Analysis of antimicrobial resistance in Non-typhoidal Salmonella collected from pork retail outlets and slaughterhouses in Vietnam using whole genome sequencing

Non-Typhoidal Salmonella (NTS) remains a significant health burden worldwide. In Vietnam, pork accounts for 70% of the total meat consumed and contamination with Salmonella is high. Until recently, antimicrobials were commonly used as a component of commercial pig feeds and as a result, high levels of antimicrobial resistance (AMR) have emerged amongst porcine NTS. Of particular concern is the emergence of colistin resistance, a 'last defence' drug against multi-drug resistant gram-negative pathogens. This study aimed to investigate the AST profiles of 49 NTS isolates collected from the pork production chains in in Northern Vietnam, and use whole genome sequencing to assess the serotype and AMR gene profiles of the isolates, with a particular focus on colistin resistance and the prevalence of mcr genesFourteen different serotypes were identified, of which S. Typhimurium (27%), S. London (12%) and S. Anatum (10%) were the most common. Phenotype AMR was common with 41 isolates having resistance to at least one antimicrobial and 57.1% of isolates were multi-drug resistant. Resistance to ampicillin (65.3%), tetracycline (57.1%) and trimethoprim (55.1%) were most common. Eight isolates were colistin resistant, of these, two carried mcr-1 and two carried mcr-3.Analysis of NTS from pork value chain show high levels of multi-drug antimicrobial resistance within slaughterhouses and on wet market meat products. Concerning was the presence high level colistin resistance including two different mcr genotypes in four isolates.