Abstract
Nontyphoidal Salmonella, an important zoonotic pathogen and a major cause of foodborne illnesses, could be a potential reservoir of plasmids harbouring mobile colistin resistance gene (mcr). This study reported, for the first time, a high rate of mcr-carrying Salmonella clinical isolates (3.3%, 24/724) in Thailand, associated with mcr-3 gene (3.0%, 22/724) in S. 4,[5],12:i:-(15.4%, 4/26), S. Typhimurium (8.8%, 5/57), and S. Choleraesuis (5.6%, 13/231). Remarkably, the increasing trends of colistin and extended-spectrum cephalosporin resistances have displayed a high agreement over the years, with a dramatic rise in the mcr-carrying Salmonella from 1.1% (6/563) during 2005–2007 to 11.2% (18/161) during 2014–2018 when CTX-M-55 became abundant. Clonal and plasmid analysis revealed that the self-transferable IncA/C and a novel hybrid IncA/C-FIIs MDR plasmids were the major vehicles to disseminate both mcr-3 and blaCTX-M55 genes among diverse Salmonella strains, from as early as 2007. To our knowledge the occurrence of mcr-3 and the co-existence of it with blaCTX-M-55 in S. Choleraesuis are reported here for the first time, leading to clinical concern over the treatment of the invasive salmonellosis. This study provides evidence of the potential reservoirs and vectors in the dissemination of the mcr and highlights the co-selection by colistin and/or cephalosporins.
Highlights
Nontyphoidal Salmonella, an important zoonotic pathogen and a major cause of foodborne illnesses, could be a potential reservoir of plasmids harbouring mobile colistin resistance gene
These bacteria are resistant to a large number of antimicrobials, especially to carbapenems and extended-spectrum cephalosporins (ESCs) that are the best available antibiotics for treating multi-drug resistant (MDR) Gram-negative bacteria
Considering that the combination of these genes could speed up the dissemination of MDR and extensively drug resistance (XDR) among Gram-negative bacteria, information regarding the co-occurrence and emergence of mcr and extended-spectrum beta-lactamases (ESBLs) genes among the isolates are needed
Summary
Nontyphoidal Salmonella, an important zoonotic pathogen and a major cause of foodborne illnesses, could be a potential reservoir of plasmids harbouring mobile colistin resistance gene (mcr). The World Health Organisation published a catalogue of 12 families of antimicrobial-resistant bacteria that pose the greatest threat to human h ealth[1] These bacteria are resistant to a large number of antimicrobials, especially to carbapenems and extended-spectrum cephalosporins (ESCs) that are the best available antibiotics for treating multi-drug resistant (MDR) Gram-negative bacteria. This leads to the use of colistin, a widely used antimicrobial in animal production for decades, as one of the last-resort therapeutic options[2]. In contrast to the extensive studies focused on E. coli, there is only limited data available for mcr-harbouring Salmonella isolates and data on the plasmids carrying mcr genes responsible for the spread of colistin resistance. We aimed to assess the dissemination mechanism of colistin resistance among Salmonella isolates, and the co-occurrence of mcr and ESBL genes in Salmonella clinical isolates in Thailand, the AMR mechanisms, clonality, and plasmid profiles of the isolates, as well as the transferability and characteristics of the resistance plasmids were investigated
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