Klebsiella pneumoniae clinical isolates with features of both multidrug-resistance and hypervirulence have unexpectedly low virulence

Successful treatment of an intra-abdominal abscess caused by KPC-2-producing hypervirulent Klebsiella pneumoniae sequence type 11 with imipenem/cilastatin/relebactam in a Japanese patient

KPC-producing K. pneumoniae is rare in Japan. In China, KPC-2-producing sequence type (ST)11 K. pneumoniae isolates have been rapidly increasing, and a subset of these isolates have acquired hypervirulence. We report a case of a 39-year-old Japanese male who developed bacteremia and intra-abdominal abscesses caused by hypervirulent carbapenem-resistant K. pneumoniae. The patient sustained abdominal injuries following a traffic accident in Xinjiang Uygur Autonomous Region and underwent abdominal surgery before being transferred to our hospital. Abscess drainage was performed, and he was initially treated with meropenem (2 g every 8 hours, prolonged infusion over 3 hours), gentamicin (5 mg/kg/day), and tigecycline (200 mg as a loading, followed by 100 mg every 12 hours). KPC carbapenemase was detected using the NG-Test® CARBA 5 (NG Biotech, France), and the minimum inhibitory concentration for imipenem/cilastatin/relebactam was 1 μg/mL, indicating susceptibility. His treatment was switched to imipenem/cilastatin/relebactam (1 g every 6 hours) for 7 weeks, resulting in clinical improvement. Whole-genome sequencing analysis revealed that the causative strain was hypervirulent KPC-2-producing K. pneumoniae (capsular type K64, ST 11) carrying blaKPC-2 and blaCTX-M-65 on a multireplicon plasmid (pMTY24772_IncFII-R), which was a fusion of IncFII and IncR. Additionally, rmpA and iucABCD genes associated with hypervirulence were detected. The strain carried a resistance plasmid and a virulence plasmid similar to those carried by ST11-K64 KPC-producing strains reported from China. Imipenem/cilastatin/relebactam is potentially an option for treating infections caused by KPC-2-producing hypervirulent K, pneumoniae with porin mutations. Cross-border spread of pathogens that are both multidrug-resistant and hyperviirulent must be closely monitored.

Dual Role for Pld1 in Klebsiella pneumoniae Virulence: Transcriptomics and Proteomics Provide Insights into Direct and Indirect Effects

Klebsiella pneumoniae is an opportunistic pathogen frequently found in healthcare settings, exhibiting resistance to carbapenems and third-generation cephalosporins. Hypervirulent community-acquired strains are also emerging. According to the World Health Organization (WHO), it is the top priority for developing new treatment strategies. A putative phospholipase D (PLD1) was linked to K. pneumoniae virulence, as a mutant strain is avirulent in a mouse model. However, the PLD1 function remains unclear. In the current study, no interaction between PLD1 and lipids was detected in a fat-blot. Lipidomic profile was not altered between strains or infected cells. To shed light on the role of PLD1, we compared the gene expression profile of a wild-type x pld1 mutant and found 330 modulated genes. Noteworthy, capsular polysaccharide genes were increased in the wild-type, while the mutant expressed higher levels of fimbriae, conjugation systems, and stress-protection proteins. Electron microscopy confirmed a loose capsule in the mutant, which also showed an enhanced adhesion to epithelial cells. A pulldown experiment using PLD1 as bait identified 48 macrophage proteins as putative ligands, including ribosomal, RNA-related, small GTPases, and cytoskeleton-related proteins. It suggests that PLD1 may modulate host cell complexes, favoring the infection. These findings provide novel clues about PLD1's role in virulence, guiding further investigations.

Epidemiological and genomic insights of mcr-1-positive colistin-resistant Klebsiella pneumoniae species complex strains from wastewater treatment plants in Shanghai

The emergence of mcr-1-positive Klebsiella pneumoniae species complex (MP-KpSC) poses a significant threat to public health due to its resistance to last-resort antibiotics like colistin. This study aimed to investigate the prevalence, genomic characteristics, and transmission features of MP-KpSC in wastewater treatment plants (WWTPs) in Shanghai, China. A total of 13 (0.36 %) MP-KpSC isolates were identified, including 12 K. pneumoniae and 1 K. quasipneumoniae subsp. similipneumoniae (Kqps). Nine multidrug-resistant (MDR) MP-KpSC and 3 extensively drug-resistant (XDR) MP-KpSC strains were identified. Twenty-two resistance determinants were present in over 30 % of the strains, with the most prevalent being mcr-1 (100 %), floR (84.62 %), mphA (69.23 %), and tet(A) (69.23 %). MP-KpSC exhibited 11 sequence types, 4 plasmid types, 6 mcr-1-flanked regions, 4 clonal groups, and diverse serotypes. In 53.85 % of strains, transposons were identified within the mcr-1-flanked regions. One strain contained both mcr-8.2 and mcr-1 gene. Notably, the mcr-1 gene was identified for the first time in Kqps and was located on the conjugative IncP1 plasmid, with ISApl1 elements upstream of it. Worryingly, two carbapenem- and colistin-resistant XDR MP-KpSC stains, and three possible hypervirulence (hv) were found in MDR MP-KpSC strains. Moreover, multiple virulence genes and mcr-1, on the same contig with IS679 insert element. The evolutionary trajectories of these strains among WWTPs-human-animals were unveiled in Shanghai. The study reveals that WWTPs serve as critical environmental reservoirs for MP-KpSC, highlighting the potential transmission risks posed by XDR and hv strains to both humans and aquatic ecosystems. These findings advocate for the implementation of active surveillance targeting WWTPs to curb the spread of MP-KpSC.

Genetic framework and evolutionary dynamics of mcr-positive Klebsiella pneumoniae from 2000 to 2023

The international transmission of the colistin resistance gene mcr in Enterobacteriaceae poses significant public health burdens, while the understanding of the population structure and evolutionary history of mcr-positive Klebsiella pneumoniae worldwide remains unclear. Here, we conducted a genomic analysis on 463 sequences of K. pneumoniae harboring mcr genes from public database between 2000 and 2023. A total of 6 mcr variants (mcr-1, -2, -3, -8 to -10) were detected, with mcr-9 (36.1%), mcr-1 (33.7%) and mcr-8 (29.2%) genes being the most common. 43.4% of total isolates (201/463) carried carbapenemase genes (blaNDM, blaKPC, blaIMP, blaOXA-48/181/232, blaVIM and blaGES) and 15.3% of isolates (71/463) contained hypervirulent genes (iucA or iroB). Correlation analysis indicated mcr-1/8/9 genes were positively correlated with specific genomic elements that were rarely described, including mcr-1 with iucABC and iutA; mcr-8 with oqxB; mcr-9 with dfrA19, ISEsa and repA (R absolute value > 0.3, p<0.01). The population of K. pneumoniae can be classified into 6 clusters, some isolates co-harboring mcr and carbapenemase genes exhibited high level of genetic similarity and dispersed in several countries, indicating the possibility of clonal transmission. mcr-9 gene was introduced into K. pneumoniae in 1978 before the time of mcr-1 gene in 1988 and mcr-8 gene in 1993. We found mcr-1/8/9 genes in K. pneumoniae evolved high-risk lineages in specific geographical location (China, Thailand and the United Kingdom) that most isolates typically contained iucA, blaNDM or blaKPC. This study highlighted that continuous surveillance for the evolution of mcr-positive K. pneumoniae harboring iucA or carbapenemase genes is essential.

Prevalence of hypervirulent Klebsiella pneumoniae and application of the novel Klebsiella phage vB_KpnP_D39 for biocontrol of serotypes K1, K2, and K57 in prepared food-related samples

In recent years, the contamination of Klebsiella pneumoniae has raised significant concerns about the potential risks to human health. The presence of K. pneumoniae in prepared food-related samples and efficient control is of importance for ensuring food safety. In this study, 300 samples were collected from markets in Hefei, China, and 45 K. pneumoniae isolates were isolated from aquatic products (n = 30), vegetables (n = 9), and ready-to-eat foods (n = 6), respectively. Among these isolates, the capsular serotypes K1, K2, and K57 accounted for the highest percentage, totaling 33.33 % (15/45), and the predominant sequence types were ST23, ST412, and ST11. Additionally, twenty-six isolates (26.9 %) were identified as hypervirulent K. pneumoniae (hvKp), and all were multidrug-resistant (MDR). Notably, the strains carrying iucA generate higher levels of siderophores compared to those that were negative for iucA (P < 0.01). Furthermore, a novel lytic phage vB_KpnP_D39 (D39), which specifically targets multiple hypervirulent capsular serotypes (K1, K2, and K57), was isolated from sewage samples collected from an effluent treatment plant in Hefei, China. D39 maintained highly lytic activity over a pH range of 3.0 to 11.0 and from 20 to 60 °C. Using transmission electron microscopy, a typical podovirus morphotype of D39 was observed. Genomic analysis indicated that D39 belongs to a novel species within genus Przondovirus, and genes associated with virulence and antibiotic resistance were not identified. In practical applications, D39 has been confirmed to significantly destroy biofilm formation and effectively prevent contamination by K. pneumoniae in food production. These findings provide information about the contamination of prepared food-related samples by MDR-hvKp, and a potential biocontrol agent for prevention and control.

Emergence and dissemination of multidrug-resistant Klebsiella pneumoniae harboring the novel tmexCD-toprJ RND efflux pump operon

The global emergence of multidrug-resistant (MDR) Klebsiella pneumoniae, particularly carbapenem-resistant K. pneumoniae (CRKP), presents a severe public health threat, limiting available treatment options. Tigecycline and eravacycline, have been considered a last-resort therapeutic against MDR Enterobacteriaceae. However, strains were resistant to these antibiotics increased recently. The tmexCD-toprJ, a plasmid-encoded resistance-nodulation-division (RND)-type efflux pump, has emerged as a critical factor conferring resistance to tigecycline and eravacycline. In this study, we reported the emergence of 11 CRKP isolates harboring tmexCD-toprJ, isolated from two lung transplant patients in a tertiary hospital in eastern China. Most of the isolates (82%) exhibited high-level resistance to tigecycline and eravacycline, along with other common antibiotics. Whole-genome sequencing (WGS) and phylogenetic analysis indicated these strains are not clonal, and resistance phenotypes were associated with the tmexCD-toprJ operon and other crucial resistance elements. We also found the tmexCD-toprJ operon was located on a conjugative plasmid, sharing high sequence similarity with the operon identified in Pseudomonas aeruginosa. Our results showed that the tmexCD-toprJ-harboring plasmid is efficiently transferable, which contributes to the dissemination of tigecycline and eravacycline resistance. At the same time, the plasmid can coexist with the blaKPC-2 -carrying plasmid, which may cause multidrug resistance. The emergence of tmexCD-toprJ-positive CRKP in lung transplant patients highlights the potential for rapid nosocomial dissemination and reduced treatment efficacy of last-line antimicrobials. Our findings emphasize the need for enhanced genomic surveillance, infection control measures, and alternative therapeutic strategies to combat the spread of tmexCD-toprJ-mediated resistance in clinical settings.

New insights and perspectives on the virulence of hypervirulent Klebsiella pneumoniae

Klebsiella pneumoniae, a Gram-negative bacterium, comprises strains with diverse virulence potentials, ranging from classical to hypervirulent variants. Understanding the genetic basis underlying the virulence disparities between hypervirulent (hvKp) and classical K. pneumoniae (cKp) strains is crucial. hvKp strains are characterized by hypermucoviscosity, attributed to the presence of specific virulence genes and the production of molecules that aid in their ability to survive, evade host immune defenses, and cause infection. In contrast, classical strains exhibit a broader array of antimicrobial resistance determinants, conferring resistance to multiple antibiotics. Although current definitions of hvKp incorporate clinical features, phenotypes, and genotypes, identifying hvKp strains in clinical settings remains challenging. Genomic studies have been pivotal and have helped to identify distinct genetic profiles in hvKp strains, including unique virulence plasmids and chromosomal variations, underscoring the genetic diversity within K. pneumoniae populations. This review examines the virulence and genetic determinants associated with hvKp. The presence of genes defining hypervirulence, alongside considerations of their utility as biomarkers and targets for therapeutic strategies, is discussed, while also providing insight into biofilm formation by hvKp and key questions that need urgent responses in understanding hvKp.

Carbapenem-Resistant, Virulence Plasmid-Harboring Klebsiella pneumoniae, United States

Carbapenem-resistant and virulence plasmid-harboring Klebsiella pneumoniae (pVir-CRKP) has emerged and spread globally, yet clinical investigations from the United States remain limited. We conducted a genomic analysis of 884 unique carbapenem-resistant K. pneumoniae isolates from a multicenter US cohort and identified 6 pVir-CRKP isolates, including 2 sequence type (ST) 23, 2 ST893, and 2 ST11 isolates. Patients infected with pVir-CRKP experienced high Pitt bacteremia scores and a 33% 30-day mortality rate. The pVir-CRKP isolates exhibited significant sequence variation in virulence genes and plasmids, along with differences in mucoviscosity, capsule production, survival in normal human serum, resistance to killing by human polymorphonuclear neutrophils, and in vivo pathogenicity. Phylogenetic analyses showed that most pVir-CRKP isolates were genetically similar to strains reported from other global regions. The emergence of pVir-CRKP with higher virulence potential and carbapenem resistance in the United States than the predominant carbapenem-resistant K. pneumoniae clone underscores the need for active global surveillance.

Regulatory effects on virulence and phage susceptibility revealed by sdiA mutation in Klebsiella pneumoniae

Introduction

The World Health Organization has identified multi-drug resistant Klebsiella pneumoniae strains as the highest priority in 2024. Understanding the regulatory routes of virulence features is crucial for the development of novel anti-virulence strategies. SdiA, a LuxR-like quorum sensing (QS) receptor that responds to N-acyl-homoserine lactones (AHLs), is involved in the regulation of virulence traits in some Gram-negative bacteria. The function of this receptor in the virulence of K. pneumoniae remains uncertain. The objective of the present study was to elucidate the function of SdiA in K. pneumoniae biofilm formation and virulence.

Methods

To this end, a genetic knockout of sdiA was conducted, and virulence-related phenotypic studies were performed following AHL provision.

Results and Discussion

The results demonstrate that sdiA deficiency increases susceptibility to phage infection and human serum resistance, and promotes biofilm maturation and cell filamentation, although no effect on virulence was observed in vivo in the Galleria mellonella infection model. On the other hand, C6-HSL promoted sdiA-dependent biofilm maturation, capsule production and serum resistance while reducing virulence against G. mellonella in the absence of sdiA. The addition of C6-HSL did not affect phage susceptibility. The results of this study demonstrate that AHLs and SdiA exert a dual influence on virulence phenotypes, operating both independently and hierarchically. These findings provide new insights into the virulence of K. pneumoniae and its regulation by SdiA.

Mechanisms of Antimicrobial Resistance in Klebsiella: Advances in Detection Methods and Clinical Implications

Klebsiella spp. are ubiquitous gram-negative bacteria, commonly present in natural environments and as part of the human microbiota. Klebsiella is involved in the occurrence and development of many diseases, and effective antibiotics for it have attracted the attention of researchers. In recent years, its multi-drug resistance, particularly to carbapenems and β-lactam antibiotics, has posed significant challenges to clinical treatment. Therefore, a comprehensive understanding of the resistance mechanisms of Klebsiella, along with the enhancement of detection methods, is crucial for effectively controlling the spread of drug-resistant strains and guiding individualized clinical treatment. This paper systematically reviews the epidemiological characteristics, resistance mechanisms, detection methods, and treatment strategies of Klebsiella, aiming to provide new insights for the clinical management of this pathogen.

Clinical and genomic characterization of Klebsiella pneumoniae infections in Dhaka, Bangladesh

BACKGROUND

Klebsiella pneumoniae (Kpn), a WHO priority pathogen with high rates of antimicrobial resistance (AMR), has emerged as a leading cause of hospital acquired pneumonia and neonatal sepsis.

OBJECTIVE

We aimed to define the clinical characteristics of a cohort of patients with Kpn infection in Dhaka, Bangladesh and to perform phenotypic and genetic characterization of the associated isolates.

METHODS

We retrospectively extracted clinical data about patients at Dhaka Medical College Hospital from whom Klebsiella spp was isolated from a clinical specimen collected between February and September 2022. We used standard microbiologic techniques to evaluate AMR and whole-genome sequencing (WGS) to assess dominant lineages, common capsular (K) and O-polysaccharide (O) antigen types, and AMR and virulence genes.

RESULTS

Ninety-eight patients were included, with diagnoses of pneumonia (38/98, 39 %), wound infection (29/98, 31 %), urinary tract infection (29/98, 31 %) and bacteremia (2/98, 2 %). We tested isolates for susceptibility to eight classes of antibiotics. Of the 98 isolates, 41 % were multidrug resistant (MDR), 15 % were extensively drug resistant (XDR), and 16 % were pan-drug resistant (PDR). Three isolates (3 %) were resistant to polymyxin B. Outcome data were available for 46 patients; 4 patients (8 %) died from infections caused by PDR (n = 2), XDR (n = 1), and MDR isolates (n = 1). WGS revealed a high degree of genomic diversity, with multiple sequence types (STs), O-types and K-types represented; ST16:K81:OL101 and ST43:K30:O1 were the most prevalent.

CONCLUSION

Our findings suggest alarming levels of AMR among Kpn isolates in Bangladesh and a critical need for improved treatment modalities and vaccine development.

Molecular epidemiology and genetic dynamics of carbapenem-resistant hypervirulent Klebsiella pneumoniae in China

Carbapenem-resistant hypervirulent Klebsiella pneumoniae (CRhvKP) poses a significant global health threat due to its enhanced virulence and resistance. This study analyzed 5,036 publicly available K. pneumoniae genomes from China (2005-2023), identifying 1,538 CRhvKP genomes, accounting for 44.6% of carbapenem-resistant isolates and 69.5% of hypervirulent isolates. Predominant carbapenemases included bla KPC (92.1%), with an increasing prevalence of bla NDM and bla OXA-48-like genes. Most isolates (93.6%) carried both aerobactin and yersiniabactin genes. The genetic background showed high diversity, characterized by 36 sequence types (STs) and 22 capsule types, with high-risk endemic STs such as ST11, ST15, and ST23 being predominant. ST23 demonstrated enhanced virulence, whereas ST11 carried more resistance genes but showed minimal presence of iroBCDN genes. A core genome MLST analysis revealed that 89.0% of CRhvKP isolates clustered into 131 clonal groups, indicating widespread dissemination, particularly in eastern China. CR and hv plasmids, primarily IncF, IncH, and IncR types, showed distinct community structures, with CR plasmids demonstrating higher mobility and diversity. Crucially, we identified 40 CR-hv convergent plasmids across five STs, likely resulting from plasmid fusions, which have become increasingly prevalent in eastern China over the last decade. Furthermore, chromosomal integration of hv genes and bla KPC-2 was detected, underscoring the stable inheritance of these traits. Class 1 Integrons were present in 84.5% of CRhvKP strains, most notably in ST11 and least in ST23. These integrons harbored genes that confer resistance to various antibiotics, including bla IMP and bla VIM, with their content varying across different STs. This study highlights the genetic complexity, rapid dissemination, and increasing prevalence of CRhvKP in China, emphasizing the urgent need for enhanced genomic surveillance and targeted interventions to mitigate the threat posed by these multidrug-resistant and hypervirulent strains.

Virulence profile of carbapenem-resistant Klebsiella pneumoniae strains by an in vivo model of Galleria mellonella

Klebsiella pneumoniae is a significant healthcare-associated pathogen, notable for its diverse virulence and antibiotic resistance profiles. This study aimed to characterize the genotypic and phenotypic diversity of K. pneumoniae isolates and evaluate their virulence using the Galleria mellonella model. Biomass production, metabolic activity, capsule formation, and siderophore production were assessed in 27 K. pneumoniae isolates from hospital-associated infections. Lethality curves were generated using the G. mellonella model, with survival monitored hourly from 16 to 48 hours. The most common sequence types (ST) identified were the high-risk clones ST307 (N = 10), ST512 (N = 8), ST101 (N = 7), and ST661 (N = 2). These STs were associated with distinct K-locus, including KL102, KL107, KL17, and KL39. Most isolates belonged to the O2afg locus (N = 18), with the K. pneumoniae carbapenemase genotype detected in 96.3% of strains. None of the isolates were classified as hypervirulent. Phenotypically, ST661 exhibited the highest biomass production despite showing similar metabolic activity to other STs. A positive correlation was observed between biomass and siderophore production, while capsule production was inversely correlated with biomass. In the G. mellonella model, ST661 demonstrated the highest virulence, resulting in 100% mortality by 48 hours, compared to survival rates of 21.4% for ST101, 38.0% for ST307, and 31.2% for ST512. These findings underscore the pathogenic potential of ST661 isolates with enhanced biofilm production. The G. mellonella model may serve as an effective in vivo system for evaluating the virulence of emerging K. pneumoniae lineages.IMPORTANCEWe demonstrate that the Galleria mellonella model is a useful tool to analyze the virulence of carbapenem-resistant Klebsiella pneumoniae strains. Our findings highlight the pathogenicity of carbapenem-resistant K pneumoniae isolates, particularly the role of the ST661 that, despite being a rare lineage, harbors the blaVIM gene and is associated with high biofilm production and the highest mortality rates.

Hypervirulent Klebsiella pneumoniae have better clinical outcomes than classical Klebsiella pneumoniae for lower respiratory tract infection patients

BACKGROUND

The clinical outcomes and microbiological features of lower respiratory tract infections (LRTIs) caused by hypervirulent Klebsiella pneumoniae (hvKp) and classical Klebsiella pneumoniae (cKp) have not been well understood.

METHODS

This study collected 287 non-repetitive Klebsiella pneumoniae isolates from 287 LRTI patients. All these strains underwent annotation for resistance and virulence factors, with 141 strains undergoing mouse infection experiments to assess their virulence. The primary clinical outcomes of these patients were evaluated, including intensive care unit (ICU) admission and in-hospital mortality rates.

RESULTS

A total of 46 capsule serotypes were identified. Among these isolates subjected to mouse infection experiments, the proportions of strains exhibiting hypervirulent phenotypes were 92.6% (25/27), 92.1% (35/38), 80% (4/5), 25% (1/4), 10.5% (2/19), and 7.1% (1/14) for K2, K1, K20, K54, K47, and K25, respectively. Therefore, K1, K2, and K20 K. pneumoniae were defined as hvKp. In addition, the rates of ICU admission and in-hospital mortality for hvKp-infected patients were significantly lower than those of cKp-infected patients (51.4% vs. 65.9%, χ2 = 4.722, p = 0.03 and 8.6% vs. 29%, χ2 = 12.133, p < 0.001). Notably, among the cKp group, the cKp-ST11 subgroup had higher rates of ICU admission (77% vs. 58.5%, χ2 = 7.981, p = 0.005) and in-hospital mortality (44.8% vs. 18.5%, χ2 = 17.585, p < 0.001) than cKp-nonST11 subgroup.

CONCLUSIONS

These findings suggest that capsule serotype is a more accurate factor for the prediction of the virulence phenotype, while hvKp have better clinical outcomes than cKp for LRTI patients. Furthermore, the cKp-ST11 subgroup has the worst prognosis than cKp-nonST11 subgroup.

Genotypic diversity and virulence factors of Klebsiella pneumoniae in a North Indian tertiary care hospital

Klebsiella pneumoniae, a pathogen of concern worldwide can be classified as classical K. pneumoniae (cKp) and Hypervirulent K. pneumoniae (HvKp). In health care settings, genotyping and identification of hypervirulent strains enables better clinical management. The present study was conducted in a north Indian tertiary care hospital which receives both Indian and foreign patients. During the study period (September -December 2022), 29 isolates of K. pneumoniae were collected from Out Patients department (OPD), Intensive Care Unit (ICU) and wards. Genotypic profiling was based on Multi Locus Sequence Typing (MLST) and wzi type. Virulence was determined by PCR based screening of genes (RmpA, iucB, ybts, iroN) as well as phenotypic tests: string test, biofilm formation and serum neutralization assay. We identified 17 Sequence Type and 14 wzi strain. The most common Sequence Type was ST231 (6/29) followed by ST 6260 (3/29)0.15 (51.7%) isolates were carbapenem resistant (CR). Eleven isolates carried the aerobactin gene iucB and/or rmpA genes. The results of the study show the presence of diverse genotypes and virulence genes of K. pneumoniae, stressing the need for stricter surveillance. We also observed a significantly higher average length of stay in patients carrying hypervirulent or carbapenem resistant strains (p < 0.05).

Diverse polysaccharide production and biofilm formation abilities of clinical Klebsiella pneumoniae

Klebsiella pneumoniae infections have become a growing threat for human health. The lack of understanding of the relationship between antibiotic resistance, mucoviscosity, and biofilm formation impedes our abilities to effectively predict K. pneumoniae infection outcomes. The Multidrug-Resistant Organism Repository and Surveillance Network offers a unique opportunity into the genetic and phenotypic variabilities in the K. pneumoniae isolates. To this end, we compared the genetic profiles of these isolates with the phenotypic biofilm formation, percent mucoviscosity, and growth rates. There was a significant phenotype-genotype correlation with decreased biofilm formation and an insertion sequence in the transcriptional activator of the type III fimbrial system. Interestingly, the most mucoid strains in the populations were lacking the genetic element regulating the mucoid phenotype and three of these isolates were able to form robust biofilms. The combination of phenotypic, genomic, and image analyses revealed an intricate relation between growth, mucoviscosity and specific virulence-associated genetic determinants.

Two outbreak cases involving ST65-KL2 and ST11-KL64 hypervirulent carbapenem-resistant Klebsiella pneumoniae: similarity and diversity analysis

The rise of the convergence of hypervirulence and carbapenem resistance in Klebsiella pneumoniae has been increasingly reported in recent years, however, there are few outbreak cases for these producing NDM carbapenemase. In this study, ST65-KL2 and ST11-KL64 hypervirulent and carbapenem-resistant K. pneumoniae (hvCRKP) were identified from two different outbreak cases: (1) clonal spreading of ST65-KL2 in five patients within transplantation wards spanning three months; and (2) clonal transmission of ST11-KL64 in ten patients across 10 months. The representative strains of ST65-KL2 and ST11-KL64 hvCRKP, K22877 and K56649, produced carbapenemase NDM-5 and dual carbapenemases KPC-2 and NDM-13, respectively, and both exhibited high-level carbapenem resistance. Moreover, virulent analysis showed that K22877 and K56649 were hypervirulent and the former possessed stronger virulence. Evolutionary pathways suggested ST65-KL2 and ST11-KL64 hvCRKP could be classified as CR-hvKP (hvKP acquiring carbapenem resistance) and hv-CRKP (CRKP acquiring hypervirulence), respectively. Unexpectedly, ST65-KL2 CR-hvKP showed resistance to ciprofloxacin mediated by plasmid acquisition as its spread, and ST11-KL64 hv-CRKP developed into enhanced virulence and macrophage resistance. Furthermore, compared to the ST65-KL2 CR-hvKP, the ST11-KL64 hv-CRKP tends to cause occult and persistent infection. Global genome analysis revealed ST11-KL64 hv-CRKP and ST65-KL2 CR-hvKP mainly carried blaKPC-2 and had significant differences in Ompk35/36, ybt, resistance and virulence. Effective surveillance should be implemented and novel therapeutic strategies are urgently needed to deal with refractory infections.

Pandrug-resistant Klebsiella pneumoniae isolated from Ukrainian war victims are hypervirulent

OBJECTIVES

Carbapenem- and colistin-resistant Klebsiella pneumoniae were isolated from war victims treated in hospitals in Ukraine. The question was whether these pandrug-resistant K. pneumoniae are pathogenic and capable of causing disease in a broader context.

METHODS

Klebsiella pneumoniae clinical isolates (n = 37) were tested for antibiotic resistance and subjected to whole-genome sequencing (WGS). In addition, their pathogenicity was tested by serum resistance and two separate animal models.

RESULTS

Isolates belonging to the sequence types (ST) 23, 147, 307, 395, and 512 were found to harbor resistance genes against carbapenems and cephalosporins. Nine isolates carried point mutations in pmrB and phoP genes associated with colistin resistance. All bacteria were equipped with multiple virulence genes, and the colistin-resistant isolates each carried 10 different genes. Colistin-resistant K. pneumoniae were more serum-resistant, more virulent against G. mellonella larvae, and displayed an increased survival in mice compared to colistin-susceptible bacteria. The iucA, peg-344, rmpA, rmpC, and rmpD genes were associated with increased virulence in animals.

CONCLUSIONS

Pandrug-resistant K. pneumoniae in Ukraine are hypervirulent and retain their pathogenicity, highlighting the need to prevent disseminated spread.

Klebsiella pneumoniae capsular polysaccharide: Mechanism in regulation of synthesis, virulence, and pathogenicity

Hypervirulent Klebsiella pneumoniae exhibits strong pathogenicity and can cause severe invasive infections but is historically recognized as antibiotic-susceptible. In recent years, the escalating global prevalence of antibiotic-resistant hypervirulent K. pneumoniae has raised substantial concerns and created an urgent demand for effective treatment options. Capsular polysaccharide (CPS) is one of the main virulence determinants contributing to the hypervirulent phenotype. The structure of CPS varies widely among strains, and both the structure and composition of CPS can influence the virulence of K. pneumoniae. CPS possesses various immune evasion mechanisms that promote the survival of K. pneumoniae, as well as its colonization and dissemination. Given the proven viability of therapies that target the capsule, improving our understanding of the CPS structure is critical to effectively directing treatment strategies. In this review, the structure and typing of CPS are addressed as well as genes related to synthesis and regulation, relationships with virulence, and pathogenic mechanisms. We aim to provide a reference for research on the pathogenesis of K. pneumoniae.

A Klebsiella-phage cocktail to broaden the host range and delay bacteriophage resistance both in vitro and in vivo

Bacteriophages (phages), viruses capable of infecting and lysing bacteria, are a promising alternative for treating infections from hypervirulent, antibiotic-resistant pathogens like Klebsiella pneumoniae, though narrow host range and phage resistance remain challenges. In this study, the hypervirulent K. pneumoniae NTUH-K2044 was used to purify phage ΦK2044, while two ΦK2044-resistant strains were used to purify two further phages: ΦKR1, and ΦKR8 from hospital sewage. A detailed characterization showed that ΦK2044 specifically killed KL1 capsule-type K. pneumoniae, while ΦKR1 and ΦKR8 targeted 13 different capsular serotypes. The phage cocktail (ΦK2044 + ΦKR1 + ΦKR8) effectively killed K. pneumoniae in biofilms, pre-treatment biofilm formation, and delayed phage-resistance. The phage cocktail improved 7-day survival in Galleria mellonella and mouse models and showed therapeutic potential in a catheter biofilm model. In summary, this proof-of-principle phage cocktail has a broad host range, including hypervirulent and highly drug-resistant K. pneumoniae, and serves as a promising starting point for optimizing phage therapy.

Combating biofilm-associated Klebsiella pneumoniae infections using a bovine microbial enzyme

The emergence of multidrug-resistant Klebsiella pneumoniae poses significant clinical challenges with limited treatment options. Biofilm is an important virulence factor of K. pneumoniae, serving as a protective barrier against antibiotics and the immune system. Here, we present the remarkable ability of a bovine microbial enzyme to prevent biofilm formation (IC50 2.50 μM) and degrade pre-formed K. pneumoniae biofilms (EC50 1.94 μM) by degrading the matrix polysaccharides. The treatment was effective against four different clinical K. pneumoniae isolates tested. Moreover, the enzyme significantly improved the biofilm sensitivity of a poorly performing broad-spectrum antibiotic, meropenem, and immune cells, resulting in facile biofilm clearance from the mouse wound infection. Notably, well-known powerful enzymes of the same class, cellulase, and α-amylase, were nearly inactive against the K. pneumoniae biofilms. The enzyme exhibited antibiofilm activity without showing toxicity to the mammalian and microbial cells, highlighting the potential of the enzyme for in vivo applications.

Hypervirulent and carbapenem-resistant Klebsiella pneumoniae: A global public health threat

The evolution of hypervirulent and carbapenem-resistant Klebsiella pneumoniae can be categorized into three main patterns: the evolution of KL1/KL2-hvKp strains into CR-hvKp, the evolution of carbapenem-resistant K. pneumoniae (CRKp) strains into hv-CRKp, and the acquisition of hybrid plasmids carrying carbapenem resistance and virulence genes by classical K. pneumoniae (cKp). These strains are characterized by multi-drug resistance, high virulence, and high infectivity. Currently, there are no effective methods for treating and surveillance this pathogen. In addition, the continuous horizontal transfer and clonal spread of these bacteria under the pressure of hospital antibiotics have led to the emergence of more drug-resistant strains. This review discusses the evolution and distribution characteristics of hypervirulent and carbapenem-resistant K. pneumoniae, the mechanisms of carbapenem resistance and hypervirulence, risk factors for susceptibility, infection syndromes, treatment regimens, real-time surveillance and preventive control measures. It also outlines the resistance mechanisms of antimicrobial drugs used to treat this pathogen, providing insights for developing new drugs, combination therapies, and a "One Health" approach. Narrowing the scope of surveillance but intensifying implementation efforts is a viable solution. Monitoring of strains can be focused primarily on hospitals and urban wastewater treatment plants.

The impact of antibiotic induction on virulence and antibiotic resistance in Klebsiella pneumoniae: a comparative study of CSKP and CRKP strains

Background

Klebsiella pneumoniae is an opportunistic pathogen causing nosocomial infections, classified into carbapenem-sensitive and carbapenem-resistant strains. Understanding the virulence factors and antibiotic resistance of these strains is essential for effective clinical management.

Objective

This study compared the virulence genes and antibiotic resistance profiles of 50 CSKP and 50 CRKP strains, examining their expression under antibiotic pressure and the mechanisms contributing to their pathogenicity.

Methods

Virulence genes (rmpA, rmpA2, iucA, iutA, Peg-344, ybts, iroB) were detected in both strains using polymerase chain reaction (PCR). Antibiotic susceptibility testing established minimum inhibitory concentrations (MICs) for key antibiotics. Gene expression analysis was performed with quantitative reverse transcription PCR (qRT-PCR) after 10 days of antibiotic exposure.

Results

CSKP strains exhibited significantly higher positivity rates for virulence genes compared to CRKP strains. CRKP strains predominantly expressed resistance genes KPC, SHV, and CTX-M3, whereas no resistance genes were found in CSKP. Antibiotic susceptibility tests showed increased MICs, particularly for ciprofloxacin and imipenem, following antibiotic induction. CSKP demonstrated elevated expression of rmpA and rmpA2, while CRKP showed increased expression of SHV, and KPC after antibiotic exposure.

Conclusion

This study highlights the intricate relationship between virulence and resistance in Klebsiella pneumoniae. CSKP strains show strong virulence factor expression, while CRKP strains adapt to antibiotic pressure through altered gene expression patterns. These findings underscore the urgent need for continuous surveillance and innovative therapeutic strategies to combat multidrug-resistant Klebsiella pneumoniae infections.

Isolation and characterization of pathogenic Klebsiella pneumoniae strains from lettuce: a potential source of antibiotic resistance and development of a mathematical model for ANOVA results

Introduction

This study aimed to evaluate the prevalence of Klebsiella pneumoniae contamination in raw lettuce from Risalpur, Pakistan, and to analyze the antibiotic susceptibility profiles of the isolated strains. The presence of foodborne pathogens such as K. pneumoniae poses significant public health risks, particularly in regions with suboptimal hygiene practices and improper food handling.

Methods

Lettuce samples were collected from various sources in Risalpur and screened for K. pneumoniae. Antimicrobial susceptibility testing was performed to evaluate the effectiveness of various antibiotics against the isolated strains. Statistical analyses, including ANOVA and linear regression, were conducted to assess differences in inhibition zones and to predict antibiotic effectiveness based on concentration.

Results

The results revealed a significant prevalence of K. pneumoniae in the lettuce samples, highlighting the risks associated with poor hygiene, transportation, storage, and contaminated irrigation water. The isolated strains exhibited high susceptibility to gentamicin but demonstrated notable resistance to doxycycline, vancomycin, and ticarcillin. Multidrug-resistant (MDR) strains were identified. ANOVA showed significant differences in inhibition zones, and the linear regression model predicted a Zone of Inhibition based on antibiotic concentration (β0 = 10.6667, β1 = 0.4556).

Discussion

The identification of MDR strains of K. pneumoniae underscores the urgent need for enhanced antibiotic stewardship and food safety protocols to manage foodborne pathogens. Improved hygiene practices throughout the food production and supply chain are critical to mitigate health risks and address the challenge of growing antibiotic resistance.

Transmission Dynamics and Novel Treatments of High Risk Carbapenem-Resistant Klebsiella pneumoniae: The Lens of One Health

The rise of antibiotic resistance and the dwindling antimicrobial pipeline have emerged as significant threats to public health. The emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a global threat, with limited options available for targeted therapy. The CRKP has experienced various changes and discoveries in recent years regarding its frequency, transmission traits, and mechanisms of resistance. In this comprehensive review, we present an in-depth analysis of the global epidemiology of K. pneumoniae, elucidate resistance mechanisms underlying its spread, explore evolutionary dynamics concerning carbapenem-resistant hypervirulent strains as well as KL64 strains of K. pneumoniae, and discuss recent therapeutic advancements and effective control strategies while providing insights into future directions. By going through up-to-date reports, we found that the ST11 KL64 CRKP subclone with high risk demonstrated significant potential for expansion and survival benefits, likely due to genetic influences. In addition, it should be noted that phage and nanoparticle treatments still pose significant risks for resistance development; hence, innovative infection prevention and control initiatives rooted in One Health principles are advocated as effective measures against K. pneumoniae transmission. In the future, further imperative research is warranted to comprehend bacterial resistance mechanisms by focusing particularly on microbiome studies' application and implementation of the One Health strategy.

Genomic study substantiates the intensive care unit as a reservoir for carbapenem-resistant Klebsiella pneumoniae in a teaching hospital in China

Carbapenem-resistant Klebsiella pneumoniae (CRKP) has recently emerged as a notable public health concern, while the underlying drivers of CRKP transmission among patients across different healthcare facilities have not been fully elucidated. To explore the transmission dynamics of CRKP, 45 isolates were collected from both the intensive care unit (ICU) and non-ICU facilities in a teaching hospital in Guangdong, China, from March 2020 to August 2023. The collection of clinical data and antimicrobial resistance phenotypes was conducted, followed by genomic data analysis for these isolates. The mean age of the patients was 75.2 years, with 18 patients (40.0%) admitted to the ICU. The predominant strain in hospital-acquired CRKP was sequence type 11 (ST11), with k-locus type 64 and serotype O1/O2v1 (KL64:O1/O2v1), accounting for 95.6% (43/45) of the cases. The CRKP ST11 isolates from the ICU exhibited a low single nucleotide polymorphism (SNP) distance when compared to isolates from other departments. Genome-wide association studies identified 17 genes strongly associated with SNPs that distinguish CRKP ST11 isolates from those in the ICU and other departments. Temporal transmission analysis revealed that all CRKP isolates from other departments were genetically very close to those from the ICU, with fewer than 16 SNP differences. To further elucidate the transmission routes among departments within the hospital, we reconstructed detailed patient-to-patient transmission pathways using hybrid methods that combine TransPhylo with an SNP-based algorithm. A clear transmission route, along with mutations in potential key genes, was deduced from genomic data coupled with clinical information in this study, providing insights into CRKP transmission dynamics in healthcare settings.

Polymyxin combined with Ocimum gratissimum essential oil: one alternative strategy for combating polymyxin-resistant Klebsiella pneumoniae

Introduction. Multidrug-resistant infections present a critical public health due to scarce treatment options and high mortality. Ocimum gratissimum L. essential oil (O.geo) is a natural resource rich in eugenol known for its antimicrobial activity.Hypothesis/Gap Statement. O.geo may exert effective antimicrobial activity against polymyxin-resistant Klebsiella pneumoniae and, when combined with Polymyxin B (PMB), may exhibit a synergistic effect, enhancing treatment efficacy and reducing antimicrobial resistance.Aim. This study aims to investigate the antimicrobial activity of O.geo against polymyxin-resistant K. pneumoniae using in vitro tests and an in vivo Caenorhabditis elegans model.Methodology. The O.geo was obtained by hydrodistillation followed by gas chromatography. The MIC and antibiofilm activity were determined using broth microdilution. Checkerboard and time-kill assays evaluated the combination of O.geo and polymyxin B (PMB), whereas a protein leakage assay verified its action.Results. Eugenol (39.67%) was a major constituent identified. The MIC of the O.geo alone ranged from 128 to 512 µg ml-1. The fractional inhibitory concentration index (0.28) and time-kill assay showed a synergism. In addition, O.geo and PMB inhibited biofilm formation and increased protein leakage in the plasma membrane. The treatment was tested in vivo using a Caenorhabditis elegans model, and significantly increased survival without toxicity was observed.Conclusion. O.geo could be used as a potential therapeutic alternative to combat infections caused by multidrug-resistant bacteria, especially in combination with PMB.

Clonal background and routes of plasmid transmission underlie antimicrobial resistance features of bloodstream Klebsiella pneumoniae

Bloodstream infections caused by the opportunistic pathogen Klebsiella pneumoniae are associated with adverse health complications and high mortality rates. Antimicrobial resistance (AMR) limits available treatment options, thus exacerbating its public health and clinical burden. Here, we aim to elucidate the population structure of K. pneumoniae in bloodstream infections from a single medical center and the drivers that facilitate the dissemination of AMR. Analysis of 136 short-read genome sequences complemented with 12 long-read sequences shows the population consisting of 94 sequence types (STs) and 99 clonal groups, including globally distributed multidrug resistant and hypervirulent clones. In vitro antimicrobial susceptibility testing and in silico identification of AMR determinants reveal high concordance (90.44-100%) for aminoglycosides, beta-lactams, carbapenems, cephalosporins, quinolones, and sulfonamides. IncF plasmids mediate the clonal (within the same lineage) and horizontal (between lineages) transmission of the extended-spectrum beta-lactamase gene blaCTX-M-15. Nearly identical plasmids are recovered from isolates over a span of two years indicating long-term persistence. The genetic determinants for hypervirulence are carried on plasmids exhibiting genomic rearrangement, loss, and/or truncation. Our findings highlight the importance of considering both the genetic background of host strains and the routes of plasmid transmission in understanding the spread of AMR in bloodstream infections.

Diverse polysaccharide production and biofilm formation abilities of clinical Klebsiella pneumoniae

Klebsiella pneumoniae infections have become a growing threat for human health. The lack of understanding of the relationship between antibiotic resistance, mucoviscosity, and biofilm formation in clinical isolates impedes our abilities to effectively predict K. pneumoniae infection outcomes. These traits are also associated with fitness in natural populations and more specifically within a host. The Multidrug-Resistant Organism Repository and Surveillance Network offers a unique opportunity into the genetic and phenotypic variabilities in the K. pneumoniae isolates encountered in the clinics today. To this end, we compared the genetic profiles of these isolates with the phenotypic biofilm formation abilities, percent mucoviscosity, and growth rates. We found most isolates formed limited biofilm, although a select group of isolates could form extremely robust biofilms. Variation in biofilm formation could not be explained by difference in growth rate, suggesting specific genetic and physical determinants. Interestingly, the most mucoid strains in the populations were lacking the genetic element regulating the mucoid phenotype and three of these isolates were able to form robust biofilms. There was a significant phenotype-genotype correlation with decreased biofilm formation and an insertion sequence in the transcriptional activator of the type III fimbrial system. Finally, confocal microscopy highlighted the structural and spatial heterogeneity of biofilm among the most robust biofilm formers not detected by traditional methods. The combination of phenotypic, genomic and image analyses allowed us to reveal an unexpected phenotypic diversity and an intricate relation between growth, mucoviscosity and specific virulence-associated genetic determinants.

Microaerobic-mediated suppression of Klebsiella pneumoniae mucoviscosity is restored by rmpD overexpression

AIMS

Hypervirulent Klebsiella pneumoniae (hvKp) causes invasive community-acquired infections in healthy individuals, and hypermucoviscosity (HMV) is the main phenotype associated with hvKp. This study investigates the impact of microaerobic environment availability on the mucoviscosity of K. pneumoniae.

METHODS AND RESULTS

By culturing 25 clinical strains under microaerobic and aerobic environments, we observed a notable reduction in mucoviscosity in microaerobic environments. RNA sequencing and qRT-PCR revealed downregulated expressions of capsule synthesis genes (galf, orf2, wzi, wza, wzb, wzc, wcaj, manC, manB, and ugd) and regulatory genes (rmpA, rmpD, and rmpC) under microaerobic conditions. Transmission electron microscopy and Indian ink staining analysis were performed, revealing that the capsular thickness of K. pneumoniae decreased by half in microaerobic conditions compared to aerobic conditions. Deletion of rmpD and rmpC caused the loss of the HMV phenotype in both aerobic and microaerobic conditions. However, compared to wild-type strain in microaerobic condition, only rmpD overexpression strain, and not rmpC overexpression strain, displayed a significant increase in capsule thickness in microaerobic conditions.

CONCLUSIONS

Microaerobic conditions can suppress the mucoviscosity of K. pneumoniae, but this suppression can be overcome by altering the expression of rmpD, indicating a specific function for rmpD in the oxygen environmental adaptation of K. pneumoniae.

Carbapenem and colistin-resistant hypervirulent Klebsiella pneumoniae: An emerging threat transcending the egyptian food chain

BACKGROUND

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is a great public health problem and is associated with many disease outbreaks and high mortality rates. Alarmingly, K. pneumoniae has been isolated from food in several recent studies. This study aimed to investigate the prevalence and characteristics of CRKP in food samples from Egypt.

METHODS

A total of 311 food samples (including 116 minced meat, 92 chicken meat, 75 diced meat, and 28 mutton) were collected from local markets in Egypt and were screened for CRKP with the determination of their antimicrobial resistance profiles. The whole genome sequence was done for 23 CRKP isolates to clarify the relationship between CRKP from food and human cases in Egypt using the SNP core genome. The conjugation probability of the blaNDM-5 harboring plasmid was identified using oriTfinder RESULTS: CRKP was isolated from 11% (35/311) of the samples, with 45.71% (16/35) of them showing resistance to colistin, one of the last-resort options for treating CRKP-mediated infections. In addition to the carbapenem and colistin resistance, the CRKP isolates frequently exhibited resistance to multiple antimicrobials including β-lactams, fluoroquinolones, aminoglycosides, tetracyclines, and chloramphenicol. In addition, most of the CRKP were potentially hypervirulent K. pneumoniae (HvKP) identified as phylogroup Kp1 and of high-risk groups as detected in STs reported in many human outbreaks globally, such as ST383 and ST147. The core-genome phylogeny showed similarities between the isolates from this study and those previously isolated from clinical human samples in Egypt. In addition, analysis of the plasmid on which blaNDM is encoded revealed that several antimicrobial resistance genes such as blaOXA-9, blaCTX-M-15, aac(6')-Ib, qnrS1, and several virulence genes are encoded on the same plasmid.

CONCLUSIONS

This study is significant for food safety and public health and is important to further identify the change in the epidemiology of CRKP infections, especially the consumption of contaminated food products.

Pyogenic liver abscess caused by an atypical hypervirulent Klebsiella pneumoniae K1-ST23 in Mexico

Hypervirulent K. pneumoniae infection has been raising worldwide and is one of the major causes of community-acquired pyogenic liver abscess. We described a case report of pyogenic liver abscess caused by an atypical hypervirulent (non-hypermucoviscous) K. pneumoniae K1 ST23 in a diabetic Asian patient who resided in Mexico. The susceptibility to antimicrobials, pathogenicity, molecular and genomic analysis were determined. A man from Guangdong (China) with a recent diagnosis of diabetes mellitus was admitted to the hospital, and he denied traveling in the last 3 months. A computed tomography revealed a right lobe liver abscess. On the third day after admission a Klebsiella pneumoniae isolate (14652) was obtained. The isolate corresponded to a susceptible K. pneumoniae with capsular type K1 and ST23 (CG23) and exhibited a non-hypermucoviscous phenotype. The isolate 14652 was genetically related to the globally distributed lineage ST23-KL1. This study describes the first case in Mexico of K. pneumoniae capsular type K1 and ST23 with an atypical hypervirulent phenotype.

Comprehensive study reveals phenotypic heterogeneity in Klebsiella pneumoniae species complex isolates

Here, we conducted a comprehensive analysis of 356 Klebsiella pneumoniae species complex (KpSC) isolates that were classified as classical (cl), presumptive hypervirulent (p-hv) and hypermucoviscous-like (hmv-like). Overall, K. pneumoniae (82.3%), K. variicola (2.5%) and K. quasipneumoniae (2.5%) were identified. These isolates comprised 321 cl-KpSC, 7 p-hv-KpSC and 18 hmv-like-KpSC. A large proportion of cl-KpSC isolates were extended-spectrum-β-lactamases (ESBLs)-producers (64.4%) and 3.4% of isolates were colistin-resistant carrying carbapenemase and ESBL genes. All p-hv-KpSC showed an antibiotic susceptible phenotype and hmv-like isolates were found to be ESBL-producers (8/18). Assays for capsule production and capsule-dependent virulence phenotypes and whole-genome sequencing (WGS) were performed in a subset of isolates. Capsule amount differed in all p-hv strains and hmv-like produced higher capsule amounts than cl strains; these variations had important implications in phagocytosis and virulence. Murine sepsis model showed that most cl strains were nonlethal and the hmv-like caused 100% mortality with 3 × 108 CFUs. Unexpectedly, 3/7 (42.9%) of p-hv strains required 108 CFUs to cause 100% mortality (atypical hypervirulent), and 4/7 (57.1%) strains were considered truly hypervirulent (hv). Genomic analyses confirmed the diverse population, including isolates belonging to hv clonal groups (CG) CG23, CG86, CG380 and CG25 (this corresponded to the ST3999 a novel hv clone) and MDR clones such as CG258 and CG147 (ST392) among others. We noted that the hmv-like and hv-ST3999 isolates showed a close phylogenetic relationship with cl-MDR K. pneumoniae. The information collected here is important to understand the evolution of clinically important phenotypes such as hypervirulent and ESBL-producing-hypermucoviscous-like amongst the KpSC in Mexican healthcare settings. Likewise, this study shows that mgrB inactivation is the main mechanism of colistin resistance in K. pneumoniae isolates from Mexico.