Effect of Beta-Lactamase Expression on Susceptibility of Local Isolates of <i>Enterobacter cloacae, Serratia marcescens </i>and <i>Pseudomonas aeruginosas</i>Beta-Lactam Antibiotics

Abstract

During surveillance studies, a total of 66 strains of gram-negative bacilli (28 Enterobacter cloacae, 20 Serratia marcescens and 18 Pseudomonas aeruginosa) with a reduced susceptibility to third-generation cephalosporins, aztreonam and amikacin were isolated from documented infections. All isolates were highly susceptible to imipenem and sparfloxacin. β-Lactamase activity was demonstrated in all isolates of E. cloacae and S. marcescens, and in 77% of P. aeruginosa isolates. Inducible β-lactamase activity was detected in 80, 65 and 40% of E. cloacae, S. marcescens and P. aeruginosa isolates, respectively, when cefoxitin was used as an inducer. More inducible β-lactamase producers were observed when imipenem was used as an inducer. Isolates of E. cloacae, and to a lesser extent S. marcescens, expressed a wide spectrum of β-lactamase activities. There was a good correlation between baseline β-lactamase activity and the respective MIC of ceftazidime, cefotaxime and ceftriaxone, and to a lesser extent aztreonam in E. cloacae and S. marcescens isolates. Only one isolate of E. cloacae demonstrated an extended β-lactamase activity. The data suggest that the resistance of E. cloacae and S. marcescens isolates to β-lactam antibiotics is largely dependent upon hyperproduction of β-lactamase.

A CTX-M extended-spectrum β-lactamase in Pseudomonas aeruginosa and Stenotrophomonas maltophilia

“…P. aeruginosa is usually resistant to cefoxitin, as it contains an inducible AmpC enzyme (Livermore, 1991). However, failure of cefoxitin to induce AmpC production in P. aeruginosa has been reported previously (Ramadan et al, 1995).…”

Effects of Aztreonam in Combination with Antipseudomonal Antibiotics against Pseudomonas aeruginosa Isolated from Patients with Chronic or Recurrent Lower Respiratory Tract Infection

“…17 Imipenem has been reported to be a strong inducer of class I beta-lactamase production. 1s, 19 It is possible that one of the mechanisms of antagonism resulted from beta-lactamase production against aztreonam that was induced by imipenem in the tested strains. Thus, the administration of aztreonam with imipenem is problematic in patients with chronic respiratory tract infection.…”