Functions of some capsular polysaccharide biosynthetic genes in Klebsiella pneumoniae NTUH K-2044

Regulation of biofilm formation in Klebsiella pneumoniae

Klebsiella pneumoniae is an important Gram-negative opportunistic pathogen that is responsible for a variety of nosocomial and community-acquired infections. Klebsiella pneumoniae has become a major public health issue owing to the rapid global spread of extensively-drug resistant (XDR) and hypervirulent strains. Biofilm formation is an important virulence trait of K. pneumoniae. A biofilm is an aggregate of microorganisms attached to an inert or living surface by a self-produced exo-polymeric matrix that includes proteins, polysaccharides and extracellular DNA. Bacteria within the biofilm are shielded from antibiotics treatments and host immune responses, making it more difficult to eradicate K. pneumoniae-induced infection. However, the detailed mechanisms of biofilm formation in K. pneumoniae are still not clear. Here, we review the factors involved in the biofilm formation of K. pneumoniae, which might provide new clues to address this clinical challenge.

Expanding of ST11 Carbapenemase-Producing Klebsiella pneumoniae Subclones in a Chinese Hospital, Shenzhen, China

Background

ST11 is the most prevalent sequence type of clinical Klebsiella pneumoniae in China.

Methods

We investigated the characteristics of the ST11 subclones using core genome multi-locus sequence typing (cgMLST). Ninety-three carbapenemase-producing K. pneumoniae isolates were collected at Shenzhen People's Hospital. Then, whole-genome sequencing and cgMLST were used to discriminate apparent subclones within the ST11 group.

Results

We analyzed the prevalence and genetic relationships of these subclones. ST11 and K. pneumoniae carbapenemase (KPC-2) were the predominant genotype and carbapenemase, respectively, in the clinical carbapenemase-producing K. pneumoniae strains. cgMLST scheme genotyping divided the ST11 group into two clades across seven complex types (CTs). CT1313 was the most prevalent subclone. The deletion of galF and a high frequency of SNPs in genes associated with the stress- and SOS-responses were found in CT1291 and CT2405 over time, respectively.

Conclusion

Our results indicated that the subclones of the ST11 group had different patterns of prevalence. Highly discriminatory genotyping techniques, such as cgMLST scheme, should be used in further molecular epidemiology investigations.

The evolutionary trade-offs in phage-resistant Klebsiella pneumoniae entail cross-phage sensitization and loss of multidrug resistance

Bacteriophage therapy is currently being evaluated as a critical complement to traditional antibiotic treatment. However, the emergence of phage resistance is perceived as a major hurdle to the sustainable implementation of this antimicrobial strategy. By combining comprehensive genomics and microbiological assessment, we show that the receptor-modification resistance to capsule-targeting phages involves either escape mutation(s) in the capsule biosynthesis cluster or qualitative changes in exopolysaccharides, converting clones to mucoid variants. These variants introduce cross-resistance to phages specific to the same receptor yet sensitize to phages utilizing alternative ones. The loss/modification of capsule, the main Klebsiella pneumoniae virulence factor, did not dramatically impact population fitness, nor the ability to protect bacteria against the innate immune response. Nevertheless, the introduction of phage drives bacteria to expel multidrug resistance clusters, as observed by the large deletion in K. pneumoniae 77 plasmid containing bla_CTX-M , ant(3″), sul2, folA, mph(E)/mph(G) genes. The emerging bacterial resistance to viral infection steers evolution towards desired population attributes and highlights the synergistic potential for combined antibiotic-phage therapy against K. pneumoniae.

Detection of several carbapenems resistant and virulence genes in classical and hyper-virulent strains of Klebsiella pneumoniae isolated from hospitalized neonates and adults in Khartoum

OBJECTIVE

Klebsiella pneumoniae (K. pneumoniae) involves both community-acquired and nosocomial infections. It is responsible for a wide variety of infections, including infections of the urinary tract, pneumonia, bacteremia, meningitis, wound infection and purulent abscesses. We constructed this study to detect several carbapenems resistant and virulence genes in classical and hyper-virulent strains of K. pneumoniae isolated from hospitalized neonates and adults in Khartoum state.

RESULTS

Seventy percent of the isolates were resistant to ceftazidime, 18(30%) to ciprofloxacin, 23(38.3%) to chloramphenicol, 24(40%) to gentamicin and 8% to imipenem, 35% were multidrug-resistant, and 7% extensively drug-resistant, all blood isolates (n = 14) were resistant to ceftazidime. entB was the most predominant virulence gene (93.3%), followed by mrkD (78.3%), kfu (60%), K2 (51.7%), magA (18.3%) and rmpA (5%). bla_OXA-48 was the most predominant carbapenem-resistant gene (68.3%), followed by bla_NDM (10%), bla_KPC (8.3%), and bla_IMP (3.3%). Eight hyper-virulent strains were positive for bla_OXA-48 and two for bla_NDM genes.

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.

Cell envelope defects of different capsule-null mutants in K1 hypervirulent Klebsiella pneumoniae can affect bacterial pathogenesis

Hypervirulent Klebsiella pneumoniae (hvKP) causes Klebsiella‐induced liver abscess. Capsule is important for the pathogenesis of Klebsiella in systemic infection, but its role in gut colonisation is not well understood. By generating ΔwcaJ, Δwza and Δwzy capsule‐null mutants in a prototypical K1 hypervirulent isolate, we show that inactivation of wza (capsule exportase) and wzy (capsule polymerase) confer cell envelope defects in addition to capsule loss, making them susceptible to bile salts and detergent stress. Bile salt resistance is restored when the initial glycosyltransferase wcaJ was inactivated together with wzy, indicating that build‐up of capsule intermediates contribute to cell envelope defects. Mouse gut colonisation competition assays show that the capsule and its regulator RmpA were not required for hvKP to persist in the gut, although initial colonisation was decreased in the mutants. Both ΔrmpA and ΔwcaJ mutants gradually outcompeted the wild type in the gut, whereas Δwza and Δwzy mutants were less fit than wild type. Together, our results advise caution in using the right capsule‐null mutant for determination of capsule's role in bacterial pathogenesis. With the use of ΔwcaJ mutant, we found that although the capsule is important for bacterial survival outside the gut environment, it imposes a fitness cost in the gut.

Variant O89 O-Antigen of E. coli Is Associated With Group 1 Capsule Loci and Multidrug Resistance

Bacterial surface polysaccharides play significant roles in fitness and virulence. In Gram-negative bacteria such as Escherichia coli, major surface polysaccharides are lipopolysaccharide (LPS) and capsule, representing O- and K-antigens, respectively. There are multiple combinations of O:K types, many of which are well-characterized and can be related to ecotype or pathotype. In this investigation, we have identified a novel O:K permutation resulting through a process of major genome reorganization in a clade of E. coli. A multidrug-resistant, extended-spectrum β-lactamase (ESBL)-producing strain - E. coli 26561 - represented a prototype of strains combining a locus variant of O89 and group 1 capsular polysaccharide. Specifically, the variant O89 locus in this strain was truncated at gnd, flanked by insertion sequences and located between nfsB and ybdK and we apply the term O89m for this variant. The prototype lacked colanic acid and O-antigen loci between yegH and hisI with this tandem polysaccharide locus being replaced with a group 1 capsule (G1C) which, rather than being a recognized E. coli capsule type, this locus matched to Klebsiella K10 capsule type. A genomic survey identified more than 200 E. coli strains which possessed the O89m locus variant with one of a variety of G1C types. Isolates from our collection with the combination of O89m and G1C all displayed a mucoid phenotype and E. coli 26561 was unusual in exhibiting a mucoviscous phenotype more recognized as a characteristic among Klebsiella strains. Despite the locus truncation and novel location, all O89m:G1C strains examined showed a ladder pattern typifying smooth LPS and also showed high molecular weight, alcian blue-staining polysaccharide in cellular and/or extra-cellular fractions. Expression of both O-antigen and capsule biosynthesis loci were confirmed in prototype strain 26561 through quantitative proteome analysis. Further in silico exploration of more than 200 E. coli strains possessing the O89m:G1C combination identified a very high prevalence of multidrug resistance (MDR) - 85% possessed resistance to three or more antibiotic classes and a high proportion (58%) of these carried ESBL and/or carbapenemase. The increasing isolation of O89m:G1C isolates from extra-intestinal infection sites suggests that these represents an emergent clade of invasive, MDR E. coli.

Whole-Genome-Sequencing characterization of bloodstream infection-causing hypervirulent Klebsiella pneumoniae of capsular serotype K2 and ST374

Hypervirulent K. pneumoniae variants (hvKP) have been increasingly reported worldwide, causing metastasis of severe infections such as liver abscesses and bacteremia. The capsular serotype K2 hvKP strains show diverse multi-locus sequence types (MLSTs), but with limited genetics and virulence information. In this study, we report a hypermucoviscous K. pneumoniae strain, RJF293, isolated from a human bloodstream sample in a Chinese hospital. It caused a metastatic infection and fatal septic shock in a critical patient. The microbiological features and genetic background were investigated with multiple approaches. The Strain RJF293 was determined to be multilocis sequence type (ST) 374 and serotype K2, displayed a median lethal dose (LD50) of 1.5 × 10² CFU in BALB/c mice and was as virulent as the ST23 K1 serotype hvKP strain NTUH-K2044 in a mouse lethality assay. Whole genome sequencing revealed that the RJF293 genome codes for 32 putative virulence factors and exhibits a unique presence/absence pattern in comparison to the other 105 completely sequenced K. pneumoniae genomes. Whole genome SNP-based phylogenetic analysis revealed that strain RJF293 formed a single clade, distant from those containing either ST66 or ST86 hvKP. Compared to the other sequenced hvKP chromosomes, RJF293 contains several strain-variable regions, including one prophage, one ICEKp1 family integrative and conjugative element and six large genomic islands. The sequencing of the first complete genome of an ST374 K2 hvKP clinical strain should reinforce our understanding of the epidemiology and virulence mechanisms of this bloodstream infection-causing hvKP with clinical significance.

Transcriptional regulation of galF by RcsAB affects capsular polysaccharide formation in Klebsiella pneumoniae NTUH-K2044

RcsAB is an atypical two-component regulatory system that can regulate exopolysaccharide biosynthesis and is involved in the virulence of K. pneumoniae. The gene galF is well known as a gene involved in the biosynthesis of capsular polysaccharide (CPS). The specific DNA identification sequence for transcriptional regulation of RcsAB was found to be present in the promoter region of galF. This study aimed to detect the function of RcsAB in virulence and in biofilm and CPS formation. In addition, the transcriptional regulation of the galF gene in K. pneumoniae was studied. To determine the function of rcsAB gene, the wild-type K. pneumoniae strain NTUH-K2044 and the rcsAB knockout and complemented strains were used. The results showed decreased virulence, biofilm formation, and CPS levels in the rcsAB knockout strain. Complementation of the knockout by introducing an rcsAB fragment on an expression plasmid partially restored the virulence, biofilm, and CPS functions of the knockout strain. It indicated that the rcsAB genes might affect CPS formation and virulence of K. pneumonia. RT-qPCR, EMSA and DNase I footprinting assays were conducted to identify the transcriptional regulation of galF by RcsAB. RcsAB was seen to bind to the galF promoter-proximal region, and the binding site was further identified to be located from -177 bp to -152 bp upstream of the galF promoter. In conclusion, RcsAB could regulate the transcription of the galF gene positively by binding to the galF promoter DNA directly, and then affects the CPS formation of K. pneumonia.

Identification of Two Regulators of Virulence That Are Conserved in Klebsiella pneumoniae Classical and Hypervirulent Strains

Klebsiella pneumoniae is widely recognized as a pathogen with a propensity for acquiring antibiotic resistance. It is capable of causing a range of hospital-acquired infections (urinary tract infections [UTI], pneumonia, sepsis) and community-acquired invasive infections. The genetic heterogeneity of K. pneumoniae isolates complicates our ability to understand the virulence of K. pneumoniae. Characterization of virulence factors conserved between strains as well as strain-specific factors will improve our understanding of this important pathogen. The MarR family of regulatory proteins is widely distributed in bacteria and regulates cellular processes such as antibiotic resistance and the expression of virulence factors. Klebsiella encodes numerous MarR-like proteins, and they likely contribute to the ability of K. pneumoniae to respond to and survive under a wide variety of environmental conditions, including those present in the human body. We tested loss-of-function mutations in all the marR homologues in a murine pneumonia model and found that two (kvrA and kvrB) significantly impacted the virulence of K1 and K2 capsule type hypervirulent (hv) strains and that kvrA affected the virulence of a sequence type 258 (ST258) classical strain. In the hv strains, kvrA and kvrB mutants displayed phenotypes associated with reduced capsule production, mucoviscosity, and transcription from galF and manC promoters that drive expression of capsule synthesis genes. In contrast, kvrA and kvrB mutants in the ST258 strain had no effect on capsule gene expression or capsule-related phenotypes. Thus, KvrA and KvrB affect virulence in classical and hv strains but the effect on virulence may not be exclusively due to effects on capsule production.

In addition to having a reputation as the causative agent for hospital-acquired infections as well as community-acquired invasive infections, Klebsiella pneumoniae has gained widespread attention as a pathogen with a propensity for acquiring antibiotic resistance. Due to the rapid emergence of carbapenem resistance among K. pneumoniae strains, a better understanding of virulence mechanisms and identification of new potential drug targets are needed. This study identified two novel regulators (KvrA and KvrB) of virulence in K. pneumoniae and demonstrated that their effect on virulence in invasive strains is likely due in part to effects on capsule production (a major virulence determinant) and hypermucoviscosity. KvrA also impacts the virulence of classical strains but does not appear to affect capsule gene expression in this strain. KvrA and KvrB are conserved among K. pneumoniae strains and thus could regulate capsule expression and virulence in diverse strains regardless of capsule type.

Biofilm Formation in Klebsiella pneumoniae Bacteremia Strains Was Found to be Associated with CC23 and the Presence of wcaG

Klebsiella pneumoniae bacteremia biofilm traits and distribution characteristics have not been clarified. This study aimed to determine the prevalence and characteristics of K. pneumoniae bacteremia biofilm formation (BF) and to explore the virulence factors associated with K. pneumoniae BF. A total of 250 K. pneumoniae bacteremia isolates were collected from patients in Shenzhen and Shanghai, China. Virulence genes in their genomes were detected by PCR. The isolates were subjected to multilocus sequence typing (MLST) and clonal complex (CC) classification based on housekeeping genes. Biofilms were detected by crystal violet staining. Greater BF was observed in isolates from young adults (<40 years old) than in those from seniors (≥65 years old; P = 0.002). MLST yielded 65 different sequence types (STs), with the most represented STs being ST11, ST23, and ST65, and the main CCs were CC23 and CC65; CC23 isolates exhibited greater BF than CC65 or ST11 isolates (both P < 0.001). BF was more pronounced among magA(K1), aero+, rmpA+, rmpA2+, allS+, wcaG+, and iutA+ isolates than in isolates that were negative for these virulence factors. Multivariate regression analysis revealed only wcaG as an independent risk factor for BF (odds ratio 11.426, P < 0.001), and BF was decreased when wcaG was silenced by antisense RNA. In conclusion, BF in K. pneumoniae bacteremia isolates was found to be associated with CC23 classification and the presence of the wcaG virulence factor gene.

Non-capsulated mutants of a chemical-producing Klebsiella pneumoniae strain

OBJECTIVES

To investigate the outcomes of capsule lost on cell transformation efficiency and chemicals (1,3-propanediol, 2,3-butanediol, and 2-ketogluconic acid) production by Klebsiella pneumoniae.

RESULTS

The cps gene cluster showed low sequence homology with pathogenic strains. The wza is a highly conserved gene in the cps cluster that encodes an outer membrane protein. A non-capsulated mutant was constructed by deletion of wza. Phenotype studies demonstrated that non-capsulated cells were less buoyant and easy to sediment. The transformation efficiency of the non-capsulated mutant reached 6.4 × 10⁵ CFU μg^-1 DNA, which is 10 times higher than that of the wild strain. 52.2 g 1,3-propanediol L^-1, 30.7 g 2,3-butanediol L^-1, and 175.9 g 2-ketogluconic acid L^-1 were produced by non-capsulated mutants, which were 10-40% lower compared to wild strain. Furthermore, viscosities of the three fermentation broths decreased to approximately 1.3 cP from the range of 1.8-2.2 cP.

CONCLUSIONS

Non-capsulated K. pneumoniae mutants should allay concerns regarding biological safety, improve transformation efficiency, lower viscosity, and subsequently ameliorate the financial burden of the downstream process of chemicals production.

Antibody-free detection of infectious bacteria using quantum dots-based barcode assay

Staphylococcus aureus, methicillin-resistant Staphylococcus aureus and Klebsiella pneumoniae are the most representative bacteria causing infectious diseases. Due to the increased application of antibiotics, the bacterial resistance is growing causing severe complications. Therefore, a sensitive determination of these pathogens is crucial for effective treatment. The aim of this study was to design an effective method for multiplex detection of Staphylococcus aureus, methicillin-resistant Staphylococcus aureus and Klebsiella pneumoniae taking advantage from properties of magnetic particles as well as fluorescent nanoparticles (quantum dots). The method was able to detect as low concentrations of bacteria as 10² CFU/mL using the bacteria-specific genes (fnbA, mecA and wcaG).

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.

H-NS Nucleoid Protein Controls Virulence Features of Klebsiella pneumoniae by Regulating the Expression of Type 3 Pili and the Capsule Polysaccharide

Klebsiella pneumoniae is an opportunistic pathogen causing nosocomial infections. Main virulence determinants of K. pneumoniae are pili, capsular polysaccharide, lipopolysaccharide, and siderophores. The histone-like nucleoid-structuring protein (H-NS) is a pleiotropic regulator found in several gram-negative pathogens. It has functions both as an architectural component of the nucleoid and as a global regulator of gene expression. We generated a Δhns mutant and evaluated the role of the H-NS nucleoid protein on the virulence features of K. pneumoniae. A Δhns mutant down-regulated the mrkA pilin gene and biofilm formation was affected. In contrast, capsule expression was derepressed in the absence of H-NS conferring a hypermucoviscous phenotype. Moreover, H-NS deficiency affected the K. pneumoniae adherence to epithelial cells such as A549 and HeLa cells. In infection experiments using RAW264.7 and THP-1 differentiated macrophages, the Δhns mutant was less phagocytized than the wild-type strain. This phenotype was likely due to the low adherence to these phagocytic cells. Taken together, our data indicate that H-NS nucleoid protein is a crucial regulator of both T3P and CPS of K. pneumoniae.

On the Ancestral UDP-Glucose Pyrophosphorylase Activity of GalF from Escherichia coli

In bacteria, UDP-glucose is a central intermediate in carbohydrate metabolism. The enzyme responsible for its synthesis is encoded by the galU gene and its deletion generates cells unable to ferment galactose. In some bacteria, there is a second gene, galF, encoding for a protein with high sequence identity to GalU. However, the role of GalF has been contradictory regarding its catalytic capability and not well understood. In this work we show that GalF derives from a catalytic (UDP-glucose pyrophosphorylase) ancestor, but its activity is very low compared to GalU. We demonstrated that GalF has some residual UDP-glucose pyrophosphorylase activity by in vitro and in vivo experiments in which the phenotype of a galU (-) strain was reverted by the over-expression of GalF and its mutant. To demonstrate its evolutionary path of "enzyme inactivation" we enhanced the catalysis by mutagenesis and showed the importance of the quaternary structure. This study provides important information to understand the structural and functional evolutionary origin of the protein GalF in enteric bacteria.

Genetic analysis of capsular polysaccharide synthesis gene clusters in 79 capsular types of Klebsiella spp

A total of 79 capsular types have been reported in Klebsiella spp., whereas capsular polysaccharide synthesis (cps) regions were available in only 22 types. Due to the limitations of serotyping, complete repertoire of cps will be helpful for capsular genotyping. We therefore resolved the rest 57 cps and conducted comparative analysis. Clustering results of 1,515 predicted proteins from cps loci categorized proteins which share similarity into homology groups (HGs) revealing that 77 Wzy polymerases were classified into 56 HGs, which indicate the high specificity of wzy between different types. Accordingly, wzy-based capsular genotyping could differentiate capsule types except for those lacking wzy (K29 and K50), those sharing identical wzy (K22 vs. K37); and should be carefully applied in those exhibited high similarity (K12 vs. K41, K2 vs. K13, K74 vs. K80, K79 vs. KN1 and K30 vs. K69). Comparison of CPS structures in several capsular types that shared similarity in their gene contents implies possible functions of glycosyltransferases. Therefore, our results provide complete set of cps in various types of Klebsiella spp., which enable the understandings of relationship between genes and CPS structures and are useful for identification of documented or new capsular types.

KpnEF, a new member of the Klebsiella pneumoniae cell envelope stress response regulon, is an SMR-type efflux pump involved in broad-spectrum antimicrobial resistance

Klebsiella pneumoniae has been frequently associated with nosocomial infections. Efflux systems are ubiquitous transporters that also function in drug resistance. Genome analysis of K. pneumoniae strain NTUH-K2044 revealed the presence of ∼15 putative drug efflux systems. We discuss here for the first time the characterization of a putative SMR-type efflux pump, an ebrAB homolog (denoted here as kpnEF) with respect to Klebsiella physiology and the multidrug-resistant phenotype. Analysis of hypermucoviscosity revealed direct involvement of kpnEF in capsule synthesis. The ΔkpnEF mutant displayed higher sensitivity to hyperosmotic (∼2.8-fold) and high bile (∼4.0-fold) concentrations. Mutation in kpnEF resulted in increased susceptibility to cefepime, ceftriaxone, colistin, erythromycin, rifampin, tetracycline, and streptomycin; mutated strains changed from being resistant to being susceptible, and the resistance was restored upon complementation. The ΔkpnEF mutant displayed enhanced sensitivity toward structurally related compounds such as sodium dodecyl sulfate, deoxycholate, and dyes, including clinically relevant disinfectants such as benzalkonium chloride, chlorhexidine, and triclosan. The prevalence of kpnEF in clinical strains broadens the diversity of antibiotic resistance in K. pneumoniae. Experimental evidence of CpxR binding to the efflux pump promoter and quantification of its expression in a cpxAR mutant background demonstrated kpnEF to be a member of the Cpx regulon. This study helps to elucidate the unprecedented biological functions of the SMR-type efflux pump in Klebsiella spp.

The UDP-glucose dehydrogenase of Escherichia coli K-12 displays substrate inhibition by NAD that is relieved by nucleotide triphosphates

UDP-glucose dehydrogenase (Ugd) generates UDP-glucuronic acid, an important precursor for the production of many hexuronic acid-containing bacterial surface glycostructures. In Escherichia coli K-12, Ugd is important for biosynthesis of the environmentally regulated exopolysaccharide known as colanic acid, whereas in other E. coli isolates, the same enzyme is required for production of the constitutive group 1 capsular polysaccharides, which act as virulence determinants. Recent studies have implicated tyrosine phosphorylation in the activation of Ugd from E. coli K-12, although it is not known if this is a feature shared by bacterial Ugd proteins. The activities of Ugd from E. coli K-12 and from the group 1 capsule prototype (serotype K30) were compared. Surprisingly, for both enzymes, site-directed Tyr → Phe mutants affecting the previously proposed phosphorylation site retained similar kinetic properties to the wild-type protein. Purified Ugd from E. coli K-12 had significant levels of NAD substrate inhibition, which could be alleviated by the addition of ATP and several other nucleotide triphosphates. Mutations in a previously identified UDP-glucuronic acid allosteric binding site decreased the binding affinity of the nucleotide triphosphate. Ugd from E. coli serotype K30 was not inhibited by NAD, but its activity still increased in the presence of ATP.

Amino acid substitutions of MagA in Klebsiella pneumoniae affect the biosynthesis of the capsular polysaccharide

Mucoviscosity-associated gene A (magA) of Klebsiella pneumoniae contributes to K1 capsular polysaccharide (CPS) biosynthesis. Based on sequence homology and gene alignment, the magA gene has been predicted to encode a Wzy-type CPS polymerase. Sequence alignment with the Wzy_C and RfaL protein families (which catalyze CPS or lipopolysaccharide (LPS) biosynthesis) and topological analysis has suggested that eight highly conserved residues, including G308, G310, G334, G337, R290, P305, H323, and N324, were located in a hypothetical loop region. Therefore, we used site-directed mutagenesis to study the role of these residues in CPS production, and to observe the consequent phenotypes such as mucoviscosity, serum and phagocytosis resistance, and virulence (as assessed in mice) in pyogenic liver abscess strain NTUH-K2044. Alanine substitutions at R290 or H323 abolished all of these properties. The G308A mutant was severely impaired for these functions. The G334A mutant remained mucoid with decreased CPS production, but its virulence was significantly reduced in vivo. No phenotypic change was observed for strains harboring magA G310A, G337A, P305A, or N324A mutations. Therefore, R290, G308, H323, and G334 are functionally important residues of the MagA (Wzy) protein of K. pneumoniae NTUH-K2044, capsular type K1. These amino acids are also likely to be important for the function of Wzy in other capsular types in K. pneumoniae and other species bearing Wzy_C family proteins.

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.