S. M Abed - Department of Medical Laboratories, College of Medical and Health Techniques, Sawa University, Samawah, Iraq
H Jabar Jasim - College of Veterinary Medicine, Al-Muthanna University, Samawah, Iraq
M Mijbas Mohammed Alomari - College of Veterinary Medicine, Al-Muthanna University, Samawah, Iraq
G Hamoodi Hussein - Department of Medical Laboratories, College of Medical and Health Techniques, Sawa University, Samawah, Iraq

Due to the increased resistance to antibiotics and chemical biocides, the use of bacterial exopolysaccharides has been considered. The objective of the current study was to investigate the strength of the antibacterial and antibiofilm activity of EPS extracted from Lactobacillus reuteri and Streptococcus mitis because previous studies showed there were structural differences between EPS, during this study, EPS extracted from Lactobacillus reuteri and Streptococcus miti by ethanol precipitation method and estimated antibacterial and antibiofilm activity against several Oral Bacteria (Staphylococcus aureus, Staphylococcus hominis, Acinetobacter baumannii, Raoultella ornithinolytica, Streptococcus thoraltensis in different concentration as (۱۰۰,۱۵۰,۲۰۰,۲۵۰,۳۰۰ mg/ml ), the results showed carbohydrates rate in extracted  EPS from L. reuteri  and S. mitis were recorded was ۸۵, ۸۰ % respectively.The concentration ۱۰۰ and ۱۵۰ mg/ml for EPS from L. reuteri  and S. mitis, there was no inhibitory effect, except in S. aureus (۱.۱±۰.۱۰)  and S. hominis (۱.۰±۰.۱۰) at ۱۰۰ mg/ml, ۳.۱±۲.۰۱, ۲.۱±۰.۵۴ mg/ml respectively at ۱۵۰ mg/ml concentration but no significant differences (P≤۰.۰۵). However, the antibacterial effect of that EPSs started at the concentration of ۲۰۰ and upwards, where different results were recorded between the concentrations of both EPSs against all bacteria isolated (P≤۰.۰۵), On the other hand, the effect of EPS from L. reuteri  and S. mitis was clear against the formation of biofilm compared with the control, worth mentioning that EPS from L. reuteri was more effective compared with EPS from S. mitis in all isolates (P≤۰.۰۵) except for S. thoraltensis where it was noted that the EPS from S. mitis is more effective than EPS from L. reuteri. Through the results obtained in this study, it was noted that the difference in the structural nature of EPS has an important role in its effectiveness as an antibacterial and anti-biofilm formation and, as it was found that the EPS from L. reuteri showed more effectiveness than EPS from S. mitis and thus the mechanism of preventing and inhibiting bacteria depending of the structural nature of EPS.

EPS, Lactobacillus reuteri, Streptococcus Mitis, Antibacterial, Antibiofilm