Potent antagonistic activity of Egyptian Lactobacillus plantarum against multiresistant and virulent food-associated pathogens

Recent years have shown a growing interest to replace the administration of antibiotics with the application of probiotics. The aim of our investigation was to screen for promising strains with broad antimicrobial activity and also more resistant to the challenges met in the gastrointestinal tract. In our study, only 32 out of 50 (64%) probiotic isolates showed antagonistic activity against certain major extensively and pandrug-resistant Grampositive and -negative food-borne pathogens. Fifteen L. plan tarum isolates had a broad antibacterial spectrum. Among these isolates, only five presented potent antibacterial activity relative to previous studies. The recorded inhibition zone diameter ranged from 25 to 44 mm. Pronounced cell-free supernatant activities (6400-25,600 AU/ml) were commonly detected at the end of the logarithmic phase at 37 degrees C. A marked increase in the range of activity (12,800-51,200 AU/ml) was recorded after the addition of 0.9% Na Cl to the media. Moreover, subjecting these isolates to different stressors, including high temperature, low pH, and different concentrations of bile and Na Cl, revealed different responses, and only two out of the five L. plantarum isolates showed marked resistance to all of the stress factors. Accordingly, this study highlights the intense and broad antagonistic activity induced by L. plan tarum against various food associated pathogens, and their ability to resist different stressors suggests that they can be used in the food and pharmaceutical industry.