title: Characterisation of penicillin and tetracycline resistance in Staphylococcus aureus isolated from bovine milk samples in Minas Gerais, Brazil.
abstract: This Regional Research Communication describes the characterisation of ampicillin, penicillin and tetracycline resistance in Staphylococcus aureus isolated from bovine subclinical mastitis in Minas Gerais State, Brazil. Ninety S. aureus isolates from bovine mastitis exhibiting phenotypic resistance to ampicillin, penicillin and/or tetracycline were selected for this study. The minimum inhibitory concentration (MIC) of each antibiotic was determined using the E-Test® and the production of beta-lactamase was determined by cefinase disks. The resistance genes blaZ, tet(K), tet(L), tet(M), and tet(O) were investigated by PCR in all of the isolates. The MIC results classified 77, 83 and 71% of the isolates as resistant to ampicillin, penicillin and tetracycline, respectively. The MIC50 and MIC90 were, respectively, 1 and 2 µg/ml for ampicillin, 0·5 and 1 µg/ml for penicillin and 32 and 64 µg/ml for tetracycline. Eighty-six per cent of beta-lactamase producing isolates were detected. Of the 90 isolates investigated, 97% amplified blaZ, 84% amplified tet(K), 9% amplified tet(L), 2% amplified tet(M) and 1% amplified tet(O). Seventy-nine isolates (88%) showed blaZ together with at least one tet gene. S. aureus isolates showed high MIC50 and MIC90 values for the three antimicrobials. The blaZ and tet(K) genes were widespread in the herds studied, and most of the isolates harboured blaZ and tet(K) concomitantly.
authors.affiliation: University of Santa Catarina State, Center of Agroveterinary Sciences,Lages, Santa Catarina,Brazil.
authors.forename: Caroline L
authors.initials: CL
authors.lastname: Martini
authors.affiliation: Embrapa Dairy Cattle Research Center,Juiz de Fora, Minas Gerais,Brazil.
authors.forename: Carla C
authors.initials: CC
authors.lastname: Lange
authors.affiliation: Embrapa Dairy Cattle Research Center,Juiz de Fora, Minas Gerais,Brazil.
authors.forename: Maria Avp
authors.initials: MA
authors.lastname: Brito
authors.affiliation: Embrapa Dairy Cattle Research Center,Juiz de Fora, Minas Gerais,Brazil.
authors.forename: João B
authors.initials: JB
authors.lastname: Ribeiro
authors.affiliation: Embrapa Dairy Cattle Research Center,Juiz de Fora, Minas Gerais,Brazil.
authors.forename: Letícia C
authors.initials: LC
authors.lastname: Mendonça
authors.affiliation: University of Santa Catarina State, Center of Agroveterinary Sciences,Lages, Santa Catarina,Brazil.
authors.forename: Eliana K
authors.initials: EK
authors.lastname: Vaz
mesh_terms: D000667:Ampicillin / Q000008:administration & dosage; D000818:Animals; D001938:Brazil; D002417:Cattle; D005260:Female; D008414:Mastitis, Bovine / Q000382:microbiology*; D008826:Microbial Sensitivity Tests; D008892:Milk / Q000382:microbiology*; D010403:Penicillin Resistance / Q000235:genetics; D010406:Penicillins / Q000008:administration & dosage; D016133:Polymerase Chain Reaction / Q000662:veterinary; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification*; D013752:Tetracycline / Q000008:administration & dosage; D013753:Tetracycline Resistance / Q000235:genetics; D001618:beta-Lactamases / Q000096:biosynthesis
chemical_list: D010406:Penicillins; D000667:Ampicillin; D001618:beta-Lactamases; D013752:Tetracycline
keywords: 
                 blaZ
              ; 
                 tet genes; E-Test®
              ; MIC; beta-lactamase