Survey of Gram Positive Bacteria (Streptococcus A)

Alpha Hemolytic

Partially breaks down red blood cells, green/brown on blood agar

Beta Hemolytic

Completely breaks down red blood cells, clearing on blood agar

Gamma Hemolytic

Does not break down red blood cells, no change in blood agar

Blood Agar Plate

Enriched and differential media that promotes growth of fastidious organisms and differentiates between hemolytic properties

Group A Streptococcus (pyogenes)

White colonies on TSA, large zones of beta hemolysis on BAP. Pathogenic strains usually have capsules

M Protein

Interferes with opsonization and digestion of the bacteria by the lysozyme. Prevents the formation of the phagolysosome

Hyaluronic Acid Capsule

Acts as a camouflage preventing detection by leukocytes

Streptokinases

Kinases specifically produced by Streptococcus that break down blood clots allowing their rapid spread through infected and damaged tissue

Deoxyribonucleases

Unwind and destroys DNA released by dead cells in infection sites. This reduces the firmness of puss allowing for quick spread of the bacteria

Pus

When cells die, they release their DNA. When DNA reacts with inflammatory fluid, it causes it to harden and turn into this. It is difficult for bacteria to move through this, streptococcus releases deoxyribonucleases to break this down

Streptolysins

A class of proteins that breakdown or lyse red blood cells, white blood cells, and platelets. These interfere with blood clotting, innate/adaptive immune responses and oxygen transport

After these bacteria have been phagocytized, streptolysins are secreted causing lysosomes to release their contents and lyse the entire phagocyte

Epidemiology of Group A Streptococcus

Typically this group infects the pharynx or skin. Often cause disease when our normal microbiota are depleted, freeing space and nutrients allow this to fill the void. Generally spreads through respiratory droplets

Streptococcal Pharyngitis

Inflammation of the pharynx. Most infections start this way and limited to this region of the body. When the bacteria spread, Rheumatic and Scarlet fever can occur

AKA Strep Throat

Rheumatic Fever

Typically develops from untreated streptococcal pharyngitis. Characterized by inflammation that damages the heart valves and muscle

Antibodies directed against streptococcus cross react with antigens on the heart and causes the adaptive immune system to destroy the heart valve while trying to kill the bacteria

Scarlet Fever

Typically develops from untreated or is secondary to streptococcal pharyngitis. Pyrogenic toxins trigger a rash and cause the tongue to appear strawberry. Characterized by rash that starts on the chest and spreads throughout the body

Necrotizing Fasciitis

Characterized by a bacterial infection in the fascia. Streptococcus A bacteria spread along the fascia and secrete enzymes and toxins that destroy the connective tissue

Fascia

A sheet of connective tissue, primarily composed of collagen that rests beneath the skin. This wraps around nerves, muscles, blood vessels, and separate organs

Rapid Strep Test

Used to diagnose respiratory infections, it looks for Group A specific antigens. Presence of streptococci in the pharynx is not a diagnostic of strep throat because wit have non pathogenic streptococcus in our pharynx.