SUSCEPTIBILITY TO ANTIMICROBIAL DRUGS AND PRODUCTION OF BETA-LACTAMASE BY STAPHYLOCOCCUS STRAINS ISOLATED FROM MASTITIS IN GOATS IN THESEMI-ARID REGION OF PARAIBA STATE, BRAZIL

ABSTRACT The present study was aimed to test the in vitro antimicrobial susceptibility using disc diffusion assay and minimum inhibitory concentration (MIC) values, as well as the production of beta-lactamase of 42 strains of Staphylococcus sp. isolated from subclinical mastitis in goats in the semi-arid region of Paraiba state, in Brazil. To this end, 14 samples of negative Staphylococcus chromogenes, 10 S. waneri, 6 S. saprophyticus, 5 S. aureus, 3 S. epidermidis, 2 S. intermedius and 2 Staphylococcus were used. Regarding the in vitro susceptibility, the highest levels of resistance observed concerned penicillin (66.67%) and ampicillin (63.89%), and the greatest sensitivity observed concerned Cefoxitin (97.22%). Multiple resistance to 3 or more antimicrobial drugs was observed in 42.86% of the isolates. Of the total Staphylococcus isolated, 73.81% were positive for the beta-lactamase production test. The minimum inhibitory concentration showed 100% of the samples susceptible to norfloxacin, and the maximum resistance values to the other antimicrobial drugs were 30%. According to the results obtained, it is concluded that, in order to select the most appropriate drug to treat mastitis in goats caused by strains of Staphylococcus, the antimicrobial sensitivity profile of the strain must be known and routine laboratory tests for detecting beta-lactamase should be performed because these enzymes are disseminated both in human and veterinary medicine. The high resistance to penicillin and ampicillin demonstrates the limitation in the use of antibiotics in the treatment of mastitis in goats. Although in the present study the cephalosporines demonstrated a considerable degree of sensitivity, the use of these antimicrobial agents in veterinary medicine becomes a matter of concern due to the incidence of strains that produce betalactamase.摘要 本研究旨在通过纸片扩散法（disc diffusion assay）与最低抑菌浓度（minimum inhibitory concentration, MIC）试验，检测巴西帕拉伊巴州半干旱地区山羊亚临床乳腺炎分离得到的42株葡萄球菌属（Staphylococcus sp.）菌株的体外抗菌药物敏感性，以及其β-内酰胺酶（beta-lactamase）产生情况。 为此，本研究共纳入14株阴性产色葡萄球菌（Staphylococcus chromogenes）、10株沃纳葡萄球菌（S. waneri）、6株腐生葡萄球菌（S. saprophyticus）、5株金黄色葡萄球菌（S. aureus）、3株表皮葡萄球菌（S. epidermidis）、2株中间葡萄球菌（S. intermedius）以及2株未明确种属的葡萄球菌菌株。 关于体外药敏结果，本研究观察到耐药率最高的抗菌药物为青霉素（66.67%）与氨苄西林（63.89%），而敏感性最高的抗菌药物为头孢西丁（97.22%）。42.86%的分离菌株呈现对3种及以上抗菌药物的多重耐药性。 在所分离的全部葡萄球菌菌株中，73.81%的菌株β-内酰胺酶检测呈阳性。最低抑菌浓度试验结果显示，所有受试菌株对诺氟沙星均表现为敏感，其余抗菌药物的最高耐药率为30%。 基于上述试验结果，本研究认为，若要筛选适用于治疗山羊葡萄球菌性乳腺炎的最优药物，需明确菌株的抗菌药物敏感性谱，并常规开展β-内酰胺酶检测——因该类酶在人类医学与兽医学领域均已广泛传播。青霉素与氨苄西林的高耐药率表明，使用抗生素治疗山羊乳腺炎的方案存在局限性。尽管本研究中头孢菌素类药物展现出较好的敏感性，但由于产β-内酰胺酶菌株的存在，该类抗菌药物在兽医学中的应用仍需引起重视。