This study sought to determine the antimicrobial susceptibility of Staphylcoccus aureus and viridans group streptococci strains collected from the forearm skin and saliva of 30 patients at high risk of endocarditis. Agar susceptibility tests of antibiotics routinely utilized in dentistry were used to verify antimicrobial resistance of bacterial strains. Of the Staphylcoccus aureus strains, 50% were resistant to ampicillin, 53.3% to amoxicillin, 60.0% to penicillin G, 13.3% to amoxicillin/clavulanate, 20.0% to azithromycin, 27.6% to clarithromycin, 23.3% to erythromycin, 3.3% to cefazolin, and 6.7% to clindamycin. Regarding streptococci, 16.7% of the strains were resistant to ampicillin, 16.7% to amoxicillin, 23.3% to azithromycin, 23.3% to clarithromycin, 30.0% to erythromycin, 13.3% to cefazolin, 26.7% to clindamycin, 16.7% to penicillin G, and 3.3% to amoxicillin/clavulanate. Pathogens associated with bacterial endocarditis exhibited elevated resistance rates against the antibiotics used for prophylaxis in dentistry.