Biofilm Formation by Pseudomonas aeruginosa in Medium Supplemented with Adult Bovine Serum and the Anti-Biofilm Activity of β-Lactam Antibiotics

Pseudomonas aeruginosa is a major opportunistic pathogen known for its ability to form biofilms in vivo, which contributes significantly to its resistance to antimicrobial treatment. In this study, we examined the biofilm-forming capacity of a clinical isolate cultured in medium supplemented with 30% adult bovine serum (ABS). Under these host-mimicking conditions, mature biofilms developed on microplate surfaces within 8 hours. Among the β-lactam antibiotics evaluated, piperacillin and cefoperazone exhibited potent anti-biofilm activity at concentrations as low as 1/8,192 to 1/256 of their respective minimum inhibitory concentrations (MICs). In contrast, ceftazidime and meropenem required significantly higher concentrations (approximately 1/16 MIC) to produce similar effects. The anti-biofilm activity of piperacillin and cefoperazone was abolished when ABS was defatted with n-hexane or when magnesium sulfate was added to the medium, suggesting that a lipid-dependent membrane permeabilization mechanism may be involved. These findings highlight the utility of host-mimicking conditions in evaluating the activity of antibiotics against biofilms and suggest that certain β-lactam agents may have previously unrecognized anti-biofilm effects mediated through serum-associated components.