ABSTRACT

       Background and Objectives: Pseudomonas aeruginosa is the most frequent opportunistic pathogen isolated from the sputum of patients with cystic fibrosis (CF). Resistance to β -lactam antibiotics may arise from over expression of the naturally occurring AmpC cephalosporinases or acquired extended-spectrum β-lactamases (ESBL). The aim of this study was to determine the antibiotic resistance profiles as well as the prevalence of ESBL and AmpC production in clinical isolates of P. aeruginosa from CF patients in Tehran.

         Methods: Antibiotic resistance of 50 non-duplicate P. aeruginosa isolates was determined by the disc diffusion method. AmpC β-lactamase production was detected by the antagonism disc test and ESBL production was detected by the phenotypic confirmatory test. The presence of ESBL and AmpC genes was assessed by PCR, followed by sequencing the PCR products.

         Results: The antibiotic resistance rates were as follows: 22% to ceftriaxone, 20% to cefotaxime, 10% to imipenem, 8% to carbenicillin and 6% to ticarcillin, 4% each to cefepime, tobramycin, amikacin and aztreonam and 2% to each piperacilin, meropenem and ceftazidime. AmpC production was observed in 47 isolates (94%) and ESBL production was observed in one isolate (2%). PCR results showed that all isolates carried the bla_AmpC β-lactamase gene. One multidrug-resistant isolate carried both bla_TEM and bla_PER-1 genes.

        Conclusion: The results showed that despite the low rate of antibiotic resistance in P. aeruginosa CF isolates,the  presence of multiple β-lactamases even in one isolate is alarming and can complicate the already difficult treatment of chronic infections in the lungs of CF patients.