Extended spectrum beta-lactamase mediated resistance to third generation cephalosporins in Klebsiella pneumoniae in Nagpur, central India

Out of 66 clinical isolates of Klebsiella pneumoniae, 17 showed resistance or decreased susceptibility to third generation cephalosporins (17 to cefotaxime, 16 to ceftriaxone, and 9 to ceftazidime) while the remaining 49 were sensitive by the disc diffusion method. The minimum inhibitory concentrations (MICs) of the third generation cephalosporins (3GC) for the strains ranged from 2-128 mu g/ml by agar dilution method. Their sensitive phenotypes had zone diameters smaller (mean difference 3.1 mm for ceftriaxone, and 6.5 mm for ceftazidime), and MICs > 10 fold higher than the corresponding values in the fully sensitive isolates. Resistance to cefotaxime was transferred to recipient Escherichia coli K12 strain in 15 isolates. All the resistant isolates were sensitive to imipenem but were variably sensitive to aminoglycosides, and quinolones. In all the 17 resistant isolates extended spectrum beta-lactamase (ES beta L) was detected. The sensitivity testing systems may fail to recognise the potential ES beta L mediated resistance to 3GC. Hence ES beta L detection should be routinely undertaken.