Bacterial Group III: STAPH AND STREP
29 July 1991, rvsd 24 Feb 1993, 12 August 1993, 21 Fe 00, 6 Aug 01, 28 Feb 02, 1 Aug 03, 9 Aug 04, 15 Aug07
See also Jensen & Wright, pp 202-228, TFC 7th: 582-586 (staph), 658-660 (strep), 690-691(staph food poisoning), Bauman 2nd: 530-542
GRAM POSITIVE COCCI:
STAPHYLOCOCCUS: (p. 530)
Staphylococcus aureus (yellow colonies) is the most problematic of Staph species (coagulase positive)
Staphylococcus epidermidis common on skin (90% of flora) and nares, in rectum. It is an opportunistic pathogen.
Aerobic or facultatively anaerobic: catalase positive (in pathogenic) distinguishes from Strep
Very strong cell walls, resistant to high salt: Can survive in cured meats, drying
Invasive because of toxins and enzymes (p 531):
coagulase indicates pathogenic: fibrinogen to fibrin, protects from phagocytosis, isolates site of infection (S. epidermidis is coagulase negative)
exfoliative toxin scalded skin syndrome, epidermis separates, sloughed off (p 532)
enterotoxin intoxication: heat resistant: nausea, vomiting, diarrhea 1-6hrs after eating. Lasts 24hrs.
Diseases:
folliculitis: pimple
boil: invades dermis
carbuncle: underlying tissue cavity, necrosis, suppuration [from under, pus]
sty folliculitis of eyelash
Impetigo mixed infection of Staph and Strep (page 533)
staph food poisoning enterotoxin (p 532) (usually coagulase positive) superantigen, T cells release cytokines
Toxic shock syndrome fever, vomiting, sunburn-like rash, shock (graph: 533)
Develops resistance to drugs faster than any other bacterium, esp prob is antibiotic abuse
Only 5 % are sensitive to penicillin now. Should test sensitivity first.
Abscesses should be drained to break up niche, remove dormant bacteria. MRSA: multiply drug resistant Staph aureus: formerly nosocomial, now found out in community(p 534)
STREPTOCOCCUS: cause more disease than any other single group of bacteria. (P 535)
Not all are pathogens (for example: lactic acid fermenters in milk)
pathogenic Strep carried in the population: 5% in summer, 10% in winter
Can be spread by aerosol in elementary schools
Distinguish among Strep by two techniques:
Hemolysis: alpha: partial clearing, green cast
beta: complete clearing, yellow cast
gamma: no clearing
Lancefield Serology (cell wall M protein, mediates attachment, retards phagocytosis) Groups A - O
Streptococcus pyogenes is most common form of Group A beta hemolytic strep.
AGENTS OF PATHOGENICITY Produced extracellular, esp. necrotizing exoenzymes: (see p 439-40)
M protein cell wall protein, used for attachment, increases pathogenicity
leukocidin disrupts lysosomes of neutrophils and macrophages, causing lysis, tissue damage
erythrogenic toxin fever and rash (causes scarlet fever)
hyaluronidase spreading factor, hydrolyzes hyaluronic acid, a polysaccharide holds C.T. together
streptokinase a kinase fibrolysin, digest fibrin in inflammatory barrier
streptolysin lyse RBC, etc
DISEASES:
Strep throat beefy red pharynx, fever, SORE throat (but 80% Strep infections are asymptomatic) children under 15 avg 1 infections/yr. (p 536)
Scarlet fever erythrogenic factor diffuses into blood, causes vasodilation
Puerperal fever infection of uterus following childbirth
tooth decay S. mutans (cariogenic) make dextran fr sugar, lactic H+ decays teeth
“Flesh eating” bacteria necrotizing fasciitis especially effective at invading (causing cellulitis, myositis) (p 537)
SEQUELAE: Rheumatic fever in 3% of untreated children, appears 1-5 wks later, arthritis,
glomerulonephritis: filtering basement membrane scarred
S. pneumoniae ( p 541) formerly “Diplococcus pneumoniae”, leading cause of community acquired pneumonia (85% of pneumonia), otitis media,