Which microorganism is a normal commensal inhabitant of the human throat and tonsils______________?
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Answer: A. Alpha hymolytic streptococci (S. viridans)
Explanation
Streptococcus viridans exhibits alpha-hemolysis and colonizes human oral mucosal surfaces natively. Throats and tonsils harbor these commensal bacteria as part of normal upper respiratory flora. Option A correctly identifies alpha-hemolytic streptococci as permanent resident microbes. Commensal microorganisms protect host tissues by outcompeting pathogenic invaders for resources. Alpha-hemolysis produces a characteristic greenish discoloration surrounding colonies on blood agar. Normal oral flora can occasionally enter the bloodstream during dental manipulation procedures.
Transient bacteremia from oral flora poses infection risks for patients with damaged heart valves. Maintaining healthy mucosal microbiome balance prevents opportunistic overgrowth of harmful pathogens. Clinical microbiology laboratories frequently isolate these normal commensals from respiratory cultures. Staphylococci include species like Staphylococcus aureus which are frequent pathogens rather than normal throat flora. Beta hemolytic streptococci like Streptococcus pyogenes are significant pathogens causing acute pharyngitis. Pneumococci typically cause invasive pulmonary infections rather than serving as stable commensal inhabitants.
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