Comparative Evaluation of the in-vitro Activity of Six β-lactam/β-lactamase Inhibitor Combinations against Gram Negative Bacilli.

BACKGROUND The extensive use of the β-lactam antibiotics in hospitals and in the community has created major resistance problems which has led to increased morbidity, mortality and healthcare costs. The use of the β-lactamase inhibitors in combination with the β-lactam antibiotics is currently the most successful strategy used for circumventing the resistance mechanisms. OBJECTIVE To evaluate the in-vitro activity of six commercially available β-lactam/β-lactamase inhibitor combinations against Gram Negative Bacilli (GNB). MATERIALS AND METHODS A total of 384 non duplicate, consecutive, gram negative bacilli (278 Enterobacteriaceae and 106 non fermenters) isolated from various clinical samples were subjected to antimicrobial sensitivity testing by the Kirby-Bauer method. The following β-lactam/β-lactamase inhibitor combinations were tested: amoxycillin-clavulanic acid, ampicillin-sulbactam, cefoperazonesulbactam, piperacillin-tazobactam, cefepime-tazobactam and ticarcillin-clavulanic acid. RESULTS Against the Enterobacteriacae, the sensitivity of Cefepime- tazobactam was 90. 64%, followed by Cefoperazone-sulbactam (84.89%) and Piperacillin - tazobactam (53.95 %). The sensitivity of the non fermenters was the highest for Cefepime- tazobactam (49.04%) and was least for Ampicillin-sulbactam and Amoxycillinclavulanic acid (4.71% each). Cefepime-tazobactam was sensitive for all the extended spectrum β-lactamase (ESBL) isolates. CONCLUSION Among the six β-lactam/β-lactamase inhibitor combinations tested, Cefepime-tazobactam exhibited the best in-vitro activity against the gram negative bacilli isolated at our centre.