Staphylococcus aureus

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Staphylococcus aureus
Gram Positive Cocci

• Ali Somily MD,FRCPC

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Staphylococcus aureus

• Staphyloccocci - derived from Greek stapyle
  (bunch of grapes)
• 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 Penicillin Binding Protein (PBP)
• MRSA
• Coagulase
• Free and bound
• Thrombin ? Fibrin
• 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)
• Panton Valentine 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
  intraepithelial Separation 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 Skin Syndrom (SSS), Burn and Wound)
• Food Poisoning (Enterotoxin A, No Bacteria, NV)
• Toxic Shock Syndrom (Tampons, Wound, Nasal
  Packing)
• Oseomyelitis (Most Common Cause, Meta in Childern
  and Epiphysis in Adult, Truma or Hematogenous)
• Infective Artheritis (Most Common Cause in Adult)
• Acute Endocarditis (Most Common Cause Normal
  Abnormal and 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 Staphylococcal infection
  by epidermolytic toxin producing strains
• Mild erythema and blistering of skin followed by
  shedding of sheets of epidermis
• Children are otherwise healthy and most
  eventually 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 CD4T-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 Activity? Urinary 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