A comparative in vitro study of cephalosporin/beta-lactamase inhibitor combinations against gram negative bacilli

The present study aims at comparing the in-vitro susceptibility of six commercially available cephalosporin--BLI combinations with cephalosporins alone against hospital isolates of Gram negative bacilli. Gram negative bacilli, numbering 500, isolated from various clinical samples, were included in the study. The isolates were also screened for ESBL production by the methods recommended by CLSI. Susceptibility pattern of six Cephalosporins/Betalactamase inhibitor (BLI) combinations were compared with their partner cephalosporins. Overall, 29.6% of Gram negative bacilli were susceptible to the five Cephalosporins (IIIrd & IVth gen); the highest activity being shown by cefepime. Susceptibility was much higher (more than double) to the Cephalosporin combinations containing Tazobactam (TZB) & sulbactam (SLB) (62.7%). However such enhanced susceptibility was completely lacking with combinations containing clavulanate (29.1%). Gram negative bacilli, as a group, exhibited very high resistance to the new cephalosporins (IIIrd & IVth gen). When these agents were tested as fixed-dose combinations with TZB & SLB, the overall susceptibility was enhanced by more than 100%. Such an enhancement was absent with clavulanate combinations. Cefepime/TZB revealed the highest activity against ESBL producing GNB. Further studies are needed in the clinical settings as they can play an important role as good alternatives to carbapenems.