits and capsular serotypes were analyzed by Polymerase Chain Reaction (PCR). Serum killing, neutrophil phagocytosis, and mice lethargy studies were performed to evaluate virulence.

RESULTS

Multilocus sequence typing (MLST) demonstrated that KPC2-TW and KPC17-TW belonged to sequence type (ST)11, and KPC2-US, KPC3-US, and KPC3-TW to ST258. KPC3-TW expressed capsular serotype K1, whereas the others were non-K1/K2/K5 isolates. MLST analysis indicated that ST11 strains were serum resistant, whereas ST258 isolates were serum sensitive. ST11 isolates exhibited significantly higher 15-minute phagocytic rates than ST258 isolates (70.28 ± 16.68% vs. 34.88 ± 10.52%, p < 0.001). The capsular serotype K1 strain was more resistant to neutrophil phagocytosis than non-K1/K2/K5 isolates (27.1 ± 10.23% vs. 54.46 ± 20.94%, p = 0.050). All KPC-producing strain variants from Taiwan and the US demonstrated less virulence in a mouse lethality study, where the LD50 ranged from approximately 10(6) colony-forming units (CFU) to >10(7) CFU. Immunological responses were not significantly correlated with KPC subtype; however, responses were associated with MLST and capsular serotype.

CONCLUSION

Production of KPC itself was not associated with increased virulence despite different variants of KPC. The ST11 KPC-producing strain was resistant to serum killing, whereas capsular ss K1 was associated with resistance to neutrophil phagocytosis.

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.

A novel PCR-based genotyping scheme for clinical Klebsiella pneumoniae

ABSTRACT: Aim: To establish a PCR-based genotyping method for clinical Klebsiella pneumoniae. Materials & methods: The prevalence of six serotype markers, 41 large variably presented gene clusters, and seven additional virulence markers were screened by PCR in 327 clinical K. pneumoniae strains from China. Results: Detection of serotype markers enabled the identification of capsular serotypes K1, K2, K5, K20, K54 and K57. K. pneumoniae isolates of different origins gave distinct profiles of virulence loci, allowing us to gain a full overview of virulence gene distribution of the strains tested. A novel genotyping scheme was established to group clinical K. pneumoniae strains into distinct complexes based on the profiles of large variably presented gene clusters and virulence markers. Conclusion: This PCR-based genotyping method would be useful to not only characterize genetic diversity and virulence gene distribution, but also for genotyping, origin tracing and risk estimation of K. pneumoniae.

Clinical and microbiological characteristics of peritoneal dialysis-related peritonitis caused by Klebsiella pneumoniae in southern Taiwan

BACKGROUND/PURPOSE(S)

Gram-negative peritonitis is a frequent and serious complication of peritoneal dialysis (PD). No previous reports have focused on Klebsiella pneumoniae infection. The aim of this study was to investigate the host and bacterial factors associated with K. pneumoniae PD-related peritonitis.

METHODS

We retrospectively studied K. pneumoniae PD-peritonitis cases treated at a university hospital in southern Taiwan during 1990-2011, and analyzed the clinical features and outcomes and bacterial characteristics of serotypes, hypermucoviscosity (HV), and virulence-associated genes such as wabG, uge, and rmpA in K. pneumoniae PD-related peritonitis. Fifty-four isolates of K. pneumoniae-related community-acquired urinary tract infection (UTI) and 76 morphologically different nonpathogenic K. pneumoniae isolates from healthy adults were used as controls.

RESULTS

K. pneumoniae was the second most common monomicrobial pathogen causing Gram-negative PD-related peritonitis (n = 13, 2.7%), and the most common pathogen involved in polymicrobial peritonitis (16/43, 37.2%) and associated with high catheter removal rate (7/16, 43.8%). Compared with Escherichia coli peritonitis cases, patients with monomicrobial K. pneumoniae peritonitis also had insignificantly higher incidence of sepsis/bacteremia [n = 5 (38%), p = 0.11] and a higher mortality rate [n = 3 (23%), p = 0.36]. The prevalence of K1/K2 (n = 1, 7.7%) serotypes was low, but there was a higher prevalence of serotype K20 (n = 3, 23.1%) in K. pneumoniae isolates derived from monomicrobial PD-related peritonitis compared with control groups. HV phenotype (p < 0.001) and rmpA genotype (p = 0.007) were absent in the peritonitis group.

CONCLUSION

This is the first study focused on clinical and microbiological characteristics of K. pneumoniae PD-related peritonitis. K. pneumoniae was a common Gram-negative pathogen causing monomicrobial and polymicrobial PD-related peritonitis in southern Taiwan. The bacterial characteristics with low percentage of capsular serotype K1/K2, no significant HV, and absence of rmpA suggest a different pathogenesis in K. pneumoniae PD-related peritonitis compared with that in UTI and liver abscess.

The route less taken: pulmonary models of enteric Gram-negative infection

Many pathogens are capable of causing a fulminant infection in pulmonary tissues of mammals. Animal models have provided an extensive understanding of the genetic and molecular mechanisms of bacterial pathogenesis as well as host immune response in the lungs. Many clinically relevant Gram-negative bacteria are host-restricted. Thus, the powerful, informative tools of mouse models are not available for study with these organisms. However, over the past 30 years, enterprising work has demonstrated the utility of pulmonary infection with enteric pathogens. Such infection models have increased our understanding host-pathogen interactions in these organisms. Here, we provide a review and comparison of lung models of infection with enteric, Gram-negative bacteria relative to naturally occurring lung pathogens.

Identification and characterization of antigens as vaccine candidates against Klebsiella pneumoniae

Nosocomial infections, also called "hospital acquired infections," occur worldwide and affect both developed and resource-poor countries, thus having a major impact on their health care systems. Klebsiella pneumoniae, which is an opportunistic Gram-negative pathogen, is responsible for causing pneumonia, urinary tract infections and septicemia in immune compromised hosts such as neonates. Unfortunately, there is no vaccine or mAb available for prophylactic or therapeutic use against K. pneumoniae infections. For this reason, we sought for a protein-based subunit vaccine capable of combating K. pneumoniae infections, by applying our ANTIGENome technology for the identification of potential vaccine candidates, focusing on conserved protein antigens present in strains with different serotypes. We identified numerous novel immunogenic proteins using genomic surface display libraries and human serum antibodies from donors exposed to or infected by K. pneumoniae. Vaccine candidate antigens were finally selected based on animal protection in a murine lethal-sepsis model. The protective and highly conserved antigens identified in this study are promising candidates for the development of a protein-based vaccine to prevent infection by K. pneumoniae.

Pyrosequencing-based analysis reveals a novel capsular gene cluster in a KPC-producing Klebsiella pneumoniae clinical isolate identified in Brazil

BACKGROUND

An important virulence factor of Klebsiella pneumoniae is the production of capsular polysaccharide (CPS), a thick mucus layer that allows for evasion of the host's defense and creates a barrier against antibacterial peptides. CPS production is driven mostly by the expression of genes located in a locus called cps, and the resulting structure is used to distinguish between different serotypes (K types). In this study, we report the unique genetic organization of the cps cluster from K. pneumoniae Kp13, a clinical isolate recovered during a large outbreak of nosocomial infections that occurred in a Brazilian teaching hospital.

RESULTS

A pyrosequencing-based approach showed that the cps region of Kp13 (cpsKp13) is 26.4 kbp in length and contains genes common, although not universal, to other strains, such as the rmlBADC operon that codes for L-rhamnose synthesis. cpsKp13 also presents some unique features, like the inversion of the wzy gene and a unique repertoire of glycosyltransferases. In silico comparison of cpsKp13 RFLP pattern with 102 previously published cps PCR-RFLP patterns showed that cpsKp13 is distinct from the C patterns of all other K serotypes. Furthermore, in vitro serotyping showed only a weak reaction with capsular types K9 and K34. We confirm that K9 cps shares common genes with cpsKp13 such as the rmlBADC operon, but lacks features like uge and Kp13-specific glycosyltransferases, while K34 capsules contain three of the five sugars that potentially form the Kp13 CPS.

CONCLUSIONS

We report the first description of a cps cluster from a Brazilian clinical isolate of a KPC-producing K. pneumoniae. The gathered data including K-serotyping support that Kp13's K-antigen belongs to a novel capsular serotype. The CPS of Kp13 probably includes L-rhamnose and D-galacturonate in its structure, among other residues. Because genes involved in L-rhamnose biosynthesis are absent in humans, this pathway may represent potential targets for the development of antimicrobial agents. Studying the capsular serotypes of clinical isolates is of great importance for further development of vaccines and/or novel therapeutic agents. The distribution of K-types among multidrug-resistant isolates is unknown, but our findings may encourage scientists to perform K-antigen typing of KPC-producing strains worldwide.

Virulence factors and TEM-type β-lactamases produced by two isolates of an epidemic Klebsiella pneumoniae strain

Two Klebsiella pneumoniae isolates of the same strain, identified in Poland, produced either TEM-47 or TEM-68, which differed by the Arg275Leu substitution. They harbored a few virulence factors, including an iron-chelating factor and capsule overproduction, suggesting that these factors were sufficient to enhance their nosocomial potency. TEM-68 and TEM-47 had similar enzymatic activities, but TEM-68 was less susceptible to inhibitors than TEM-47. These results confirm the role of the Arg275Leu substitution in the evolution of TEM enzymes.

PCR-based identification of Klebsiella pneumoniae subsp. rhinoscleromatis, the agent of rhinoscleroma

Rhinoscleroma is a chronic granulomatous infection of the upper airways caused by the bacterium Klebsiella pneumoniae subsp. rhinoscleromatis. The disease is endemic in tropical and subtropical areas, but its diagnosis remains difficult. As a consequence, and despite available antibiotherapy, some patients evolve advanced stages that can lead to disfiguration, severe respiratory impairment and death by anoxia. Because identification of the etiologic agent is crucial for the definitive diagnosis of the disease, the aim of this study was to develop two simple PCR assays. We took advantage of the fact that all Klebsiella pneumoniae subsp. rhinoscleromatis isolates are (i) of capsular serotype K3; and (ii) belong to a single clone with diagnostic single nucleotide polymorphisms (SNP). The complete sequence of the genomic region comprising the capsular polysaccharide synthesis (cps) gene cluster was determined. Putative functions of the 21 genes identified were consistent with the structure of the K3 antigen. The K3-specific sequence of gene Kr11509 (wzy) was exploited to set up a PCR test, which was positive for 40 K3 strains but negative when assayed on the 76 other Klebsiella capsular types. Further, to discriminate Klebsiella pneumoniae subsp. rhinoscleromatis from other K3 Klebsiella strains, a specific PCR assay was developed based on diagnostic SNPs in the phosphate porin gene phoE. This work provides rapid and simple molecular tools to confirm the diagnostic of rhinoscleroma, which should improve patient care as well as knowledge on the prevalence and epidemiology of rhinoscleroma.

Clinical and microbiological characteristics of Klebsiella pneumoniae isolates causing community-acquired urinary tract infections

BACKGROUND

Klebsiella pneumoniae is the second most common species causing urinary tract infections (UTI). However, the host factors and virulence genes of K. pneumoniae related to UTI are poorly understood. The aim of this study was to analyze the capsular phenotype and virulence genes of K. pneumoniae isolates and host factors potentially relevant to community-acquired UTI.

METHODS

Fifty-four K. pneumoniae isolates from patients with community-acquired UTI, 76 isolates from healthy adults, and 29 from patients with community-acquired pneumonia were compared. The virulence genes (rmpA, magA, uge, and wabG) and serotype (K1, K2, K5, K20, K54, or K57) were characterized by polymerase chain reaction (PCR). The modified string test was used to determine the hypermucoviscosity.

RESULTS

Diabetes mellitus was the most frequent underlying disease among UTI patients (53.7%, 29/54). No predominant K serotype was found in UTI strains. The hypermucoviscosity phenotype and rmpA gene were more often found in UTI isolates than in those from healthy adults (27.8 vs. 2.6%, P < 0.01; 29.6 vs. 11.8%, P < 0.01, respectively), whereas no significant difference in the frequency of magA, uge, wabG, or serotype genes was found. The prevalence of rmpA was significantly lower in isolates from patients with immunosuppression, chronic renal insufficiency, and urinary tract obstruction. Multivariate analysis showed that immunosuppression was negatively associated with the prevalence of rmpA.

CONCLUSION

Hypermucoviscosity was highly correlated with the presence of the rmpA gene in UTI strains, and rmpA may have a role in community-acquired UTI, especially in hosts without immunosuppression.

Antiserum against Raoultella terrigena ATCC 33257 identifies a large number of Raoultella and Klebsiella clinical isolates as serotype O12

Raoultella terrigena ATCC 33257, recently reclassified from the genus Klebsiella, is a drinking water isolate and belongs to a large group of non-typeable Klebsiella and Raoultella strains. Using an O-antiserum against a capsule-deficient mutant of this strain, we could show a high prevalence (10.5%) of the R. terrigena O-serotype among non-typeable, clinical Klebsiella and Raoultella isolates. We observed a strong serological cross-reaction with the K. pneumoniae O12 reference strain, indicating that a large percentage of these non-typeable strains may belong to the O12 serotype, although these are currently not detectable by the K. pneumoniae O12 reference antiserum in use. Therefore, we analyzed the O-polysaccharide (O-PS) structure and genetic organization of the wb gene cluster of R. terrigena ATCC 33257, and both confirmed a close relation of R. terrigena and K. pneumoniae O12. The two strains possess an identical O-PS, lipopolysaccharide core structure, and genetic organization of the wb gene cluster. Heterologous expression of the R. terrigena wb gene cluster in Escherichia coli K-12 resulted in the WecA-dependent synthesis of an O-PS reactive with the K. pneumoniae O12 antiserum. The serological data presented here suggest a higher prevalence of the O12-serotype among Klebsiella and Raoultella isolates than generally assumed.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2003-2004

This review is the third update of the original review, published in 1999, on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings the topic to the end of 2004. Both fundamental studies and applications are covered. The main topics include methodological developments, matrices, fragmentation of carbohydrates and applications to large polymeric carbohydrates from plants, glycans from glycoproteins and those from various glycolipids. Other topics include the use of MALDI MS to study enzymes related to carbohydrate biosynthesis and degradation, its use in industrial processes, particularly biopharmaceuticals and its use to monitor products of chemical synthesis where glycodendrimers and carbohydrate-protein complexes are highlighted.

The ionic interaction of Klebsiella pneumoniae K2 capsule and core lipopolysaccharide

The complete structures of LPS core types 1 and 2 fromKlebsiella pneumoniaehave been described by other authors. They are characterized by a lack of phosphoryl residues, but they contain galacturonic acid (GalA) residues, which contribute to the necessary negative charges. The presence of a capsule was determined in core-LPS non-polar mutants from strains 52145 (O1 : K2), DL1 (O1 : K1) and C3 (O8 : K66). O-antigen ligase (waaL) mutants produced a capsule. Core mutants containing the GalA residues were capsulated, while those lacking the residues were non capsulated. Since the proteins involved in the transfer of GalA (WabG) and glucosamine residues (WabH) are known, the chemical basis of the capsular-K2–cell-surface association was studied. Phenol/water extracts fromK. pneumoniae52145ΔwabH waaLand 52145ΔwaaLmutants, but not those from fromK. pneumoniae52145ΔwabG waaLmutant, contained both LPS and capsular polysaccharide, even after hydrophobic chromatography. The two polysaccharides were dissociated by gel-filtration chromatography, eluting with detergent and metal-ion chelators. From these results, it is concluded that the K2 capsular polysaccharide is associated by an ionic interaction to the LPS through the negative charge provided by the carboxyl groups of the GalA residues.

Association between rmpA and magA genes and clinical syndromes caused by Klebsiella pneumoniae in Taiwan

BACKGROUND

The association of the magA gene with the hypermucoviscosity phenotype relevant to the pathogenesis of Klebsiella pneumoniae liver abscess has been reported in Taiwan. Similarly, the rmpA gene, known as a positive regulator of extracapsular polysaccharide synthesis that confers a mucoid phenotype, may be another candidate gene causing hypermucoviscosity. However, the association of rmpA with K. pneumoniae clinical syndromes is unreported. We aimed to investigate the clinical correlation between rmpA and primary Klebsiella abscess, focusing on sites other than the liver.

METHODS

From July 2003 through December 2004, a total of 151 K. pneumoniae isolates recovered from 151 patients with bacteremia were collected from 2 large medical centers in southern Taiwan. Clinical data were collected from medical records. The genes rmpA and magA were amplified by polymerase chain reaction using specific primers.

RESULTS

The prevalences of hypermucoviscosity, rmpA, and magA were 38%, 48%, and 17%, respectively. As determined by statistical multivariate analysis, strains carrying rmpA were significantly associated with the hypermucoviscosity phenotype, and there was a significant correlation with purulent tissue infections, such as liver abscess and lung, neck, psoas muscle, or other focal abscess.

CONCLUSION

Our data support a statistical correlation between the rmpA gene and virulence in terms of abscess formation for these hypermucoviscous K. pneumoniae strains. Hypermucoviscosity associated with rmpA, together with a thorough physical examination, may be helpful as a guide to carry out appropriate diagnostic tests on patients with an initially unknown source of K. pneumoniae bacteremia, particularly when looking for the occurrence of an underlying abscess.

Dodecaprenyl phosphate-galacturonic acid as a donor substrate for lipopolysaccharide core glycosylation in Rhizobium leguminosarum

The lipid A and inner core regions of Rhizobium leguminosarum lipopolysaccharide contain four galacturonic acid (GalA) residues. Two are attached to the outer unit of the 3-deoxy-D-manno-octulosonic acid (Kdo) disaccharide, one to the mannose residue, and one to the 4'-position of lipid A. The enzymes RgtA and RgtB, described in the accompanying article, catalyze GalA transfer to the Kdo residue, whereas RgtC is responsible for modification of the core mannose unit. Heterologous expression of RgtA in Sinorhizhobium meliloti 1021, a strain that normally lacks GalA modifications on its Kdo disaccharide, resulted in detectable GalA transferase activity in isolated membrane preparations, suggesting that the appropriate GalA donor substrate is available in S. meliloti membranes. In contrast, heterologous expression of RgtA in Escherichia coli yielded inactive membranes. However, RgtA activity was detectable in the E. coli system when total lipids from R. leguminosarum 3841 or S. meliloti 1021 were added. We have now purified and characterized dodecaprenyl (C60) phosphate-GalA as a minor novel lipid of R. leguminosarum 3841 and S. meliloti. This substance is stable to mild base hydrolysis and was purified by DEAE-cellulose column chromatography. Its structure was established by a combination of electrospray ionization mass spectrometry and gas-liquid chromatography. Purified dodecaprenyl phosphate-GalA supports the efficient transfer of GalA to Kdo2-1-dephospho-lipid IV(A) by membranes of E. coli cells expressing RgtA, RgtB, and RgtC. The identification of a polyisoprene phosphate-GalA donor substrate suggests that the active site of RgtA faces the periplasmic side of the inner membrane. This work represents the first definitive characterization of a lipid-linked GalA derivative with the proposed structure dodecaprenyl phosphate-beta-D-GalA.

Expression cloning of three Rhizobium leguminosarum lipopolysaccharide core galacturonosyltransferases

The lipid A and core regions of the lipopolysaccharide in Rhizobium leguminosarum, a nitrogen-fixing plant endosymbiont, are strikingly different from those of Escherichia coli. In R. leguminosarum lipopolysaccharide, the inner core is modified with three galacturonic acid (GalA) moieties, two on the distal 3-deoxy-D-manno-octulosonic acid (Kdo) unit and one on the mannose residue. Here we describe the expression cloning of three novel GalA transferases from a 22-kb R. leguminosarum genomic DNA insert-containing cosmid (pSGAT). Two of these enzymes modify the substrate, Kdo2-[4'-(32)P]lipid IV(A) and its 1-dephosphorylated derivative on the distal Kdo residue, as indicated by mild acid hydrolysis. The third enzyme modifies the mannose unit of the substrate mannosyl-Kdo2-1-dephospho-[4'-(32)P]lipid IV(A). Sequencing of a 7-kb subclone derived from pSGAT revealed three putative membrane-bound glycosyltransferases, now designated RgtA, RgtB, and RgtC. Transfer by tri-parental mating of these genes into Sinorhizobium meliloti 1021, a strain that lacks these particular GalA residues, results in the heterologous expression of the GalA transferase activities seen in membranes of cells expressing pSGAT. Reconstitution experiments with the individual genes demonstrated that the activity of RgtA precedes and is necessary for the subsequent activity of RgtB, which is followed by the activity of RgtC. Electrospray ionization-tandem mass spectrometry and gas-liquid chromatography of the product generated in vitro by RgtA confirmed the presence of a GalA moiety. No in vitro activity was detected when RgtA was expressed in Escherichia coli unless Rhizobiaceae membranes were also included.

Magnetic resonance imaging of Klebsiella pneumoniae-induced pneumonia in mice

In vivo imaging of small animals is a rapidly developing field. However, the potential of global imaging of infectious processes in animal models remains poorly explored. We used magnetic resonance imaging (MRI) to follow the development and regression of inflammatory lesions caused by infection by Klebsiella pneumoniae in mouse lungs. A virulent strain caused an intense inflammation within 2 days in the whole lungs, while an avirulent strain did not show significant changes. Mice infected with the virulent strain and subsequently treated with antibiotics presented a severe inflammation localized mainly in the left lung that disappeared after a week. The lesions observed by MRI correlated with the damage seen by histological analysis and a 3D representation of the tissue allowed better visualization of the development and healing of inflammatory lesions. MRI thus represents a powerful technique to study in vivo the interactions between a pathogen and its host in real time.

Characterization of Gla(KP), a UDP-galacturonic acid C4-epimerase from Klebsiella pneumoniae with extended substrate specificity

In Escherichia coli and Salmonella enterica, the core oligosaccharide backbone of the lipopolysaccharide is modified by phosphoryl groups. The negative charges provided by these residues are important in maintaining the barrier function of the outer membrane. In contrast, Klebsiella pneumoniae lacks phosphoryl groups in its core oligosaccharide but instead contains galacturonic acid residues that are proposed to serve a similar function in outer membrane stability. Gla(KP) is a UDP-galacturonic acid C4-epimerase that provides UDP-galacturonic acid for core synthesis, and the enzyme was biochemically characterized because of its potentially important role in outer membrane stability. High-performance anion-exchange chromatography was used to demonstrate the UDP-galacturonic acid C4-epimerase activity of Gla(KP), and capillary electrophoresis was used for activity assays. The reaction equilibrium favors UDP-galacturonic acid over UDP-glucuronic acid in a ratio of 1.4:1, with the K(m) for UDP-glucuronic acid of 13.0 microM. Gla(KP) exists as a dimer in its native form. NAD+/NADH is tightly bound by the enzyme and addition of supplementary NAD+ is not required for activity of the purified enzyme. Divalent cations have an unexpected inhibitory effect on enzyme activity. Gla(KP) was found to have a broad substrate specificity in vitro; it is capable of interconverting UDP-glucose/UDP-galactose and UDP-N-acetylglucosamine/UDP-N-acetylgalactosamine, albeit at much lower activity. The epimerase GalE interconverts UDP-glucose/UDP-galactose. Multicopy plasmid-encoded gla(KP) partially complemented a galE mutation in S. enterica and in K. pneumoniae; however, chromosomal gla(KP) could not substitute for galE in a K. pneumoniae galE mutant in vivo.

The role of galacturonic acid in outer membrane stability in Klebsiella pneumoniae

In most members of the Enterobacteriaceae, including Escherichia coli and Salmonella, the lipopolysaccharide core oligosaccharide backbone is modified by phosphoryl groups. The negative charges provided by these residues are important in maintaining the barrier function of the outer membrane. Mutants lacking the core heptose region and the phosphate residues display pleiotrophic defects collectively known as the deep-rough phenotype, characterized by changes in outer membrane structure and function. Klebsiella pneumoniae lacks phosphoryl residues in its core, but instead contains galacturonic acid. The goal of this study was to determine the contribution of galacturonic acid as a critical source of negative charge. A mutant was created lacking all galacturonic acid by targeting UDP-galacturonic acid precursor synthesis through a mutation in gla(KP). Gla(KP) is a K. pneumoniae UDP-galacturonic acid C4 epimerase providing UDP-galacturonic acid for core synthesis. The gla(KP) gene was inactivated and the structure of the mutant lipopolysaccharide was determined by mass spectrometry. The mutant displayed characteristics of a deep-rough phenotype, exhibiting a hypersensitivity to hydrophobic compounds and polymyxin B, an altered outer membrane profile, and the release of the periplasmic enzyme beta-lactamase. These results indicate that the negative charge provided by the carboxyl groups of galacturonic acid do play an equivalent role to the core oligosaccharide phosphate residues in establishing outer membrane integrity in E. coli and Salmonella.

Biosynthesis of a Novel 3-Deoxy-D-manno-oct-2-ulosonic Acid-containing Outer Core Oligosaccharide in the Lipopolysaccharide of Klebsiella pneumoniae

The core oligosaccharide region of Klebsiella pneumoniae lipopolysaccharide contains some novel features that distinguish it from the corresponding lipopolysaccharide region in other members of the Enterobacteriaceae family, such as Escherichia coli and Salmonella. The conserved Klebsiella outer core contains the unusual trisaccharide 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo)-(2,6)-GlcN-(1,4)-GalUA. In general, Kdo residues are normally found in the inner core, but in K. pneumoniae, this Kdo residue provides the ligation site for O polysaccharide. The outer core Kdo residue can also be non-stoichiometrically substituted with an l-glycero-d-manno-heptopyranose (Hep) residue, another component more frequently found in the inner core. To understand the genetics and biosynthesis of core oligosaccharide synthesis in Klebsiella, the gene products involved in the addition of the outer core GlcN (WabH), Kdo (WabI), and Hep (WabJ) residues as well as the inner core HepIII residue (WaaQ) were identified. Non-polar mutations were created in each of the genes, and the resulting mutant lipopolysaccharide was analyzed by mass spectrometry. The in vitro glycosyltransferase activity of WabI and WabH was verified. WabI transferred a Kdo residue from CMP-Kdo onto the acceptor lipopolysaccharide. The activated precursor required for GlcN addition has not been identified. However, lysates overexpressing WabH were able to transfer a GlcNAc residue from UDP-GlcNAc onto the acceptor GalUA residue in the outer core.

The biosynthesis of D-Galacturonate in plants. functional cloning and characterization of a membrane-anchored UDP-D-Glucuronate 4-epimerase from Arabidopsis

Pectic cell wall polysaccharides owe their high negative charge to the presence of D-galacturonate, a monosaccharide that appears to be present only in plants and some prokaryotes. UDP-D-galacturonate, the activated form of this sugar, is known to be formed by the 4-epimerization of UDP-D-glucuronate; however, no coding regions for the epimerase catalyzing this reaction have previously been described in plants. To better understand the mechanisms by which precursors for pectin synthesis are produced, we used a bioinformatics approach to identify and functionally express a UDP-D-glucuronate 4-epimerase (GAE1) from Arabidopsis. GAE1 is predicted to be a type II membrane protein that belongs to the family of short-chain dehydrogenases/reductases. The recombinant enzyme expressed in Pichia pastoris established a 1.3:1 equilibrium between UDP-D-galacturonate and UDP-D-glucuronate but did not epimerize UDP-D-Glc or UDP-D-Xyl. Enzyme assays on cell extracts localized total UDP-D-glucuronate 4-epimerase and recombinant GAE1 activity exclusively to the microsomal fractions of Arabidopsis and Pichia, respectively. GAE1 had a pH optimum of 7.6 and an apparent Km of 0.19 mm. The recombinant enzyme was strongly inhibited by UDP-D-Xyl but not by UDP, UDP-D-Glc, or UDP-D-Gal. Analysis of Arabidopsis plants transformed with a GAE1:GUS construct showed expression in all tissues. The Arabidopsis genome contains five GAE1 paralogs, all of which are transcribed and predicted to contain a membrane anchor. This suggests that all of these enzymes are targeted to an endomembrane system such as the Golgi where they may provide UDP-D-galacturonate to glycosyltransferases in pectin synthesis.