Molecular characterization of Thai Salmonella enterica serotype typhimurium and serotype 4,5,12:i:- reveals distinct genetic deletion patterns.

In order to better understand the relationship between Salmonella serotypes Typhimurium and its monophasic variant 4,5,12:i:- found in Thailand, a total of 138 isolates from various sources were characterized using different molecular subtyping methods (i.e., pulsed-field gel electrophoresis [PFGE] and polymerase chain reaction [PCR]) and antibiotic resistance (AbR) patterns. PFGE revealed 52 distinct band patterns among these isolates, 3 of which were shared between the two serotypes. PCR characterization of genomic deletion patterns reveals that Thai S. 4,5,12:i:- isolates contain a distinct deletion pattern in the fljAB region, which can be used as a specific genetic marker for primary identification of S. 4,5,12:i:- sources. AbR study shows that, among 50 representative serotype-confirmed strains, 48.28% (14/29) of Salmonella Typhimurium and 90.48% (19/21) of 4,5,12:i:- isolates are multidrug-resistant Salmonella as they are resistant to at least 3 antimicrobial categories. The AmpST pattern for resistance to ampicillin, streptomycin, and tetracycline was found in high proportions of Salmonella Typhimurium (10 of 29) and S. 4,5,12:i:- (15 of 21) isolates.