Prevalence and antimicrobial susceptibility of non-typhoidal Salmonella (NTS) from salad vegetables at farms and retail markets in Terengganu, Malaysia

In recent years, the consumption of vegetables has increased due to their health benefits. There are several foodborne outbreaks related to raw vegetable consumption and nontyphoidal Salmonella (NTS) is one of them. In connection with the worrying issue, this study was conducted to determine the occurrence of NTS from salad vegetables from farms, wet markets and supermarkets, and antimicrobial susceptibility profiling of NTS isolates. Samples were collected from farms (n = 270), wet markets (n = 216) and supermarkets (n = 180) in Kuala Terengganu and Kuala Nerus, Terengganu. The samples were analysed according to International Standard protocol ISO 6579:2002(E) and serotyping was performed by Ipoh Public Health Laboratory, Perak. The isolated NTS from the samples were tested resistant against 20 antibiotics of clinical and agricultural importance. Out of 666 samples analyzed, 58 (8.71%) samples were NTS positive. The prevalence of NTS in samples from farms, wet markets and supermarkets were found to be 2.96% (n = 8), 20.37% (n = 44) and 3.33% (n = 6), respectively. The serotyping analysis had identified 23 NTS serovars, the most predominant was Salmonella enterica serovar Weltevreden (20.69%), followed by Salmonella enterica serovar Albany (10.34%), Salmonella enterica serovar Hvittingfoss (8.62%) and Salmonella enterica serovar Aberdeen (6.90%). Among the isolates, 34.48% (20/58) showed resistance toward at least one antibiotic tested with 95% of them were the isolates from wet markets. Resistances among isolates were observed in the highest rate for ampicillin (20.69%), followed by tetracycline (18.97%), doxycycline (17.24%), trimethoprim-sulfamethoxazole (17.24%) and chloramphenicol (15.52%). Multidrug-resistant (MDR) characteristic was found in six serovars and S. enterica serovar Albany represents the highest prevalence of 83.33%. One and two isolates were also found resistant toward ertapenem and colistin (last resort antibiotics), respectively. Based on the findings, salad vegetables can be considered as one of the important vehicles of MDR NTS to cause salmonellosis in humans. The wet market shows a significant risk of transmitting MDR NTS through vegetables. Thus, it is important to have proper handling to prevent cross-contamination of Salmonella in vegetables.