GHENT/BELGIUM, June 21st (Biermann) – In a Belgium-wide study, researchers under the lead of Dr. Wannes Vanderhaeghen wanted to see whether cows that suffer from mastitis are infected with MRSA. They performed a DNA analysis by searching for the resistance gene mecA in 118 S. aureus strains won from diagnostic mastitis milk probes from 118 different farms experiencing S. aureus mastitis. The MRSA strains were then further characterized by disk diffusion susceptibility tests, spa-typing, MLST and SCCmec-typing, the authors write. In an additional study, four MRSA-positive farms were selected to evaluate the in-herd prevalence of MRSA by sampling all lactating cows. The MRSA strains originating from these samples were characterized the same way.

In eleven of the 118 S. aureus isolates (9.3 percent), mecA was detected. This indicates that nearly ten percent of the Belgian farms suffering from S. aureus mastitis have an MRSA problem. The in-herd prevalence varied between none and 7.4 percent. Besides being methicillin-resistant, all were also resistant to tetracycline. In some cases, resistances to macrolides, lincosamides and aminoglycosides were detected.

The strains found were ST398, spa-types t011, or t567 and were of SCCmec-type Iva or V. This proves the belong to the “emerging livestock-associated MRSA (LA-MRSA) strains of CC398”, Vanderhaeghen and his team write.

Not only Belgian pigs, horses and poultry seem to be affected by LA-MRSA, but now also cows. The researchers fear that the spread of LA-MRSA strains in cow farms with S. Aureus mastitis may cause serious problems in the future.

References

• Vet Microbiol 144(1-2):166-17111, Pages 1230-1237