Vietnam: study shows high levels of drug resistance Salmonella in pork

Research published on Frontiers in Veterinary Sciences found high levels of antimicrobial resistance in porcine Salmonella in Vietnam. The researchers raised particular concerns regarding the emergence of colistin resistance since colistin is the last defence antibiotics against multi-drug resistant Gram-negative pathogens like Salmonella.  

The study assessed the antibiotic resistance of 69 gene samples of non-typhoidal Salmonella (NTS), which are collected from the pork retail outlets and slaughterhouses in Vietnam in 2014 and 2018/19. The isolates came from the PigRISK project, carried out from 2012 to 2017, and the SafePORK project, from 2017 to 2022, which aims at reducing the burden of foodborne illness in Vietnam. The study also explores the roles of slaughterhouses and retail outlets such as supermarkets, traditional markets, and convenience stores in ensuring food safety regarding pork.  

High levels of antimicrobial resistance (AMR) are a prominent problem in Vietnam, where pork consumption accounts for more than 70% of all meats consumed. AMR is the ability of microorganisms such as fungi, viruses, parasites, and bacteria to resist antimicrobial treatments. It happens when these microbes are exposed to antimicrobial drugs, i.e. antibiotics, over time. AMR is a natural process yet has been accelerated by the misuse and overuse of antimicrobials in the past two decades, becoming a significant global challenge nowadays. It makes treatments ineffective, posing a serious risk to public health, and consequently causes a great economic burden.  

The researchers used phenotypic testing and whole-genome sequencing to investigate the serotype and AMR gene profiles of the 69 NTS isolates. They analyzed multi-drug resistance levels of the pathogen – when it shows resistance to different antimicrobials – and looked for mobilized colistin resistance (mcr) genes, which can give high-level resistance to the last-resort antibiotic colistin. As a result, mcr-1 was identified in seven isolates and mcr-3 in two isolates. Besides colistin, high levels of AMR have also been found to ampicillin, tetracycline, piperacillin and several other antibiotics that are considered to be vital in the treatment of human diseases according to the World Health Organization.  

Multi-drug resistance strains were most common in slaughterhouses (83%) and supermarkets (75%) and lowest in traditional markets (38%) and convenience stores (40%). Surprisingly, the findings showed high levels of multi-drug resistance (60%), including 5/20 isolates with mcr-1, in samples from boutique stores, where pork is claimed to be high quality, traceable, and environmental-friendly marketed toward higher income consumers.