Streptococcus Viridans

INTRODUCTION:
  • The viridans streptococci are a large group of commensal streptococcal bacteria species that are either α-hemolytic, producing a green coloration on blood agar plates or nonhemolytic.
  • Strep viridans are actually a commensal group of bacteria. 
  • On blood agar, after incubation for 18 hrs, the colonies of pneumococci are small, dome shaped and glistening with an area of green discoloration (alpha hemolysis) around them, resembling colonies of Str. viridans.
  1. The viridans streptococci are normally found in:
  2. The mouth. This is their main place of residence.
  3. The upper respiratory tract, which includes the nose.
  4. The gastrointestinal system, which is our digestive tract. They are found throughout this system.
  5. The genitourinary tract, or the one involving our urinary system and genitals, namely in women.
  • On occasion, they can be found on our skin as well. Now let's look at how these bacteria can sometimes cause issues.
STREPTOCOCCUS VIRIDANS INFECTION:
  • The viridans streptococci normally do not harm healthy people but may cause disease in people with compromised immune systems.
  • There are various such infections and consequent diseases that these bacteria may cause. These include:
  1. Endocarditis, or the inflammation of the inner lining of the heart. This can damage the heart's valves and lead to heart failure.
  2. Shock, which can cause multiple organ failure because these organs do not receive enough blood in this condition.
  3. Intra-abdominal infection, or infection within the abdomen.
  4. Meningitis, or inflammation of the meninges, a protective layer of the brain and spinal cord. This can be life threatening.
  5. Pneumonia, or inflammation of the lungs, as a result of bacteria in this case. This can also be deadly if left untreated.
  • Viridans streptococci are normally resident in the mouth and upper respiratory tract. 
  • They cause transient bacteremia following tooth extraction or other dental procedures; and get implanted on damaged or prosthetic valves or in a congenitally diseased heart, and grow to form vegetations.
  • Str. mutans is important in causation of dental caries.
  • Causes of community acquired native valve endocarditis are Staphylococcus aureus ( most common),Streptococcus ( Str viridans, Str bovis, other non group A Streptococci) The transient viridans streptococcal bacteremia induced by eating, tooth-brushing, flossing and other source of minor trauma, together with adherence to biological surfaces, is thought to account for the predilection of these organisms to cause endocarditis.
  • Viridans streptococci are also isolated, often as a part of a mixed flora, from sites of sinusitis, brain abscess and liver abscess.
  • Viridans streptococcal bacteremia occurs relatively frequently in neutropenic patients, particularly after bone marrow transplantation or high dose chemotherapy for cancer.
  • TREATMENT:
  1. Bacteremia in neutropenic patients → Vancomycin.
  2. Other infection → Penicillin
Exam Question
  • On blood agar, after incubation for 18 hrs, the colonies of pneumococci are small, dome shaped and glistening with an area of green discoloration (alpha hemolysis) around them, 
  • resembling colonies of Str. viridans.
  • Infective endocarditis after tooth extraction is probably due to Streptococcus viridans
  • SABE is most commonly due to Streptococcus viridan
  • Causes of community acquired native valve endocarditis are Staphylococcus aureus ( most common),Streptococcus ( Str viridans, Str bovis, other non group A Streptococci)

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