Microbiology - Staphylococcal Infections Lecture (PDF)

LECTURE (1) Staphylococcal Infections   Gram positive cocci  Clusters  Non motile  Non spore forming  S. aureus forms microcapsule,  Other species may produce slime layer  S. aureus....

LECTURE (1) Staphylococcal Infections   Gram positive cocci  Clusters  Non motile  Non spore forming  S. aureus forms microcapsule,  Other species may produce slime layer  S. aureus.  S. epidermidis  S. saprophyticus.  It is a major pathogen for humans.  Present as normal flora on: ① Skin. ② Upper respiratory tract: 10-40 % of normal individuals carry S. aureus in anterior nares. ① Cell wall associated proteins and polymers: Inhibits phagocytosis and chemotaxis.  Major protein in the cell wall.  Binds to the Fc portion of IgG.  Inhibits opsonization. ② Enzymes and toxins produced by S. aureus:  Causes clotting plasma to clot by converting prothrombin to thrombin which converts fibrinogen to fibrin coats the bacterial cell interfere with opsonization and phagocytosis. -  Inactivates toxic H2O2 inside phagocytes → enhance survival of S. aureus in phagocytes.  Proteases, lipase and DNase. ① Haemolysin. ② Leucocidin.  Cause food poisoning when ingested.  Heat and acid stable.  5 types (A, B, C, D, E).  Causes toxic shock syndrome.  Causes scalded skin syndrome in neonates. ① Skin infection: as boils, stye & furunculosis. ② Abscess & Acute Endocarditis ③ Pneumonia and Bacteremia. ④ Hospital acquired (nosocomial) infections: as Urinary tract infection & phlebitis. ① Scalded skin syndrome:  Widespread blistering  Loss of the epidermis in neonates.  Production of epidermolytic (exfoliative) toxin. ② Food poisoning:  Food improper cooked as milk  Five enterotoxins.  Few hours (1-6 hours).  Vomiting and diarrhea.  Fluid therapy & may be self-limited. ③ Toxic shock syndrome (TSS):  Skin desquemation  Shock (hypotension)  Tampon contain TSST ( occurs in young females with menstruation)   Differ according to site of infection: ① Swabs ③ Sputum ⑤ Blood. ② Pus ④ CSF  Gram stain for characteristic morphology.  Facultative anaerobes, optimum temperature: 370C, normal atmospheric CO2  Can grow on ordinary media.  S. aureus produce golden yellow endopigments.  S. aureus causes α-hemolysis on blood agar.  Selective media is mannitol salt agar, where S.aureus ferments mannitol and salt inhibits other normal flora. ① Film stained by Gram: for characteristic morphology. ② Biochemical reactions:  All staphylococci are catalase positive.  S. aureus is coagulase and DNAase +ve & ferment mannitol.  To select the effective drug.  Penicillinase-resistant β-lactams.  Normal flora of the skin, nonpathogenic.  Infections in immunocompromised individuals.  UTI in young females.  Infections on prosthetic implants such as heart valves and hip joints. + - - + - - + - - + - - + - - + - - - - + ▶ A 2-month-old female infant presents with extensive blisters. Her mother had suffered from staphylococcal mastitis 1 week ago. On examination: blisters are filled with fluid and have thin walls which rupture easily, skin redness ‘erythema’ covers most of the body, and large areas of the skin are exfoliated and painful ① What is the most likely case diagnosis? ② What is the most likely causative organism? ③ Mention the toxin responsible for the disease ④ How does the causative organism appear in direct smear? ⑤ Mention 2 other toxigenic diseases caused by this organism ?