Microbiology Streptococci & Enterococci Quiz

Streptococci & Enterococci Overview

• Streptococci and enterococci are primarily found in chains and are Gram-positive bacteria.
• They are facultative anaerobes, nonmotile, and lack catalase.

Hemolysis Types

• Beta Hemolysis: Complete lysis of red blood cells (RBCs) creates a clear zone around colonies.
• Alpha Hemolysis: Partial breakdown of hemoglobin in RBCs results in a green discoloration around colonies.
• Gamma Hemolysis: No hemolysis occurs, with no effect on RBCs.

Beta Hemolytic Groups

• Group A Streptococci (S. pyrogenes): Most serious, primarily found in the pharynx, skin, and rectum; produces hemolysins causing complete lysis of RBCs.
• Group B Streptococci (S. agalactiae): Common in the genital and intestinal tracts; significant neonatal infections including sepsis and meningitis. Identified by positive CAMP reaction.
• Group C Streptococci (S. dysgalactiae): Uncommon pathogens; involved in pharyngitis and endocarditis, differentiated by Bacitracin resistance and negative CAMP test.

Alpha Hemolytic Groups

• Streptococcus pneumoniae: Causes bacterial pneumonia, meningitis, and otitis media; virulent strains have a polysaccharide capsule and are positive for optochin susceptibility.
• Viridans Streptococci: Opportunistic infections, associated with dental caries; appear small and grayish on blood agar, with negative bile esculin and variable salt tolerance test results.

Enterococci Groups

• Group D Enterococci (E. faecalis and E. faecium): Inhabit the GI tract and oral cavity; can cause urinary tract infections, bacteremia, and endocarditis. Show large non-hemolytic colonies.
• Group D Nonenterococci (S. bovis): Present in the intestinal tract; associated with GI malignancies and can cause endocarditis.

Sensitivity Tests

• Optochin Sensitivity: Pneumococci are sensitive; viridans are resistant.
• Bacitracin Sensitivity: S. pyrogenes is sensitive, while S. agalactiae is resistant.
• SXT Sensitivity: Useful for identifying group C streptococci.

Identification Tests

• CAMP Test: Positive for S. agalactiae, indicating enhanced breakdown of RBCs.
• Lancefield Antigen Testing: Differentiates between streptococcal groups based on carbohydrate antigens.
• NaCl Tolerance Test: Distinguishes enterococci from other group D streptococci.
• SXT Test: Group A strep is resistant, while group C is sensitive.

Clinical Applications

• Throat Swab on Blood Agar: Stabbing creates anaerobic conditions, improving hemolysis development.
• Pregnant Women Screening: Focus on S. agalactiae (group B strep) status during the third trimester.
• Dental Caries Development: Caused by viridans streptococci like S. mutans fermenting sugars and producing enamel-eroding acids.