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Description of Staphylococcus aureus

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  1. 1. STAPHYLOCOCCI MaheshYadav Medical Microbiology Central Dept. Of Microbiology TU, Nepal
  2. 2. INTRODUCTION • Family: Micrococceae (consists of Gram positive cocci, arranged in tetrads, clusters) • Genus : Staphylococcus • Term “staphylococcus” derived from Greek :Staphyle = bunch of grapes and Kokkos = berry, meaning bacteria occurring in grapelike clusters or berry.
  3. 3. History • Robert Koch (1878)- first to see staphylococci in pus specimen • Louis Pasteur (1880)- first to cultivate in liquid medium • Sir Alexander Ongston (1881)- named the bacteria as “staphylococcus”
  4. 4. Classification • Based on pathogenecity: – Pathogenic:- includes only one i.e., S.aureus – Non-pathogenic:- includes S.epidermidis, S.saprophyticus, S.albus, S. citrus, S.hominis,etc. • Based on coagulase production: – Coagulase positive: S. aureus – Coagulase negative: S. epidermidis, S. saprophyticus S. albus , S. aureus , S. citrus on Nutrient Agar •Based on pigment production: •S.aureus :-golden-yellow pigmented colonies •S.albus :- white colonies •S.citrus :-lemon yellow colonies
  5. 5. S.aureus • Natural habitat:-Nostril and skin Morphology:- – Gram-positive, cocci, 0.5-1.5µm in diameter; occur characteristically in group, also singly and in pairs – Form irregular grapelike clusters (since divide in 3 planes) – Non-motile, non- sporing and few strains are capsulated
  6. 6. Culture • Aerobes and facultative anaerobes • Opt. Temp. For growth= 37°C • Opt. pH for growth= 7.5 • On Nutrient agar, – golden yellow and opaque colonies with smooth glistening surface, 1-2 mm in diameter (max. pigment production@22 °C)
  7. 7. Culture (contd...) • On Blood agar, – golden yellow colonies, surrounded by a clear zone of hemolysis (beta- hemolysis),esp. When incubated in sheep or rabbit blood agar in atmosphere of 20% CO2 • On MacConkey agar, – Smaller colonies than those on NA(0.1-0.5 mm) and are pink coloured due to lactose fermentation
  8. 8. Culture (....contd) • On Mannitol salt agar, – S.aureus ferments mannitol and appear as yellow colonies – MSA is a useful selective medium for recovering S.aureus from faecal specimens, when investigating food poisoning
  9. 9. Biochemical Properties • Catalase positive; oxidase negative • Ferment glucose, lactose, maltose, sucrose and mannitol, with production of acid but no gas • Mannitol fermentation carries diagnosis significance
  10. 10. Biochemical Properties(....contd) • Indole test= negative • MR test= positive • VP test= positive • Urease test= positive • Hydrolyse gelatin • Reduces nitrate to nitrite • Phospahatase= positive • DNA-ase test= positive • Coagulase test= positive
  11. 11. Virulence Factors Cellwall associated structures • Peptidoglycan • Capsule • proteinA • Clumping factor (bound coagulase) Extracellular toxins • Haemolysin • Leukocidin • Enterotoxin • TSST • Exfoliatin toxin Coagulase • staphylokinase • DNAase • Phosphatase • lipase • Phospholipase • hyaluronidase • serokinase • protease
  12. 12. Virulence Factors
  13. 13. Virulence Factors(contd....) Cellwall asssociated structures Capsule Adhere to host cell Resist phagocytosis Peptidoglycan Inhibits inflammatory response Protein A Binds to Fc moiety of IgG, exerting antiopsomin (and therefore strongly antiphagocytic effect) Clumping factor(bound coagulase) Cause organism to clump in presence of plasma
  14. 14. Virulence Factors(contd....) Extracellular toxins Haemolysin (α,β,γ,δ) Haemolytic dermo-necrotic and leucocidal Leucocidin (Panton- Valentine factor) Kills WBCS by producing holes in their CM Enterotoxin Act on ANS to cause illness TSST (toxin shock syndrome toxin) Produce fever, skin rashes,diarrhoea,conjunctivitis,and eath to shock Exfoliatin toxin Breaks intracellular bridges in the stratum granulosum of epidermis and causes its separation from underlying tissue, resulting in a blistering and exfoliating disease of skin
  15. 15. Virulence Factors(....contd) Extracellular Enzymes Free coagulase Clots plasma by acting along with CRF present in plasma, binding to prothrombin and converting fibrinogen to fibrin Staphylokinase Degrades fibrin clots Hyaluronidase Hydrolyze the acidic mucopolyysaccharides present in matrix of connective tisues DnAase, Lipase, Phospholipase, protease Degrades DNA, lipid, phospholipid, and protein respectively
  16. 16. Pathogenesis • Adhere to damaged skin, mucosa or tissue surfaces – At these sites, they evade defence mechanisms of the host, colonize and cause tissue damage • S.aureus produces disease by – Multiplying in tissues – Liberating toxins, – Stimulating inflammation
  17. 17. Clinical Syndromes
  18. 18. Clinical Syndromes 1. Cutaneous infections – Folliculitis – Boils/furuncles – Carbuncle – Impetigo – Wound infections 2. Deep infections – Osteomyelitis – Periostitis – endocarditis 3. Exfoliative diseases 4. Toxin shock syndrome 5. Staphylococcal food intoxication
  19. 19. 1) Cutaneous Infections • Folliculitis: It is inflammation of the hair follicles. • A small red bump or pimple develops at infection sites of hair follicle. •Sty: A sty is folliculitis affecting one or more hair follicles on the edge of the upper or lower eyelid.
  20. 20. Cutaneous Infections(contd....) • Furuncle/boils: Furuncle is deep seated infection, originating from folliculitis,( if infection extends from follicle to neighbour tissue) • Causes redness, swelling, severe pain • Commonly found on the neck, armpit and groin regions • Carbuncle: Carbuncle is an aggregation of infected furuncles. Carbuncles may form large abscesses. • It is a large area of redness, swelling and pain, punctuated by several sites of drainage pus.
  21. 21. Cutaneous Infections(contd....) • Impetigo: a very superficial skin infection common in children, usually produces blisters or sores on the face, neck, hands, and diaper area. • It is characterized by watery bristles, which become pustules and then honey coloured crust impetigo with vesicles, pustules, and sharply demarcated regions of honey-colored crusts.
  22. 22. 2) Deep Infections • Osteomyelitis: inflammation of bone • Bacteria can get to the bone – Via bloodstream – Following an injury Clinical features: pain, swelling, deformity, defective healing, in some case pus flow, Diagnosis: X-ray, MRI, bone aspirates
  23. 23. Deep Infections(contd....) • Periostitis: inflammation of periosteum • Clinical features: fever, localised pain, leucocytosis • Diagnosis: needle aspiration of subperiosteal fluid
  24. 24. Deep Infections(....contd) • Endocarditis: It is an inflammation of the inner layer of the heart, the endocardium • Endocarditis occurs when bacteria enter bloodstream, travel to heart, and lodge on abnormal heart valves or damaged heart tissue.
  25. 25. 3)Exfoliative Disease • (Exfoliate= scaling off tissues in layers) • Also known as ‘Staphylococcal skin scalded syndrome’ • previously called dermatitis exfoliativa, pemphigus neonatorum, Lyell’s disease and Ritter’s disease • Epidermal toxin produced by S.aureus at skin and is carried by bloodstream to epidermis , where it causes a split in a cellular layer i.e., this toxin separates outer layer of epidermis from underlying tissue
  26. 26. 4) Toxic Shock Syndrome • Caused when Toxin shock syndrome toxin (TSST) liberated by S.aureus enters bloodstream • It is a multisystem illness, characterized by: Vomiting Diarrhoea Skin rashes Kidney failure High Fever Headache Conjunctival reddening Hypotension
  27. 27. 5) Staphylococcal Food Poisoning • Caused when consuming food in which S.aureus has multiplied and formed endotoxin • Symptoms: – Nausea – Vomiting – Severe abdominal cramp – Diarrhoea – Sweating – Headache,etc.
  28. 28. Mode Of Transmission Person with lesions Airborne droplets Asymptomatic carrier Cross-infection Mode of transmission
  29. 29. Prevention Wash your hands Keep wounds covered Reduce tampon risks Avoid sharing personal care items Cooking and storing food properly
  30. 30. Treatment and Drugs Antibiotic therapy Wound drainage Device removal Removal of dead tissue
  31. 31. Laboratory Diagnosis A. Haematological Investigation: 1. TLC (Total leukocyte count): Normal: 4000-10000 cells/mm³ In case of infection: > 10000 cells/mm³ 2. DLC (Differential leukocyte count): Normal neutrophil : 80% In case of infection: > 80%
  32. 32. Laboratory Diagnosis (contd....) B. Bacteriological Investigation: • Specimens: – Pus: from wound or abscess or burns] – Nasal Swab: from suspected carrier – Food: to diagnose staphylococcal intoxication – Blood: to diagnose endocarditis and bacteremia – Sputum: to diagnose lower respiratory tract infection
  33. 33. Laboratory Diagnosis (contd....) • Culture and isolation: – Specimens are cultured on BA plate and are incubated @ 37 °C for 24 hours – After incubation, BA plate is observed for significant bacterial growth (> 2mm in diameter) – Then, Gram-staining is performed of the isolated organisms – Then, subcultured on NA plate for further biochemical tests • Tube coagulase test: – i. Mix 0.5ml of human plasma with 0.1ml of an overnight broth culture of S.aures – ii. Incubate the mix in a water bath @ 37°C for 3-6 hours – Result: plasma clots and doesn’t flow if the tube is inverted
  34. 34. MRSA • Most strains of S.aureus, even those acquired in community, are penicillin resistant – Resistance is attributable to beta-lactamase production due to genes located on extrachromosomal plasmids. • Some are resistant to the newer beta-lactamase resistant semisynthetic penicillins, such as methicillin, oxacillin, nafcillin. – Resistance is due to presence of unusual penicillin-binding protein(PBP)in the cellwall of resistant strains • Infection with MRSA is likely to be more severe and require longer hospitalization, with incumbent increased costs than infection with a methicillin susceptible strain.
  35. 35. CONS • Coagulase Negative Staphylococci(CONS) that are commonly implicated as pathogens include • Staphylococcus epidermidis: causes infection of native heart valves and intravascular protheses. • Staphylococcus saprophyticus: causes urinary tract infections, mainly in sexually active women. • CONS that are less commonly implicated as pathogens include: S.hominis, S.haemolyticus, S.cohnii, s.lugdunensis, S.saccharolyticus, S.schleiferi, S.simulans and S. warneri
  36. 36. THANK YOU