The emergence of carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKp) is a new threat to healthcare. In this study, we analyzed nine CR-hvKp isolates of different sequence-types (ST) recovered from patients with nosocomial infections in two hospitals in Saint Petersburg. Whole-genome sequencing showed that eight of them harbored large mosaic plasmids carrying resistance to carbapenems and hypervirulence simultaneously, and four different types of hybrid plasmids were identified. BLAST analysis showed a high identity with two hybrid plasmids originating in the UK and Czech Republic. We demonstrated that hybrid plasmids emerged due to the acquisition of resistance genes by virulent plasmids. Moreover, one of the hybrid plasmids carried a novel New Delhi metallo-beta-lactamase (NDM) variant, differing from NDM-1 by one amino acid substitution (D130N), which did not provide significant evolutionary advantages compared to NDM-1. The discovery of structurally similar plasmids in geographically distant regions suggests that the actual distribution of hybrid plasmids carrying virulence and resistance genes is much wider than expected.

An Escherichia coli sequence type 31 isolate co-harbouring mcr-1 and bla NDM-1 genes on the plasmids of Incl2 and IncC groups, respectively, was recovered from a newborn with ventilator-associated pneumonia in Moscow, Russia. The convergence of polymyxin and carbapenem resistance and its expansion beyond Southeast Asia is a serious threat to human health.

Escherichia coli isolates from various sources from 2018 to 2019 were included in the study. Mcr-1 genes were found in two of 105 animal strains (2%) and seven of 928 human strains (0.8%). All mcr-1-positive strains showed a low level of resistance to colistin (MIC ranged from 4 to 8 µg/ml). Both strains isolated from animals remained sensitive to betalactam antibiotics and did not contain beta-lactamase genes. Beta-lactamases were absent only in one of the strains isolated from humans. Four strains were resistant to cephalosporins with sensitivity to carbapenems and carried class A (blaCTX-M-15 or blaCTX-M-1) or class C (blaCMY-2) extended-spectrum beta-lactamases genes. One strain showed resistance to cephalosporins and meropenem and contained four beta-lactamase genes: blaNDM-1, blaCTX-M-15, blaTEM-1B, and blaCMY-6. Only one strain isolated from animals remained sensitive to ciprofloxacin, the rest showed high level of resistance, had amino acid substitutions in the DNA gyrase genes or mutations leading to overexpression of the mdfA gene. In terms of resistance to aminoglycosides, the strains varied widely and carried up to four aminoglycoside-modifying enzyme genes. One strain isolated from humans showed resistance to tigecycline, but no genes conferring resistance to this antibiotic were found. The data obtained substantiate the need for extended studies on the molecular epidemiology of associated resistance to polymyxins and beta-lactams.

OXA-48 carbapenemases are frequently expressed by Klebsiella pneumoniae clinical isolates; they decrease the effectiveness of carbapenem therapy, particularly with meropenem. Among these isolates, meropenem-susceptible carbapenemase-producers may show decreased meropenem effectiveness. However, the probability of the emergence of resistance in susceptible carbapenemase-producing isolates and its dependence on specific K. pneumoniae meropenem MICs is not completely known. It is also not completely clear what resistance patterns will be exhibited by these bacteria exposed to meropenem, if they would follow the patterns of non-beta-lactamase-producing bacteria and other than beta-lactams antibiotics. These issues might be clarified if patterns of meropenem resistance related to the mutant selection window (MSW) hypothesis. To test the applicability of the MSW hypothesis to meropenem, OXA-48-carbapenemase-producing K. pneumoniae clinical isolates with MICs in a 64-fold range (from susceptible to resistant) were exposed to meropenem in a hollow-fiber infection model; epithelial lining fluid meropenem pharmacokinetics were simulated following administration of 2 grams every 8 hours in a 3-hour infusion. Strong bell-shaped relationships between the meropenem daily dose infused to the model as related to the specific isolate MIC and both the antimicrobial effect and the emergence of resistance were observed. The applicability of the MSW hypothesis to meropenem and carbapenemase producing K. pneumoniae was confirmed. Low meropenem efficacy indicates very careful prescribing of meropenem to treat K. pneumoniae infections when the causative isolate is confirmed as an OXA-48-carbapenemase producer.