Lactobacillus acidophilus–Derived Cell-Free Supernatant Augments Methylene Blue–Mediated Photodynamic Inactivation Efficacy Against Methicillin Resistant Staphylococcus aureus Planktonic Suspension and Biofilms

Infections caused by antimicrobial drug-resistant (AMR) pathogens like methicillin-resistant Staphylococcus aureus (MRSA) have triggered global scale search for innovative, clinically viable and cost affordable alternatives that do not generate resistance. Antimicrobial photodynamic therapy (aPDT) and postbiotics are innovative alternatives to circumvent AMR pathogens. However, MRSA biofilms reduce microbial susceptibility to aPDT and postbiotics. Integrating both modalities can be a novel MRSA anti-biofilm therapeutics avenue, but further studies are needed to validate the efficacy and applicability. We investigated the potentiality of methylene blue (MB)-mediated aPDT (MB-aPDT) followed by Lactobacillus acidophilus-derived cell-free supernatant (LA-CFS) treatment on MRSA planktonic culture, pre-formed biofilms, biofilm initiation, and maturation. Compared to aPDT or LA-CFS monotherapy, MB-aPDT followed by LA-CFS (20 and 40% v/v) treatment for 2 h leads to augmentation in inactivation of MRSA planktonic culture and CFU data correlates with flow cytometry data (R² = 0.87). Atomic force microscopy (AFM) unravels different pattern of morphological alterations elicited by aPDT or LA-CFS, but extensive cellular damage and cell fragmentation results from the combinatorial treatment. The determinants of LA-CFS-based augmented action seem to be pH labile. Further, destruction of preformed biofilm shows the following trend: aPDT < LA-CFS < aPDT + LA-CFS. Furthermore, MRSA surviving LA-CFS or aPDT can either adhere to the substratum or form loose biofilms, respectively, but the combinatorial regimen remarkably inhibits adherence and subsequent biofilm initiation, as well as maturation. The augmentation of MRSA inactivation using aPDT-postbiotics can be a new therapeutic avenue for the management of MRSA biofilm-associated infections.