Epidemiological dynamic of salmonella on human-animals-environment interface in the Middle Mekong Basin Area

Abstract

Salmonella is one of the most frequently reported causes of bacterial foodborne outbreaks in the world. Along with the direct effects Salmonella spp. have on the gastrointestinal tract, evidence of drug resistance is also a major public health concern. The surrounding areas of the middle Mekong basin, particularly along the border between Thailand and Lao People’s Democratic Republic (Lao PDR), are high-risk areas for many livestock-associated foodborne illnesses, especially salmonellosis. Multilocus sequence typing (MLST), Molecular technique typing, is obviously and accurately differentiates the genotypic diversity of bacteria. It can easily be compared through the technique from different laboratories. Objective of this study was to determine the prevalence and characteristics of Salmonella spp. contamination in pork, beef, chicken meats and raw vegetables sold at retail markets in the Thailand-Laos border area surrounding the Thai-Lao Friendship Bridge I and to an overview of the role of vegetables as a concern of Salmonella circulating in Vientiane capital, the Lao People's Democratic Republic (Lao PDR). All of 450 samples were purchased from pork, chicken, beef and raw vegetables in five retail markets in Vientiane Capital, Lao PDR and six retail markets in Nong Khai Province, Thailand during the period of January to May 2019. From a total of 370 meat samples collected, 63% were positive for Salmonella, with the prevalence of 73%, 60% and 56% from pork, beef and chicken meat samples, respectively. Of all the positive samples, 53 serotypes were identified. Of these, Salmonella enterica serovar London accounted for the majority (27%), followed by serovars Corvallis (14%), and Rissen (6%). Resistance against tetracycline was found at the highest frequency (50%), followed by ampicillin (35%) and sulfamethoxazole-trimethoprim (28%). The prevalence, serotype, antimicrobial resistance pattern and genetic profile of Salmonella were investigated. In this study, a total of 80 vegetable samples were collected. Positive of 26 (32.5%) isolates consisting of 13 different serotypes were determined. S. Corvallis was the most common serotype detected (4/26; 15.4%). Six (23.1%) isolates were found to be resisted against ampicillin, and five (19.2%) isolates resisted to sulfamethoxazole-trimethoprim, tetracycline and amoxicillin-clavulanic acid. MLST revealed no evidence of shared genetic relatedness of Salmonella at retail sites among Thailand-Laos border zone. However, a diverse range of Salmonella genotypes were spread over the area. Besides, the persistence of the residential pathogen and sharing of the supply route within country can be inferred. In addition, a genetic comparison of the vegetable-originated Salmonella with the isolates recovered from hospitalized patients and meats for consumption was carried out using Multilocus sequence typing (MLST). Identical clones of “ST469-S. Rissen” derived from humans, meats and vegetable were evidenced. The inter-species transmission between hosts highlights an alarming possible trend of human-food interface in salmonellosis in Vientiane capital. Given the high levels of contamination of retail meats, regular disinfecting of all working areas and quality control checking at pre-retail stage must be applied to reduce the transmission of Salmonella and other foodborne pathogens to consumers. addition more, educating individuals on hygienic practices should be recommended. Likewise, intersectoral collaborations should be pay more attention to this issue and scale-up interventions to the entire of food chain at the policy level for successful salmonellosis control.