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Initial Investigation of the Burden of Methicillin-Resistant
Staphylococcus aureus (MRSA) in Cattle

McCarthy, Rebecca; Loneragan, Guy; Brashears, Mindy
Texas Tech University
West Texas A&M University
Start date
End date
Antimicrobial use in animal production has been scrutinized in recent years and believed by some to be potentiating the burden of drug-resistant organisms. Some of these drug-resistant bacteria are capable of causing or complicating disease in humans. Methicillin-resistant Staphylococcus aureus (MRSA) is one such pathogen. This phenotype of S. aureus resists β- lactam drug therapy, thus leaving limited therapeutic options to treat disease caused by MRSA.

MRSA is a well-known cause of nosocomial infections worldwide, and recently, evidence has suggested it can be a community acquired and zoonotic pathogen. Consequently, public-health control of this organism poses new challenges for both human and animal practitioners. MRSA has been identified in numerous animal species including pigs, cattle, and horses.

In light of MRSA being detected in food-producing animals and reports of food borne transmission of MRSA in other countries, we sought to investigate the burden of MRSA in beef cattle in the Texas High Plains in order to evaluate cattle as a potential reservoir for the pathogen and subsequently a possible food-borne source of MRSA and assess the susceptibility of methicillin-susceptible S.aureus (MSSA) recovered from cattle of the Texas High Plains.

More information
Findings: Samples were collected from 111 beef-type cattle housed in feedlots. Of these, 60 were close to harvest and the remainder was new arrivals. Eighty-one samples were collected from dairy-type cattle at a regional livestock auction facility; these animals were culled from their herd of origin for poor productivity reasons. One hundred and nine samples were collected from beef-type animals at the same salebarn.

MRSA was not recovered from any of the samples collected (0.0%, n=0; 95% CL=0, 1.3%). Of the 301 animals sampled, MSSA was isolated from 14.3% (n=42) of cattle resulting in 82 isolates. MSSA was recovered from 21.1% of beef-type and 2.5% of dairy-type cattle from the auction, and 16.2% of feedlot-origin cattle.

Overall, samples collected from the nares yielded the greatest recovery of S. aureus (58.7%). Susceptibility results for disk diffusion are still being analyzed. Sensititre results are reported here. Of the isolates, 17.1% were susceptible to all drugs tested. The most commonly observed resistance was to chloramphenicol (53.7%) followed by daptomycin (50%), tetracycline (1.2%) and erythromycin (1.2%). No isolate was resistant to four or more drugs.

Funding Source
Nat'l. Cattlemen's Beef Assoc.
Project number
Bacterial Pathogens
Antimicrobial Resistance