Modulation of Antimicrobial Activity in Probiotic Lactobacillus Strains by Biowavelength Laser Irradiation

Abstract

This study investigated the effect of diode laser irradiation on the antibacterial activity and metabolite profile of a local Lactobacillus isolate and evaluated its potential to modulate the production of bioactive antimicrobial metabolites. A local Lactobacillus isolate, designated Lactobacillus sp, was selected based on its inherent antibacterial activity against the tested pathogenic bacteria. De Man, Rogosa and Sharpe (MRS) broth adjusted to pH 5 was used for bacterial cultivation and antimicrobial metabolite production. Cultures were incubated at 40 °C for 60h under shaking conditions. The inoculum was exposed to diode laser irradiation at wavelengths of 532 and 650 nm for 1, 2, and 3 min, with a non-irradiated culture serving as the control. Each treatment was performed in five replicates. The antibacterial activity of the treated and control cultures was evaluated against Escherichia coli and Staphylococcus aureus using an agar-based antimicrobial assay. Furthermore, Gas Chromatography–Mass Spectrometry (GC-MS) was used to characterize the metabolite profiles and identify compounds detected following laser exposure. The results demonstrated that laser irradiation enhanced the antibacterial activity of Lactobacillus sp., with the response varying according to the irradiation wavelength and exposure conditions. Compared with the non-irradiated control, selected irradiation treatments increased the antibacterial activity, as evidenced by the greater inhibition of the tested bacterial pathogens. Furthermore, GC–MS analysis revealed qualitative and quantitative alterations in the detectable metabolite profile, including the appearance or increased abundance of several compounds with reported or potential antimicrobial properties. These findings suggest that laser irradiation may enhance the antibacterial potential of Lactobacillus sp. by modulating its metabolite production. These findings suggest that diode laser irradiation can influence the metabolic behavior of Lactobacillus sp and may serve as a physical stimulus for modulating the production of bioactive antimicrobial metabolites. Further studies are required to elucidate the underlying mechanisms and experimentally confirm the antimicrobial contribution of the individual compounds identified by GC-MS.