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United States Department of Agriculture

Agricultural Research Service

Research Project: Monitoring of Antimicrobial Resistance in Food Animal Production

Location: Bacterial Epidemiology and Antimicrobial Resistance

Title: Salmonella prevalence and antimicrobial susceptibility from the National Animal Health Monitoring System's (NAHMS) Swine 2000 and 2006 Studies

Authors
item Haley, Charles -
item Dargatz, David -
item Bush, Eric -
item Erdman, Matthew -
item Cray, Paula

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 29, 2011
Publication Date: March 1, 2012
Citation: Haley, C.A., Dargatz, D.A., Bush, E.J., Erdman, M.M., Cray, P.J. 2012. Salmonella prevalence and antimicrobial susceptibility from the National Animal Health Monitoring System's (NAHMS) Swine 2000 and 2006 Studies. Journal of Food Protection. 75(3):428-436.

Interpretive Summary: Food borne illness is often associated with food of animal origin. In particular, foods contaminated with Salmonella can cause cramping and diarrhea. Most often food borne illness is self-limiting and does not require treatment with antibiotics. However, when antibiotics are needed, bacteria that have developed resistance to the antibiotic may be difficult to treat. In order to determine if and how animals are contaminated with Salmonella and the extent to which the Salmonella have developed antimicrobial resistance, it is necessary to conduct prevalence studies within each commodity. As part of the National Animal Health Monitoring System’s (NAHMS) Swine 2000 and 2006 studies fecal samples were cultured for Salmonella. Fecal samples were collected from 123 operations in 17 states in 2000 and 135 operations in 17 states in 2006. On each operation, 50 and 60 fecal samples were collected from late finisher pig pens in 2000 and 2006, respectively. Salmonella isolates were characterized to determine serogroup and serotype, and were tested for susceptibility to a panel of 17 and 15 antimicrobial drugs in 2000 and 2006, respectively. A total of 5,470 and 7,788 samples were cultured for Salmonella in 2000 and 2006, respectively. Overall, 6.2% of the samples and 34.2% of the farms were positive for Salmonella in 2000. In 2006, 7.2% of the samples and 52.6% of the farms were positive. Salmonella serotypes Derby, Typhimurium var. 5- (Typhimurium var Copenhagen) and Agona were the three serotypes most often recovered in both study years. The most common antimicrobial resistance pattern for Salmonella serotype Derby in the two study years was resistance to streptomycin, sulfisoxazole and tetracycline. Most isolates were resistant to tetracycline, sulfisoxazole and streptomycin, in both study years. The percentage of Salmonella isolates tested that were susceptible to all antimicrobials (pansusceptible) was 38.1% in 2000 and 20.4% in 2006. The percentage of Salmonella isolates tested that were resistant to three or more antimicrobials (multidrug resistant) was similar in 2000 and in 2006 (52.8% and 57.7%, respectively). These data indicate that the prevalence of Salmonella in swine remained relatively stable over the study period but the total number of farms testing positive for Salmonella increased. Additionally, there was no change in the types of Salmonella recovered between study years and antimicrobial resistance was observed primarily in drugs that are not used to treat salmonellosis. These data are important to epidemiologists, veterinarians and public health officials as they monitor the health of food animals, status of the food supply and conduct food borne outbreak investigations.

Technical Abstract: Concern over Salmonella contamination of food is compounded by fear that antimicrobials traditionally used to combat the infection will become useless due to rising antibiotic resistance. Livestock, in particular swine, are often blamed for illnesses caused by Salmonella and for increasing antibiotic resistance due to antibiotic use in pigs. As part of the National Animal Health Monitoring System’s (NAHMS) Swine 2000 and 2006 studies fecal samples were cultured for Salmonella. Fecal samples were collected from 123 operations in 17 states in 2000 and 135 operations in 17 states in 2006. On each operation, 50 and 60 fecal samples were collected from late finisher pig pens in 2000 and 2006, respectively. Salmonella isolates were characterized to determine serogroup and serotype, and were tested for susceptibility to a panel of 17 and 15 antimicrobial drugs in 2000 and 2006, respectively. A total of 5,470 and 7,788 samples were cultured for Salmonella in 2000 and 2006, respectively. Overall, 6.2% of the samples and 34.2% of the farms were positive for Salmonella in 2000. In 2006, 7.2% of the samples and 52.6% of the farms were positive. Salmonella serotypes Derby, Typhimurium var. 5- (Typhimurium var Copenhagen) and Agona were the three serotypes most often recovered in both study years. The most common antimicrobial resistance pattern for Salmonella serotype Derby in the two study years was resistance to streptomycin, sulfisoxazole and tetracycline. Most isolates were resistant to tetracycline, sulfisoxazole and streptomycin, in both study years. The percentage of Salmonella isolates tested that were susceptible to all antimicrobials (pansusceptible) was 38.1% in 2000 and 20.4% in 2006. The percentage of Salmonella isolates tested that were resistant to three or more antimicrobials (multidrug resistant) was similar in 2000 and in 2006 (52.8% and 57.7%, respectively).

Last Modified: 7/24/2014