Streptococcus mitis colony morphology on blood agar
Introduction
Table of Contents
Streptococcus mitis is a Gram-positive, alpha-hemolytic bacterium commonly found as a harmless commensal in the human oral cavity, but it can act as an opportunistic pathogen causing severe infections like infective endocarditis.
Fig. Streptococcus mitis colony characteristics on blood agar
Classification: Belongs to the Viridans streptococci group.
Habitat: Inhabits the human oral cavity, throat, and nasopharynx.
Nature: Primarily a harmless commensal organism.
Risk: Causes severe opportunistic infections if it enters the bloodstream.
Morphology
Fig. Streptococcus mitis colony morphology on blood agar
Gram Stain: Gram-positive cocci.
Arrangement: Cells appear in chains or pairs.
Fig. Gram-positive cocci of Streptococcus mitis
Shape: Oval or spherical cells.
Motility: Non-motile organism.
Spores: Non-spore-forming bacterium.
Capsule: Some strains possess a polysaccharide capsule.
Pathogenicity
Entry: Enters the bloodstream during dental procedures or vigorous brushing.
Endocarditis: Binds to damaged heart valves, forming biofilms.
Bacteremia: Causes bloodstream infections, especially in neutropenic cancer patients.
Virulence Factors: Utilizes surface adhesins to bind to host tissues.
Toxins: Produces pneumolysin-like cytolysins in certain strains.
Lab Diagnosis
Specimen: Blood, cerebrospinal fluid, or oral swabs.
Microscopy: Gram-positive cocci arranged in chains.
Fig. Oval or spherical cells, Gram-positive cocci (GPC) in chains or pairs of Streptococcus mitis, and a few resemble Gram-negative due to older cultureFig. Oval or spherical cells, Gram-positive cocci (GPC) in chains or pairs of Streptococcus mitis at magnification of 1000x with 8x optical zoom
