Molecular epidemiology of colistin-resistant Enterobacteriaceae in inpatient and avian isolates from China: high prevalence of mcr-negative Klebsiella pneumoniae.

Whether chromosomal and transmissible mechanisms contribute simultaneously to colistin resistance in Klebsiella pneumoniae and Escherichia coli remains unknown. This study aims to identify the underlying mechanisms of colistin resistance in inpatient and avian K. pneumoniae and E. coli in China. We retrospectively screened 2353 Enterobacteriaceae isolates from inpatients at multiple centers during 2011-2014, and 168 avian isolates from one slaughterhouse in 2013 for the presence of MCR-1/MCR-2. Mutations and transcriptional levels of the chromosomal RamA, PhoPQ, and PmrAB genes were determined by PCR and RT-qPCR. The transferability and genetic characteristics of the underlying colistin-resistance genes were detected by conjugation and whole-genome sequencing. The MIC90 for colistin in colistin-resistant K. pneumoniae (ColRKP, 128 mg/L, N = 17) was 16-fold higher than in colistin-resistant E. coli (ColREC, 8 mg/L, N = 33). The dominant sequence types of ColRKP were ST2018 and ST37, whereas ColREC displayed diversity. The chromosomal genes ramA, pmrB, and phoQ were not associated with colistin resistance in ColRKP. The transcriptional levels of PmrB in ColREC were 7.5-fold greater than in colistin-susceptible isolates. The carrying rates of MCR-1 in ColREC and ColRKP were 100% (33/33) and 23.5% (4/17), respectively. Plasmid IncI2 (~60 kb) carrying MCR-1 could be transferred to recipient E. coli EC600 with frequencies ranging from 8.74 × 10-6 to 1.31 × 10-4. No transferable genes were identified in mcr-1-negative ColRKP. MCR-1 combined with upregulated PmrB was associated with low-level colistin resistance in ColREC. However, two-thirds of the ColRKP isolates were mcr-negative and need to be studied further.

Wang X ，Liu Y ，Qi X ，Wang R ，Jin L ，Zhao M ，Zhang Y ，Wang Q ，Chen H ，Wang H ... -  《-》

Prevalence of mcr-1 in Escherichia coli and Klebsiella pneumoniae recovered from bloodstream infections in China: a multicentre longitudinal study.

Quan J ，Li X ，Chen Y ，Jiang Y ，Zhou Z ，Zhang H ，Sun L ，Ruan Z ，Feng Y ，Akova M ，Yu Y ... -  《-》

Prevalence of the colistin resistance gene mcr-1 in colistin-resistant Escherichia coli and Klebsiella pneumoniae isolated from humans in Thailand.

Historically, colistin has been considered a last-line therapeutic option against multidrug-resistant Gram-negative bacterial infections. However, chromosomally-encoded and plasmid-mediated colistin resistance is increasingly being reported worldwide. Spread of the plasmid-borne colistin resistance gene mcr-1 is of great concern since it can be transferred between bacteria. The aim of this study was to investigate the prevalence of mcr-1 in Escherichia coli and Klebsiella pneumoniae collected from human clinical specimens in Thailand during 2014-2017. Minimum inhibitory concentrations (MICs) of colistin were determined by the broth microdilution method for 317 non-duplicate Enterobacteriaceae clinical isolates (37 E. coli and 280 K. pneumoniae). All isolates were screened for the mcr-1 gene by PCR. The colistin MIC50, MIC90 and MIC range for the 37 E. coli isolates were 0.5, 8 and 0.5-32mg/L, respectively. The mcr-1 gene was detected in 11 E. coli isolates (29.7%). Escherichia coli harbouring the mcr-1 gene had a colistin MIC range of 4-32mg/L. The colistin MIC50, MIC90, and MIC range for the 280 K. pneumoniae isolates were 32, >128, and 0.25 to >128mg/L, respectively. The mcr-1 gene was detected in 4 K. pneumoniae isolates (1.4%). Klebsiella pneumoniae harbouring the mcr-1 gene had a colistin MIC range of 4-64mg/L. This is the first report on the prevalence of the mcr-1 gene in colistin-resistant E. coli and K. pneumoniae isolated from humans in Thailand. These data provide added insight into the mechanism of colistin resistance among Enterobacteriaceae pathogens.

Eiamphungporn W ，Yainoy S ，Jumderm C ，Tan-Arsuwongkul R ，Tiengrim S ，Thamlikitkul V ... -  《-》

Colistin resistance in ESBL- and Carbapenemase-producing Escherichia coli and Klebsiella pneumoniae clinical isolates in Cambodia.

Despite the critical importance of colistin as a last-resort antibiotic, limited studies have investigated colistin resistance in human infections in Cambodia. This study aimed to investigate the colistin resistance and its molecular determinants among Extended-spectrum beta-lactamase (ESBL)- and carbapenemase-producing (CP) Klebsiella pneumoniae (K. pneumoniae) and Escherichia coli (E. coli) isolated in Cambodia between 2016 and 2020. E. coli (n = 223) and K. pneumoniae (n = 39) were tested for colistin minimum inhibitory concentration (MIC) by broth microdilution. Resistant isolates were subjected to polymerase chain reaction (PCR) for detection of mobile colistin resistance genes (mcr) and chromosomal mutations in the two-component system (TCS). Eighteen isolates (10 K. pneumoniae and 8 E. coli) revealed colistin resistance with a rate of 5.9% in E. coli and 34.8% in K. pneumoniae among ESBL isolates, and 1% in E. coli and 12.5% in K. pneumoniae among CP isolates. The resistance was associated with mcr variants (13/18 isolates, mcr-1, mcr-3, and mcr-8.2) and TCS mutations within E. coli and K. pneumoniae, with the first detection of mcr-8.2 in Cambodia, the discovery of new mutations potentially associated to colistin resistance in the TCS of E. coli (PhoP I47V, PhoQ N352K, PmrB G19R, and PmrD G85R) and the co-occurrence of mcr genes and colistin resistance conferring TCS mutations in 11 of 18 isolates. The findings highlight the presence of colistin resistance in ESBL- and CP- Enterobacteriaceae involved in human infections in Cambodia as well as chromosomal mutations in TCS and the emergence of mcr-8.2 in E. coli and K. pneumoniae. It underscores the need for continuous surveillance, antimicrobial stewardship, and control measures to mitigate the spread of colistin resistance.

Hide M ，Meng S ，Cheng S ，Bañuls AL ，Ky S ，Yay C ，Laurent D ，Delvallez G ... -  《-》

The prevalence of colistin resistance in Escherichia coli and Klebsiella pneumoniae isolated from food animals in China: coexistence of mcr-1 and bla(NDM) with low fitness cost.

Increasing colistin resistance is a global concern because colistin is used as a last resort for the treatment of carbapenem-resistant Enterobacteriaceae infections. The plasmid-mediated colistin resistance gene, mcr-1 was found in distinct bacterial species isolated from humans, animals, and the environment. In this study, farms in four different agricultural provinces in China were investigated to determine the occurrence of the antimicrobial resistance and related genes. A total of 373 Escherichia coli and 54 Klebsiella pneumoniae were isolated from 510 non-duplicated samples. Of the E. coli and K. pneumoniae isolates, 72.7% and 66.7%, respectively, were susceptible to colistin. Isolates resistant to colistin comprised 46.6% of the samples isolated from Shandong, and 17.8% and 16.4% of the samples from Jilin and Henan, respectively. Twenty-six carbapenem-resistant E. coli isolates were resistant to colistin, in which both mcr-1 and blaNDM were present. Specifically, the co-existence was found in isolates from animals and sewage. Most of the resistance genes were located on plasmids and were 40-244 kilobases. Growth curves of transconjugants carrying mcr-1, blaNDM-1, blaNDM-4, blaNDM-5, and blaNDM-9 showed a low fitness cost compared with the recipient. In conclusion, mcr-1 was widespread in E. coli and K. pneumoniae isolated from farms in China. Co-existence of mcr-1 and blaNDM-9 was identified in different sequence types of E. coli with low fitness cost from various origins, indicating an urgent need to take measures for decreasing dissemination.

Wang R ，Liu Y ，Zhang Q ，Jin L ，Wang Q ，Zhang Y ，Wang X ，Hu M ，Li L ，Qi J ，Luo Y ，Wang H ... -  《-》