Staphylococcus aureus is a common cause of skin infections that forms clusters resembling bunches of grapes under the microscope. It is resistant to many antibiotics but can be treated with penicillin, methicillin, or vancomycin. S. aureus produces several virulence factors like toxins and enzymes that allow it to infect humans and cause diseases ranging from minor skin infections to life-threatening conditions like toxic shock syndrome. Laboratory tests help identify S. aureus and determine appropriate antibiotic treatment.

1. STAPHYLOCOCCUS GRAM + COCCI “BUNCH OF GRAPES”

2. Staph.aurues

4. Ubiquitous-,most common cause of localised supperative lesions in the human beingsHas ability to devlp resistance against penicilline First observed in human pyogenic lesions-Von Recklinghousen Pasteur-obtained liquid cultures of the cocci from pus& inoculated them into rabbits Sir Alexander Ogston-causitve role of coccus in abcess.,named staphylococccus,found nonvirulent strains in skin Mostly frm,pyogenic-golden yellow colonies

5. Nl skin-white colonies Rosenbach-Staph.aureus & albus Passet-citreus-lemon yellow colonies Indicators of virulence-hemolysis,gelatin liquifaction,lipolytic activity,production of urease,phosphatase,etc-not reliable Most constant asso.-virulence---coagulase enz. Production Lesser eztend to fermentaion of mannitol

6. Staph.aureus/s.albicans-C+,Mf+,pathogenic Staph.epidermidis/s.albus-C-,Mf-,non patho Staph-haemolyticus-patho,C- Staph.saprphyticus-patho,C- Staph.hominis,S.capitus-commensal flora of human skin

7. Staphylococcus aureus MOPHOLOGY spherical cocci—1micron d—grape like clusters—found singly—long chains never occur—NONMOTILE--NONSPORING—NONCAPSULATED Some small am.capsular mat. Stains-aniline dyes,G+ Under penicillin,may change to L forms

8. CULTURAL CH. Grows in ordinary media—optimum temt-37C—PH 7.4-7.6—aerobes &facultative anaerobes On nutrient agar-colonies large,circular,covex,smooth,shiny,opaque& easily emulsfiable.pigment prodcn.22C,only on aerobic cultures Pigment=Lipoprotein+carotene -slope-Oil paint appearance-llr 2 in blood agar --most strains r haemolytic

14. Esp.20-25%Co2 MacConkys agar-smaller colonies-pink-lactoseF Liquid media-uniform turbidity- Selective media 4 isolation-4m specimens-feces-----8-10% NaCl(salt-milk ag.,salt broth)—LiCl,Tellurite(Ludlam’s media),& Polymyxin) Prim isolation-Sheep blood ag. Human blood not used-antibodies and othr inhibitors

15. BIOCHEMICAL REACTIONS F-sugars,----acid,no gas MannitolF-Staph.aureus,C+, Urea hydrolysis Reduce nitrates 2 nitites Liquify gelatin MR+,VP+,Indole- Most—lipolytic,in egg yolk—dense opacity Phophatse prdcn-aureus+,epidemidis- K.tellurite---black colonies Thermostable nucleases

16. RESISTANCE Well resistant non sporing—dried threads-3-6 months Thermal death point-62c for 30 min-----some 80C,sm grow at 45C Most grow-10-15% NaCl---imp in food preservation Resist 1% phenol for 15 min HgCl(1%)-10 min,aniline dyes bactericidal,crystal violet FA inhibits growth-highly unsaturated—more on C+ than C-

17. Uniformly resistant 2 lysozymes----ex.sm micrococci Sensitive 2 LYSOSTAPHIN-mix of enz produced by particular strains of Staph.epidermidis * PENICILLIN Resistance 3 types 1.Prodcn of beta –lactamase(penicillinase)-4types-A(hospital strains),B,C,D-inducible,controlld by plasmids,transmitted-transduction/conjugation

18. 2.Chromosomal chng---chng in receptors,ruduce binding---covers beta lactamase resistnt penicilline-METHICILLINS,CLOXACILLINS EMRSA-epidemic Methicilline resist.staph.aureus-----hospital inf. 3.Devlpmnt of tolerence-only inhibited not killed * Pathogenecity & virulence Staph-2 typs of infections-infections& intoxications

19. Infections-damaged skin—adhere 2 cells---evade host’s defence mech.—multiply—tissue damage Intoxications-d/s-bac.toxins---exotoxins Virulence factors 1.Cell associatd polymers 2.Cell surface proteins 3.Extracellular enzymes 4.Toxins

20. Cell associated polymers 1.Cell wall polysach,peptidoglycan----+ts complements-release of inflammatory cytokines 2.Teichoic acid-complement mediated opsonisation 3.Capsular poly sach. Surrounding cellwall----inhibits opsonisation

21. Cell surface proteins *Protein A-chemotactic,antiphagocytic,anticomplementaryplt damage hypersensitivity *binds 2 Fc (Ig),except IgG3,Fab free---proteinA +IgG---mixd with corresponding antgen—agglutination----used fr grouping P-A is a B cell mitogen Also used as ligand fr isolation of IgG Clumping Factor(bound coagulase),heat stable,no need of CRF 2 coagulate-anothr surf.pro.---recp. fr Slide coagulase test.

22. Slide Coagulase Test Saline staph.aureus+human plasma---cocci clumped---for identification of aures Capsulated—negas clumping f,envelopd by capsular polysach *Extra cellular Enzymes Coagulase-binds CRF(reacting factor)—bins 2 prothrombin-fibrinogen tom fibrin---clots human plasma Coagulase 8 types-,eg,C-A in human strains Coagulase is secretd into medium-clotting

23. Lipases To infect skin& subcutaneous tissue----Hyaluronidase breaks down connective tissue,Staphylokinase(fibrinolysin),fatty acid modifying enzymes& proteases---initiation &spresd of infestion *Nuclease *Protein receptor Posses rec. for many human proteins-fibronectin,fibrinogen,IgG,C1q----facilitate adhesion

24. Toxins 1.Cytotoxin 2.Enterotoxin 3.Exfoliative toxin Cytotoxins Membrane active substances-4haemolysins+1lecocidin *Alpha,Beta,Gamma,Delta Alpha Inactivatd at 70C,reactivatd at 100C-at 60C it combines with a heat labile inhibitor which is denatured at 100C

25. Less active against human cells,leucocidal,cytotoxic,dermonecrotic,neurotoxic,lethal,toxic to macrophages,lysosomes,muscle tissues,renal cortex,circulatory sys. Beta Sphingomyelinase,hemolytic for sheep cells,not for human cells, Exhibits a HOT-COLD phenomenon,hemolysis being initiatd at 37C,but become evident only after chilling

26. Gamma-twp separate pro. Delta detergnt like action on macro,rbc,wbc,plts Leucocidin/Panton Valentine Toxin-two compont toxin(s&f),---Synergohymenotropic hormones * Enterotoxin Cause food poi.NVD—2-6hrs after intake of preformd toxin Heat stable,100C—10-40min,mostly-meat,fish,milk and milk products---at room temp Illness self limited,recovery in a day,eight antigenic types—A,B,C(1-3),D,E,H Directly act on ANS-fever,thn on GI mucosa,toxin is antigenic-neutralisd by specific antitoxin,

27. Serological test-latex agglutination,ELISA Potent toxin,microgrms-illness,sm cause post antibiotic diarrhoea,-----also exhibits miogenic,pyogenic,hypotensive,thrombocytopenic,and cytotoxic TSST(Toxic Shock SyndromeToxin) Multisystem ds.fever,hypotn,myalgia,v,d,mucosal hyperemia,erythromatous rash,-desquamate latr Inf-by staph.aureus producing TSST,(bacteriophage group 1)

28. TSST type 1,/enterotoxin type F/pyogenic exotoxin C, *TSST 1-superantigens---potent activators of Tlymphocytes Being Vbeta restrictd T cell mitogens-+ts laege no. of T cells—without relation to their epitope specificity---dys regulatd immune response.---with release of cytokines,IL1,2,TNF,TNgamma--- explains multisystem inv.

29. Exfoliative Toxin/ET/Exfoliatin Resp.4 SSSS-Staph.scalded skin syndrome Outr layr of epidermis gets seperatd from the underlying tissue Sevr form—Ritter’s Ds.(newborn).& Toxic epidermal necrolysis(older) Milder forms r pemphigus neonatorum&bullous empetigo

30. Staphylococcus diseases Mostly localised pyogenic lesions Skin and soft tissue-folliculitis-furuncle-abcess-carbuncle-wnd inf-impetigo-paronychia-cellulits Muskuloskeltal-Osteoarthritis-arthritis-bursitis-pyomyositis Respiratory-Tonsilitis-pharyngitis-sinusitis-otitis-bronchopnuemonia-lung abcess-empyems- CNS-abcess-meningitis-intracranial thrombophlebitis Endovascular-Bacteremia,septicemia,pyemia,endocarditis Urinary-uncommon-bt with instrumnts,implants,diabets,urinary isolats-sigfic-related to bacteremia

31. Bacteriophage typing Staphylococci typed basd on their susceptability to bacteriophage Acceptd set of phages r thr Staph stain-culturd in nutrint agar-dried—phage applied—if lysed by phage---typed * Epedemiology Primary parasites of humans-colonising skin-skin glands-mucus memb.carries in nose ,perinium, hairs,vagina(rises during mensus-TSS relatd 2 menstruation) Shedders-large no. of coccal spread MOT-fomites,dust,airborne droplts Common cause of post operative wound inf.hosp.staff attackd—local application neomycin,chlorhexidine

32. Lab diagnosis Specimen-pus,supperative lesions-sputum,feces Carriers-nasal swab diagnosis---by culturing—platd on blood agar appear aftr overnight incubation Scanty no.-ludlam’s media/salt milk agar/Robertson’s cookd meat medium+10% NaCl Coagulase test done-Tube & Slide Tube-detects free coagulase

33. 0.1 ml cultr+0.5ml human/rabbit plasma-----EDTA,oxalate/heparin----incubatd in water bath at 37C---3-6hrs If poitive----plasma clots and does not flow when the tube is tilted Citrates not used-utilised by conatminent bact Continued incubation-not preferrd-clot lysed by fibrinogen of sm strains Slide test-bound coagulase-in divergence tube test is the determinent.Slide coagulse test Antibiotics sensitivity checkd Bacteriuophage typing-epidemiological Hidden deep inf—Antistaphylolysin titres of more than 2unitsper ml---deep seatd---bone abcess

34. Treatment Benzyl penicilln-most effective Methicilline Cloxacilline Vancomysin Other C+ Staphylococci-intermedius,hyicus C- staphs…nl flora---epidermidis,hemlyticus,saprophyticus Epidermidis-human skin----stitch abcess—rows on implanted foreign bodies

35. Micrococci G+ Pairs tetrads,irregular clusters C+,O+ Aerobic +strictly respiratory met,parasitic nl skin Resmble staph—in staind smears generally larger & more gram variable—in cultures form small colonies Differentiate---HUGH & LEIFSON’S oxidation fermentation tests---micrococci-oxidative Staph--fermentation