[Prevalence of Staphylococcus aureus isolated from subclinical bovine mastitis in dairies of the city of San Luis].

In order to detect subclinical mastitis by means of California Mastitis Test and recounting of somatic cells, 163 cows from the dairies of San Luis city, Argentina, were examined. Seventy six individuals (46.6%) exhibited an inflammatory response ranging > or = 2+ grade and a cellular recounting value of > or = 5 x 10(5), data compatible with those of subclinical mastitis. Staphylococcus aureus was isolated from 39 (51.3%) cultures as estimated by the sum of the two last values listed in Table 1. Organisms were isolated by plating on brain heart infusion agar with 5% of sheep blood and on Baird-Parker media. One hundred and three S. aureus isolates recovered from 51 of 63 cows were characterized by coagulase activity by the tube method using human and bovine plasma; clumping factor; glucose and mannitol fermentation; thermonuclease (TNase), pigment, gelatinase, fibrinolysin, acetoin, hemolysin production; egg yolk, tellurite and catalase reaction and crystal violet types. All isolates were susceptible to cephalothin, clindamycin, methicillin, gentamycin and vancomycin; 94.1% were susceptible to chloramphenicol and 53.8% to G penicillin. Sixty three isolates (61.1%) were classified according to Hájek and Marsálek scheme as biotype C (bovine and ovine ecovar), 33 isolates (32.0%) were classified as biotype B (swine and poultry ecovar); 1 isolated (0.9%) as intermediate between B and D; 5 isolates (4.8%) as biotype A (human ecovar) and 1 isolated (0.9%) as biotype D (ecovar silvestres spp) (Table 2). Production of enterotoxins A to E and toxic shock syndrome toxin-1 (TSST-1) was determined by the optimal susceptibility plate method on 27 isolates (26.2%) which were coagulase 3+ to 4+ and TNase highly positive. None of them produced enterotoxins including TSST-1. The subclinical mastitis data and the prevalence of S. aureus coincide with those of other authors, both from Argentina and from other countries.