Pathology At birth mouth is sterile,first bacteria to appear in oral cavity: A Streptococcus salivarius. B Streptococcus mutans. C Streptococcus sanguis. D Streptococcus mitis. 💡 Explanation At birth mouth is sterile,first bacteria to appear in oral cavity: ✓ Correct Answer: A. Streptococcus salivarius.