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Staphylococci - Prac. Microbiology


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Staphylococci - Prac. Microbiology

  1. 1. Staphylococci
  2. 2. Morphology Gram positive cocci in clusters
  3. 3. Catalase: +ve (streptococci catalase –ve) :Coagulase ve: S. aureus+ ve: CoNS-
  4. 4. Coagulase Test :Principle Fibrinogen Plasma Coagulase enzyme Fibrin Visible Clot Broth :Procedure culture 2 (organism) 1 ml dil. citrated plasma 1 3 Incubate at 37oC, observe for formation of visible clot.
  5. 5. S.aureus ((coagulase +ve staphylococci
  6. 6. Morphology Gram positive cocci in clusters
  7. 7. Culture (Nutrient agar (golden yellow endopigment
  8. 8. (Blood agar (ß-haemolysis
  9. 9. (Mannitol-Salt agar (MSA • Selective, differential medium. • 7.5% sodium chloride + mannitol sugar. S. aureus (ferment( • Mannitol Acid (yellow( CoNS (No fermentation( • Mannitol No acid (Red(
  10. 10. Virulence Factors for Pyogenic Diseases
  11. 11. PYOGENIC DISEASES A- Localized Skin infections
  12. 12. B- Staphylococcal Pneumonia
  13. 13. C- Invasive Infections • • • • • Bacteremia. Osteomyelitis. Acute bacterial endocarditis. Meningitis. Septicemia.
  14. 14. Diagnosis of Pyogenic Diseases :Specimen -1 Abscess ----- pus Endocarditis ----- blood Meningitis --- CSF, blood Pneumonia ----- sputum UTI ----- urine Direct detection- 2
  15. 15. Culture- 3 Blood Other than blood (pus, CSF, urine) subculture
  16. 16. Identification- 4 A- Colony Morphology
  17. 17. B- Microscopy
  18. 18. C- Biochemical Reactions Coagulase-1 Catalase-3 Clumping factor-2
  19. 19. Toxin-Mediated Diseases A- SSS Exfoliatin B- TSS TSST-1 C- Food poisoning Enterotoxins
  20. 20. A- Staph. Scalded Skin Syndrome
  21. 21. B- Toxic Shock Syndrome Predisposing factors: - First observed in Menstruating females using tampons )tampon retained in vagina for 4-5 days( - Any staphylococcal lesion can predispose to TSS. Virulence factor: TSST-1 Diagnosis: clinical picture. culture: for isolation & identification. ELISA: for toxin detection in blood
  22. 22. C- Staph. aureus food poisoning I.P: 1- 6 hrs. Clinical picture: Colic, vomiting, mild Diarrhea, but no fever Diagnosis: 1. Specimen: food, vomitus, stools. 2. Culture: on MSA. 3. ELISA: for toxin detection in sample or in isolated organism. 4. Strain typing: to trace source of infection )e.g. phage typing(.
  23. 23. Strain Typing • • • • • • Phage typing. Colony morphology. Biotyping. Plasmid profile. Ribotyping. Chromosomal analysis.
  24. 24. Treatment Penicillin-resistant S.aureus- 1 .MRSA- 2 VISA- 3 VRSA
  25. 25. Coagulase negative Staphylococci (CoNS) • General Characters: – Non-hemolytic on blood agar – Coagulase negative – Mannitol non-fermenter • Diseases: S. epidermidis: – Device-related infections (prosthetic valve endocarditis, shunt infections, … etc…) – Urinary tract infection – Wound infection S. saprophyticus: UTI (honeymoon) cystitis
  26. 26. Case 1 A man underwent an emergency operation for perforated appendix. He required admission to the Intensive Care Unit. On the 5th day of hospitalization he developed fever, and the wound was erythematous, swollen, with purulent discharge (Surgical site infection “SSI”). The surgeon requested bacteriological examination (culture and sensitivity) of the wound pus
  27. 27. Surgical site infection
  28. 28. Specimen • Wound swabs were obtained. • Gram staining & Microscopy Gram-positive cocci arranged in clusters amongst pus cells.
  29. 29. Culture On Blood agar → Beta-hemolysis On nutrient agar → Golden yellow pigment On MSA → Yellow colonies
  30. 30. Identification: Film from colonies Gram-positive cocci in clusters
  31. 31. Biochemical reactions Catalase +ve Coagulase +ve Clumping factor +ve
  32. 32. Which organism is causing this condition? • Gram-positive cocci in clusters, catalase positive staphylococci • β-hemolysis , golden yellow pigment, yellow colonies on MSA and coagulase positivity S. aureus .
  33. 33. Antimicrobial susceptibility “Disc diffusion” the organism is resistant: to oxacillin, penicillin, erythromycin, & gentamicin but sensitive to: vancomycin.
  34. 34. How do you interpret the ?susceptibility data The organism is multi-resistant, including oxacillin-resistant methicillin-resistant S. aureus (MRSA).
  35. 35. Name other diseases caused by .this organism 1. Pyogenic infections a. Localized skin infections, e.g. folliculitis, furuncles, abscess. b. Staph pneumonia c. Invasive staph. infections, e.g. endocarditis, cellulitis, osteomyelitis, and septic arthritis 2. Toxin-mediated diseases , a. Toxic shock syndrome ,b. Scalded skin syndrome c. Food poisoning.
  36. 36. Case 2 A group of people shared a carbohydrate- rich meal. 1-6 hours later, they manifested vomiting, diarrhea but no fever. The condition was mild and self- limited. a) What could be the clinical diagnosis? b) What is the possible causative organism? c) What is the virulence factor responsible for this condition? d) What is the mechanism of action of such virulence factor? e) What is the laboratory test that is used to trace the source of this outbreak?
  37. 37. MCQs
  38. 38. 1. All the following are characteristic features of staphylococci except: a) b) c) d) e) Gram positive cocci. Arranged in clusters. Catalase negative . Usually grow on simple media. Usually inhabit skin and mucosa.
  39. 39. 2. The following medium is used to isolate S. aureus from specimens contaminated by other bacteria: a) Nutrient agar. b) MacConkey's agar. c) Blood agar . d) Mannitol salt agar. e) Chocolate agar
  40. 40. 3. The localized nature of S. aureus lesions is due to: a) Adhesins. b) Protein A. c) Staphylocoagulase d) Staphylokinase e) Exfoliatin
  41. 41. 4. S. aureus growth can be identified by the following characters except: a) Colony on blood agar is golden yellow. b) Colony on blood agar is surrounded with a clear zone. c) Colony on Mannitol salt agar is rose pink. d) Protein A positive. e) Coagulase test positive.
  42. 42. 5. One of the following is a S. aureus toxinmediated disease: a) Folliculitis b) Staphylococcal pneumonia. c) Toxic shock syndrome. d) Osteomyelitis e) Carbuncles
  43. 43. 6. Staphylococcal strain typing is used : a) To diagnose staphylococcal pyogenic diseases. b) To differentiate between coagulase -ve and coagulase +ve staphylococci. c) To differentiate between staphylococci & streptococci. d) To trace the source of outbreaks of S. aureus in the epidemiological studies. e) To identify enterotoxin-producing strains of S. aureus.