Skip to main content
ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Environmental Microbial & Food Safety Laboratory » Research » Publications at this Location » Publication #316944
Title: Antimicrobial resistance of Salmonella and E. coli from Pennsylvania dairy herds

Author
item CAO, HUILIN - University Of Maryland
item PRADHAN, ABANI - University Of Maryland
item Karns, Jeffrey
item WOLFGANG, DAVE - Pennsylvania State University
item HOVINGH, ERNEST - Pennsylvania State University
item Van Kessel, Jo Ann

Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: 5/6/2015
Publication Date: 5/20/2015
Citation: Cao, H., Pradhan, A., Karns, J.S., Wolfgang, D., Hovingh, E., Van Kessel, J.S. 2015. Antimicrobial resistance of Salmonella and E. coli from Pennsylvania dairy herds. BARC Poster Day.

Interpretive Summary: Antimicrobial resistance in bacterial pathogens is an increasing public health concern. The objective of this study was to examine antimicrobial resistance in Salmonella and E. coli isolates from Pennsylvania dairy herds. Salmonella and E. coli strains were isolated from manure composite samples collected from 76 farms and evaluated for resistance to ampicillin, cefoxitin, chloramphenicol, tetracycline, streptomycin, kanamycin, ciprofloxacin or cefotaxime. Salmonella was isolated from at least one composite sample from 51 of 76 farms (67%), and the farm prevalence was found to be correlated with the age of the animals; prevalence was 15% for pre-weaned calves, 28% for post-weaned calves, 65% for dry cows and 67% for lactating cows. The predominant Salmonella serotypes were Montevideo, Cerro and Kentucky. When tested on a panel of eight antibiotics, most Salmonella isolates were pan-susceptible. Overall, E. coli isolates were commonly resistant to tetracycline, streptomycin, ampicillin, and kanamycin: isolates from calves (84%, 68%, 62%, and 61% farm prevalence, respectively) were more resistant than those from adult cows (51%, 30%, 15%, and 7% farm prevalence, respectively). Multi-drug resistant (MDR) (resistant to =4 antimicrobials) E. coli were found primarily among young animal groups, and resistance to up to 7 antibiotics was observed. The presence of MDR E. coli on dairy farms poses potential risks to human health.

Technical Abstract: Antimicrobial resistance in bacterial pathogens is an increasing public health concern. The objective of this study was to examine antimicrobial resistance in Salmonella and E. coli isolates from Pennsylvania dairy herds. Manure composite samples were collected from 76 farms: on each farm one sample was collected from the pens of pre-weaned calves, post-weaned calves, dry cows, and up to three groups of lactating cows. Five E. coli isolates (n=2267) and five Salmonella isolates (n=1090) from each sample, when present, were screened for antimicrobial resistance with Mueller Hinton agar supplemented with NARMS breakpoint concentrations of ampicillin, cefoxitin, chloramphenicol, tetracycline, streptomycin, kanamycin, ciprofloxacin or cefotaxime. Salmonella was isolated from at least one composite sample from 51 of 76 farms (67%), and the farm prevalence was found to be correlated with the age of the animals; prevalence was 15% for pre-weaned calves, 28% for post-weaned calves, 65% for dry cows and 67% for lactating cows. The predominant Salmonella serotypes were Montevideo, Cerro and Kentucky. When tested on a panel of eight antibiotics, most Salmonella isolates were pan-susceptible. Overall, E. coli isolates were commonly resistant to tetracycline, streptomycin, ampicillin, and kanamycin: isolates from calves (84%, 68%, 62%, and 61% farm prevalence, respectively) were more resistant than those from adult cows (51%, 30%, 15%, and 7% farm prevalence, respectively). Multi-drug resistant (MDR) (resistant to =4 antimicrobials) E. coli were found primarily among young animal groups, and resistance to up to 7 antibiotics was observed. The results of this study indicate that resistant E. coli are more prevalent in calves than in adult cows within the same herd. Higher prevalence of resistant E. coli in calves may be due to the selective pressures associated with higher exposure to antimicrobials. The presence of MDR E. coli on dairy farms poses potential risks to human health.