Staphylococcus Bacteria Study PDF

Cocci Gram +ve Gram –ve Ex. Neisseria Staphylococci Streptococci Pneumococci Staphylococci...

Cocci Gram +ve Gram –ve Ex. Neisseria Staphylococci Streptococci Pneumococci Staphylococci Morphology: They are Gram +ve, cocci, arranged in grape-like clusters.  The genus staphylococci includes 3 species: 1-Staph aureus (Pathogenic) 2-Staph epidermidis (Commensal) 3-Staph saprophyticus (saprophytic) Coagulase +ve staphylococci 1-Staph aureus Virulence factors: I-Cell wall components: 1-Protein A: it is anti-complementry and anti-phagocytic 2-Teichoic acid: mediates adherence. 3-Some strains have a microcapsule that is antiphagocytic. II-Enzymes: 1-Coagulase enzyme: causes coagulation of plasma by converting: Fibrinogen Fibrin which is deposited around the infection and the organism rendering them resistant to phagocytosis and also leads to localization of infection. -Due to coagulase, Staph aureus causes pyogenic infections (infection that contain pus) ‫عدوى بها صديد‬ ex. Abscess, boils and carbuncles, hospital-acquired wound infection ‫تلوث الجرح في المستشفيات‬. 2-Catalase enzyme: converts 2H2O2 2H2O+O2 (this enzymes is produced by all types of Staph but not produced by Streptococci).  III-Toxins: 1-Enterotoxins: they cause food poisoning ‫مهم‬ -They are more heat-stable than Staph aureus  so enterotoxin may persist after cooking even though the bacteria are killed. -They cause food poisoning ‫ مهم‬which is characterized by the following: -Source: the hands or the nose of food handlers (carriers or cases). -Cause: Preformed toxin (not the organism) -Incubation period is short (1-8 hr) after ingestion of the food because the toxin is preformed. -Type of food: associated with carbohydrate rich food (coshary, cakes, coskosy) -Signs: Nausea, vomiting, watery diarrhoea and NO FEVER. Usually self-limited. 2-Exfoliative toxin ‫ سم يقشر الجلد‬ causes Scalded Skin Syndrome (SSS) 3-Toxic shock syndrome toxin: it acts as a super Ag  causes Toxic shock syndrome 5-Hemolysin: cause haemolysis to RBCs Diseases: I-local abscess formation: Due to coagulase production 1. Superficial abscess 2. Deep abscess: eg. osteomyelitis ‫التهاب في العظام‬ 3. Outbreaks of hospital acquired wound infections 4. Septicemia. II- Diseases due to toxin production = Toxigenic staphylococcal diseases: 1. Food poisoning: results from ingestion on the preformed toxin……….. 2. Toxic shock syndrome. 3. Scalded Skin Syndrome: it is due to exfoliative toxin.  Diagnosis: 1-Sample: pus. 2-Film: stained by Gram's stain  shows Gram +ve cocci arranged in grape-like clusters. 3-Culture 1-Nutrient agar (Simple media) or Milk agar (Enriched media): a) Staph aureus golden yellow endopigments. b) Staph albus "epidermidis" white endopigments. c) Staph citrus lemon yellow endopigments. 2-Blood agar (Enriched media): -Staph aureus produces β-haemolysis (=Complete haemolysis of blood with clear zone around the colonies). 3-Mannitol salt agar (Selective media):  produce yellow colonies surrounded by yellow zone. N.B: the medium contains 7.5% NaCl (but staphylocci are Halophilic bacteria= salt loving) 4-Biochemical reactions: 1-Coagulase +ve (only pathogenic Staph aureus) Add few drops of a broth culture of the test organism to 0.5 ml of human or rabbit plasma in test tube coagulation occurs within few hours. 2-Catalse +ve: all Staphylococci (note that Streptococci are catalase –ve)  Treatment Antibiotic sensitivity test should be done in staphylococcal infections. Why???  Due to rapid development of resistance to antibiotics. 1- 90% of hospital strains of Staph aureus are resistant to Penicillin G, Ampicillin  This is due to production of B-lactamase enzyme. 2-This bacteria be treated with Methicillin, Oxacillin  But 20% of Staph aureus developed resistance & called MRSA(=Methicillin resistant Staph aureus) This is due to mutation in mec A gene that leads to change in the penicillin binding proteins (PBP) receptor. 3- This bacteria be treated with Vancomycin. -BUT VRSA are developed (Vancomycin resistant Staph aureus). 4-These VRSA can be treated by linezolide ------------------------------------------------------------------------------------------------------------ Coagulase negative staphylococci 1- Staph epidermidis: 2-Staph saprophyticus: They are normal inhabitants of skin. Saprophytic bacteria Disease: It causes infections on the artificial joints and IV catheters, and prosthetic devices. Most infections are in immunosuppressed patients. They form Biofilm due to production of slime which participates in its adherence to the surface of devices. novobiocin sensitive. novobiocin resistant. Both of them do not cause haemolysis on blood agar and not ferment mannitol ------------------------------------------------------------------------------------------------------------  Important questions I-Comment: a-staphylococci can produce food poisoning? Due to production of enterotoxin that cause vomiting and diarrhea. b-Penicillin not recommended for treatment of staph? Staph. Produce penicillinase (β-Lactamase) enzyme which inactivate the functional group ((β- Lactam ring) in penicillin. c-Antibiotic sensitivity test is required in treatment of staph infections? Due to high level of resistance II--Complete: a) Staph food poisoning is characterized by presence of ………..toxin and …….…type of food b) ………..enzyme is responsible for the localized infections caused by staph aureus infections c) The drug of choice for treatment of MRSA is………………….while VRSA can be treated by …… d) Resistance to penicillin is due to ……….while resistance to MRSA is due to ………… e) Staph aureus release …………………… that cause Skin Scalded syndrome f) Major products produced by Staph aureus are …………..,…………………,……………. g) Resistance of staph aureus to B-Lacatam antibiotic is due to …………………….. while resistance to Methicillin is due to …………………………………………………. h) Localized pyogenic infection of staph aureus is due to ………………….., while Food poisoning is due to ……………….. III) Choose the most correct answer: 1-Which of the following correctly describe the genus staphylococci ? a- Susceptabile to bacteroicin b- catalase positive c-Spore forming d-Motile 2-Most important feature of S aureus pathogenicity is : a-Coagulase positive b-Capsule formation c-Intracellular survival d-Endotoxin formation 3-The drug of choice in treatment of MRSA infection is : a-Ampicillin b-Aminoglycoside c-Vancomycin d-Tetracycline 4- The predominant bacterial species that colonizes the human skin is: a-Lactobacillus b-Candida albicans. C-Streptococcus pneumoniae. d-Staphylococcus epidermidis. e-Bacteroides fragilis 5-Which one of the following laboratory criteria would establish Staph aureus, rather than Streptococcus pyogenes, as the causative organism? a-Growth on blood agar. b-Production of catalase c-Presence of gram-positive cocci. d-Growth under anaerobic conditions. e- Motility. 6- Which of the following used in differentiation between pathogenic staph , non pathogenic staph: a- Catalase test b- Presence of Gm+ve cocci in clusters c-Coagulase test d- Tolerance to 7.5% NaCL 7-Staph. aureus exfoliative toxins a-Cause peeling of mammalian cell membranes and thus cell lysis. b-Are important causes of toxic shock syndrome in menstruating women. c-Cause scaled skin syndrom. d-Act as virulence factors in staphylococcal pharyngitis, requiring prompt antitoxin administration. e-Are restricted to the periplasmic space