Biofilm Formation and Antibiotic Resistance in <i>Pseudomonas aeruginosa</i> Isolates: Insights from Co-culture Experiments

Abstract

Background: Pseudomonas aeruginosa is a multidrug-resistant opportunistic pathogen known for its robust ability to form biofilms. This characteristic contributes to chronic infections in clinical settings and persistent contamination in industrial environments. Biofilms protect bacteria from hostile conditions, including antibiotics, making treatment more challenging. Objectives: The primary aim of this study was to isolate and characterize P. aeruginosa strains from diverse sources and to investigate how co-culturing influences biofilm formation and antibiotic resistance. Understanding these interactions may offer insights into microbial behavior and inform more effective therapeutic approaches. Methods: Ten P. aeruginosa isolates were collected from human, animal, and environmental samples. Each isolate was evaluated for molecular and phenotypic traits, including biofilm-forming capacity and susceptibility to 26 antibiotics. Twenty co-culture experiments were conducted by pairing two strains in equal ratios to assess inter-strain interactions and their effects on biofilm development and resistance profiles. Results: In mono-culture, all isolates formed biofilms: Ten percent were very strong producers, 40% strong, and 50% weak. At least one isolate was susceptible to 14 antibiotics. Co-culturing altered biofilm behavior significantly — 35% of combinations produced weak biofilms, while others failed to form biofilms entirely. Antibiotic resistance patterns also shifted, with some isolates acquiring resistance to up to four additional antibiotics. Interestingly, amikacin and colistin remained effective against most isolates in co-culture, even when susceptibility decreased in mono-culture. Conclusions: Co-culturing P. aeruginosa strains significantly affects both biofilm formation and antibiotic resistance, revealing complex inter-strain dynamics. These findings underscore the importance of considering microbial interactions in the development of antimicrobial strategies. A deeper understanding of these behaviors could lead to improved treatment protocols for multidrug-resistant infections and better management of microbial contamination in clinical and industrial environments.