Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2003
Publication Date: 7/1/2003
Citation: Dargatz, D.A., Cray, P.J., Ladely, S.R., Kopral, C.A., Ferris, K.E., Headrick, M.L. 2003. Prevalence and antimicrobial susceptibility of salmonella spp. isolates from us cattle in feedlots in 1999 and 2000. Journal of Applied Microbiology. 95(4):753-761. Interpretive Summary: Salmonella are bacteria that often cause food borne illness, particularly in the young, the elderly and those with diseases such as cancer and AIDS that compromise the immune system. However, Salmonella are ubiquitous in nature and most warm blooded animals can harbor Salmonella without causing illness, including food animals such as cattle, swine and poultry. We conducted a study to test for the presence of Salmonella in cattle in US feedlots and tested them for resistance to 17of antimicrobials. Fecal samples (10,417) were collected from 73 feedlots in 12 states from pens of cattle that had been in the feedlot for the shortest period of time (3,482 pens), the longest period of time (3,485 pens) and randomly from the remaining pens (3,400 pens) and cultured for Salmonella. Overall, 6·3% of the samples were positive for Salmonella and there was little difference in the proportion of positive samples from short-fed (6·1%), random (6·4%) and long-fed (6·4%) pens of cattle. The majority of isolates (62·8%, 441/702) were sensitive to all of the antimicrobials tested. Resistance was most frequently observed to tetracycline, followed by streptomycin, ampicillin, and chloramphenicol. These data indicate that Salmonella was isolated at low frequency from feces of feedlot cattle. In addition most of the Salmonella isolates were sensitive to all the antimicrobials tested. These data are important for veterinarians, the cattle industry, pharmaceutical representatives, public health officials and scientists who study the impact of food borne infections on humans and develop ways to limit Salmonella in food animals and antimicrobial resistance in food borne bacteria.
Technical Abstract: Aims: Faecal samples from cattle in US feedlots were evaluated for the presence of Salmonella. When Salmonella isolates were recovered the antimicrobial resistance patterns were determined. Methods and Results: Faecal samples were collected from pen floors in 73 feedlots in 12 states during the period from October 1999 to September 2000. Pens of cattle selected for sampling were those that had been in the feedlot for the shortest period of time, the longest period of time and a randomly selected pen from the remaining pens. Faecal samples were cultured for Salmonella spp. and all Salmonella isolates were categorized by serotype. The susceptibilities of all isolates were determined using a panel of 17 antimicrobials. Overall, 6·3% (654/10 417) of the samples cultured positive for Salmonella spp. and 22·2% (94/422) of pens and 50·7% (37/73) of feedlots had one or more positive samples. There was little difference in the proportion of positive samples from short-fed (6·1%, 212/3482), random (6·4%, 217/3400) and long-fed (6·4%, 224/3485) pens of cattle. One of two pens of cattle that could not be attributed to a pen type had a single positive sample (2·0%, 1/50). Samples collected during the period of April to June (6·8%, 209/3054) and July to September (11·4%, 286/2500) were more likely to be positive than those collected during October to December (4·0%, 73/1838) and January to March (2·8%, 86/3025). The most common serotypes of Salmonella were dissimilar from those that are typically seen in human illness and cattle illness. The majority of isolates (62·8%, 441/702) were sensitive to all of the antimicrobials tested. Resistance was most frequently observed to tetracycline (35·9%, 252/702) followed by streptomycin (11·1%, 78/702), ampicillin (10·4%, 73/702) and chloramphenicol (10·4%, 73/702). Multiple resistance (resistance to greater than or equal to 2 antimicrobials) was observed for 11·7% (82/702) of the isolates. Conclusions: Salmonella was isolated at low frequency from faeces of feedlot cattle and the serotypes were not those commonly associated with human illness. In addition most of the Salmonella isolates were sensitive to all the antimicrobials tested. Significance and Impact of the Study: This study contributes to understanding the ecology of Salmonella in cattle feedlots and the prevalence of resistance among potential food-borne pathogens.