Clinical and Microbiologic Analysis of Klebsiella pneumoniae Infection: Hypermucoviscosity, Virulence Factor, Genotype, and Antimicrobial Susceptibility

Hypervirulent Klebsiella pneumoniae (KP) is defined according to hypermucoviscosity or various virulence factors and is clinically associated with community-acquired liver abscess (CLA). In this study, we investigated the clinical and microbiological characteristics of KP and significant factors associated with hypervirulence. The clinical characteristics, antimicrobial susceptibility, hypermucoviscosity, serotypes, hypervirulence-related genes, and biofilm formation of 414 KP isolates collected from the Keimyung University Dongsan Hospital between December 2013 and November 2015 were analyzed according to CLA. Significant risk factors for hypervirulent KP (HvKP) associated with CLA were investigated using logistic regression analysis. Notably, 155 (37.4%) isolates were hypermucoviscous, and 170 (41.1%) harbored aerobactin. CLA was present in 34 cases (8.2%). Epidemiology and treatment outcomes did not differ significantly between the CLA and non-CLA groups. The CLA group had significantly higher antibiotic susceptibility, K1/K2, rmpA, magA, allS, kfu, iutA, string test-positive result, and biofilm mass. Multivariate logistic regression revealed rmpA (OR, 5.67; 95% CI, 2.09-15.33; p = 0.001), magA (OR, 2.34; 95% CI, 1.01-5.40; p = 0.047), and biofilm mass >0.80 (OR, 2.13; 95% CI, 1.00-4.56; p = 0.050) as significant risk factors for CLA. rmpA was identified as the most significant risk factor for CLA among KP strains, implying that it is an important factor associated with HvKP.

Highly conserved composite transposon harbouring aerobactin iuc3 in Klebsiella pneumoniae from pigs

Klebsiella pneumoniae is an important opportunistic pathogen associated with severe invasive disease in humans. Hypervirulent K. pneumoniae, which are K. pneumoniae with several acquired virulence determinants such as the siderophore aerobactin and others, are more prominent in countries in South and South-East Asia compared to European countries. This Klebsiella pathotype is capable of causing liver abscesses in immunocompetent persons in the community. K. pneumoniae has not been extensively studied in non-human niches. In the present study, K. pneumoniae isolated from caecal samples (n=299) from healthy fattening pigs in Norway were characterized with regard to population structure and virulence determinants. These data were compared to data from a previous study on K. pneumoniae from healthy pigs in Thailand. Lastly, an in-depth plasmid study on K. pneumoniae with aerobactin was performed. Culturing and whole-genome sequencing was applied to detect, confirm and characterize K. pneumoniae isolates. Phylogenetic analysis described the evolutionary relationship and diversity of the isolates, while virulence determinants and sequence types were detected with Kleborate. Long-read sequencing was applied to obtain the complete sequence of virulence plasmids harbouring aerobactin. A total of 48.8 % of the investigated Norwegian pig caecal samples (n=299) were positive for K. pneumoniae. Acquired virulence determinants were detected in 72.6 % of the isolates, the most prominent being aerobactin (69.2 %), all of which were iuc3. In contrast, only 4.6 % of the isolates from Thailand harboured aerobactin. The aerobactin operon was located on potentially conjugative IncFIB_K/FII_K plasmids of varying sizes in isolates from both countries. A putative, highly conserved composite transposon with a mean length of 16.2 kb flanked by truncated IS3-family IS407-group insertion sequences was detected on these plasmids, harbouring the aerobactin operon as well as several genes that may confer increased fitness in mammalian hosts. This putative composite transposon was also detected in plasmids harboured by K. pneumoniae from several countries and sources, such as human clinical samples. The high occurrence of K. pneumoniae harbouring aerobactin in Norwegian pigs, taken together with international data, suggest that pigs are a reservoir for K. pneumoniae with iuc3. Truncation of the flanking ISKpn78-element suggest that the putative composite transposon has been permanently integrated into the plasmid, and that it is no longer mobilizable.

Multiple detection of hypermucoviscous and hypervirulent strains of Klebsiella pneumoniae: An emergent health care threat

This study focused on the characterization of 19 hypermucoviscous Klebsiella pneumoniae strains, that were identified from 26 hypermucosal strains. In order to identify hypermucoviscous strains of K. pneumoniae, the string test was applied. This phenotype is known in the literature as one of the virulence factors of this species together with the production of biofilm and other hypervirulence factor genes such as: rmpA, rmpA2, iucA, iroB, peg-344. We also investigated presence of magA gene that correlates with the hyper-production of capsule of K1 serotype. Of the strains under study, 13 out of 19 harboured at least one virulence factor.Sequence type (ST) was determined in order to identify known high-risk clones or new emerging high-risk clones and their variability in a single clinical setting. Important STs found among these strains were ST65 and ST29. Carbapenem resistance was also investigated and 4 out of 19 strains harboured at least a carbapenemase: one strain harboured a KPC enzyme alone, one strain carried a KPC and an OXA-48 like, one strain produced OXA-48-like alone, and the last strain harboured two metallo-β-lactamases (VIM-1 and NDM-5) plus OXA-48-like. In particular, this latter strain belongs to ST383, which was recently reported in Northern Italy as a hypervirulent and XDR strain.The global spread of hypervirulent K. pneumoniae is an important epidemiological issue that should be considered in diagnostic and therapeutic managements of patients with K. pneumoniae infections.

Effects of aerobactin-encoding gene iucB and regulator of mucoid phenotype rmpA on the virulence of Klebsiella pneumoniae causing liver abscess

This study aimed to analyze the influence of the main aerobactin-encoding gene iucB and the regulator of mucoid phenotype rmpA on the virulence of Klebsiella pneumoniae causing liver abscess. In addition, the possible regulatory effects of the main encoding gene iucB on the regulator of mucoid phenotype rmpA were explored, thus providing novel strategies for the prevention and control of hypervirulent K. pneumoniae (hvKp) causing liver abscess. The virulence-related genes iucB and rmpA of K. pneumoniae were detected by PCR. iucB and rmpA were cloned into K. pneumoniae strain by using plasmid pET28b as vector. Quantitative real-time PCR (RT-qPCR) was employed to detect the relative expression of rmpA gene in K. pneumoniae. We investigated the potential effects of aerobactin coding gene iucB and regulator of mucoid phenotype rmpA on the virulence of K. pneumoniae by establishing the Galleria mellonella infection model. Capsule quantitative experiment was conducted to investigate the impact of aerobactin-encoding gene iucB on the modulation of regulator of mucoid phenotype rmpA. The results of the G. mellonella infection model indicated that iucB gene could significantly enhance the virulence of K. pneumoniae, but the presence of rmpA gene did not markedly affect the virulence of K. pneumoniae. RT-qPCR showed that iucB inhibited the expression of rmpA gene. Quantitative capsulation experiments showed that the presence of rmpA gene could not increase the capsulation production of K. pneumoniae. The main encoding gene of aerobactin, namely iucB, could substantially enhance the virulence of K. pneumoniae. The gene iucB might be involved in the biosynthesis of the capsular polysaccharide through an unknown mechanism instead of the gene rmpA. Overall, these findings provide important theoretical support for the treatment of infections caused by hvKp.

Siderophore iucA of hypermucoviscous Klebsiella pneumoniae promotes liver damage in mice by inducing oxidative stress

The hypermucoviscosity/hypervirulent K. pneumoniae (hvKP) is a dominant cause of pyogenic liver abscess (PLA) and has contributed to the endemicity of disease in Asian country. The siderophore aerobactin (iucA) is highly expressed in hvKP and acting virulence role during hvKP infection. However, its role in the PLA is poorly understood. We constructed iucA deletion mutant (ΔiucA-hvKP852) and used animal study to characterize the role of siderophore iucA in K. pneumoniae liver abscess. The animal experiments showed that ΔiucA-hvKP852 strain had lower virulence in mice compared to hvKP852 wild type strain. At 24 h after infection, only two of ten mice developed liver abscess during infection with ΔiucA-hvKP852 strain, while nine of ten mice infected with wild type hvKP852 strain showed multiple lesions of liver abscess. The liver tissue infected with ΔiucA-hvKP852 exhibited low reactive oxygen stress levels compared to those infected by wild type hvKP852 strain (P < 0.05). The results suggest that siderophore iucA play an important role in the liver abscess by inducing oxidative stress.

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iucA positive strains produces more siderophore than iucA negative hvK. pneumoniae.

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Siderophore production is positively related with Oxidative stress in hvK. pneumoniae.

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iucA enhances oxidative stress in liver and forms liver abscess during hvK. pneumoniae infection.

Iron-Utilization System in Vibrio vulnificus M2799

Vibrio vulnificus is a Gram-negative pathogenic bacterium that causes serious infections in humans and requires iron for growth. A clinical isolate, V. vulnificus M2799, secretes a catecholate siderophore, vulnibactin, that captures ferric ions from the environment. In the ferric-utilization system in V. vulnificus M2799, an isochorismate synthase (ICS) and an outer membrane receptor, VuuA, are required under low-iron conditions, but alternative proteins FatB and VuuB can function as a periplasmic-binding protein and a ferric-chelate reductase, respectively. The vulnibactin-export system is assembled from TolCV1 and several RND proteins, including VV1_1681. In heme acquisition, HupA and HvtA serve as specific outer membrane receptors and HupB is a sole periplasmic-binding protein, unlike FatB in the ferric-vulnibactin utilization system. We propose that ferric-siderophore periplasmic-binding proteins and ferric-chelate reductases are potential targets for drug discovery in infectious diseases.

Aerobactin Seems To Be a Promising Marker Compared With Unstable RmpA2 for the Identification of Hypervirulent Carbapenem-Resistant Klebsiella pneumoniae: In Silico and In Vitro Evidence

Background

The incidence of hypervirulent (hv) carbapenem-resistant (CR) Klebsiella pneumoniae (Kp) is increasing globally among various clones and is also responsible for nosocomial infections. The CR-hvKp is formed by the uptake of a virulence plasmid by endemic high-risk clones or by the uptake of plasmids carrying antimicrobial resistance genes by the virulent clones. Here, we describe CR-hvKp from India belonging to high-risk clones that have acquired a virulence plasmid and are phenotypically unidentified due to lack of hypermucoviscosity.

Methods

Twenty-seven CRKp isolates were identified to possess rmpA2 by whole-genome sequencing; and resistance and virulence determinants were characterized. By in silico protein modeling (and validation), protein backbone stability analysis, and coarse dynamics study, the fitness of RmpA, RmpA2, and aerobactin-associated proteins-IucA and IutA, were determined to establish a reliable marker for clinical identification of CR-hvKp.

Results

The CR-hvKp belonged to multidrug-resistant (MDR) high-risk clones such as CG11, CG43, ST15, and ST231 and carried OXA-232 as the predominant carbapenemase followed by NDM. The virulence plasmid belonged to IncHI1B replicon type and carried frameshifted and truncated rmpA and rmpA2. This resulted in a lack of hypermucoviscous phenotype. However, functional aerobactin was expressed in all high-risk clones. In silico analysis portrayed that IucA and IutA were more stable than classical RmpA. Furthermore, IucA and IutA had lower conformational fluctuations in the functional domains than the non-functional RmpA2, which increases the fitness cost of the latter for its maintenance and expression among CR-hvKp. Hence, RmpA and RmpA2 are likely to be lost among CR-hvKp owing to the increased fitness cost while coding for essential antimicrobial resistance and virulence factors.

Conclusion

Increasing incidence of convergence of AMR and virulence is observed among K. pneumoniae globally, which warrants the need for reliable markers for identifying CR-hvKp. The presence of non-functional RmpA2 among high-risk clones highlights the significance of molecular identification of CR-hvKp. The negative string test due to non-functional RmpA2 among CR-hvKp isolates challenges phenotypic screening and faster identification of this pathotype. This can potentially be counteracted by projecting aerobactin as a stable, constitutively expressed, and functional marker for rapidly evolving CR-hvKp.

Aerobactin-Mediated Iron Acquisition Enhances Biofilm Formation, Oxidative Stress Resistance, and Virulence of Yersinia pseudotuberculosis

Aerobactin is a citrate-hydroxamate siderophore that is critical for the virulence of pathogenic enteric bacteria. However, although the aerobactin-producing iucABCD-iutA operon is distributed widely in the genomes of Yersinia species, none of the pathogenic Yersinia spp. was found to produce aerobactin. Here, we showed that the iucABCD-iutA operon in the food-borne enteric pathogen Yersinia pseudotuberculosis YPIII is a functional siderophore system involved in iron acquisition. The expression of the operon was found to be directly repressed by the ferric uptake regulator (Fur) in an iron concentration-dependent manner. In addition, we demonstrated that the aerobactin-mediated iron acquisition contributes to bacterial growth under iron-limited conditions. Moreover, we provided evidence that aerobactin plays important roles in biofilm formation, resistance to oxidative stress, ROS removal, and virulence of Y. pseudotuberculosis. Overall, our study not only uncovered a novel strategy of iron acquisition in Y. pseudotuberculosis but also highlighted the importance of aerobactin in the pathogenesis of Y. pseudotuberculosis.

Genome-Based Analysis of Klebsiella spp. Isolates from Animals and Food Products in Germany, 2013-2017

The increase in infections with multidrug-resistant and virulent Klebsiella pneumoniae (K. pneumoniae) strains poses a serious threat to public health. However, environmental reservoirs and routes of transmission for Klebsiella spp. that cause infections in humans and in livestock animals are not well understood. In this study, we aimed to analyze the distribution of antibiotic resistance genes and important virulence determinants (ybt, clb, iro, iuc, rmpA/A2) among 94 Klebsiella spp. isolates from different animal and food sources isolated between 2013 and 2017 in Germany. Antibiotic susceptibility testing was performed, and the genomes were sequenced by Illumina and Nanopore technology. Genetic relationships were assessed by conducting core genome multilocus sequence typing (cgMLST). Kleborate was used to predict resistance and virulence genes; Kaptive was used to derive the capsule types. The results revealed that 72 isolates (76.6%) belonged to the K. pneumoniae sensu lato complex. Within this complex, 44 known sequence types (STs), 18 new STs, and 38 capsule types were identified. Extended-spectrum beta-lactamase (ESBL) genes were detected in 16 isolates (17.0%) and colistin resistance in one (1.1%) K. pneumoniae isolate. Virulence genes were found in 22 K. pneumoniae isolates. Overall, nine (9.6%) and 18 (19.1%) isolates possessed the genes ybt and iuc, respectively. Notably, aerobactin (iuc lineage 3) was only detected in K. pneumoniae isolates from domestic pigs and wild boars. This study provides a snapshot of the genetic diversity of Klebsiella spp. in animals and food products in Germany. The siderophore aerobactin was found to be more prevalent in K. pneumoniae strains isolated from pigs than other sources. Further investigations are needed to evaluate if pigs constitute a reservoir for iuc lineage 3.

Vibrio fischeri siderophore production drives competitive exclusion during dual-species growth

When two or more bacterial species inhabit a shared niche, often, they must compete for limited nutrients. Iron is an essential nutrient that is especially scarce in the marine environment. Bacteria can use the production, release, and re-uptake of siderophores, small molecule iron chelators, to scavenge iron. Siderophores provide fitness advantages to species that employ them by enhancing iron acquisition, and moreover, by denying iron to competitors incapable of using the siderophore-iron complex. Here, we show that cell-free culture fluids from the marine bacterium Vibrio fischeri ES114 prevent the growth of other vibrio species. Mutagenesis reveals the aerobactin siderophore as the inhibitor. Our analysis reveals a gene, that we name aerE, encodes the aerobactin exporter, and LuxT is a transcriptional activator of aerobactin production. In co-culture, under iron-limiting conditions, aerobactin production allows V. fischeri ES114 to competitively exclude Vibrio harveyi, which does not possess aerobactin production and uptake genes. In contrast, V. fischeri ES114 mutants incapable of aerobactin production lose in competition with V. harveyi. Introduction of iutA, encoding the aerobactin receptor, together with fhuCDB, encoding the aerobactin importer are sufficient to convert V. harveyi into an "aerobactin cheater."

Characteristics of Hypervirulent Klebsiella pneumoniae: Does Low Expression of rmpA Contribute to the Absence of Hypervirulence?

Multidrug-resistant hypervirulent Klebsiella pneumoniae (MDR-hvKP) has been increasingly reported and is now recognized as a significant threat to public health; however, characterization of MDR-hvKP has not been systematically investigated. In the present study, 124 of 428 (28.92%) K. pneumoniae clinical isolates collected from January 2010 to December 2016 were identified with aerobactin and defined as hvKP; these included 94 non-MDR-KP, 20 extended-spectrum β-lactamase-producing K. pneumoniae (ESBL-KP), and 10 carbapenem-resistant K. pneumoniae (CR-KP) isolates. The remaining 304 isolates without presence of virulence factor aerobactin were defined as classic K. pneumoniae (cKP). The antimicrobial resistance rate of cKP was significantly higher than that of the hvKP isolates in the non-MDR-KP group, but showed no significant differences in the ESBL-KP and CR-KP groups. The detection frequencies of capsular serotype K1 (magA), hypermucoviscosity, sequence type 23 (ST23), and the virulence gene rmpA were significantly higher in the hvKP than cKP isolates in all three groups (P < 0.05). Most of the hypervirulent ESBL-KP and CR-KP isolates were K non-typeable (16/30) and harbored at least one gene for virulence (26/30). The hypervirulent ESBL-KP isolates primarily carried bla_CTX–M (12/20, 60%) genes, and the hypervirulent CR-KP isolates mainly carried bla_NDM–1 (8/10, 80%) genes. Moreover, three hypervirulent ESBL-KP and two hypervirulent CR-KP isolates showed resistance to tigecycline but were sensitive to colistin. The transcriptional levels of rmpA in cKP were much lower than that in hvKP isolates in all three groups. Furthermore, overexpression of rmpA in the rmpA-low-expression cKP isolates could enhance bacterial virulence in the mouse infection experiment. In conclusion, our data suggest that the capsular serotype K1 (magA), rmpA, hypermucoviscosity, and ST23 were strongly associated with hvKP in non-MDR-KP, ESBL-KP, and CR-KP groups, and low rmpA expression levels contributed to the absence of hypervirulent phenotype.

The pathogenicity of rmpA or aerobactin-positive Klebsiella pneumoniae in infected mice

Objectives

To investigate the pathogenicity of Klebsiella pneumoniae (KPN) possessing rmpA or the aerobactin gene in infected mice.

Methods

BALB/c mice were divided into four groups (n = 10 per group) and infected with: string test-positive and rmpA-positive or aerobactin-positive KPN (group 1), string test-negative but rmpA-positive KPN (group 2), string test-negative but aerobactin-positive KPN (group 3), or string test- and rmpA/aerobactin-negative KPN (group 4). Mouse survival time was compared among groups, and the infection of livers, spleens, lungs, and kidneys and KPN growth were assessed in infected mice.

Results

Compared with the negative group (group 4), the survival rates of mice infected with rmpA- or aerobactin-positive KPN (groups 1–3) were significantly lower, their multi-organ injuries were significantly more severe, and bacterial enumeration was significantly higher.

Conclusions

Despite being string test-negative, aerobactin- or rmpA-positive KPN still exhibit high virulence and anti-immune effect activity. Therefore, the combination of the string test and gene detection of aerobactin and rmpA will be helpful in screening hypervirulent KPN.

Hypervirulent Klebsiella pneumoniae

Hypervirulent K. pneumoniae (hvKp) is an evolving pathotype that is more virulent than classical K. pneumoniae (cKp). hvKp usually infects individuals from the community, who are often healthy. Infections are more common in the Asian Pacific Rim but are occurring globally. hvKp infection frequently presents at multiple sites or subsequently metastatically spreads, often requiring source control. hvKp has an increased ability to cause central nervous system infection and endophthalmitis, which require rapid recognition and site-specific treatment. The genetic factors that confer hvKp's hypervirulent phenotype are present on a large virulence plasmid and perhaps integrative conjugal elements. Increased capsule production and aerobactin production are established hvKp-specific virulence factors. Similar to cKp, hvKp strains are becoming increasingly resistant to antimicrobials via acquisition of mobile elements carrying resistance determinants, and new hvKp strains emerge when extensively drug-resistant cKp strains acquire hvKp-specific virulence determinants, resulting in nosocomial infection. Presently, clinical laboratories are unable to differentiate cKp from hvKp, but recently, several biomarkers and quantitative siderophore production have been shown to accurately predict hvKp strains, which could lead to the development of a diagnostic test for use by clinical laboratories for optimal patient care and for use in epidemiologic surveillance and research studies.

High prevalence of hypervirulent Klebsiella pneumoniae infection in the genetic background of elderly patients in two teaching hospitals in China

Purpose

Aerobactin is a critical factor for hypervirulent Klebsiella pneumoniae (hvKp) in genetic backgrounds, but data based on the genotype for the elderly is limited.

Materials and methods

A retrospective study was conducted on elderly patients from June 2008 to July 2017 in 2 teaching hospitals. The clinical and microbiological data, including antimicrobial susceptibility testing, string test, extended-spectrum β-lactamase (ESBL) production, virulence gene, and multilocus sequence typing, of the hvKp group defined as aerobactin positive were compared with those of classic K. pneumoniae isolates.

Results

A total of 45.7% of 202 K. pneumoniae isolates were hvKp.ST23, which were predominant in 2 hospitals, but they were not highly associated with hvKp in different hospitals. Hypermucoviscosity, K1, K2, magA, and rmpA/A2 genes were highly related to hvKp (P=0.000). With regard to the host, invasive infections (P=0.000), liver abscess (P=0.000), abdominal infection (P=0.000), pneumonia (P=0.037), and septic shock (P=0.045) were significantly higher in the elderly with hvKp. In the hvKp group, patients with better nutritional status were associated with a more severe sequential organ failure assessment score and a more serious inflammation reaction. Patients with diabetes (odds ratio [OR]=2.566) are more likely to be infected with hvKp. Previous hvKp is associated with hypermucoviscosity (OR=15.249) are often paralleled with hvKp. Importantly, 26% of hvKp isolates produced ESBLs, and most of them showed a carbapenems-resistant (CR) phenotype. Multivariate analysis implied that patients with a history of surgery within the last 1 month (OR=15.999) is an independent risk factor for CR-hvKp infection.

Conclusion

The prevalence of hvKP is high in the elderly. ESBL-hvKp, especially CR-hvKp, is emerging, which is a sign that clinical awareness and infection monitoring needs to improve.

Comparison of pyogenic liver abscesses caused by hypermucoviscous Klebsiella pneumoniae and non-Klebsiella pneumoniae pathogens in Beijing: a retrospective analysis

OBJECTIVE

To perform a retrospective comparison of the clinical and radiological features of Klebsiella pneumoniae (KP)-associated and non-KP-associated pyogenic liver abscesses (PLA) in Chinese patients.

METHODS

Patients with confirmed diagnoses of bacterial liver abscess at three Beijing hospitals were enrolled. Clinical isolates from liver abscesses were used to determine serology and expression of hypermucoviscosity genes. Basic clinical, ultrasonographic (US) and computed tomography (CT) data were recorded and compared between patients with KP- and non-KP-associated PLA.

RESULTS

A total of 101 (77.10%) and 30 (22.90%) cases were due to KP and non-KP pathogens, respectively. Compared with the non-KP cohort, the KP cohort demonstrated a significantly higher incidence of underlying diabetes mellitus, and more gas-forming abscesses, as demonstrated by US and CT examinations. Prior abdominal surgery or chemoradiation therapy was significantly associated with non-KP cases. The non-KP group had a higher chance of a clear edge, compared with the KP group, on pre-contrast CT images.

CONCLUSION

KP and non-KP-associated PLA have distinctive risk factors and unique US and CT features, in Chinese patients.