Transmission and stable inheritance of carbapenemase gene (blaKPC-2 or blaNDM-1)-encoding and mcr-1-encoding plasmids in clinical Enterobacteriaceae strains

Sporadic clone Escherichia coli ST615 as a vector and reservoir for dissemination of crucial antimicrobial resistance genes

There is scarce information concerning the role of sporadic clones in the dissemination of antimicrobial resistance genes (ARGs) within the nosocomial niche. We confirmed that the clinical Escherichia coli M19736 ST615 strain, one of the first isolates of Latin America that harbors a plasmid with an mcr-1 gene, could receive crucial ARG by transformation and conjugation using as donors critical plasmids that harbor bla CTX-M-15, bla KPC-2, bla NDM-5, bla NDM-1, or aadB genes. Escherichia coli M19736 acquired bla CTX-M-15, bla KPC-2, bla NDM-5, bla NDM-1, and aadB genes, being only blaNDM-1 maintained at 100% on the 10th day of subculture. In addition, when the evolved MDR-E. coli M19736 acquired sequentially bla CTX-M-15 and bla NDM-1 genes, the maintenance pattern of the plasmids changed. In addition, when the evolved XDR-E. coli M19736 acquired in an ulterior step the paadB plasmid, a different pattern of the plasmid's maintenance was found. Interestingly, the evolved E. coli M19736 strains disseminated simultaneously the acquired conjugative plasmids in different combinations though selection was ceftazidime in all cases. Finally, we isolated and characterized the extracellular vesicles (EVs) from the native and evolved XDR-E. coli M19736 strains. Interestingly, EVs from the evolved XDR-E. coli M19736 harbored bla CTX-M-15 though the pDCAG1-CTX-M-15 was previously lost as shown by WGS and experiments, suggesting that EV could be a relevant reservoir of ARG for susceptible bacteria. These results evidenced the genetic plasticity of a sporadic clone of E. coli such as ST615 that could play a relevant transitional link in the clinical dynamics and evolution to multidrug/extensively/pandrug-resistant phenotypes of superbugs within the nosocomial niche by acting simultaneously as a vector and reservoir of multiple ARGs which later could be disseminated.

The evolution of infectious transmission promotes the persistence of mcr-1 plasmids

Conjugative plasmids play a vital role in bacterial evolution and promote the spread of antibiotic resistance. They usually cause fitness costs that diminish the growth rates of the host bacteria. Compensatory mutations are known as an effective evolutionary solution to reduce the fitness cost and improve plasmid persistence. However, whether the plasmid transmission by conjugation is sufficient to improve plasmid persistence is debated since it is an inherently costly process. Here, we experimentally evolved an unstable and costly mcr-1 plasmid pHNSHP24 under laboratory conditions and assessed the effects of plasmid cost and transmission on the plasmid maintenance by the plasmid population dynamics model and a plasmid invasion experiment designed to measure the plasmid's ability to invade a plasmid-free bacterial population. The persistence of pHNSHP24 improved after 36 days evolution due to the plasmid-borne mutation A51G in the 5'UTR of gene traJ. This mutation largely increased the infectious transmission of the evolved plasmid, presumably by impairing the inhibitory effect of FinP on the expression of traJ. We showed that increased conjugation rate of the evolved plasmid could compensate for the plasmid loss. Furthermore, we determined that the evolved high transmissibility had little effect on the mcr-1-deficient ancestral plasmid, implying that high conjugation transfer is vital for maintaining the mcr-1-bearing plasmid. Altogether, our findings emphasized that, besides compensatory evolution that reduces fitness costs, the evolution of infectious transmission can improve the persistence of antibiotic-resistant plasmids, indicating that inhibition of the conjugation process could be useful to combat the spread of antibiotic-resistant plasmids. IMPORTANCE Conjugative plasmids play a key role in the spread of antibiotic resistance, and they are well-adapted to the host bacteria. However, the evolutionary adaptation of plasmid-bacteria associations is not well understood. In this study, we experimentally evolved an unstable colistin resistance (mcr-1) plasmid under laboratory conditions and found that increased conjugation rate was crucial for the persistence of this plasmid. Interestingly, the evolved conjugation was caused by a single-base mutation, which could rescue the unstable plasmid from extinction in bacterial populations. Our findings imply that inhibition of the conjugation process could be necessary for combating the persistence of antibiotic-resistance plasmids.

Non-corresponding contaminants in marine surface sediments as a factor of ARGs spread in the Sea of Azov

The present study aims to analyze the level and total toxicity of the most common pollutants in surface sediments and assess their impact on the occurrence of antibiotic resistance genes (ARGs) in the Sea of Azov. Biotesting using the whole-cell bacterial lux-biosensors showed high integral toxicity of surface sediments and the presence of genotoxicants and substances that cause oxidative stress and protein damage. Using cluster analysis, it was shown that the distribution of pollutants in the Sea of Azov depends on the type of surface sediments. The relative abundance and distribution of 14 ARGs in surface sediments were shown. Principle component analyses results suggest that non-corresponding contaminants do not exert direct influence on the ARGs abundance in the surface sediments of the Sea of Azov. Thus, the need to investigate the significance of non-corresponding pollutants in the selection and distribution of ARGs in the aquatic environment remains a pressing problem.

Carriage of the mcr-9 and mcr-10 genes in clinical strains of the Enterobacter cloacae complex in China: a prevalence and molecular epidemiology study

OBJECTIVES

Enterobacter cloacae complex (ECC) is among the most common carbapenem-resistant Enterobacteriaceae in China. The emergence of the mcr renders CRE strains resistant to the last-line antibiotic colistin. We investigated the prevalence of mcr-9 and mcr-10 in carbapenem-resistant ECC (CRECC) and carbapenem-susceptible ECC (CSECC) in China.

METHODS

We collected CRECC and CSECC strains from different regions of China. The antimicrobial susceptibility tests, conjugation experiments, whole genome sequencing, bioinformatic analysis, and quantitative RT-PCR were performed to understand the mechanisms of resistance and transmission of mcr in ECC.

RESULTS

A total of 534 ECC were collected, among which 57 (10.7%) and 23 (4.3%) were positive for mcr-9 and mcr-10, respectively. The prevalence of mcr-9 in CRECC was significantly higher than that in CSECC (31.8% vs 3.7%, p < 0.001), while the prevalence of mcr-10 in CRECC was significantly lower (0.8% vs 5.5%, p < 0.05). Most mcr-9-positive strains (n=45, 78.9%) exhibited multidrug-resistant phenotype, and four (17.4%) of the mcr-10-positive strains exhibited multi-drug resistance. Coexistence of mcr and carbapenemase genes was commonly observed, including 41 (71.9%) mcr-9-positive strains and one (4.3%) mcr-10-positive strain, and the possibility of co-transfer was confirmed by conjugation experiments. The mcr-positive ECC were highly diverse, while most mcr genes were plasmid-encoded indicating the important role of plasmids on the transmission of mcr in ECC. Furthermore, the expression of mcr-9 was increased after induction by colistin.

CONCLUSIONS

The widespread of mcr genes, as well as its co-transfer with carbapenemase genes among ECC strains, posed an urgent threat to public health.

Outbreak of IncX8 Plasmid-Mediated KPC-3-Producing Enterobacterales Infection, China

Carbapenem-resistant Enterobacterales (CRE) infection is highly endemic in China; Klebsiella pneumoniae carbapenemase (KPC) 2-producing CRE is the most common, whereas KPC-3-producing CRE is rare. We report an outbreak of KPC-3-producing Enterobacterales infection in China. During August 2020-June 2021, 25 bla_KPC-3-positive Enterobacteriale isolates were detected from 24 patients in China. Whole-genome sequencing analysis revealed that the bla_KPC-3 genes were harbored by IncX8 plasmids. The outbreak involved clonal expansion of KPC-3-producing Serratia marcescens and transmission of bla_KPC-3 plasmids across different species. The bla_KPC-3 plasmids demonstrated high conjugation frequencies (10^-3 to 10^-4). A Galleria mellonella infection model showed that 2 sequence type 65 K2 K. pneumoniae strains containing bla_KPC-3 plasmids were highly virulent. A ceftazidime/avibactam in vitro selection assay indicated that the KPC-3-producing strains can readily develop resistance. The spread of bla_KPC-3-harboring IncX8 plasmids and these KPC-3 strains should be closely monitored in China and globally.