Viridans group streptococci

Definition

Viridans group streptococci are a heterogeneous group of alpha-hemolytic and non-hemolytic streptococci that are part of the normal microbiota of the human oral cavity and upper respiratory tract. They are generally non-pathogenic but can cause serious infections like endocarditis under certain conditions.

5 Must Know Facts For Your Next Test

1. Viridans group streptococci are primarily found in the oral cavity and upper respiratory tract as part of normal microbiota.
2. They exhibit alpha-hemolysis on blood agar, producing a greenish discoloration around colonies.
3. Though typically non-pathogenic, they can enter the bloodstream during dental procedures and potentially cause endocarditis.
4. They lack the Lancefield carbohydrate antigens that classify other groups of streptococci, making them difficult to categorize.
5. Common species include Streptococcus mutans, Streptococcus sanguinis, and Streptococcus mitis.

Review Questions

• What type of hemolysis is exhibited by viridans group streptococci on blood agar?
• How can viridans group streptococci become pathogenic despite being part of normal microbiota?
• Name three common species within the viridans group streptococci.

Related terms

Alpha-hemolysis: Partial hemolysis of red blood cells causing a greenish discoloration on blood agar.

Endocarditis: An infection of the inner lining of the heart chambers and valves often caused by bacteria entering the bloodstream.

Normal Microbiota: Microorganisms that reside in or on specific areas of the body without causing disease under normal conditions.