RESUMO
INTRODUCTION: Staphylococci are the most important agents associated with bovine mastitis. This study aimed at characterizing resistance factors to antimicrobials in Staphylococcus spp. isolated from the milk of cows with subclinical mastitis. METHODOLOGY: In vitro resistance of 243 Staphylococcus spp. isolates to antimicrobials commonly used in clinical practice was evaluated. The detection and expression of genes encoding resistance mecA (gene encoding penicillin binding protein 2a) mecALGA251 (mecA homologue), blaZ (gene encoding penicillin resistance), femA and femB (genes encoding essential factors - A and B - for the expression of methicillin resistance) and aacA-aphD (gene encoding for a bifunctional enzyme that confers resistance to gentamicin) using PCR and RT-PCR was investigated. RESULTS: One or more genes encoding resistance to different antimicrobials were detected in 184 Staphylococcus spp. SAMPLES: The femA and femB genes were the most frequent. Regarding the variables' detection (N = number of strains) and expression (% of strains), the following results were obtained: blaZ (N = 40 - 82.5%), femA (N = 147 - 47.6%), aacAaphD (N = 30 - 43.3%), femB (N = 138 - 29.7%), mecA (N = 33 - 27.3%), mecALGA251 (N = 01 - 0.0%). There was a higher occurrence of phenotypic resistant strains for amoxicillin, ampicillin and penicillin in isolates positive for detection and/or expression of blaZ gene when compared with the other genes. CONCLUSIONS: The present study provides new information on genotypic traits of Staphylococcus isolates from bovine subclinical mastitis especially regarding the evaluation of expression of genes associated with antimicrobial resistance in Staphylococcus spp. using molecular tools.
Assuntos
Farmacorresistência Bacteriana/genética , Mastite Bovina/microbiologia , Leite/microbiologia , Infecções Estafilocócicas/veterinária , Staphylococcus/efeitos dos fármacos , Staphylococcus/genética , Animais , Antibacterianos/farmacologia , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Brasil , Bovinos , DNA Bacteriano , Feminino , Resistência a Meticilina , Testes de Sensibilidade Microbiana , Resistência às Penicilinas , Proteínas de Ligação às Penicilinas/genética , Proteínas de Ligação às Penicilinas/metabolismo , Infecções Estafilocócicas/tratamento farmacológico , Infecções Estafilocócicas/microbiologia , Staphylococcus/isolamento & purificaçãoRESUMO
The objective of this randomized, controlled superiority trial was to assess the efficacy of ketoprofen for the treatment of spontaneous, culture-negative clinical mastitis cases that were not treated with antimicrobials. Holstein cows from 3 herds were eligible for inclusion if they had mild or moderate culture-negative clinical mastitis cases in 1 quarter or more. Upon detection of clinical mastitis, farm personnel performed on-farm culture (OFC) using commercially available bi-plates. Samples used for OFC were also cultured in a research laboratory. Cows with culture-negative clinical mastitis that met the inclusion criteria were randomly allocated to 1 of 2 experimental groups: in the ketoprofen (KET) group, cows received an intramuscular injection of 3 mg/kg of ketoprofen upon confirmation of a negative OFC result; and in the control (CON) group, cows received no treatment or placebo. Milk samples were collected 14 and 21 d after detection of clinical mastitis for microbiological examination and somatic cell counting. Study outcomes were clinical cure (within 7 d after inclusion in the study), relapse (within 14 d after inclusion) and recurrence of clinical mastitis (15 to 90 d after inclusion), risk of new intramammary infection, and quarter milk somatic cell count at 14 and 21 d. We used Cox proportional hazards, logistic regression, and repeated-measures models to compare each outcome between groups. After exclusion of moderate cases (n = 6), a total of 123 clinical mastitis cases (CON = 58 and KET = 65) were used for analyses. Risks of clinical cure [83.08% (54/65) and 91.23% (52/57); hazard ratio = 1.20, 95% confidence interval (CI) = 0.82-1.76], relapse [19.23% (10/52) and 18.00% (9/50); hazard ratio = 1.09, 95% CI = 0.45-2.62], and recurrence of clinical mastitis [17.31% (9/52) and 18.00% (9/50); hazard ratio = 1.26, 95% CI = 0.49-3.38] were not different between the KET and CON groups, respectively. The odds of a new intramammary infection at 14 d [20.75% (11/53) and 29.79% (14/47); odds ratio = 1.76, 95% CI = 0.66-4.73] or 21 d [28.57% (12/42) and 15.22% (7/46); odds ratio = 0.45, 95% CI = 0.16-1.30] were not different between the KET and CON groups, respectively. Mean somatic cell count was not different between the groups at 14 or 21 d. The results of this study suggest that a single intramuscular injection of ketoprofen as sole treatment for OFC-negative, mild clinical mastitis did not reduce time to clinical cure, relapse or recurrence of clinical mastitis, risk of subsequent intramammary infection, or milk somatic cell count compared with untreated controls.