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Staphylococcus aureus
The document discusses Staphylococcus aureus, a significant pathogenic bacterium that exhibits various virulence factors, including toxins that contribute to a wide range of infections, from superficial skin conditions to severe systemic diseases. It highlights its classification, culture characteristics, clinical syndromes, transmission, prevention, and laboratory diagnosis methods. Staphylococcus aureus is known for diseases like toxic shock syndrome, food poisoning, and various skin infections, requiring careful management and treatment.
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Staphylococcus aureus
- 1. STAPHYLOCOCCUS AUREUS BY, ATHIRA B 1STMSC MICROBIOLOGY
- 2. INTRODUCTION o FAMILY :-MICROCOCCI (CONSISTS OF GRAM POSITIVE COCCI,ARRANGED IN TETRADS,CLUSTERS) o GENUS:- STAPHYLOCOCCUS o TERM “STAPHYLOCOCCUS” DERIVED FROM GREEK : STAPHYLE=BUNCH OF GRAPES AND KOKKOS=BERRY, MEANING BACTERIA OCCURING IN GRAPE LIKE CLUSTERS OR BERRY
- 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. CLASSIFICATION BASED ONPIGMENT PRODUCTION: o S.aureus:- golden –yellow pigmented colonies o S.albus:-white colonies o S.citrus:-lemon yellow colonies BASED ON PATHOGENICITY: -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
- 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 From irregular grapelike clusters(since divided in 3 planes) Non-motile,non-sporing and few starins are capsulated
- 6. Culture Aerobes andfacultative anaerobes Opt.Temp. for growth= 37°c Opt.PH for growth=7.5 0n Nutrient Agar, - golden yellow and opaque colonies with smooth glistening surface 1-2mm in diameter (max pigment production @22°c)
- 7. Culture (contd..) OnBlood Agar, - golden yellow colonies, surrounded by a clear zone of hemolysis(beta hemolysis),esp. When incubated in sheep or rabbit blood agar in atmosphere 0f 20% co2 On MacConkey Agar, - Smaller colonies than those on NA (0.1-0.5mm) and are pink coloured due to lactose fermentation
- 8. Culture (contd..) OnMannitol 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. Biochemical Properties IndoleTest = negative MR Test = Positive Vp Test = Positive Urease Test = positive Hydrolyse gelatin Reduces nitrate to nitrite Phosphatase = Positive DNAase Test =Positive Coagulase Test = Positive Catalase = Positive Oxidase = Negative Ferment glucose, lactose, maltose, sucrose and mannitol with production of acid but no gas MR VP MEDIUM
- 10. Virulence Factors Cellwall associated structures Capsule Peptidoglycan ProteinA Clumping factor(bound coagulase) Adhere to host cell Result phagocytosis Inhibits inflammatory response Binds to Fc moiety of IgG,exerting antiopsonin(and therefore strongly antiphagocytic effect Cause organism to clump in presence of plasma
- 11. Extracellular Toxins Leucocidin(panton- valentine factor) Enterotoxin TSST(toxin shock syndrometoxin) Haemolysin (alpha,β,gamma,δ) Exofoliatin toxin Haemolytic dermo-necrotic and leucocidal Kills WBCS by producing holes in their CM Act on ANS to cause illness Produce fever,skin rashes,diarrhea,coonjuncivitis,and eath to shock Breaks intracellular bridges in the stratum granulosm of epidermis and causes its seperstion from underlying tissue,resulting in a blistering and exfoliating disease of skin Virulence factors(contd…)
- 12. Pathogenesis Adhere todamaged skin,mucosa or tissue surfaces - At these sites, they evade defence mechanism of the host,colonize and causes tissue damage S.aureus produces disease by - Multiplying in tissues - Liberating toxins - Stimulating inflammation
- 13. Clinical Syndromes 1. Cutaneousinfection -Folliculitis - Boils/furuncles - Carbuncle - Wound infections 2. Deep infections - Osteomyelitis - Periostitis - Endocarditis 3. Exfoliative Diseases 4. Toxin shock syndrome 5. Staphylococcal food intoxication
- 14. 1. Cutaneous Infections Folliculitis : It is inflammation of the hair follicels A small red bump or pimple develops at infection sites of hair follicle
- 15. Cutaneous infection (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
- 16. Cutaneous Infection (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 characterised by watery bristles , which become pustules and then honey coloured crust
- 17. 2. Deep Infections Osteomylitis : Inflammation of bone Bacteria can get to the bone - via bloodstream - Following an injury Clinical Featues : pain, swelling, deformity, defective healing, in some case pus flow Diagnosis : X-ray, MRI, Bone aspirates
- 18. Deep Infections(Contd….) Periostitis: Inflammation of periosteum Clinical features : fever , localised pain , leucocytosis Diagnosis : Needle aspiration of subperiosteal fluid
- 19. Deep Infections(contd…) Endocarditis: It is an inflammation of the inner layer of the heart,the endocardium Endocarditis occurs when bacteria enter blood stream, travel to heart , and lodge on abnormal heart valves or damaged heart tissue.
- 20. 3.Exfoliative Disease (Exfoliate= scaling off tissues in layers) Also known as “Staphylococcal skin scalded syndrome Previously called dermatitis exfoliative, pemphigus neonatorum,Lyell’s disease and Ritter’s disease Epidermal toxin produced by s.aureus at skin and is carried by blood stream to epidermis,where it causes a split in a cellular layer i.e; this toxin separates outer layer of epidermis from underlying tissues.
- 21. Clinical Syndromes(contd…) 4.Toxic shocksyndrome Caused when toxin shock syndrome toxin (TSST) liberated by s.aureus enters blood stream It is a multisystem illness,characterized by: 5.Staphlococcal food poisoning Caused when consuming food in which s.aureus has multiplied and formed endotoxin Symptoms: - Nausea - Vomiting - Severe abdominal pain - Diarrhoea - Sweating - Headache,etc.
- 22. Mode Of Transmission Personwith lesions Airborne droplets Asymptomatic carrier Cross-infection Mode of transmission
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- 24. Laboratory Diagnosis A. HaematologicalInvestigations : 1. TLC(Total Leukocyte count) Normal : 4000 – 10000 cells/mm³ In case of infection : > 10000 cells/mm³ 2. DLC(Differential Leukocyte Count) Normal: 80% In case of infection : > 80%
- 25. Laboratory Diagnosis (contd..) B.Bacteriological Investigations Specimens: - Pus : from wound or abcess 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 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 plates for further biochemical tests Tube Coagulase Test: -1. Mix 0.5ml of human plasma with 0.1ml of an overnight broth culture of s.aureus -2. 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
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