ANTIMICROBIAL RESISTANCE AND PREVALENCE OF EXTENDED-SPECTRUM BETA-LACTAMASE AMONG CLINICAL ISOLATES OF GRAM-NEGATIVE BACTERIA IN RIYADH

The activity of ciprofloxacin, imipenem and 12 other commonly used ant ibiotics was evaluated against 106 documented clinical isolates from a medical Intensive Care Unit (ICU). The resistance rates to ceftriaxon e, cefotaxime, aztreonam and ceftazidime were 42, 25, 24 and 21%, resp ectively. Apart from Pseudomonas aeruginosa, all isolates were sensiti ve to ciprofloxacin and imipenem. Complete cross resistance among test ed beta-lactam groups was uniformly evident in Enterobacter cloacae, C itrobacter freundii and P. aeruginosa. On the other hand, penicillins and second generation cephalosporins showed cross resistance among Esc herichia coli and Klebseilla pneumoniae isolates. Induction experiment s indicate that 70 and 62% of P. aeruginosa and E. cloacae or C. freun dii produce class I cephalosporinase, respectively. Among all tested i solates, plasmid mediated extended spectrum beta-lactamase (ESBL) was detected in one isolate of K. pneumoniae. The plasmid mediated beta-la ctamase is transferable and inhibited by beta-lactamase inhibitors. Th e transconjugates not only expressed resistance to extended spectrum b eta-lactams and aztreonam but also toward tested aminoglycoside antibi otics, with the exception of gentamicin. The obtained transconjugates conferred high level resistance to ceftazidime and aztreonam but consi derably low resistance to ceftriaxone and cefotaxime. The isoelectric point for the extended-spectrum beta-lactamase is 8.2.