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


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.
<P> 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.

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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. <P>
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. <P> 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.

McCarthy, Rebecca; Loneragan, Guy ; Brashears, Mindy
Texas Tech University
West Texas A&M University
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