A high proportion of staphylococci isolated from pigs affected with exudative epidermitis were found to be resistant to β-lactam antimicrobials.

The primary objective of research published in BMC Veterinary Research by Jeonghwa Park and colleagues at the Univeristy of Guelph in Canada was to investigate and characterise β-lactam resistance in Staphylococcus hyicus, Staphylococcus aureus and other staphylococci isolated from these pigs.

The antimicrobial resistance patterns of 240 staphylococci isolates were determined by disk diffusion, of which 176 (73.3 per cent) of the isolates were resistant to three β-lactams (penicillin G, ampicillin and ceftiofur).

The presence of mecA gene was identified in 63 staphylococci isolates from skin samples by PCR. The mecA gene was identified in 19 S. aureus, 31 S. hyicus, nine Staphylococcus chromogenes, two Staphylococcus pseudintermedius isolates, and in one isolate each of Staphylococcus arlettae, and Staphylococcus cohnii subspecies urealyticus.

From SCCmec typing results, the majority (45/63, 71.4 per cent) were shown to be SCCmec type V. One isolate was SCCmec III.

Fourteen isolates were detected as mec class A, mec class C or ccr type 5. The ccr complex and mec complex was not detected in three isolates of methicillin-resistant S. hyicus (MRSH) based on multiplex PCR.

Of the 30 isolates of MRSA identified from nasal samples of the pigs, 29 isolates were SCCmec type V and one isolate was SCCmec type II.

Staphyloccoci isolates that were mecA-negative but resistant to β-lactam antimicrobials were further examined by screening for mecC; however, all were negative.

Furthermore, the majority of mecA-negative β-lactam resistant staphylococci isolates were susceptible to oxacillin and amoxicillin-clavulanic acid in a double disk diffusion test.

Park and colleagues concluded that methicillin resistance can be identified in a variety of staphylococcal species isolated from pigs.

In this study, there was a great deal of similarity in the SCCmec types between staphylococcal species, suggesting that resistance may be passed from one species of staphylococci to another species of staphylococci.

While this has been reported for acquisition of methicillin-resistance from coagulase-negative staphylococci to S. aureus, these data suggest that transmission to or from the porcine pathogen S. hyicus may also occur.

The identification of methicillin resistance in a variety of staphylococcal species in pigs does raise concerns about the spread of serious multi-drug resistance in food-producing animals and warrants further study, the University of Guelph researchers added.

Reference

^{Park J., R.M. Friendship, J. S. Weese, Z. Poljak and C.E. Dewey. 2013. An investigation of resistance to β-lactam antimicrobials among staphylococci isolated from pigs with exudative epidermitis. BMC Veterinary Research. 9:211. doi:10.1186/1746-6148-9-211}

November 2013