Antimicrobial and antibiofilm effects of Lactobacillus cell-free supernatants against standard and antibiotic-resistant Pseudomonas aeruginosa and Staphylococcus aureus.

Biofilm-producing pathogens, including multidrug-resistant Pseudomonas aeruginosa and Staphylococcus aureus, pose significant clinical challenges within medical settings. Eradication of the biofilm remains a challenging mission, prompting ongoing scientific research for effective solutions. This research investigated the high antimicrobial and antibiofilm capacity of cell-free supernatants (CFS) from Lacticaseibacillus casei PTCC 1608 and Lactobacillus acidophilus PTCC 1643 against these challenging-to-treat pathogens. We tested these Lactobacilli's CFS antibacterial potential against P. aeruginosa ATCC 27,853, S. aureus ATCC 25,923, P. aeruginosa PAO1, and methicillin-resistant Staphylococcus aureus (MRSA; UTMC 1442) by the microdilution technique to find out the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values. Subsequently, the inhibitory and disruptive capacity of the CFS for established biofilms was tested at concentrations corresponding to their respective MIC and MBC values. Ultimately, the chemical characterization of Lactobacillus supernatant compositions by the gas chromatography-mass spectrometry (GC-MS) technique helped reveal the antibacterial and antibiofilm-active organic compounds. Notably, the P. aeruginosa ATCC 27,853 biofilm was significantly eliminated by L. casei and L. acidophilus supernatants at 3×MBC by 88.39 ± 3.6% and 80.47 ± 6.3%, respectively. Furthermore, at ¼ MIC, L. casei inhibited MRSA biofilm by 80.17 ± 6.2%. Acetic acid derivatives, lactic acid, and phthalic acid were identified by GC-MS analysis as important constituents of the Lactobacillus supernatants. Further confirmed by electron microscopy, our findings highlight strong in vitro antibiofilm and antibacterial activities of indigenous Iranian Lacticaseibacillus casei PTCC 1608 and Lactobacillus acidophilus PTCC 1643 supernatants. These results suggest their potential as natural sources of bioactive compounds that could be further explored for developing biotherapeutic strategies against biofilm-associated infections and antibiotic resistance.