Antimicrobial and immunoregulatory effects of Lactobacillus delbrueckii 45E against genitourinary pathogens

Lactobacilli are essential microbiota that maintain a healthy, balanced vaginal environment. Vaginitis is a common infection in women during their reproductive years. Many factors are associated with vaginitis; one of them is the imbalance of microbiota in the vaginal environment. This study aimed to evaluate the antimicrobial properties of Lactobacillus delbrueckii 45E (Ld45E) against several species of bacteria, namely, Group B Streptococcus (GBS), Escherichia coli, Klebsiella spp., and Candida parapsilosis, as well as to determine the concentration of interleukin-17 (IL-17) in the presence of Ld45E.

The probiotic characteristics of Ld45E were evaluated by examining its morphology, pH tolerance, adhesive ability onto HeLa cells, hemolytic activity, antibiotic susceptibility, and autoaggregation ability. Then, the antimicrobial activity of Ld45E was determined using Ld45E culture, cell-free supernatant, and crude bacteriocin solution. Co-aggregation and competition ability assays against various pathogens were conducted. The immunoregulatory effects of Ld45E were analyzed by measuring the proinflammatory cytokine IL-17. A p-value less than 0.05 was considered statistical significance.

Ld45E is 3-5 mm in diameter and round with a flat-shaped colony. pH 4 and 4.5 were the most favorable range for Ld45E growth within 12 h of incubation. Ld45E showed a strong adhesion ability onto HeLa cells (86%) and negative hemolytic activities. Ld45E was also sensitive to ceftriaxone, cefuroxime, ciprofloxacin, and doxycycline. We found that it had a good autoaggregation ability of 80%. Regarding antagonistic properties, Ld45E culture showed strong antimicrobial activity against GBS, E. coli, and Klebsiella spp. but only a moderate effect on C. parapsilosis. Cell-free supernatant of Ld45E exerted the most potent inhibitory effects at 40 °C against all genital pathogens, whereas bacteriocin showed a robust inhibition at 37 °C and 40 °C. The highest co-aggregation affinity was observed with GBS (81%) and E. coli (40%). Competition ability against the adhesion of GBS (80%), E. coli (76%), Klebsiella (72%), and C. parapsilosis (58%) was found. Ld45E was able to reduce the induction of the proinflammatory protein IL-17.

Ld45E possessed antimicrobial and immunoregulatory properties, with better cell-on-cell activity than supernatant activity. Thus, Ld45E is a potential probiotic candidate for adjunct therapy to address vaginal infections.