Staphylococcus
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Most important bacteria for undergraduate students. This topic packs up lot of short notes and viva questions. Examiner's Favorite
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Staphylococcus
- 2. Staphylococcus • Ubiquitous • Gram positive • Cocci • Staphyle - Bunch of grapes • Kokkos - Berry • Discovered by Von Recklinghausen • Named by Sir Alexander Ogston
- 3. Staphylococcus • Pyogenic infections • Pigment production not associated with virulence – Golden yellow colonies Staphylococccus aureus – White colonies Staphylococcus epidermidis – White colonies Staphylococcus albus – Lemon yellow colonies Staphylococcus citreus
- 13. Generally! • Non motile • Non sporing • Young cultures may have capsules • Stain with aniline dyes • Uniformly gram positive • L forms may be seen
- 14. Current classification • 32 species • 15 sub species • Coagulase positive Staphylococcus aureus • Coagulase negative – Staph. epidermidis – Staph hemolyticus – Staph saprophyticus – Staph hominis – Staph capitis Commensal flora
- 15. Staphylococcus aureus • Gram positive cocci • Arranged in grape like clusters • Cluster formation is d/t division in 3 planes and daughter cells remain in close proximity • May appear in singles, pairs or short chains • Some bacteria may have capsules
- 16. Culture characteristics • Grow on ordinary media • Temp 10-42°C. optimum is 37°C • pH range 7.4 – 7.6 • Aerobes • Facultative anerobes • Nutrient agar – Large, Circular, Smooth, Shiny, Opaque & easily emulsifiable colonies – Yellow pigment which does not diffuse into medium – Pigment is carotene like lipoprotein – Pigment production best at 22°C or when glycerol monoacetate / milk is incorporated into medium
- 17. culture characteristics (Cont'd) • Nutrient slope – Oil paint appearance • Blood agar – Marked hemolysis on sheep blood agar – 20-25% Co2 – Rabbit / Sheep blood • Mac Conkey agar – Pink colonies due to lactose fermentation • Liquid media – Uniform turbidity • Selective medium – Salt milk agar – Salt broth – Ludlam’s medium ( Lithium chloride, Tellurite)
- 22. Salt milk agar
- 23. Biochemical reactions • Catalase Positive • Indole Negative • MR Positive • VP Positive • Urease Positive • Nitrate reduction Positive • Mannitol fermentation Positive • Phosphatase production Positive
- 24. Indole
- 25. Mr / vp
- 26. Urease test
- 28. Resistance • Withstand upto 60°C, die at 62°C • Can grow upto 45°C • Can grow in medium containing 10-15% NaCl • Resist 1% phenol for 15mins • 1% mercuric perchloride kills staphylococci in 10mins • Aniline dyes lethal – Crystal violet 1:5,00,000 concentration – Brilliant green 1: 1,00,00,000 concentration • Fatty acids inhibit growth of staphylococci
- 29. Penicillins & Staphylococci • Sensitive in pre-antibiotic era • Few strains evolved !! • Pencillinase • Inducible enzyme • Plasmid mediated : Transduction / conjugation • 4 types A-D • Newer antibiotic resistant bacteria spread far and wide …. • Hospital strains belong to group A
- 30. Resistance to drugs - Penicillin • Changes in bacterial surface receptors (PBP2a) • Avoids binding of antibiotic to cell wall • Development of tolerance to penicillin • Also includes beta-lactamase resistance penicillins like Methicillin & Cloxacillins : MRSA • Plasmid borne resistance to Erythromycin, Tetracyclines, Aminoglycosides etc • Cause hospital infections & epidemics EMRSA • Methicillin Oxacillin Cefoxitin
- 31. Pathogenicity • Infections – Cocci enter via damaged skin/ mucousa/tissue – Colonise locally – Evade host mechanism – Tissue damage • Intoxications – Disease caused by bacterial toxins – In vitro/ in vivo
- 32. virulence • Cell associated polymers – Cell wall polysaccharide peptidoglycan • Rigidity and structural integrity • Activates complement • Induces release of inflammatory cytokines – Techoic acid • Antigenic component • Adhesion • Protect from complement mediated opsonisation – Capsular polysacchride • Inhibit opsonization
- 33. virulence • Cell surface proteins – Protein A • Chemotactic • Anti – phagocytic • Anti-Complementary • Induces platelet damage & hypersensitivity – Clumping factor – Bound coagulase – slide coagulase test • Extracellular enzymes – Coagulase clots human/rabbit plasma – Coagulase enzyme + CRF coagulum (fibrinogen to fibrin clot) – free coagulase- Tube coagulase test
- 36. virulence – Lipases – Hyaluronidase – Nucleases – Protein receptors
- 37. Toxins • Cytolytic toxins – Alpha Hemolysin – Beta Hemolysin – Gamma Hemolysin – Delta Hemolysin – Leucocidin - (Panton –Valentine toxin or PVL) • Enterotoxin – Staphylococcal food poisoning – Nausea , Diarrhoea , vomiting after 2-6hrs of ingestion of contaminated food – Heat stable toxin : 100°C for 10-40mins – Common food products : Meat, Fish, Milk or Milk products • A, B,C1,C2,C3,D,E & H
- 38. Summation of Factors associated with virulence Hemolysis Gelatin liquefaction Lipolytic activity Production of urease Production of phosphatase Coagulase formation Mannitol fermentation
- 39. Toxin mediated syndromes • TSST & SSSS toxins are called superantigens • Potent activators of T-Lymphocytes • Stimulate wide variety of T Lymphocyte regardless of antigen specificity • Excessive improper immune response, Massive release of cytokines , TNF & INF Ɣ
- 40. Toxin mediated syndromes • Toxic Shock Syndrome Toxin TSST – Multisystem disease – Older days : Tampon usage – Follows infection of mucosa / site by toxin producing strains • Fever • Hypotension • Myalgia • Vomiting • Diarrhoea • Mucousal hyperemia • Rash – TSST 1 Antibody is seen in patients recovering from TSST
- 41. Toxin mediated syndromes • Exfoliative (epidermolytic) toxin SSSS • Staphylococcal Scalded Skin Syndrome • Exfoliative disease • Outer layer of epidermis gets separated from underlying tissue • Severe form of SSSS in new born Ritter’s disease • In older patients Toxic epidermal Necrolysis • Milder forms – Phemphigus neonatorum – Bullous impetigo
- 43. Staphylococcal diseases • Skin and soft tissue infections – Folliculitis – Furancle – Boils – Abscess – Wound infection – Carbuncle – Impetigo – Paronychia – Cellulitis • Musculoskeletal – Osteomyelitis – Arthritis – Bursitis – Pyomyositis
- 45. Staphylococcal diseases • Respiratory – Tonsillitis – Pharyngitis – Sinusitis – Otitis – Bronchopneumonia – Lung abscess – Empyema • Central nervous system – Abscess – Meningitis – Intra cranial thrombophlebitis
- 46. Staphylococcal diseases • Endovascular – Bacteremia – Septicemia – Pyemia – Endocarditis • Urinary tract infection – Uncommon – Present with instrumentation – Diabetes – Significant when associated with Bacteremia
- 47. Bacteriophage typing • Strain to be typed is inoculated as lawn culture on nutrient agar • After drying phages are applied on marked squares in a fixed dose • After overnight incubation cultures will be observed to be lysed by some phages • Phage type of strain is expressed by the phages which lyse the bacteria • Phage typing is important in epidemiological studies.
- 49. Epidemiology • Primarily colonize skin • Respiratory & superficial infections disseminate into environment • 10-30% carry staphylococci in nose • 10 % have staphylococcal carriage in hair& perineum • 5-10% carriage is seen in vagina • Transmission of infection can be by contact, direct or through fomites, by dust or by airborne droplets • Nosocomial cross infection is very important resistant strains
- 50. LAB DIAGNOSIS • SPECIMEN COLLECTION • Microscopy • Culture • Identification – Catalase test – Coagulase test • Slide • Tube – Antibiotic sensitivity – Phage typing
- 51. Treatment • Penicillin is drug of choice • Methicillin/ cloxacillin in penicillin resistant cases • For MRSA Vancomycin • Vancomycin, Teicoplanin resistant strains have appeared • Superficial infection local application with bacitracin, Chlorhexidine or Mupirocin • Very resistant cases & chronic resistant carriers Rifampicin along with oral antibiotic
- 52. Coagulase negative Staphylococcci • Staphylococcus epidermidis – Commensal on skin – Can cause cystitis – Stitch abscess, artificial heart valves, shunts, intra vascular catheters& prosthetic appliances • Staphylococcus hemolyticus • Staphylococcus saprophyticus – Uti in young women