Synergy in penicillin, cephalosporin, amphenicols, and aminoglycoside against MDR S. aureus isolated from Camel milk

Abstract This study investigated the synergy testing of penicillin, cephalosporin, amphenicols, and aminoglycoside in the camel milk (n=768 samples), subsequently used for isolation of MDR S. aureus targeting mecA gene. Antibiotic susceptibility of S. aureus showed >90% isolates were sensitive to ciprofloxacin and trimethoprim and resistant against oxacillin, ampicillin, and cefoxitin. Further, 50-85% of the S. aureus were sensitive to gentamicin, oxytetracycline, and chloramphenicol and resistant against cefotaxime, vancomycin, and cefixime. Minimum inhibitory concentration (MIC) of cefotaxime, (C) and ampicillin (A) in combination with gentamicin (G) was reduced by 99.34% and 70.46%, respectively, while with chloramphenicol (Ch), reduction was 57.49% and 60%, respectively. In addition, the Fractional Inhibitory Concentration Index (FICI) of G+A, Ch+C and Ch+G combinations showed synergy against 80%, 60%, and 30% of MDR S. aureus, respectively. Similarly, C+A and Ch+G displayed indifferent interaction against 70 % and 30% of isolates, respectively, while the later showed additive interaction against 10% of MDR S. aureus. Altogether, our results described effective combination of gentamicin and chloramphenicol with ampicillin and cefotaxime to combat MDR S. aureus.

摘要 本研究针对768份驼乳样本开展青霉素、头孢菌素、酰胺醇类及氨基糖苷类抗生素的协同药效试验，后续以mecA基因为靶标分离多重耐药（Multidrug Resistant, MDR）金黄色葡萄球菌（S. aureus）。药敏试验结果显示，90%以上的金黄色葡萄球菌分离株对环丙沙星与甲氧苄啶呈敏感状态，对苯唑西林、氨苄西林及头孢西丁则表现为耐药。进一步研究表明，50%~85%的金黄色葡萄球菌分离株对庆大霉素、土霉素及氯霉素敏感，对头孢噻肟、万古霉素及头孢克肟耐药。联合庆大霉素（G）时，头孢噻肟（C）与氨苄西林（A）的最低抑菌浓度（Minimum Inhibitory Concentration, MIC）分别下降99.34%与70.46%；联合氯霉素（Ch）时，二者的MIC分别下降57.49%与60%。此外，庆大霉素+氨苄西林（G+A）、氯霉素+头孢噻肟（Ch+C）及氯霉素+庆大霉素（Ch+G）组合的分级抑菌浓度指数（Fractional Inhibitory Concentration Index, FICI）显示，其分别对80%、60%及30%的多重耐药金黄色葡萄球菌具有协同抑菌活性。同理，头孢噻肟+氨苄西林（C+A）与氯霉素+庆大霉素（Ch+G）组合分别对70%及30%的分离株表现为无关相互作用，而后者还对10%的多重耐药金黄色葡萄球菌表现为相加相互作用。综上，本研究结果证实，庆大霉素、氯霉素分别与氨苄西林、头孢噻肟联合使用，可有效对抗多重耐药金黄色葡萄球菌。