Antagonistic properties of probiotic Bacillus strains against multidrug-resistant clinical isolates of E. coli, S. aureus and P. aeruginosa

Introduction.Multidrug-resistant (MDR) strains of Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa are among the most clinically important pathogens responsible for healthcare-associated and community-acquired infections. The growing prevalence of antimicrobial resistance has reduced the effectiveness of conventional antibiotic therapy, creating an urgent need for alternative antimicrobial approaches. One promising strategy involves probiotic bacteria of the genus Bacillus. These microorganisms produce biologically active compounds, including bacteriocins, antimicrobial peptides, and hydrolytic enzymes, contributing to their antagonistic activity against pathogens. The findings may facilitate the development of novel probiotic formulations and therapeutic strategies for combating antibiotic-resistant bacterial infections.

Methods.The study was conducted by the well method. Cultures of test bacteria were seeded with a lawn on Mueller-Hinton agar. In a dense nutrient medium, wells with a diameter of 5 mm were made with a glass tube. A bacterial suspension with a concentration of 1x10⁸ CFU/ml in a volume of 10 μl of each probiotic strain was added to the wells. Antagonistic properties were assessed by the zone of growth inhibition in mm around the wells after 24 hours of incubation at 37C.

Results.B. pumilus LA56 had the greatest antagonistic activity against E. coli (8-9mm), S. aureus (10-12mm) and P. aeruginosa (10-15mm). B. licheniformis EA22 did not show any antagonistic activity against the test bacterial cultures. B. mucilaginosus ACH82 was effective against E. coli (6-7mm) and S. aureus (17-19mm), while B. subtilis AX20 was effective only against E. coli (5-6mm).

Conclusions.The probiotic Bacillus spp. exhibited strain-dependent antagonistic activity against multidrug-resistant clinical isolates of E. coli, S. aureus, and P. aeruginosa. Among the tested strains, B. pumilus LA56 demonstrated the broadest and strongest inhibitory activity, whereas B. licheniformis EA22 showed no antagonistic effect under the experimental conditions.