Klebsiella pneumoniae is an important multidrug-resistant (MDR) pathogen affecting humans and a major source for hospital infections associated with high morbidity and mortality due to limited treatment options. We summarize the wide resistome of this pathogen, which encompasses plentiful chromosomal and plasmid-encoded antibiotic resistance genes (ARGs). Under antibiotic selective pressure, K. pneumoniae continuously accumulates ARGs, by de novo mutations, and via acquisition of plasmids and transferable genetic elements, leading to extremely drug resistant (XDR) strains harboring a ‘super resistome’. In the last two decades, numerous high-risk (HiR) MDR and XDR K. pneumoniae sequence types have emerged showing superior ability to cause multicontinent outbreaks, and continuous global dissemination. The data highlight the complex evolution of MDR and XDR K. pneumoniae, involving transfer and spread of ARGs, and epidemic plasmids in highly disseminating successful clones. With the worldwide catastrophe of antibiotic resistance and the urgent need to identify the main pathogens that pose a threat on the future of infectious diseases, further studies are warranted to determine the epidemic traits and plasmid acquisition in K. pneumoniae. There is a need for future genomic and translational studies to decipher specific targets in HiR clones to design targeted prevention and treatment.

Extraintestinal multidrug resistant Escherichia coli sequence type (ST) 131 is a worldwide pandemic pathogen and a major cause of urinary tract and bloodstream infections. The role of this pandemic lineage in multidrug resistance plasmid dissemination is still scarce. We herein performed a meta-analysis on E. coli ST131 whole-genome sequence (WGS) databases to unravel ST131 plasmidome and specifically to decipher CTX-M encoding plasmids-clade associations. We mined 880 ST131 WGS data and proved that CTX-M-27-encoding IncF[F1:A2:B20] (Group1) plasmids are strictly found in clade C1, whereas CTX-M-15-encoding IncF[F2:A1:B-] (Group2) plasmids exist only in clade C2 suggesting strong plasmid-clade adaptations. Specific Col-like replicons (Col156, Col(MG828), and Col8282) were also found to be clade C1-associated. BLAST-based search revealed that Group1 and Group2 plasmids are narrow-host-range and restricted to E.coli. Among a collection of 20 newly sequenced Israeli ST131 CTX-M-encoding plasmids (2003–2016), Group1 and Group2 plasmids were dominant and associated with the expected clades. We found, for the first time in ST131, a CTX-M-15-encoding phage-like plasmid group (Group3) and followed its spread in the WGS data. This study offers a comprehensive way to decipher plasmid-bacterium associations and demonstrates that the CTX-M-encoding ST131 Group1 and Group2 plasmids are clade-restricted and presumably less transmissible, potentially contributing to ST131 clonal superiority.

Extended-spectrum β-lactamase Enterobacteriaceae (ESBL-E) have been investigated in adult horses, but not in foals. We aimed to determine shedding and infection in neonatal foals and mares. Rectal swabs were sampled from mare and foal pairs on admission and on the 3rd day of hospitalization; enriched, plated, and bacteria were verified for ESBL production. Identification and antibiotic susceptibility profiles were determined (Vitek2). Genotyping was performed by multilocus sequence typing (MLST). Genes were identified by PCR and Sanger sequencing. Medical data were analyzed for risk factors (SPSS). On admission, 55 pairs were sampled, of which 33 pairs were re-sampled. Shedding rates on admission in foals and mares were 33% (95% CI 21–47%) and 16% (95% CI 8–29%), respectively, and during hospitalization, these increased significantly to 85% (95% CI 70–94%) and 58% (95% CI 40–73%), respectively. Foal shedding was associated with umbilical infection on admission (P = 0.016) and with ampicillin treatment during hospitalization (p = 0.011), and was independent of the mare’s shedding. The most common ESBL-E was Escherichia coli. During hospitalization, species diversity increased. Four foals were infected with ESBL-E strains, including umbilical infections and wounds. This study substantiates an alarming prevalence of shedding in neonatal foals, which should be further investigated in order to reduce resistance rates.

Salmonella enterica is a major causative pathogen of human and animal gastroenteritis. Antibiotic resistant strains have emerged due to the production of extended-spectrum β-lactamases (ESBLs) posing a major health concern. With the increasing reports on ESBL-producing Enterobacterales that colonize companion animals, we aimed to investigate ESBL dissemination among ESBL-producing Salmonella enterica (ESBL-S) in hospitalized horses. We prospectively collected ESBL-S isolates from hospitalized horses in a Veterinary-Teaching Hospital during Dec 2015–Dec 2017. Selection criteria for ESBL-S were white colonies on CHROMagarESBL plates and an ESBL phenotypic confirmation. Salmonella enterica serovars were determined using the Kaufmann-White-Le-Minor serological scheme. ESBL-encoding plasmids were purified, transformed and compared using restriction fragment length polymorphism (RFLP). Whole genome sequencing (Illumina and MinION platforms) were performed for detailed phylogenetic and plasmid analyses. Twelve ESBL-S were included in this study. Molecular investigation and Sequence Read Archive (SRA) meta-analysis revealed the presence of three unique Salmonella enterica serovars, Cerro, Havana and Liverpool, all reported for the first time in horses. PFGE revealed the clonal spread of S. Cerro between seven horses. All twelve isolates carried bla_CTX–M–3 and showed an identical multidrug resistance profile with co-resistance to trimethoprim/sulfamethoxazole and to aminoglycosides. Plasmid RFLP proved the inter-serovar horizontal spread of a single bla_CTX–M–3-encoding plasmid. Complete sequence of a representative plasmid (S. Havana strain 373.3.1), designated pSEIL-3 was a -86.4 Kb IncM2 plasmid, that encoded nine antibiotic resistance genes. pSEIL-3 was virtually identical to pCTX-M3 from Citrobacter freundii, and showed high identity (>95%) to six other bla_CTX–M–3 or bla_NDM–1 IncM2 broad host range plasmids from various Enterobacterales of human origin. Using a specific six gene-based multiplex PCR, we detected pSEIL-3 in various Enterobacterales species that co-colonized the horses’ gut. Together, our findings show the alarming emergence of ESBL-S in hospitalized horses associated with gut shedding and foal morbidity and mortality. We demonstrated the dissemination of CTX-M-3 ESBL among different Salmonella enterica serovars due to transmission of a broad host range plasmid. This report highlights horses as a zoonotic reservoir for ESBL-S, including highly transmissible plasmids that may represent a ‘One-Health’ hazard. This risk calls for the implementation of infection control measures to monitor and control the spread of ESBL-S in hospitalized horses.

Purpose. Extended-spectrum β-lactamase (ESBL)-producing extraintestinal pathogenic Escherichia coli (ExPEC) sequence type ST131 is pandemic, and it is the major contributor to antibiotic resistance in E. coli. Despite its epidemiological superiority, the physiological reasons that decipher its success remain elusive. We aimed to compare the adhesion, invasion and motility potential of ST131 versus other E. coli lineages. Methodology. In this in vitro comparative study, 14 ESBL-producing ExPEC community-onset bacteremia isolates were chosen from a reported clinical collection (Karfunkel D, Carmeli Y, Chmelnitsky I, Kotlovsky T, Navon-Venezia S. Eur J Clin Microbiol Infect Dis 2013;32:513–521). Isolates were divided into two groups, ST131 (n=7) and ‘non-ST131’, sporadic sequence types (STs) (n=7). Virulence and adhesion genes were screened by PCR in all isolates. Virotyping and serotyping were performed for ST131 isolates. Adhesion and invasion to Caco-2 epithelial cells, and motility on semi-solid agar were quantified and compared between the two groups. Fluorescence microscopy using anti-LPS E. coli antibodies was used for visualization and confirmation of adhesion and invasion. Results. ST131 isolates belonged to the O25b:H4-B2 subclone. Two ST131 virotypes were found, A (two bla CTX-M-15 H30-Rx) and C (two bla CTX-M-15 H30-Rx and three bla CTX-M-14 H30 isolates). The average number of adhesion and virulence genes carried by ExPEC ST131 isolates and non-ST131 isolates was 5.3 and 3.7, respectively (P<0.05). Group analysis showed that ST131 surpassed non-ST131 lineages in all three physiological properties: adherence (17.1 vs 13.1 %, P<0.001), invasion (0.4 vs 0.17 %, P<0.01), and swarming motility on all media tested (P<0.05). Conclusion. This study demonstrates ST131 superiority that may explain its improved gut-colonization and dissemination capabilities within the host. These insights are an important step in our understanding of ST131 epidemiological success.

The emergence of extended-spectrum β-lactamase (ESBL)-producing multidrug resistant Klebsiella pneumoniae causing community urinary tract infections (CA-UTI) in healthy women undermines effective treatment and poses a public health concern. We performed a comprehensive genomic analysis (Illumina and MinION) and virulence studies using Caenorhabditis elegans nematodes to evaluate KpnU95, a bla_CTX-M-15-producing CA-UTI K. pneumoniae strain. Whole genome sequencing identified KpnU95 as sequence type 1412 and revealed the chromosomal and plasmid-encoding resistome, virulome and persistence features. KpnU95 possess a wide virulome and caused complete C. elegans killing. The strain harbored a single novel 180.3Kb IncFIB(K) plasmid (pKpnU95), which encodes ten antibiotic resistance genes, including bla_CTX-M-15 and qnrS1 alongside a wide persistome encoding heavy metal and UV resistance. Plasmid curing and reconstitution were used for loss and gain studies to evaluate its role on bacterial resistance, fitness and virulence. Plasmid curing abolished the ESBL phenotype, decreased ciprofloxacin MIC and improved bacterial fitness in artificial urine accompanied with enhanced copper tolerance, without affecting bacterial virulence. Meta-analysis supported the uniqueness of pKpnU95 and revealed plasmid-ST1412 lineage adaptation. Overall, our findings provide translational data on a CA-UTI K. pneumoniae ST1412 strain and demonstrates that ESBL-encoding plasmids play key roles in multidrug resistance and in bacterial fitness and persistence.