Antimicrobial Resistance and Phylogenetic Analysis of Multidrug-Resistant Non-Typhoidal Salmonella Isolates from Different Sources in Southern Vietnam

<b>Background/Objectives:</b> Non-typhoidal <i>Salmonella</i> (NTS) is one of the most common causative agents of food poisoning in Vietnam, and contaminated livestock meat poses a major risk to human health. The present study aims to provide the genetic characteristics of NTS with a particular focus on antimicrobial resistance and determine phylogenetic relationships between isolates from different sources in Southern Vietnam based on whole-genome sequencing (WGS) data. <b>Methods:</b> A total of 49 NTS isolates from pork/broiler meat, pigs, chickens, and humans were collected in Ho Chi Minh City and four provinces of Southern Vietnam. Phenotypic antimicrobial susceptibility testing (AST) and WGS for all isolates were performed. <b>Results</b>: As a result, 14 different serotypes were identified, among which <i>S.</i> Typhimurium and its monophasic variant were the dominant serotypes for human and pig sources. All chicken samples belonged to <i>S</i>. Indiana, whereas <i>S</i>. Infantis predominated in broiler meat. AST results revealed that 98% of isolates were multidrug resistant. NTS strains isolated from poultry and pigs exhibited resistance to the highest priority antimicrobials-quinolones and polymyxin, as well as to β-lactams, aminoglycosides, tetracycline, and sulfonamide, which are considered to be critical for the treatment of severe diseases. <b>Conclusions:</b> The results highlight the utmost importance of issues related to the selection, spreading, and transmission of multi-resistant strains from animals to humans.