Strict anaerobic bacteria: comparative study of various beta-lactam antibiotics in combination with tazobactam or sulbactam

The minimal inhibitory concentrations of piperacillin (PIP) or cefotaxime (CTX) alone or in combination with tazobactam (TAZ) were determined against 168 anaerobes. All the strains were inhibited by PIP + TAZ, but certain strains resistant to CTX + TAZ were found among B. fragilis, Eubacterium and Peptostreptococcus. The second investigations included 30 strains of Bacteroides fragilis. Concentrations of 2, 4 and 8 mg/l of TAZ and sulbactam (SUL) were combined with piperacillin or cefotaxime. The two beta-lactamase-inhibitors had similar activities when used at 2 or 4 mg/l, but at 8 mg/l TAZ was more active than SUL. All B. fragilis strains were inhibited by PIP + TAZ or PIP + SUL, whereas resistance was observed with CTX + SUL or CTX + TAZ. On the same strains the activities of 6 beta-lactams (PIP, mezlocillin, ticarcillin (TIC), CTX, ceftriaxone and ceftazidime) were determined in combination with either SUL 4 mg/l or TAZ 8 mg/l. Only PIP or TIC + SUL or TAZ were able to inhibit at least 90% of tested strains. No resistance could be detected with PIP + TAZ combination. As conclusion, the two inhibitors when combined with PIP or TIC offered greater activity against both Gram positive or negative anaerobes and PIP + TAZ remained the more potent combination.