Molecular characterization of Irish Salmonella enterica serotype typhimurium: Detection of class I integrons and assessment of genetic relationships by DNA amplification fingerprinting

Salmonella enterica is among the principal etiological agents of food-borne illness in humans. Increasing antimicrobial resistance in S. enterica is a cause for worldwide concern. There is concern at present in relation to th e increasing incidence of human infection with antimicrobial agent-resistan t strains of S. enterica serotype Typhimurium, in particular of phage type DT104. Integrons appear to play an important role in the dissemination of a ntimicrobial resistance genes in many Enterobacteriaceae including S. enter ica. In this study the antimicrobial susceptibilities and phage types of 74 randomly collected strains of S. enterica serotype Typhimurium from the Co rk region of southern Ireland, obtained from human, animal (clinical), and food sources, were determined. Each strain was examined for integrons and t yped by DNA amplification fingerprinting (DAF). Phage type DT104 predominat ed (n = 48). Phage types DT104b (It = 3), -193 (n = 9), -195 (n = 6), -208 (n = 3), -204a (n = 2), PT U302 (n = 1), and two nontypeable strains accoun ted for the remainder. All S. enterica serotype Typhimurium DT104 strains w ere resistant to ampicillin, chloramphenicol, streptomycin, Sulfonamide Dup lex, and tetracycline, and one strain was additionally resistant to trimeth oprim. All DT104 strains but one were of a uniform DAF type (designated DAF -I) and showed a uniform pattern of integrons (designated LP-I). The DT104b and PT U302 strains also exhibited the same resistance phenotype, and both had the DAF-I and IF-I patterns. The DAF-I pattern was also observed in a single DT193 strain in which no integrons were detectable. Greater diversit y of antibiograms and DAF and IP patterns among non-DT104 phage types was o bserved. These data indicate a remarkable degree of homogeneity at a molecu lar level among contemporary isolates of S. enterica serotype Typhimurium D T104 from animal, human, and food sources in this region.