Emergence of a clinical isolate of E. coil ST297 co-carrying blaNDM-13 and mcr-1.1 in China

Coexistence of blaNDM-1, mcr-1 and blaCTX-M-199 in an ST499 multidrug resistant Klebsiella pneumoniae iIsolate

The coexistence of multiple resistance genes within a single bacterial strain presents a significant public health challenge, as it complicates treatment options and accelerates the spread of multidrug resistance. While the co-occurrence of blaNDM-1 and mcr-1 genes in Klebsiella pneumoniae (KP) is uncommon, this study reports the biological characterization of a K. pneumoniae isolate, L5151, derived from a patient with diarrhea. This strain carries blaNDM-1, mcr-1, and blaCTX-M-199 resistance genes simultaneously. Multilocus sequence typing (MLST) analysis identified the L5151 strain as an ST499 type. Antimicrobial susceptibility testing (AST) was conducted via agar dilution and the broth microdilution procedure. The AST results revealed that L5151 is resistant to a variety of antibiotics. Whole-genome sequencing (WGS) and bioinformatics analysis were performed to determine the genetic composition of the strain, including the presence and characteristics of resistance genes. The results of S1 nuclease-pulsed field gel electrophoresis (S1-PFGE) and Southern blotting confirmed that the L5151 strain harbors three plasmids and that the plasmid carrying mcr-1 (pL5151_MCR_CTX) is of the IncI2(Delta) type, whereas the plasmid carrying blaNDM-1 (pL5151_NDM) is of the IncN type. The combination of these plasmids in recipient strains conferred enhanced resistance to carbapenems and colistin, highlighting the potential for increased treatment challenges. This study emphasizes the importance of ongoing surveillance of multidrug-resistant strains to prevent their spread and outbreaks. These findings provide critical insights for clinical treatment strategies and infection prevention and control measures. Enhanced surveillance and targeted interventions are essential to manage the public health risks posed by multidrug-resistant strains.

One Health at Risk: Plasmid-Mediated Spread of mcr-1 Across Clinical, Agricultural, and Environmental Ecosystems

The global dissemination of plasmid-mediated mcr genes, which confer resistance to the last-resort antibiotic colistin, represents a critical public health challenge driven by the interplay of clinical, agricultural, and environmental factors. This review examines the genetic and ecological dynamics of mcr-bearing plasmids, focusing on their role in disseminating colistin resistance across diverse bacterial hosts and ecosystems. Key plasmid families demonstrate distinct evolutionary strategies, including IncI2, IncHI2, and IncX4. IncI2 plasmids favor stability in livestock and clinical settings. IncHI2 plasmids, on the other hand, leverage transposons to co-select for multidrug resistance, while IncX4 plasmids achieve global dissemination through streamlined, conjugation-efficient architectures. The pervasive spread of mcr genes is exacerbated by their integration into chromosomes via mobile genetic elements and co-selection with resistance to other antibiotic classes, amplifying multidrug-resistant phenotypes. Environmental reservoirs, food chains, and anthropogenic practices further facilitate cross-niche transmission, underscoring the interconnectedness of resistance under the One Health framework. Addressing this crisis requires coordinated strategies, including reducing colistin misuse in agriculture, enhancing surveillance of high-risk plasmid types, and fostering international collaboration to preserve antimicrobial efficacy and mitigate the threat of untreatable infections.

Investigation of Plasmid-Mediated Colistin Resistance Genes (mcr-1-8) in Enterobacterales Isolates

Background The escalating global rise in multidrug-resistant gram-negative bacteria presents an increasingly substantial threat to patient safety. Over the past decade, carbapenem-resistant Enterobacterales (CRE) have emerged as one of the most critical pathogens in hospital-acquired infections, notably within intensive care units. Colistin has become one of the last-resort antimicrobial agents utilized to combat infections caused by CRE. However, the use of colistin has been accompanied by a notable increase in the prevalence of colistin-resistant bacteria. This study aimed to investigate plasmid-mediated colistin resistance genes ranging from mcr-1 to mcr-8 among members of the Enterobacterales order. Materials and methods This prospective study was conducted in the microbiology laboratory of Afyonkarahisar Health Sciences University Health Research and Practice Center between May 1, 2021 and July 31, 2022. A total of 2,646 Enterobacterales isolates were obtained from all culture-positive clinical samples sent from various clinics. Of these, 79 isolates exhibiting resistance to carbapenem antibiotics were included in the study. Among the 79 isolates, the presence of mcr-1 to mcr-8 genes was investigated in 27 isolates that were shown to be resistant to colistin. The identification of bacteria at the species level and antibiotic susceptibility tests were conducted using the VITEK 2 automated system (bioMérieux, USA). Colistin resistance among Enterobacterales strains exhibiting carbapenem resistance was evaluated using the broth microdilution technique (ComASP™ Colistin, Liofilchem, Italy), in accordance with the manufacturer's instructions. Results In our in vitro investigations, the minimum inhibitory concentration (MIC) values for meropenem were determined to be >8 µg/ml, whereas for colistin, the MIC50 value was >16 µg/ml and the MIC90 value was 8 µg/ml. A total of 27 colistin-resistant strains were identified among the 79 carbapenem-resistant Enterobacterales strains analyzed. The most prevalent agent among colistin-resistant strains was Klebsiella pneumoniae (K. pneumoniae), representing 66.7% of the isolates. This was followed by Proteus mirabilis (P. mirabilis) with 29.6% and Escherichia coli (E. coli) with 3.7%. The colistin resistance rate among carbapenem-resistant strains was found to be 34.2%, with colistin MIC values in strains tested by the broth microdilution method ranging from 4 to >16 µg/ml concentrations. In polymerase chain reaction (PCR) studies, the mcr-1 gene region was successfully detected by real-time PCR in the positive control isolate. Nevertheless, none of the gene regions from mcr-1 to mcr-8 were identified in our study investigating the presence of plasmid-mediated genes using a multiplex PCR kit. Conclusion Although our study demonstrated the presence of increased colistin resistance rates in carbapenem-resistant Enterobacterales isolates, it resulted in the failure to detect genes from mcr-1 to mcr-8 by the multiplex PCR method. Therefore, it is concluded that the colistin resistance observed in Enterobacteriaceae isolates in our region is not due to the mcr genes screened, but to different resistance development mechanisms.