Abstract
Food-producing animals are the major reservoir for Salmonella infections in humans. Salmonella contamination and spread of antimicrobial resistance genes can occur during the production chain of animal products. The aims of this study were to investigate antimicrobial resistance patterns and compare the proportions of multidrug resistance and the presence of mobile colistin resistance (mcr) genes, mcr-1, mcr-2 and mcr-3, among Salmonella isolates which were recovered from pork at two different standard practice slaughterhouses and retails during 2014-2017 in Thailand. Salmonella isolates recovered from good standard practice slaughterhouses (GSH, n=75), below standard practice slaughterhouses (BSH, n=75), good standard practice retails (GRT, n=75) and below standard practice retails (BRT, n=75) were examined for their antimicrobial resistance patterns and the existence of mcr-1 to mcr-3 genes. Salmonella strains of the 4 origins showed similar resistance rates to almost all antimicrobial agents tested. BRT origin (33/75, 44%) had slightly higher proportion of MDR Salmonella than the others group with no statistical difference. Five MDR Salmonella isolates carrying the mcr-3 gene were detected among isolates of all origins, while only 4 isolates (1.33%) displayed colistin resistance phenotype (MIC 4-8 ug/mL). This study revealed that MDR Salmonella isolates have widely spread in both standard and low hygiene practice slaughterhouses and retails. This is the first report of mcr-3 positive MDR Salmonella isolates from pork in Thailand. Effective monitoring program in slaughterhouses and retails should be continually implemented to reduce the contamination of MDR Salmonella carrying the mcr gene to consumers.
Highlights
Salmonella spp. has been recognized over more than a century as a major and serious foodborne pathogen causing global morbidity and mortality in humans (Scallan et al, 2011)
This study demonstrated the presence of colistin resistance in Salmonella isolates in pork from the two different types of slaughterhouses and retails in Thailand, where colistin is used in pigs under veterinary supervision
This is the first report of mcr-3 positive MDR Salmonella isolates from pork in Thailand despite at the low percentage
Summary
Salmonella spp. has been recognized over more than a century as a major and serious foodborne pathogen causing global morbidity and mortality in humans (Scallan et al, 2011). Like other countries (Majowicz et al, 2010; Evangelopoulou et al, 2014), most foodborne disease outbreaks in Thailand have been caused by Salmonella spp. and most Salmonella outbreaks are associated with ingestion of contaminated livestock products (Chanachai et al, 2008). The emergence of multidrug-resistant (MDR) Salmonella has been continuously reported during the past few years which included the isolates from chicken and pork meats (Phongaran, et al, 2019; Vidayanti et al 2021). Resistance to colistin, the last-line treatment of multidrug-resistant Gram-negative bacterial infections, in Salmonella isolates from animal-based products has been frequently reported in several countries worldwide, including Germany, Spain (EFSA and ECDC, 2019), Portugal (Campos et al, 2016), China (Zhang et al, 2018) and Thailand (Sinwat et al, 2016). The occurrence of MDR and colistin resistant Salmonella in animal products poses a potential threat to humans since it may lead to increased severity of foodborne illness, and higher rates of hospitalization and death (Crump et al, 2015)
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