Different Photoresponses of Microorganisms: From Bioinhibition to Biostimulation.

The effective treatment of antimicrobial modalities continues to be a serious challenge, mainly due to the increasing number of multidrug resistance pathogenic microorganisms. Microbial bioinhibition is an alternative method that has shown to be effective. This study investigated and described the effect of the visible light on five different microorganisms. The studied groups were composed by the species Acanthamoeba polyphaga, Candida albicans, Mycobacterium massiliense, Pseudomonas aeruginosa, and Staphylococcus aureus. These microorganisms were analyzed after six light doses exposition with three different wavelengths: 450, 520, and 630 nm. The present study indicates two different behaviors: bioinhibition and/or biostimulation. The bioinhibition effect was calculated using different percentages of the microorganism population, compared to the control group, in which the maximum value corresponds to 94% growth inhibition. The biostimulation effect was evaluated by the microorganism population increment for specific light doses. Our results showed a 132% population growth as the maximum value. These results were assessed by variance analysis. The Tukey's test was used for differentiating or comparing, depending on the circumstances. The obtained results suggested a visible light phototherapeutic effect that could be used as a microorganism inactivation method for the studied microorganisms. In some approaches, the biostimulation effect might also be a very interesting effect to be considered. This study supports the relevance of understanding the important role that phototherapy plays as a useful method for microbiological control studies and applications.