Survey of Salmonella serotypes shed in feces of beef cows and their antimicrobial susceptibility patterns

Salmonella prevalence on cow-calf operations was studied as a part of a nat ional study of health and management of the U.S. beef cow-calf industry and was conducted as part of the National Animal Health Monitoring System. Wit hin this study, the prevalence of Salmonella spp. shed in feces was determi ned. A total of 5,049 fecal samples were collected from 187 beef cow-calf o perations each visited on a single occasion. The number of fecal samples co llected per operation was predetermined based on herd size. Salmonellae wer e recovered from 1 or more fecal samples collected on 11.2% (21 of 187) of the operations. Overall 78 salmonellae representing 22 serotypes were recov ered from 1.4% (70 of 5,049) of samples. Multiple serotypes were recovered from eight samples from a single operation. The five most common serotypes were Salmonella Oranienburg (21.8% of isolates), and Salmonella Cerro (21.8 %), followed by Salmonella Anatum (10.3%), Salmonella Bredeney (9.0%), and Salmonella Mbandaka (5.1%). The most common serogroups identified were C-1 (33.3%), K (21.8%), B (16.7%), and E (15.4%). Even though the recovery rate of salmonellae from fecal samples was very low, 43.6% (34 of 78) and 38.5% (30 of 78) of the isolates were among the 10 most common serotypes from ca ttle with clinical signs of disease or isolated from humans, respectively. The majority of the isolates (50 of 78; 64.1%) were recovered from fecal sa mples from two operations. All isolates were screened for resistance to a p anel of 17 antimicrobics, and 87.2% (68 of 78) were susceptible to all of t he antimicrobics. The resistant isolates were most commonly resistant to st reptomycin (n = 9) and/or sulfamethoxazole (n = 9). Nine isolates showed mu ltiple (greater than or equal to2 antimicrobics) resistance most commonly t o streptomycin and sulfamethoxazole (n = 6).