Introduction: Although bacteria producing biofilm are more resistance to antimicrobial agents, biofilm formation can stimulated by sub-minimal inhibitory concentrations (sub-MICs) of some antimicrobial agents. Therefore, we designed present study to investigate the  in vitro efficacy of several antibiotics (including ceftazidime, piperacillin, ticarcillin, carbenicillin, aztreonam, meropenem, gentamicin, amikacin and ciprofloxacin) and biocides (including savlon, benzalkonium chloride and chlorohexidin) on biofilm formation in Pseudomonas aeruginosa (P. aeruginosa) isolates.

Materials and methods: A total of 10 uropathogenic P. aeruginosa isolates were collected from Mostafa Khomaini Hospital in Ilam. The isolates were evaluated for MIC, biofilm formation ability and finally the effect of different concentration of antimicrobial agents on the biofilm formation.

Results: Our finding demonstrated that all antimicrobial agents except gentamicin, aztreonam, and savlon were able to induce biofilm formation at sub-MICs. Moreover, savlon was the best agents for encountering biofilm formation in P. aeruginosa.

Conclusion: Some antimicrobial agents are able to induce biofilm formation at sub-MICs. Biofilm formation inducement depended on antimicrobial agents, strains, and matrix composition.