Exploring the antimicrobial potential of lactobacilli against early-stage and mature biofilms of Staphylococcus aureus and Pseudomonas aeruginosa.

Bacterial biofilms are dynamic, complex, and very adaptive, and they can cause health problems in both humans and animals while also posing a serious threat to various industries. This study explores the potential of cell-free preparations of lactobacilli isolated from breast milk (HM; n = 11) and infant fecal (IF; n = 15) samples to impact the growth of Staphylococcus aureus and Pseudomonas aeruginosa biofilms. The anti-biofilm activity of three distinct cell-free preparations, namely, untreated cell-free supernatant (CFS), pH-neutralized CFS (N-CFS), and heat-treated CFS (H-CFS), was examined against both early-stage and mature biofilms. The post-incubation strategy examined the impact on mature biofilms, while the co-incubation treatment assessed the impact of CFS on adhesion and initial colonization. Compared to post-incubation treatment (HM3, 67.12%), the CFSs exhibited greater inhibitory activity during co-incubation (IF9, 85.19%). Based on the findings, untreated CFS exhibited the most promising biofilm inactivation, although its activity was not completely lost upon pH neutralization and heat treatment. Treatment with H-CFSs and N-CFSs moderately reduced the population of S. aureus and P. aeruginosa bacterial cells within the biofilm by 40%-60%. Microscopic observations showed that after CFS treatment, the integrity of the biofilm conformation was disrupted. According to principal component analysis (PCA) (significance level at p < 0.05), the most promising anti-biofilm activity against both test pathogens was found in the CFS of Lacticaseibacillus paracasei HM1.