The prevalence of different antimicrobial resistance profi les and variants of the Salmonella genomic island 1 (SGI1) was reported for Salmonella enterica serovar Typhimurium DT104 strains isolated from patients in Denmark. Variation in antimicrobial resistance and corresponding changes of SGI1 were shown among isolates from a foodborne outbreak. Phenotypic and genotypic typing methods are important for surveillance and outbreak detection of Salmonella infections. The stability of the markers assessed by the typing method helps identify clusters and the source of outbreaks (1). The phenotypic tests, including antimicrobial-drug resistance profiles and phage typing, are usually considered very stable and therefore often used for surveillance of S. enterica serovar Typhimurium. To obtain the discrimination needed for outbreak investigations, high-discriminatory molecular methods like pulsed-field gel electrophoresis (PFGE) and multiple-locus variable number of tandem repeats analysis (MLVA) are favorable. However, band shifts in PFGE and changes in number of repeat units in MLVA can occur for epidemiologically linked isolates. DT104 is the most prevalent phage type in Denmark, accounting for 21 % of the S. enterica ser. Typhimurium cases in 2006. Most DT104 isolates are resistant to at least ampicillin (A), chloramphenicol (C), streptomycin (S), sulfonamides (Su), and tetracycline (T) (ACSSuT). The 5 resistance genes are found in a multidrug resistance (MDR) region that is located on the chromosome in a region termed Salmonella genomic island 1 (SGI1) (2). Recently, SGI1 has also been found in other Salmonella serovars (3), and several variants of the SGI1 MDR regions have been described (4)
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