Background & Objectives: Pseudomonas aeruginosa is a Gram-negative and aerobic bacterium. Exotoxin A is one of the important toxins produced by the bacterium and it is the main cause of mortality. About 90% of P. aeruginosa strains produce this toxin. Biofilm is a functional consortium of microorganisms attached to the body surfaces and bacteria are embedded in extracellular polymeric substances produced by the microorganisms. This bacterium is nontoxic in the planktonic form, but as a biofilm is highly toxic. In this study, we examined the association between the presence of exo-A gene and antibiotic resistance patterns with biofilm formation in Pseudomonas aeruginosa strains.

  Methods: In this study 110 strains of Pseudomonas aeruginosa isolated from various infections with defined antibiotic resistance patterns were used. The PCR method was used to detect the presence or absence of Exotoxin A gene (exo-A). Ability of biofilm formation was evaluated by spectrophotometry. Association between exo-A gene and antibiotic resistance patterns with biofilms formation was analyzed statistically by Fishers and Chi-square tests.

  Results: exo-A gene was detected in 93 strains (84.5%). Sixty two strains were multidrug resistant and they produced broad spectrum beta-lactamase enzyme. Results showed that, exo-A positive strains had significantly higher ability to biofilm formation in comparison with exo-A negative strains (p<0.05). Also the biofilm formation was significantly higher in multidrug resistant and ESBL producing strains (p<0.05).

  Conclusion: The results of this study indicate that there is a significant association between exo-A gene as well as antibiotic resistance pattern and ESBl producing with biofilm formation in Pseudomonas aeruginosa. Because of importance of biofilms in the pathogenesis of this bacterium, our study could open a new window for investigation of the molecular processes involved in the formation of biofilms.