Genetic analysis of multidrug-resistant Salmonella enterica serovars Stanley and Typhimurium from cattle.
During 2005-2008, a longitudinal study was conducted in southern Japan to detect and characterize multidrug-resistant Salmonella enterica serovars recovered from cattle diagnostic specimens. Determination of antimicrobial resistance phenotypes and genotypes, identification of Salmonella genomic island 1 (SGI1), detection of virulence genes, plasmid analysis, conjugal transfer experiments, and sequencing of class 1 integrons were conducted. Multidrug-resistant Salmonella detected were serovars Stanley, Typhimurium, and O4:d. Salmonella Stanley isolates exhibited resistance to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, oxytetracycline, trimethoprim, and kanamycin (ACSSuT+) encoded by bla(TEM), catA, aadA2, tetA, sul1, dfrA12, and aphA1 genes, respectively. Sequencing analysis revealed that aadA2 and dfrA12 were integrated as gene cassettes within the class 1 integrons of 1.5kb size. Importantly, the isolates harboured easily transferable plasmids of ca. 210kb with the potential of transmitting resistance phenotype and genotype detected in the donor isolates. Moreover, Salmonella Typhimurium DT104 isolates with typical SGI1 were detected and presented ACSSuT+ resistance phenotype encoded by bla(PSE-1) and bla(TEM); floR; aadA1; sul1; and tetA and tetG, respectively. Salmonella Typhimurium isolates carried plasmids of variable sizes ranging from 3.5 to 100 kb with DT104 isolates harbouring plasmids of ca. 90 kb. Salmonella serovar O4:d had ACSSuT+ resistance phenotype mediated by bla(TEM), catA, aadA1, sul1, tetA, and aphA1 genes. A virulence gene invA was found in all multidrug-resistant Salmonella Typhimurium, Stanley and O4:d clinical isolates. In conclusion, this is the first report describing the occurrence of multidrug-resistant Salmonella Stanley from bovine species. The emergence of Salmonella Stanley isolates exhibiting plasmid-encoded high-level multidrug resistance is an important health concern because this new pathogenecity was associated with mortality in cattle.
Dahshan H
，Shahada F
，Chuma T
，Moriki H
，Okamoto K
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Genetic analysis of multiple antimicrobial resistance in Salmonella isolated from diseased broilers in Egypt.
To date, no information has been available on the molecular bases of antimicrobial resistance in Salmonella spp. from poultry in Egypt or even in Africa. Therefore, the objective of this study was to analyze, at the molecular level, the mechanisms of multidrug-resistance in isolates of Salmonella recovered from diseased broilers in Egypt. Twenty-one Salmonella isolates were identified; 13 of these isolates were Salmonella enterica serovar Enteritidis and eight Salmonella enterica serovar Typhimurium. 17 (81%). Salmonella isolates displayed multidrug resistance phenotypes, particularly against ampicillin, streptomycin, spectinomycin, kanamycin, tetracycline, chloramphenicol, and trimethoprim/sulfamethoxazole. PCR and DNA sequencing identified class 1 integrons in nine (42.9%) isolates and class 2 integrons in three (14.3%) isolates. The identified resistance genes within class 1 integrons were aminoglycoside adenyltransferase type A, aadA1, aadA2 and aadA5 and dihydrofolate reductase type A, dfrA1, dfrA5, dfrA12, dfrA15 and dfrA17. The β-lactamase encoding genes bla(TEM-1) and bla(CMY-2) and florfenicol resistance gene floR were also identified. Furthermore, the tetracycline resistance gene tet(A) was identified in 14 (66.7%) Salmonella isolates. To the best of our knowledge, this is the first report of the molecular basis of antimicrobial resistance in Salmonella spp. isolated from poultry in Africa.
Ahmed AM
，Shimamoto T
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Characterization of integrons and resistance genes in multidrug-resistant Salmonella enterica isolated from meat and dairy products in Egypt.
Foodborne pathogens are a leading cause of illness and death, especially in developing countries. The problem is exacerbated if bacteria attain multidrug resistance. Little is currently known about the extent of antibiotic resistance in foodborne pathogens and the molecular mechanisms underlying this resistance in Africa. Therefore, the current study was carried out to characterize, at the molecular level, the mechanism of multidrug resistance in Salmonella enterica isolated from 1600 food samples (800 meat products and 800 dairy products) collected from different street venders, butchers, retail markets and slaughterhouses in Egypt. Forty-seven out of 69 isolates (68.1%) showed multidrug resistance phenotypes to at least three classes of antimicrobials. The incidence of multidrug-resistant isolates was higher in meat products (37, 69.8%) than in dairy products (10, 62.5%). The multidrug-resistant serovars included, S. enterica serovar Typhimurium (24 isolates, 34.8%), S. enterica serovar Enteritidis, (15 isolates, 21.8%), S. enterica serovar Infantis (7 isolates, 10.1%) and S. enterica non-typable serovar (1 isolate, 1.4%). The highest resistance was to ampicillin (95.7%), then to kanamycin (93.6%), spectinomycin (93.6%), streptomycin (91.5%) and sulfamethoxazole/trimethoprim (91.5%). PCR and DNA sequencing were used to screen and characterize integrons and antibiotic resistance genes and 39.1% and 8.7% of isolates were positive for class 1 and class 2 integrons, respectively. β-lactamase-encoding genes were identified in 75.4% of isolates and plasmid-mediated quinolone resistance genes were identified in 27.5% of isolates. Finally, the florphenicol resistance gene, floR, was identified in 18.8% of isolates. PCR screening identified S. enterica serovar Typhimurium DT104 in both meat and dairy products. This is the first study to report many of these resistance genes in dairy products. This study highlights the high incidence of multidrug-resistant S. enterica in meat and dairy products in Egypt, with the possibility of their transfer to humans leading to therapeutic failure. Therefore, the overuse of antibiotics in animals should be drastically reduced in developing countries.
Ahmed AM
，Shimamoto T
，Shimamoto T
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