Colistin resistance and plasmid-mediatedmcrgenes inEscherichia coliandSalmonellaisolated from pigs, pig carcass and pork in Thailand, Lao PDR and Cambodia border provinces

Abstract

Background Colistin and carbapenem-resistant bacteria have emerged and become a serious public health concern, but their epidemiological data is still limited. Objectives This study examined colistin and carbapenem resistance in Escherichia coli and Salmonella from pigs, pig carcasses, and pork in Thailand, Lao PDR, and Cambodia border provinces. Methods The phenotypic and genotypic resistance to colistin and meropenem was determined in E. coli and Salmonella obtained from pigs, pig carcasses, and pork (n = 1,619). A conjugative experiment was performed in all isolates carrying the mcr gene (s) (n = 68). The plasmid replicon type was determined in the isolates carrying a conjugative plasmid with mcr by PCR-based replicon typing (n = 7). The genetic relatedness of mcr -positive Salmonella (n = 11) was investigated by multi-locus sequence typing. Results Colistin resistance was more common in E. coli (8%) than Salmonella (1%). The highest resistance rate was found in E. coli (17.8%) and Salmonella (1.7%) from Cambodia. Colistin-resistance genes, mcr-1 , mcr-3 , and mcr-5 , were identified, of which mcr-1 and mcr-3 were predominant in E. coli (5.8%) and Salmonella (1.7%), respectively. The mcr-5 gene was observed in E. coli from pork in Cambodia. Two colistin-susceptible pig isolates from Thailand carried both mcr-1 and mcr-3 . Seven E. coli and Salmonella isolates contained mcr-1 or mcr-3 associated with the IncF and IncI plasmids. The mcr -positive Salmonella from Thailand and Cambodia were categorized into two clusters with 94%–97% similarity. None of these clusters was meropenem resistant. Conclusions Colistin-resistant E. coli and Salmonella were distributed in pigs, pig carcasses, and pork in the border areas. Undivided-One Health collaboration is needed to address the issue.

Low Level of Colistin Resistance and mcr Genes Presence in Salmonella spp.: Evaluation of Isolates Collected between 2000 and 2020 from Animals and Environment

“…Regarding mobile colistin-resistance genes, few isolates scored positive (5.93%) for one or more genes. This finding is in agreement with other studies reporting a percentage of mcr -positive Salmonella strains ranging between 0.6% and 3.3% [ 15 , 17 , 18 , 19 , 29 ]. The slightly higher positivity detected in our survey may be related to the extended set of investigated genes.…”

“…In our study, the percentage of colistin-resistant strains was 17.79%, which is slightly higher than the data reported in recent literature. Recent surveys registered percentages of colistin-resistant Salmonella strains ranging between 1% and 12% [ 15 , 17 , 18 , 29 , 30 ]. These differences may be due to many factors: source, geographic area, and serotype.…”

“…Phenotypic resistance to colistin in Salmonella is variable in relation to serotypes, year of isolation, source (humans, animals, food, and environment), and geographic area. However, percentages of resistant strains are generally low, ranging between about 1% and 12% [ 15 , 16 , 17 , 18 ], with some exceptions (40%) [ 19 ]. The gene mcr-1 was the most frequently detected in Salmonella , but mcr-2 , mcr-3 , mcr-4 , mcr-5 , and mcr-9 were also detected [ 20 ].…”

“…However, detection rate of mcr -positive Salmonella strains is generally low [ 17 , 18 , 21 ], with some exceptions [ 22 ]. As reported for other bacteria, the direct relation between the presence of mcr genes and colistin resistance in Salmonella has not been fully clarified; these genes have also been found in susceptible strains [ 15 ], and, frequently, only a small number of resistant strains carry these genes [ 16 , 17 , 18 ], suggesting other mechanisms of resistance [ 2 ]. In S. enterica , different chromosomally encoded mechanisms were identified as conferring resistance to colistin.…”

Antibiotic resistant Escherichia coli from diarrheic piglets from pig farms in Thailand that harbor colistin-resistant mcr genes

“…Bacteria carrying mcr gene have been found in humans and animals in many countries. Recently, it has been demonstrated that E. coli strains carrying mcr-1 and mcr-3 genes were found not only in pig feces, but also from contaminated pig carcasses and pork 30 , 31 . This indicates a high risk of spreading bacteria-harboring mcr genes to humans and other environments.…”