RESUMEN
Probiotics have been used for over a century to prevent and treat diseases. They can reduce the effects of gastroenteritis and are now used to treat acute diarrhea. This study aimed to evaluate the co-aggregative effects of probiotics bacteria against diarrheal causative bacteria. For this purpose, 11 isolates of probiotic bacteria were used in the current study, including three Lactobacillus plantarum, one Lactobacillus gasseri, two Lactobacillus fermentum, three Lactobacillus acidophilus, and two Lactococcus garvieae isolates. All isolates were tested for antibiotic susceptibility, autoaggregation ability, adhesion ability, antibacterial activity, acid tolerance, and bile salts tolerance. The results showed that most of them had the ability to autoaggregate after 4 h, with the highest percentage of 57.14% for L. fermentum. For the antibiotic susceptibility test, all the isolates showed resistance against trimethoprim/sulfamethoxazole, except one isolate. Moreover, all the isolates, except one, were susceptible to both vancomycin and tetracycline. All tested isolates had adhesion ability with different survival rates, which reached 34.57% for L. plantarum in acidic conditions. Besides, the highest survival rate was 85.17%, which belonged to L. garvieae, for bile salt tolerance. Probiotic isolates had an antibacterial effect against diarrhea-causative bacteria with an inhibition diameter of 17-49 mm for different Lactobacillus spp. and Lactococcus spp. isolates. Furthermore, the co-aggregation ability of probiotic isolates against diarrhea-causative bacteria was studied, and results showed that probiotic isolates had a co-aggregative effect against diarrhea-causative bacteria, Escherichia coli, Shigella sonnei, and Providencia alcalifaciens, after 24 h of incubation. The highest co-aggregative effect of probiotics isolates belonged to L. fermentum and L. acidophilus against P. alcalifaciens with a co-aggregation percentage of 100%, while the lowest co-aggregation rate was 14.29% against E. coli. The findings revealed the probiotic properties and co-aggregative effects of probiotic bacteria against diarrhea-causative bacteria.