Streptococcal Infections

1. Droplet infection (this is a disease of winter and spring and is usually caused by M types 3,5,6,19, and 12. A DNase.)

   1. GAS adhere to cell

   2. Colonize upper respiratory tract (the major reservoir). ~20% of kids in winter are colonized without being sick. The bacteria can only live long enough outside the body to infect another person.

   3. Occasionally critical mass is reached

   4. Invade submucosa

   5. Tonsillitis, Pharyngitis, Otitis

   6. 95% of cases the infections are resolved with no further problems. Some strains make pyrogenic toxins which lead to scarlet fever

   7. Sometimes when the infection was caused by rheumatogenetic strain after the infection goes away ~ 3% of cases rheumatic fever, which can attack the joints and/or heart.

   8. Invasive strain can get into the blood and cause toxic shock syndrome.

2. Skin Infection (This is a disease of summer and fall and is caused by M types 49, 2, and 55, but they tend to lose their M antigens. ASLO & ADNase .)

   1. Through direct contact with mosquitoes

   2. Occasionally critical mass is reached

   3. Invade dermis

   4. Pyoderma inflamed skin infection,

   5. Impetigo skin lesions,

   6. if it spreads subcutaneously it can cause Erysipelas acute superficial cellulitis, hot red and sharply defined bumps

   7. Usually cured

   8. Sometimes, if nephritogenic strain is the cause of the infection glomerulonephritis. It occurs 10-14 days after the infection and can also be caused by throat infections.

   9. If necrotizing strain (aka flesh eating bacteria) causes the infection, it can lead to a soft tissue infection called necrotizing fascitis. If it gets into the blood it can lead to toxic shock syndrome. Once this strain gets in the tissue there is a 30% death rate, even with antibiotics. The penicillin window is only the first 3 days. By day 4 it is too late because the bacteria are already in the blood.

NONGROUP A β- HEMOLYTIC STREP

These bacteria also cause disease, but not as much, even though they are commonly found in the throat. It is associated with food consumption. Groups C and G are the most prevalent. The infection is usually short, but long infections are seen in poor people.

Other bacteria that don’t cause disease very often include diphtheria, which is mostly caused by the toxin, and Borditella pertussis, which causes whooping cough.

Category: Microbiology Notes