BACTERIOCIN-PRODUCING LACTOBACILLI AS POTENTIAL BIOLOGICAL AGENTS FOR ANTI-Candida CONTROL

MONTÓN, MARCOS; RUIZ, FRANCISCO; ASURMENDI, PAULA; PASCUAL, LILIANA; BARBERIS, LUCILA

Córdoba

Congreso; XI Congreso Argentino de Microbiología General; 2015

In the last years, there has been a global increase of invasive and non-invasive infections produced by different Candida spp. Thus, research on probiotic lactobacilli has become relevant as biocontrol strategy. The aims of this study were i) to evaluate the antifungal activity of two human lactobacilli on different clinical isolates of Candida spp., ii) to determine the minimum inhibitory concentrations of the bacteriocins L23 and L60 on susceptible Candida strains, iii) to study the types of interactions between the bacteriocin-producing lactobacilli strains on the yeast growth. Lactobacillus fermentum L23 and L. rhamnosus L60 were selected for both, their relevant probiotic properties and the production of organic acids, bacteriocins (L23/L60) and, in the case of L60 strain, for the release of hydrogen peroxide in cell-free supernatants (CFSs). Pathogenic Candida species belong to the strain collection of our research group. The antimicrobial activity test of each Lactobacillus strains was performed by a cross streak-diffusion method using Candida spp. as indicator microorganisms. The CIMs of L23 and L60 were carried out by a well-diffusion method. To obtain these metabolites, each CFS of Lactobacillus strains was treated with NaOH 1 N to inhibit the organic acid action and, only in the case of L60 strain; it was also treated with peroxidase (NP-CFS) to prevent the H2O2 action. Thus, the NCFS of L23 and the NP-CFS of L60 contains the bacteriocins L23 and L60, respectively. To determine the interactions, a qualitative perpendicular-streaks-diffusion method was used. Two perpendicular streaks of lactobacilli describing a right angle were done on agar plates, incubated in optimal conditions. A suspension of Candida spp. (1.5 x108 CFU mL-1 ) was seeded in the free zone between the lactobacilli streaks. Interactions, synergistic indifferent, and antagonistic, were interpreted based on the shape of the inhibition zone. Seventy six percent of all Candida species tested (n=21), including different strains of C. albicans, C. tropicalis and C. guilliermondi, were inhibited by each Lactobacillus species. The antifungal activity of the L23 and L60 strains did not show statistically significant differences (P < 0.05). High inhibition values on the growth of C. albicans (89%), C. tropicalis (83%) and C. guilliermondii (75%) strains were found. The average sizes of theinhibition zones were 17.33 mm and 16.73 mm for L23 and L60 strains. The MIC range of bacteriocin L23 was 40-160 AU mL−1 for C. albicans strains, 40-80 AU mL-1 for C. tropicalis strains and 40 AU mL-1 for C. guilliermondii. While the MIC ranges of bacteriocin L60 were 80-160 AU mL−1 for C. albicans and C. tropicalis strains, and 80 AU mL-1 for C. guilliermondii. A 73% of synergism and a 27% of indifference between the lactobacilli was found. Antagonistic interactions were not observed. In conclusion, the combined use of these lactobacilli strains together with the antimicrobial potential of their bacteriocins could represent a valuable biological alternative for future anti-Candida agents.