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Antibacterial Activity, Biofilm Inhibition, and Modulation of Virulence-Associated Gene Expression by Probiotic-Derived Cell-Free Supernatants Against Multidrug-Resistant Serratia marcescens

Year: 2026

Type: article

Abstract: Background: Multidrug-resistant (MDR) Serratia marcescens is an important opportunistic pathogen associated with persistent healthcare-associated infections, partly because of its capacity to form biofilms and express virulence-associated factors. Probiotic-derived cell-free supernatants (CFSs) contain secreted metabolites that may provide non-antibiotic approaches for controlling resistant bacteria. However, comparative data on bacterial- and yeast-derived CFSs against S. marcescens remain limited. Methods: CFSs were prepared from Lacticaseibacillus rhamnosus GG, Bacillus coagulans , Bifidobacterium longum , and Saccharomyces boulardii . Metabolite profiles were examined by GC–MS. Antibacterial activity was assessed by disk diffusion and broth microdilution. Biofilm-formation inhibition was evaluated by crystal violet staining at 1/2 and 1/4 MIC. Expression of fimA, bsmA , and shlA was examined by qRT-PCR, and HEK293 cell viability was assessed by MTT. Results: All four CFSs inhibited S. marcescens growth in a concentration-dependent manner. L. rhamnosus GG showed the greatest activity, with a MIC/MBC of 0.375/0.75 mg/mL and a 26-mm inhibition zone at 12 mg/mL. At 1/2 MIC, biofilm-formation inhibition was 71%, 57%, 47%, and 32%, respectively. All four CFSs significantly reduced fimA and bsmA expression, whereas shlA expression was significantly reduced by L. rhamnosus GG, B. coagulans , and B. longum , but not by S. boulardii . HEK293 cell viability remained above 80% under the tested conditions. Conclusion: Probiotic-derived CFSs demonstrated antibacterial and biofilm-formation inhibitory activities and were associated with reduced expression of selected virulence-associated genes in S. marcescens. L. rhamnosus GG-derived CFSs showed the strongest overall activity, supporting further mechanistic and in vivo studies. Keywords: Serratia marcescens , multidrug-resistant bacteria, cell-free supernatants, antibacterial activity, antibiofilm activity

Source: Infection and Drug Resistance

DOI: 10.2147/idr.s647738

Authors: Mahdi Asghari Ozma, Niloofar Fallahi Alileh, Seyyed Reza Moaddab

Institutions: Qom University of Medical Science and Health Services, Tabriz University of Medical Sciences

Language: English

Topic: Probiotics and Fermented Foods

Subfield: Food Science

Field: Agricultural and Biological Sciences

Domain: Life Sciences

SDG: Good health and well-being

Open Access status: gold

Estimated APC paid: $2,836