ANTIBACTERIAL ACTIVITY OF PROBIOTIC STRAINS AGAINST Escherichia coli AND Klebsiella oxytoca

The introduction of microorganisms like the probiotics that confer a health benefit on the host can be a strategy to restore intestinal microbiota diversity, improve host health, and suppress clinical dysbiosis. Escherichia coli and Klebsiella oxytoca are common human and animal opportunistic pathogens often correlate with dysbioses and responsible for causing mild to severe illness. Therefore, the aim of this study was investigate the antibacterial activity of probiotic strains against E. coli and K. oxytoca. The probiotic strains employed in this study were Bifidobacterium animalis, Lactobacillus acidophilus ATCC 4356, L. fermentum ATCC 23271, L. paracasei ATCC 335 and L. brevis ATCC 367. Each probiotic strain was adjusted to the optical density of 0.3 at 600 nm, spread onto the Man Rogosa Sharpe (MRS) agar with sterile swabs and incubated for 36 hours at 37 °C. After, E. coli ATCC 25922 and K. oxytoca culture were adjusted at the same optical density and spread onto the Mueller Hinton (MH) agar with a sterile swab. Then, the probiotic cultures plates were cut into circles of agar (5mm) and placed on MH agar previously inoculated with the target bacterial strains. After 2 hours in the refrigerator the plates were incubated for 24 hours at 37 °C. The inhibitory activity was evaluated based on the formation of a clear zone around the agar disc. This test was repeated 3 times for each strain. The results showed that B. animalis was the most effective strain in inhibiting the growth of E. coli (p < 0,05) with an inhibition halo of 1,03 cm ± 0,06 and a very good reproducibility of the results. The other strains tested, had a slight to moderate inhibition feature, with L. acidophilus rated as the second most effective bacterium against E. coli. Furthermore L. acidophilus was the most effective strain in inhibiting the growth of K. oxytoca with an inhibition halo of 1,2 cm ± 0,06 and L. brevis was the second. In contrast, L. fermentum was the least (p < 0.05) effective strain, showing the lowest inhibitory activities against both pathogens. Since some strains showed strong antagonistic activities against E. coli and K. oxytoca, mainly B. animalis and L. acidophilus, they could be considered as good probiotics for treatment and prevention of infections caused by these opportunistic pathogens. In vivo studies will be needed to confirm and extend these preliminary indications.