Detection of AmpC and extended-spectrum β-lactamases producing strains in lower respiratory tract infections

Objective: The prevalence of AmpC β lactamases and extended spectrum β lactamases (ESBLs) producing strains were investigated from specimens of lower respiratory tract. Methods: AmpC β lactamases producing and AmpC β lactamases combined with ESBLs producing strains were detected by three dimensional test, ESBLs producing isolates were identified using method recommended by the National committee for Clinical Laboratory Standard (NCCLS). Results: Among 226 clinical isolates of Gram negative bacilli including E. cloacae, C. freundii, K. pneumoniae, E. coli, A. baumannii and P. aeruginosa , resistant to the first , second and at least one third generation cephalosporins, AmpC β lactamases, AmpC β lactamases combined with ESBLs, and ESBLs producing strains were found in 34, 15 and 109 strains, respectively, the incidence being 15.0%, 6.6% and 48.2%, respectively. AmpC β lactamases was detected in 57.9% of E. cloacae ESBLs detected in 78.5% of K.pneumoniae and 77.8% of E. coli. Conclusions: AmpC β lactamases and ESBLs are common in clinical strains of lower respiratory tract infections, the former mainly existed in E. cloacae strains and the latter in mainly K. pneumoniae and E. coli. strains.