Phenotypic and molecular characterization of extended spectrum- and metallo- beta lactamase producing Pseudomonas aeruginosa clinical isolates from Egypt.

Background: Antimicrobial resistance among Pseudomonas aeruginosa (P. aeruginosa), a leading cause of nosocomial infections worldwide, is escalating. This study investigated the prevalence of extended-spectrum β-lactamases (ESBLs) and metallo-β-lactamases (MBLs) among 104 P. aeruginosa clinical isolates from Alexandria Main University Hospital, Alexandria, Egypt.

Methods: Antimicrobial susceptibility testing was performed using agar dilution technique, or broth microdilution method in case of colistin. ESBL and MBL prevalence was assessed phenotypically and genotypically using polymerase chain reaction (PCR). The role of plasmids in mediating resistance to extended-spectrum β-lactams was studied via transformation technique using plasmids isolated from ceftazidime-resistant isolates.

Results: Antimicrobial susceptibility testing revealed alarming resistance rates to carbapenems, cephalosporins, and fluoroquinolones. Using PCR as the gold standard, phenotypic methods underestimated ESBL production while overestimating MBL production. Eighty-five isolates (81.7%) possessed only ESBL encoding genes, among which 69 isolates harbored a single ESBL gene [bla (n = 67) and bla (n = 2)]. Four ESBL-genotype combinations were detected: bla + bla (n = 8), bla + bla (n = 6), bla + bla (n = 1), and bla + bla + bla (n = 1). Three isolates (2.9%) possessed only the MBL encoding gene bla. Three ESBL + MBL- genotype combinations: bla + bla, bla + bla, and bla + bla + bla were detected in 2, 1 and 1 isolate(s), respectively. Five plasmid preparations harboring bla and bla were successfully transformed into chemically competent Escherichia coli DH5α with transformation efficiencies ranging between 6.8 × 10 3 and 3.7 × 10 4    CFU/μg DNA plasmid. Selected tested transformants were ceftazidime-resistant and harbored plasmids carrying bla.

Conclusions: The study highlights the importance of the expeditious characterization of ESBLs and MBLs using genotypic methods among P. aeruginosa clinical isolates to hinder the development and dissemination of multidrug resistant strains.