title: Anti-microbial susceptibility of Streptococcus spp. isolated from bovine mastitis in Argentina.
abstract: 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.
authors.affiliation: Microbiología, Facultad de Ciencias Veterinarias, Universidad de Buenos Aires, Chorroain 280 (1427) Buenos Aires, Argentina.
authors.forename: G
authors.initials: G
authors.lastname: Denamiel
authors.forename: P
authors.initials: P
authors.lastname: Llorente
authors.forename: M
authors.initials: M
authors.lastname: Carabella
authors.forename: M
authors.initials: M
authors.lastname: Rebuelto
authors.forename: E
authors.initials: E
authors.lastname: Gentilini
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001118:Argentina; D002417:Cattle; D002981:Clindamycin / Q000494:pharmacology; D015169:Colony Count, Microbial; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial; D024901:Drug Resistance, Multiple, Bacterial; D004917:Erythromycin / Q000494:pharmacology; D005260:Female; D008414:Mastitis, Bovine / Q000188:drug therapy* / Q000382:microbiology; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D010400:Penicillin G / Q000494:pharmacology; D013290:Streptococcal Infections / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary*; D013291:Streptococcus / Q000187:drug effects*
chemical_list: D000900:Anti-Bacterial Agents; D002981:Clindamycin; D004917:Erythromycin; D010400:Penicillin G