A total of 206 strains of Staphylococcus aureus isolated from bovine clinical and subclinical mastitis in Argentina during 1996 to 1998 were investigated for their in vitro susceptibility to several antimicrobial agents. Minimum inhibitory concentrations that inhibit 90% of the strains tested reported in micrograms per milliliters were: 1.5, 0.5, 0.75, 1.50, 0.75, 1.0 and 0.125 for penicillin, oxacillin, cephalothin, gentamicin, erythromycin, clindamycin and ampicillin-sulbactam, respectively. Resistance was detected in 83 (40.3%), 24 (11.6%), 16 (7.7%) and 7 (3.4%) S. aureus isolates for penicillin, erythromycin, pirlimycin and gentamicin, respectively. No resistance was detected for oxacillin, cephalothin and ampicillin-sulbactam. Results indicated that S. aureus isolates in Argentina exhibited high resistance to penicillin of all antimicrobial agents tested.

The in vitro susceptibility to penicillin G, erythromycin and clindamycin was determined by the disc diffusion test and by E-test for a total of 47 streptococcal strains (three Streptococcus uberis, 36 Streptococcus agalactiae, eight Streptococcus dysgalactiae spp. dysgalactiae) isolated from bovine intramammary infections in Argentina. Moreover, resistance phenotypes of erythromycin-resistant streptococcal isolates was characterized. MIC90 of penicillin G, erythromycin and clindamycin for S. agalactiae were 0.75, 8.0 and 12.0 microg/ml respectively. Resistance to erythromycin and clindamycin was detected in 13 (27.6%) and 12 (25.5%) isolates respectively. No isolate was resistant to penicillin G. Resistance against macrolides, lincosamides and streptogramin B (MLS(B)) represented by the constitutive MLS(B) phenotype was present in 11 (23.4%) erythromycin-resistant isolates and two isolates (4.3%) expressed the M phenotype. The inducible MLS(B) phenotype was not identified. Results suggest that beta-lactams are the first-line antibiotics when treating streptococcal udder infections; however, the continuous monitoring of the antibiotic resistance is essential, as the emergence of resistant strains has become a growing concern on the therapy of bovine mastitis.

The killer properties of yeasts isolated from olive brines were examined in the absence and presence of sodium chloride in concentrations of up to 6% (wt/vol). An apparent enhancement of the killing action as the salt concentration increased, as well as changes in the spectra of activity against selected target strains, was observed in a few strains. Culture filtrates from killer strains grown at different NaCl concentrations (0, 3, or 6% [wt/vol]) were tested against sensitive yeasts cultivated under the same conditions. While the sensitivity of the target strain greatly increased in the presence of salt, no significant effect on toxin production was noticed.

Consumption of raw/undercooked ground beef is the most common route of transmission of Shiga toxin-producing E. coli (STEC). The aim of the study was to determine the STEC contamination level of the ground beef samples collected in 36 markets of different socioeconomic strata in Buenos Aires, Argentina, and the characterization of the isolated strains. Ninety-one out of 252 (36.1%) samples were stx+. Fifty-seven STEC strains were recovered. Eleven STEC strains belonged to O157 serogroup, and 46 to non-O157 serogroups. Virulence markers of the 57 STEC were stx1, 5.3% (3/57); stx2, 86.0% (49/57); stx1/stx2, 8.8% (5/57); ehxA, 61.4% (35/57); eae, 26.3% (15/57); saa, 24.6% (14/57). Shiga toxin subtypes were stx2, 31.5% (17/54); stx2c-vhb, 24.1% (13/54); stx2c-vha, 20.4% (11/54); stx2/stx2c-vha, 14.8% (8/54); stx2/stx2c-vhb, 5.6% (3/54); stx2c-vha/vhb, 3.7% (2/54). Serotypes O178:H19 and O157:H7 were prevalent. Contamination rate of STEC in all strata was high, and the highest O157 contamination was observed at low strata at several sampling rounds. Persistence of STEC was not detected. Sixteen strains (28.1%) were resistant to ampicillin, streptomycin, amikacin, or tetracycline. The STEC contamination level of ground beef could vary according to the sociocultural characteristics of the population.

Dorta de Mazzonelli y col., 1997; ). From these results, it might be inferred that urine of domestic or wild species which lived with studied camelids, could have been the contagious source.]]>