04 Staphylococcus Aureus

8/12/2019 04 Staphylococcus Aureus

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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


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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Opsonization

Phagocytosis

Cytokines



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Treatment

Vancomycin

Cephalosporins : First generation if Sensitive



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Staphylococcus saprophyticus


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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Opsonization

Phagocytosis

Cytokines



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Treatment

Trimethoprime / Sulphamethoxazole (TMP-

SMZ)

Ciprofluxacin : Alternative


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04 Staphylococcus Aureus