Atividade de Bifidobacterium animalis subsp. lactis INL1 sobre bactérias patogênicas isoladas de ambiente hospitalar

Abstract

Probiotics are living microrganisms that, when administered in appropriate amounts, confer benefits to the health of the host. Among several applications the regulation of intestinal microbiota stands out. They present antibacterial activity in front of several Gram-positive and negative species through some action mechanisms, being the main suggested the capacity of production of antimicrobial substances, as the bacteriocins. Bifidobacterium is a probiotic bacterial genus present in the microbiota of some human sites, being the species B. animalis subsp. lactis one of the known strains with good results of its probiotic action, but little explored in relation to the antibacterial activity. The growing reports of resistance, mainly nosocomial, and the search for new antimicrobial agents justify the realization of this work, which aimed to evaluate the activity of the cell-free supernatant (CFS) of B. animalis subsp. lactis INL1 culture against methylicin-resistant Staphylococcus aureus (MRSA), carbapenemase producing Klebsiella pneumoniae and extended spectrum beta-lactamase producing Escherichia coli (ESBL) isolated from hospital environment. The CFS of the probiotic strain was tested using three methods. For all, pathogenic microorganisms were prepared in 0.89% saline suspension, adjusted to McFarland's 0.5 scale. By diffusion on agar, the suspension was sown in plate and 40 µL of the supernatant was added to the wells made in the soft agar in order to allow the diffusion of CFS through the medium. In the disc-diffusion methodology, the CFS in test was applied on previously sterilized discs, in the same volume of 40 µL, also on plates with previous sowing of the adjusted solutions. For both were tested together with negative control wells and discs with 0.89% sterile saline solution. For the microdilution in the broth, the antimicrobial activity was evaluated using 100 µL of CFS on the same volume of each microbial suspension. They were also applied in the microplate wells with sterility control (only with Brain Heart Infusion broth - BHI) and growth control, (BHI broth + bacterial suspension). The results showed that CFS was not able to inhibit the growth of pathogenic strains and there is a need for further studies to optimize the growth of B. animalis subsp. lactis INL1 that favor the production of bacteriocins and allow better investigation of the antimicrobial action in vitro.