Variation in Clonality and Antibiotic-Resistance Genes Among MultiresistantSalmonella entericaSerotypetyphimuriumPhage-Type U302 (MR U302) from Humans, Animals, and Foods

Abstract

Since 1990 multiresistant (MR) Salmonella enterica serotype Typhimurium definitive phage-type (DT) 104 (MR DT104) and closely related phage types have emerged as a worldwide health problem in humans and food animals. In this study the presence of the blaCARB-2 (ampicillin), cmlA (chloramphenicol), aadA2 (streptomycin/spectinomycin), sul1 (sulphonamide), and tetG (tetracycline) resistance genes in isolates of one such phage type, U302, have been determined. In addition blaTEM primers have been used for the detection of TEM-type beta-lactamases. Isolates have also been characterized by plasmid profile and pulsed field gel electrophoresis (PFGE). Thirty-three of 39 isolates were positive for blaCARB-2, cmlA, aadA2, sul1 and tetG, four for blaTEM, aadA2 and sul1, one for aadA2 and sul1, and one for blaTEM only. blaTEM-mediated ampicillin resistance was transferred to Escherichia coli K12 from three isolates along with other resistance markers, including resistance to chloramphenicol, streptomycin, spectinomycin, sulphonamides, and tetracyclines. Strains carried up to 6 plasmids and 34 plasmid profiles were identified. Although the majority of strains (33/39) produced a PFGE profile identical to that predominant in MR DT104, six different patterns were generated demonstrating the presence of various clones within MR U302. The results show that the majority of the MR U302 strains studied possessed the same antibiotic resistance genes as MR DT104. However, isolates with distinctive PFGE patterns can have different mechanisms of resistance to ampicillin, chloramphenicol, streptomycin, sulphonamides, and tetracyclines. Such resistance genes may be borne on transmissible plasmids.

Molecular Characterization of Multidrug-Resistant Salmonella enterica subsp. enterica Serovar Typhimurium Isolates from Swine

“…In addition to DT104, 11 of 14 phage type U302 isolates also exhibited pentaresistance of the AmCmStSuTe type. Genetic characterization also revealed that these U302 isolates carried the same resistance genes that DT104 carries (Table 2), a finding consistent with recent reports (33,42). Although this phage type is infrequently isolated in most present studies, its close relationship to DT104 may signify its potential public health importance.…”

Multiple Genetic Typing of Salmonella enterica Serotype Typhimurium Isolates of Different Phage Types (DT104, U302, DT204b, and DT49) from Animals and Humans in England, Wales, and Northern Ireland

“…In addition to these prevalent clones, a variety of less frequent clones are present within each of the phage types included in the study. The PFGE data suggest a relationship between phage types DT104 and U302 and between phage types DT204b and DT49, which is in agreement with previous reports (4,22,30). It has been reported that the majority of Salmonella serotype Typhimurium strains carry the serotype-specific plasmid of 60 MDa, alone or in combination with other plasmids.…”

Integron content of Salmonella enterica serotype Typhimurium strains isolated in Hungary in the years 1997-1999

“…In contrast, Markogiannikis et al (2000) supposed the existence of 6 clones among Greek DT104 strains, primarily on the basis of PFGE; the dominant type 'A' was carrying the two integrons typical of DT104 (0.9 and 1.1 kb). Various clones of DT104 have been reported also by Walker et al (2001).…”