Toxin genes of Staphylococcus aureus isolated from bovine intramammary infection of different clinical characteristics and outcome

The material comprised 161 Staphylococcus aureus strains isolated from 116 dairy cows with mastitis and treated with antimicrobials. The strains originated from pre- and post-treatment samples and represented different PFGE types. The aim of the study was to investigate the relationship between the toxin determinants of the strains and clinical characteristics of mastitis caused by them. A selection of 18 toxin determinants of the bacterial strains for haemolysins (hla-hlg), leukocidins (lukE-D, lukM) and superantigens (entA-E, entH-J, tst, etA, and etB), as welt as penicillin and methicillin resistance genes (blaZ and mecA) was determined by PCR. Prevalence of the determinants and their combinations were compared with severity and outcome of mastitis. The genes No, lukE-D, hlg and hid and were the most common genes present (in 95.7%, 95.7%, 87.1% and 87.1%), but entE, etA and etB were not found. The most frequent superantigen determinants entG (31.9%), entI (31.9%) and entJ (19.0%) were detected from several PFGE types, but the others were linked with the types. A combination of hla, hlb, hid, hlg, lukE-D, lukM, entC, entG, entI, and tst was unique to one PFGE type previously associated with severe signs but short persistence. For 40/45 isolates (88.9%), persistency of infection could be demonstrated by similarity of PFGE- and toxin gene patterns between pre- and post-treatment isolates. Isolates Lacking superantigen determinants were more common (P < 0.05) among cows that recovered than among chronically infected cows (53.7% vs. 28.2%). ent3 was associated with persistent mastitis (P < 0.01); in particular ent3 increased the probability of chronic mastitis in blaZ positive strains (P < 0.05).