Detection of methicillin-resistant Staphylococcus aureus sequence type 8 in pigs, production environment, and human beings.

Two follow-up studies of a positive methicillin-resistant Staphylococcus aureus (MRSA) finding in the 2008 European Union baseline survey on MRSA in pig herds were performed to gain more knowledge about the epidemiology of the particular MRSA type, a known human type (ST8/t008), among pigs. Two persons on a Norwegian farm in the study were found to be MRSA carriers, and human-to-animal transmission was suspected. In the first follow-up study, all pigs (n  =  346) were sampled by taking nasal swabs. A pooled sample from 5 individual pigs housed together in a single pen, and a dust sample from the equipment in the same room, were positive. Dust samples from a building housing MRSA-negative animals were negative. The MRSA was not detected in the second follow-up, after removing positive animals from the farm and cleaning and disinfecting. A low MRSA occurrence among the animals was found, suggesting that MRSA ST8/t008 may be less able to colonize and persist in pig holdings compared with more host-adapted S. aureus strains.

Antimicrobial resistance in Staphylococcus pseudintermedius in the Norwegian dog population.

The occurrence of antimicrobial resistance in Staphylococcus pseudintermedius from skin and ear infections in a representative sample of dogs unexposed to antimicrobial treatment before sampling was examined. The obtained isolates were further examined for genetic polymorphism and genetic background of resistance. A total of 59 isolates of S. pseudintermedius originating from 96 samples of 91 dogs in five different regions in Norway were included in this study. Susceptibility testing was performed using a broth dilution method. Resistant isolates were subjected to polymerase chain reaction for detection of resistance genes. All isolates were subjected to pulsed-field gel electrophoresis to examine the genetic polymorphism. In total, 19% of the isolates were susceptible to all antimicrobial agents included. Resistance to penicillin was most prevalent (70%), followed by resistance to fusidic acid (49%) and oxytetracycline (42%). Resistance to quinolones or cephalosporins was not observed. Resistance to penicillin, tetracycline, and erythromycin was mediated by the blaZ beta-lactamase gene, the tetM gene, and the ermB gene, respectively. One of the fusidic acid-resistant isolates harbored a fusC gene, whereas the mechanisms involved in resistance in the other fusidic acid-resistant isolates remained unknown. Pulsed-field gel electrophoresis showed a high genetic polymorphism of S. pseudintermedius. This study indicates that the occurrence of antimicrobial resistance is common among S. pseudintermedius from dogs unexposed to antimicrobial treatment before sampling, and that there is a high genetic polymorphism among S. pseudintermedius.