Introduction: Antimicrobial resistance is one of the most significant challenges globally that threatens our ability to treat infectious diseases. This study investigated Streptococci and Enterococci in dental caries and healthy individuals and determined antibiotic resistance in the recovered bacteria. Methods: One hundred and twelve samples were collected, 56 from patients with dental caries and 56 samples from the teeth and saliva of healthy people. The samples were cultured on blood agar and purified on Mitis Salivarius agar. All isolates were identified by biochemical tests and Vitek 2 system and then examined for antibiotic susceptibility by disc diffusion method. Results: Streptococci and enterococci were the most isolated agents from dental caries and the teeth and saliva of healthy people. Streptococcus spp. comprised 48.61% of bacteria in dental caries and 28.40% in healthy individuals, while Enteroccus spp. was 22.22% in dental caries and 30.84% in healthy individuals. Streptococcus mutans and Streptococcus salivarius were more prevalent in dental caries and healthy individuals, respectively, while Enterococcus faecium was detected in both dental caries and healthy individuals. Also, there were significant differences between the number of streptococci isolated from healthy and caries people (P<0.05). In isolates recovered from healthy people, the streptococcal spp. exhibited high resistance to azithromycin (82.6%), cefixime and tetracycline (91.3%), and amoxicillin (60.8%). In contrast, enterococci were resistant to tetracycline (92%) and cefixime (76%). In dental caries isolates, the streptococcal and enterococcal spp. showed the highest resistance to amoxicillin (> 68%). Conclusions: The streptococcal and enterococcal spp. comprised the most isolated bacteria from healthy individuals and dental caries and exhibited multidrug resistance.

Background: Bacteriocin is a peptidic toxin has many advantages to bacteria in their ecological niche and has strong antibacterial activity. Objective: The aim of this study was to evaluation of bacteriocin using Streptococcus sanguinis isolated from human dental caries. Subjects and Methods: Thirty five streptococcus isolates were diagnosed and tested for their production of bacteriocin, and then the optimal conditions for production of bacteriocin were determined.  After that, the purification of bacteriocin was made partially by ammonium sulfate at 95% saturation levels, followed by and gel filtration chromatography using Sephadex G-50 column. Finally, physical characteristics were also studied and determined the bacteriocin stability. Results: Among all streptococcal isolates, the S. sanguinis SH3 isolate with batter antimicrobial activity was selected, and used in further experiments. The optimum conditions for bacteriocin production were in Todd Hewitt broth (THB) supplemented with 1% glucose at 37°C for 24h under anaerobic conditions and inoculum size of (1.2 ˟ 109CFU/ml) and pH 7, where the inhibition zone diameter reached to 29 mm against Enterococcus faecalis. The purified bacteriocin had high inhibitory activity against S. pneumoniae, S. pyogenes, E. faecalis, E. faecium and  Leuconostoc mesenteroides. Streptocin SH3 keeps its effectiveness within the pH range 3-10, and temperature until 80ºC for 20 min. Conclusion: Bacteriocin produced from S. sanguinis has high activity against many pathogens and has high stability over wide ranges of temperature and pH, which makes it a good alternative in the medical and food preservation fields