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Staphylococcus aureusAli Somily MD,FRCPC
Gram Positive Cocci
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Staphylococcus aureus
Staphyloccocci - derived from Greek stapyle (bunch ofgrapes)
Gram Stain : Gram Positive Cocci
Aerobic
Extracellular Features
Morphology : Cocci
Arrangement : Clusters
Colonies: White /yellow , rounded on blood agar plate
Non motile Non motile
No capsule
No glycocalyx
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Virulence Factors
Exotoxins
-Lactamase
Plasmid ,Penicillin resistant
Mutant PenicillinBindingProtein (PBP)
MRSA
Coagulase
Free and bound
ThrombinFibrin
Protein A Bind to Fc of IgG, Block complement and opsonization
Other enzymes
Lipase, Protease, Hyaluronidase, Nuclease, Fibrinolysin
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Exotoxins
Hemolysins of RBCs Alpha toxin ( septic Shock and Dermonecrosis)
Beta toxin (Shingomyelinase)
Delta toxin (Leukocidin)
Gamma toxin (Tissue Necrosis)
PantonValentine Leukocidin (PMNs and Micros) Influx of Ca++,Degranulation and Lysis
Enterotoxins Toxin A (Food Poisoning) and F (Similar to TSST)
Toxic Shock Syndrom Toxin(TSST) Release of IL2 CD4 T-cell and IL1
Exfoliation ( Phage Group II , Epidermolytic; intraepithelialSeparation at Stratum Granulosum)
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Laboratory Tests
Catalase : +ve
Coagulase: +ve
DNase: +ve Mannitol: +ve
Hemolysis: Beta
6.5 % NaCl : Growth
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Source and Transmission
Colonization
Human : Nose, Skin, Groin, Other moist area
Horizontal Transmission : Human contact, Sneeze
and Contaminated environment
Nosocomial Transmission:
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Clinical Syndroms
Skin Infections (Furuncles, Boils, Carbuncles, Scalded SkinSyndrom (SSS), Burn and Wound)
Food Poisoning (Enterotoxin A, No Bacteria, N&V)
Toxic Shock Syndrom (Tampons, Wound, Nasal Packing)
Oseomyelitis (Most Common Cause, Meta in Childern andEpiphysis in Adult, Truma or Hematogenous)
Infective Artheritis (Most Common Cause in Adult)
Acute Endocarditis (Most Common Cause Normal Abnormaland Prosthetic Valves )
Post viral lobar Pneumonia ( Especially Flu) Bacteremia and Sepsis (Most Common Cause ,Community
Acquired)
Parotitis ( Gland and Duct of Stensen)
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TOXIN MEDIATED DISEASES
1. Staphylococcal food poisoning
Due to production of entero toxins
heat stable entero toxin acts on gut
produces severe vomiting following a very short
incubation period
Resolves on its own within about 24 hours
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2. Toxic shock syndrome
High fever, diarrhoea, shock and erythematous
skin rash which desquamate
Mediated via toxic shock syndrome toxin
10% mortality rate
Described in two groups of patients
Associated With young women using tampones during
menstruation Described in young children and men
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3. Scalded skin syndrome
Disease of young children
Mediated through minor Staphylococcalinfection by epidermolytic toxin producing
strains Mild erythema and blistering of skin
followed by shedding of sheets of epidermis
Children are otherwise healthy and mosteventually recover
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Pustular impetigo
Hordeolum-furuncle
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Bacteremia-
hemorrhage
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Bacteremia-gangrene
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Host Defense and Immunity
Opsonization (IgG, C3b or IgM +C3b)
Phagocytosis (by PMNs)
Cytokines (By CD4+T-Cells)
No Immunity Gained by Infection
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Treatment
Methicillin : Drug of Chice
Penicillin : If sensitive
Vancomycin: If MRSA
Linazolid : If vancomycin Rsistant
Cephalosporins : First Generation
Bacitricin : Topical
Special Situation :Rifampin ,Doxycyclin,Trimethoprime / Sulphamethoxazole
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Prevention
MRSA
Infection control
Isolation, Treatment , Decolonization Contact percussion
Vaccine and Toxoid : Not Available yet
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Staphylococcus epidermidis
Gram Stain : Gram Positive Cocci
Aerobic
Extracellular
Features Morphology : Cocci
Arrangement : Clusters, Tetrads
Colonies: White/yellow , rounded on blood agar plate
Non motile
No capsule
Glycocalyx : Exopolysaccharide
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Virulence Factors
Glycocalyx
- Lactamase
Mutant PBP
Exotoxins : None
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Laboratory Tests
Catalase : +ve
Coagulase: -ve
DNase: -ve Mannitol: -ve
Hemolysis: None
Novobiocin : Susceptible
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Source and Transimission
Normal Flora : Skin and Mucous membrane
Infections : Trauma and Foreign bodies
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Clinical
Bacteremia and Sepsis
Subacte Endocarditis
Neonatal Bacteremia
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Host Defense and Immunity
Opsonization
Phagocytosis
Cytokines
No Immunity Gained by Infection
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Treatment
Vancomycin
Cephalosporins : First generation if Sensitive
Vaccine and Toxoid : Not Available yet
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Staphylococcus saprophyticus
Gram Stain : Gram Positive Cocci
Aerobic
Extracellular
Features Morphology : Cocci
Arrangement : Clusters, Tetrads
Colonies: White /yellow , rounded on blood agar plate
Non motile No capsule
No Glycocalyx
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Virulence Factors
Multiple Drug Resistant
Hemagglutinin proteins and Surface Proteins
Urease
Exotoxins : None
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Laboratory Tests
Catalase : +ve
Coagulase: -ve
DNase: -ve Mannitol: -ve
Hemolysis: None
Novobiocin : Resistant
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Source and Transimission
Normal Flora : of genitourinary Skin
Poor Hygiene : Sexual ActivityUrinary
Tract
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Clinical
Urinary Tract Infection (UTI)
Healthy, young, sexual active women
Cystitis (Lower UTI) or Pyelonephritis (upper
UTI)
Pyuria : Most cases
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Host Defense and Immunity
Opsonization
Phagocytosis
Cytokines
No Immunity Gained by Infection
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Treatment
Trimethoprime / Sulphamethoxazole (TMP-
SMZ)
Ciprofluxacin : Alternative
Vaccine and Toxoid : Not Available yet