Comparison of the phenotypic antimicrobial resistances and spa-types of methicillin-resistant Staphylococcus aureus (MRSA) isolates derived from pigs in conventional and in organic husbandry systems.

The purposes of this study were to identify differences in the phenotypic resistance to antimicrobials and in the spa-types between 273 methicillin-resistant Staphylococcus aureus (MRSA) isolates derived from conventional (n = 21) versus organic pig farms (n = 10) located in Germany. The susceptibility of the isolates against 19 antimicrobial agents was tested and then compared between the two different husbandry systems. A statistically significant difference was observed between the MRSA strains isolated on conventional and on organic pig farms for the antimicrobials tilmicosin (61.8% vs. 40.0%; OR: 2.42), clindamycin (63.5% vs. 45.7%; OR: 2.06), gentamicin (14.7% vs. 34.3%; OR: 0.33), apramycin (3.8% vs. 22.9%; OR: 0.13) and enrofloxacin (13.9% vs. 34.3%; OR: 0.31). Finally, the results of the susceptibility testing were analysed in order to determine the resistance pattern per isolate. Among the tested isolates a kind of"basic resistance pattern of MRSA"to penicillin, ampicillin and tetracycline was identified. The predominant spa-types in both groups were t011 and t034. Less frequently detected spa-types were t1430, t1197, t2510, t779, t1451 and t1250.