Somali Medical Forums
Allied Health Professions => Lab Students and Technicians => Topic started by: Seeraar on November 06, 2009, 12:37:58 AM
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STAPHYLOCOCCI:-
• Gram +ve spherical cells arranged in grape-like clusters.
• Ferment carbohydrates &produce pigments.
• Some are members of m\m &skin flora of humans.
• Produce PYOGENIC infections.
• Pathogenic Staph.haemolizes blood-coagulate plasma &produce extra cellular enzymes &toxins.
• Enterotoxin produces food poisoning.
• Develop resistance to antibiotics .
• 30 sps. are known &the 3 of medical importance are Staph. aureus.- Staph.epidermidis &Staph.saprophiticus.
• Non-motile.
CULTURE:
• Best growth on bacteriologic media under aerobic conditions at 37C.Form pigment at room temperature.
• Produces smooth round colonies.
• Produces CATALANE which differentiate it from STREP.
• Ferment carbohydrates &produce lactic acid but no gas.
• Sesitive to antibiotics- some strains are resistant.
ANTIGENIC STRUCTURE
o Contain antigenic polysaccharides &proteins.
o Peptidoglycan-(cell wall) a poly saccharide polymer-is destroyed by strong acids &lysozyme &it is important in pathogensis of infection &production of Interlukin-1 &opsonic anyibodies.
o Teichoic acid-polymers of glycerol or ribitol phosphate linked to peptidoglycan &can be antigenic.Antiteichoic antibodies could be detected in parients with endocarditis due to Staph.aureus.
o Protein A- a cell wall component that binds to IgG.
TOXINS &ENZYMES:-
• Catalane convertsHO2 into H2O &O2 .test differenciate Staph.(+ve) from Strep.(- ve).-
• COAGULASEP:-enzyme-like protein that clot oxalated or citrated plasma.Coagulase deposit fibrin on the surface of Staph.altering phagocytosis.
• Hyaluronidase:- spreading factor.
Exotoxins:-
Several lethal toxins to animals on injection cause necrosis of skin(alpha-beta-gama &delta toxins).
-Leukocidin: can kill white blood cells of many animals.
-Exfoliative toxin: includes 2 proteins that lead to the generalized desquamation of the Staph.scalded skin syndrome.
-Toxic shock syndrome toxin: patients with toxic shock syndrome produce(TSST-1) which resembles enterotoxinF &pyrogenic exotoxin-C.In humans produces feverand shock.
Enterotoxins:-
Six(A-B-C-D-E&f) soluble toxins: produced by 50% of Staph.aureus strains.They are heat stable and resist boiling for 30 minutes.Important cause of food poisoning.
PATHOGENISIS:-
Staph. are members of normal flora of human skin- occurs in nasal passage-found in clothing-bed linens &other fomites.
Pathogenic capacity depends on extracellular factors &toxins and invasive properties of the strain.
Food poisoning depends on injestion of enerotoxins.
Bacteremia & abcesses in all organs.
Pathogenic Staph.aureus produces coagulase-yellow pigment and is hemolytic.Staph. epidermidis is non-pathogenic andStaph.saprophiticus causes urinary tract infection in young women.
CLINICAL FINDINGS:-
*Pimple—hair follicle infection or abscess.
*Direct contamination of wounds-post operative surgery or trauma.
*Bacteremia-endocarditis-osteomyelitis-meningitis &pulmonary infection.
*Food poisoning with short incubation period(1-8 hr.)-violent nausea-vomiting-
&diarrhea and rapid convalescence –no fever.
Toxic Shock Syndrome:
high fever – vomiting – diarrhea – mualgias - scarlatiniform rash - hypotention with cardiac &renal failure in severe cases
It occurs in young women 5days after menses who use tampons- but also in children or men with Staph. infection.The syndrome is found in vagina-on tampons-in wounds-other localized infection &throat BUT never in blood stream.
DIAGNOSTIC LABORATORY TESTS:-
o Specimens:-surface swab-pus-blood-tracheal aspirate-spinal fluid for culture-Antibody demonstration in serum is of no value.
o Smears:-Staph. are seen in stained smears of pus &sputum.
o CULTURE:-Blood agar –typical colonies in 18hrs.at 37 incubation.Pigments are produced on optimal room temperature.Contaminants are inhibited by 7.5% salt on media.
o CATALASE TEST:-drop of H2O2+small amount of bacterial growth is placed in solution-O2 is released in bubbles.
o COAGULATE TEST:-Citrated rabbit or human plasma diluted 1:5 is mixed with equal volume of broth culture or colonies incubated at37C-clot is formed in 1-4hrs if test is +ve.
o Susceptibility testing.
Serological typing tests:- no practical value.
Epidomiology :-
Staph. are ubiquitous human parasites &human infection chiefly shed infection &also fomites-respiratory tract &skin.
Carriers of antibiotic resistant strains constitute a hazard in hospitals