Características probióticas e imunomoduladoras de cepas de Bacillus velezensis e seus impactos na infecção in vitro por Leishmania braziliensis

Abstract

Leishmaniasis comprises a group of neglected tropical diseases of major public health relevance, associated with high morbidity and important therapeutic limitations, such as toxicity, high cost, and resistance to available drugs. The immune response against infection is complex and decisive for the clinical outcome, making modulation of the host response a promising strategy for the development of new therapeutic approaches. Organisms with probiotic properties have emerged as potential immunomodulators, and species of the genus Bacillus present advantages such as the ability to survive adverse conditions of the gastrointestinal tract and to produce bioactive metabolites. This study aimed to characterize the probiotic properties of Bacillus velezensis strains (1273, 144, and 118) and to evaluate the potential application of their cell-free supernatants (CFS) in modulating the immune response, as well as their activity against Leishmania braziliensis in vitro. To this end, the ability of the strains to survive exposure to acidic pH and bile salts—simulating passage through the gastrointestinal tract—was assessed, along with their adhesion capacity and interaction with pathogenic microorganisms, in addition to determining their antibiotic susceptibility and resistance profiles. Furthermore, the activity of the CFS was investigated on cell lines and promastigote forms of L. braziliensis, including the evaluation of immunomodulatory effects under pre- and post-parasitic infection conditions, as well as the measurement of reactive oxygen species and nitric oxide production. The evaluated strains exhibited characteristics indicative of potential probiotic application. Although no significant direct leishmanicidal effect was observed at safe concentrations, the CFS promoted a significant reduction in the infection index and parasite burden in macrophages, associated with increased reactive oxygen species and cytokine modulation. These findings indicate that metabolites derived from B. velezensis may act through modulation of the host immune response, highlighting their potential as an adjuvant strategy in the control of cutaneous leishmaniasis. However, further studies are needed to validate their applicability in in vivo models.