title: Technical note: Antimicrobial susceptibility of Portuguese isolates of Staphylococcus aureus and Staphylococcus epidermidis in subclinical bovine mastitis.
abstract: To evaluate the antimicrobial resistance traits of staphylococci responsible for subclinical bovine mastitis in Portugal, the minimum inhibitory concentrations (MIC) of 7 antimicrobial agents, frequently administered for mastitis treatment, were determined for 30 Staphylococcus aureus and 31 Staphylococcus epidermidis field isolates. Beta-lactamase production was detected through the use of nitrocefin-impregnated discs. The MIC that inhibited 90% of the isolates tested (MIC90) of penicillin, oxacillin, cefazolin, gentamicin, sulfamethoxazole/trimethoprim, oxytetracycline, and enrofloxacin were, respectively, 4, 0.5, 1, 1, 0.25, 0.25, and 0.06 microg/mL for Staph. aureus and > or = 64, 8, 1, 32, > or = 64, > or = 64, and 0.06 microg/mL for Staph. epidermidis. All Staph. aureus isolates showed susceptibility to oxacillin, cefazolin, gentamicin, sulphamethoxazole/trimethoprim, and enrofloxacin. Beta-lactamase production was detected in 20 of these isolates (66.7%), all of which were resistant to penicillin. Of the 31 Staph. epidermidis tested, 24 (77.4%) were beta-lactamase positive. All isolates were susceptible to both cefazolin and enrofloxacin. Nine Staph. epidermidis isolates were resistant to oxacillin, with MIC values ranging from 4 to 8 microg/mL. The MIC values of 5 antimicrobial agents tested were higher than those reported in other countries. Enrofloxacin was the only exception, showing lower MIC values compared with other reports. Overall, the antimicrobial agents tested in our study, with the exception of penicillin, were active against the 61 isolates studied.
authors.affiliation: Centro de Investigação Interdisciplinar em Sanidade Animal, Faculdade de Medicina Veterinária, Av. Universidade Técnica, 1300-477 Lisbon, Portugal. amsandronunes@fmv.utl.pt
authors.forename: S F
authors.initials: SF
authors.lastname: Nunes
authors.forename: R
authors.initials: R
authors.lastname: Bexiga
authors.forename: L M
authors.initials: LM
authors.lastname: Cavaco
authors.forename: C L
authors.initials: CL
authors.lastname: Vilela
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D002417:Cattle; D024881:Drug Resistance, Bacterial; D008414:Mastitis, Bovine / Q000382:microbiology*; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D011174:Portugal; D013203:Staphylococcal Infections / Q000382:microbiology / Q000662:veterinary*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D013212:Staphylococcus epidermidis / Q000187:drug effects* / Q000302:isolation & purification
chemical_list: D000890:Anti-Infective Agents