Detection of multidrug-resistant Salmonella enterica serotype typhimurium DT104 based on a gene which confers cross-resistance to florfenicol and chloramphenicol

Salmonella enterica serotype typhimurium (S. typhimurium) DT104 (DT104) fir st emerged as a major pathogen in Europe and is characterized by its pentad rug-resistant pattern. It has also been associated with outbreaks in the Un ited States. The organism typically carries resistance to ampicillin, chlor amphenicol, streptomycin, sulfonamides, and tetracycline. The mechanism of chloramphenicol resistance in DT104 Has determined by producing antibiotic- resistant Escherichia call host strain clones from DT104 DNA, DNA from chlo ramphenicol-resistant clones was sequenced, and probes specific for the gen es flo(S. typhmurium) (flo(St)), int, invA, and spvC Here produced for colo ny blot hybridizations. One hundred nine Salmonella isolates, including 44 multidrug-resistant DT104 isolates, were tested to evaluate the specificiti es of the probes. The gene flo(St), reported in this study, confers chloram phenicol and florfenicol resistance on S. typhimurium DT104. Florfenicol re sistance is unique to S. typhimurium DT104 and multidrug-resistant S. typhi murium isolates with the same drug resistance profile among ail isolates ev aluated. Of 44 DT104 isolates tested, 98% were detected based on phenotypic florfenicol resistance and 100% had the flo(St)-positive genotype, Resista nces to Borfenicol and chloramphenicol are conferred by the gene flo(St), d escribed in this paper. Presumptive identification of S. typhimurium DT104 can be made rapidly based on the presence of the flo(St) gene or its result ing phenotype.