title: Characterization of multiple-antimicrobial-resistant salmonella serovars isolated from retail meats.
abstract: A total of 133 Salmonella isolates recovered from retail meats purchased in the United States and the People's Republic of China were assayed for antimicrobial susceptibility, the presence of integrons and antimicrobial resistance genes, and horizontal transfer of characterized antimicrobial resistance determinants via conjugation. Seventy-three (82%) of these Salmonella isolates were resistant to at least one antimicrobial agent. Resistance to the following antibiotics was common among the United States isolates: tetracycline (68% of the isolates were resistant), streptomycin (61%), sulfamethoxazole (42%), and ampicillin (29%). Eight Salmonella isolates (6%) were resistant to ceftriaxone. Fourteen isolates (11%) from the People's Republic of China were resistant to nalidixic acid and displayed decreased susceptibility to ciprofloxacin. A total of 19 different antimicrobial resistance genes were identified in 30 multidrug-resistant Salmonella isolates. The bla(CMY-2) gene, encoding a class A AmpC beta-lactamase, was detected in all 10 Salmonella isolates resistant to extended-spectrum beta-lactams. Resistance to ampicillin was most often associated with a TEM-1 family beta-lactamase gene. Six aminoglycoside resistance genes, aadA1, aadA2, aacC2, Kn, aph(3)-IIa, and aac(3)-IVa, were commonly present in the Salmonella isolates. Sixteen (54%) of 30 Salmonella isolates tested had integrons ranging in size from 0.75 to 2.7 kb. Conjugation studies demonstrated that there was plasmid-mediated transfer of genes encoding CMY-2 and TEM-1-like beta-lactamases. These data indicate that Salmonella isolates recovered from retail raw meats are commonly resistant to multiple antimicrobials, including those used for treating salmonellosis, such as ceftriaxone. Genes conferring antimicrobial resistance in Salmonella are often carried on integrons and plasmids and could be transmitted through conjugation. These mobile DNA elements have likely played an important role in transmission and dissemination of antimicrobial resistance determinants among Salmonella strains.
authors.affiliation: Department of Nutrition and Food Science, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Sheng
authors.initials: S
authors.lastname: Chen
authors.forename: Shaohua
authors.initials: S
authors.lastname: Zhao
authors.forename: David G
authors.initials: DG
authors.lastname: White
authors.forename: Carl M
authors.initials: CM
authors.lastname: Schroeder
authors.forename: Ran
authors.initials: R
authors.lastname: Lu
authors.forename: Hanchun
authors.initials: H
authors.lastname: Yang
authors.forename: Patrick F
authors.initials: PF
authors.lastname: McDermott
authors.forename: Sherry
authors.initials: S
authors.lastname: Ayers
authors.forename: Jianghong
authors.initials: J
authors.lastname: Meng
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics; D002681:China; D003227:Conjugation, Genetic; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D022761:Gene Transfer, Horizontal; D032023:Integrons; D008460:Meat / Q000382:microbiology*; D008826:Microbial Sensitivity Tests; D012475:Salmonella / Q000145:classification* / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D012481:Salmonella Infections, Animal / Q000382:microbiology; D012703:Serotyping; D014481:United States
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins