Salicylate induction of phenotypic resistance to ceftazidime in pseudomonas aeruginosa and serratia marcescens possessing AmpC gene, isolated form nosocomial wound infections

ABSTRACT

Pseudomonas aeruginosa and Serratia marcescens is prevalent opportunistic pathogens in humans, causing many nosocomial infections including burn and surgical wounds that difficult to treat because of high resistance to a wide variety of antibiotics including cephalosporins, quinolones, aztreonam and imipenem. For many gram-negative bacteria, including Enterobacteriaceae and Pseudomonas spp., the production of the Chromosomally encoded, class C beta-lactamase, or the AmpC enzyme, represents the intrinsic mechanism of resistance to beta-lactam antibiotics. AmpC expression is under the control of a regulatory gene system. Many inducers cause constitutive overproduction of the enzyme and an increased resistance to agents, such as oxyiminocephalosporins including ceftazidime. AmpC is a group I, class C beta-lactamase present in most Enterobacteriaceae and in P. aeruginosa and other non-fermenting gram-negative bacilli. Salicylate and antibiotics are often administrated simultaneously, and subsequent high levels of both drugs can compromise their effectiveness. In this study, we aim to detect the effect of concomitant administration of salicylate and ceftazidime, on the sensitivity patterns of S. aeruginosa and S. marcescens. 20 [54.05%] out of 37 pseudomonas aeruginosa isolates are possessing the gene, where only 2 [30.00%] Serratia marcescens isolates out of 6 were positive for AmpC ACC-1 gene. Efficiency of plating and time kill study showed a decrease in the susceptibility to ceftazidime in the presence of salicylate concentration of 100 micro g/ml and 150 micro g/ml but not with 50 micro g/ml concentration with no significant difference to concentration higher than 100 micro g/ml. After subculturing in the absence of salicylate only 10 [62.5%] pseudomonas strains out of 16 recover their original susceptibility patterns, where the 2 tested Serratia strains recover their original susceptibility patterns. Also we test the same original 16 strains after exposure to ceftazidime alone without salicylate, on their resubculturing, also 11 strains only regain their original susceptibility pattern