Antimicrobial susceptibility of Salmonella isolated from various products, from 1999 to 2003.

Foodborne salmonellosis continues to be a major health concern worldwide; thus, detection and tracking of antimicrobial resistance in Salmonella isolates is of interest. The U.S. Food and Drug Administration initiated antimicrobial sensitivity screening of Salmonella isolates from food and related samples in 1999. This paper summarizes the antimicrobial resistance data for Salmonella isolates obtained from 1999 to 2003. A total of 22,231 imported and domestic samples were analyzed for Salmonella, of which 1,319 (5.9%) yielded the pathogen. Since more than one culture was isolated from some samples, the total number of isolates obtained and tested for antimicrobial sensitivity was 1,382. Antimicrobial sensitivity screening was performed with the disc diffusion assay on 11 antimicrobial agents. Of the 1,108 food isolates screened, 42.1% (n = 467) were serotypes Weltevreden, Newport, Lexington, Senftenberg, Typhimurium, Saint Paul, Paratyphi, Enteritidis, Thompson, and Bareilly. A total of 249 (18.0%) isolates from all sources were resistant to two or more antimicrobials. Resistance to sulfisoxazole, streptomycin, and tetracycline was most common, whereas resistance to ciprofloxacin was least common. Weltevreden (n = 148) was the most common serotype isolated from food, but only nine (6.1%) of these isolates were resistant to two or more antimicrobials. In contrast, although Derby was recovered only 19 times, 11 (57.9 %) of these isolates were resistant to two or more antimicrobials. Of the 274 isolates from animal feed, dog treats and environmental swabs, 49.6% (n = 136) belonged to serotypes Infantis, Mbandaka, Anatum, Senftenberg, Typhimurium, Montevideo, Cerro, Enteritidis, and Bredeney, with 76 (27.7%) of these isolates resistant to two or more antimicrobials. Only limited trends in antimicrobial resistance were observed over time, with resistance to sulfisoxazole increasing, resistance to tetracycline decreasing, and resistance to streptomycin fluctuating.

Antimicrobial resistance of food-related Salmonella isolates, 1999-2000.

Salmonellosis is a major foodborne infection in the United States, and strains of Salmonella that are resistant to a variety of antimicrobial agents have become a major public health concern. To estimate the incidence of antimicrobial-resistant Salmonella in our food supply, the U.S. Food and Drug Administration (FDA) has initiated screening of foodborne isolates for sensitivity to antimicrobial agents, including several antibiotics. Salmonella cultures (n = 502) isolated by FDA laboratories during fiscal year 2000 (1 October 1999 through 30 September 2000) from domestic and imported food products and related samples were tested for susceptibility to each of 12 antimicrobial agents using a disc diffusion assay. Because all isolates were resistant to rifampin (5 or 25 microg), only results with the remaining 11 antimicrobial agents are discussed in this paper. Of the 502 isolates, 247 (49.2%) were resistant to one or more antimicrobial agents, and of these 247 isolates, 170 (68.8%) were resistant to one antimicrobial agent, 33 (13.4%) to two antimicrobial agents, 25 (10.1%) to three antimicrobial agents, 7 (2.8%) to four antimicrobial agents, 8 (3.2%) to five antimicrobial agents, and 2 (0.8%) each to six and seven antimicrobial agents. No isolates were resistant to norfloxacin, whereas only seven were resistant to sulfamethoxazole/trimethoprim, six to trimethoprim, three to gentamicin, and one to ciprofloxacin. These results, for the first time, provide a baseline of data on the incidence of antimicrobial-resistant Salmonella in the U.S. food supply, which should be useful in determining the evolution of antimicrobial resistance in the future.