Staphylococci

• Facultative, non-sporulating, non-motile, Gram positive cocci

• Cell Division 3 planes– Daughter cells don’t fully separate form

clusters

• Greek nouns– Staphyle – “ a bunch of grapes– Coccus – “grain or berry”

Staphylococci

27 species Three Important Species• Staphylococcus aureus

– Important human pathogen

• Staphylococcus epidermidis– Normal skin flora, disease under special

circumstances

• Staphylococcus saprophyticus– UTI’s in young females

S. aureus S. epidermidis S. saprophyticus

 

Catalase positive positive positive

 

Coagulase positive negative negative

 

Novobiocin negative negative positive

Resistance

STAPHYLOCOCCI - Cell Wall

1) Peptidoglycan – main component of the cell wall• Hydrated, semi-rigid polymer of two sugar derivatives:

• N-Acteylglucosamine & N-Acetylmuramic acid

• 90% of cell wall may contain peptidoglycan • Less in Gram negative organism

 

STAPHYLOCOCCI - Cell Wall

2) Teichoic Acid• Polymer of glycerol or ribitol joined by phosphate groups• Covalently linked to muramic acid of peptidoglycan• Links various layers of the peptidoglycan mesh together.

2 classes of teichoic acidsLipoteichoic acid

– Embedded in the peptidoglycan layer – Linked to the cytoplasmic membrane

Wall teichoic acid – Linked to only the peptidoglycan layer

Teichoic acid is responsible for the antigenic determinant of the organism  

STAPHYLOCOCCI - Cell Wall3) Protein A

– Bind the Fc component of antibodies

 4) Coagulase

– Bound and soluble forms– Activates the coagulation cascade

• Fibrin meshwork abscess formation

 5) Capsule – Variable

S. aureus - Epidemiology• Reservoir – Humans

• Asymptomatic Carriage Sites:– Nares– Rectum– Perineum– Pharynx

• Skin Colonization - Brief, Repeated • Transmission - Person to Person

S. aureus Carriage RatesPopulation Carriage Rate (%)

 General Population 25 Hemodialysis 75

  Diabetic on insulin 50

  Patients receiving 50allergy shots

 Intravenous Drug Users 40

Staphylococcal Infections - Risk Factors

• Skin Disease – Increased colonization

• Trauma – Expose binding sites

• Viral Respiratory Tract Infection (Influenza) – Expose binding sites– Decreased clearance

• Foreign Body• Liver disease• Neoplasia

• Diabetes• Renal Failure• Leukocyte &

Immunoglobulin Defects • Elevated Serum IgE

Levels • Narcotics Addiction• Broad Spectrum

Antibiotic Therapy

In general Healthy people don’t get serious Staph infections

Patterns of Disease - S. aureus

1) Invasion with Tissue Destruction

2) Toxin Mediated – Toxic Shock Syndrome– Scalded Skin Syndrome– Staphylococcal Food Poisoning

S. aureus - Invasive Infections

A Two Step Process:

1. Binding (adherence) to host tissues

2. Invasion

Staphylococcal Virulence Factors - Adherence

1) Nasal Mucosa – Teichoic Acid

2) Traumatized Skin and Foreign Surfaces Breech in normal barrier of mucosa or skin Unmasked host

proteins that S. aureus has specific receptors• Fibronectin • Fibrinogen• Laminin • Type IV collagen

3) Endothelial Cell S. aureus has a unique affinity for the vascular tree

• Attach to Fibronectin, Laminin and Endothelium Itself

Staphylococcal Virulence Factors - Invasion

A. Tissue Degrading Enzymes1) Hyaluronidase

Hydrolyzes hyaluronic acid in connective tissue matrix

2) LipaseBreak down lipids in matrix

3) DNase4) Hemolysins and Leukocidins

Family of membrane damaging toxins Dissolve RBCs, WBCs and tissue cells

5) CoagulaseCauses plasma to clot– Promotes abscess formation (wall)– Fibrin deposition around bacteria may protect from phagocytosis

Staphylococcal Virulence Factors - Invasion

B. Anti-Phagocytic Factors

1) Catalase• Made by all Staph (not Streptococcus)• Leukocytes use oxidative mechanism to kill bacteria

– Inactivates Hydrogen Peroxide H2O + O2

2) Protein A• Binds the Fc component of IgG• Inhibits opsonization by antibody

3) Capsule• Stearic Hindrance• Variable

Anterior Nares

Skin Trauma Localized

Colonization Infection

BacteremiaMetastatic

Foci

Lungs

Endocarditis Liver/Spleen

CNS

Kidneys

Furuncle

• Often starts as infection of hair follicle Folliculitis

• Firm, tender red nodule Painful

• Fluctuant with time Drain spontaneously

Carbuncle

Larger than furuncle• Extends into

subcutaneous fat• Interconnected• Firm, inelastic skin

Impetigo• Superficial infection of

skin• Usually

– S. aureus – Streptococcus pyogenes

• Children• Hot Weather• Minor Trauma• Initially vesicles

Impetigo

• Later: Crusted with yellow dark brown material

Erysipelas

• Strep pyogenes or S. aureus

• Sharp, raised borders

Cellulitis• Acute, spreading

Infection• Involves both skin and

subcutaneous tissues• Prior trauma to skin• Warm and

erethematous

Mitral Valve Endocarditis

Endocardits

Patterns of Disease - S. aureus

1) Invasion with Tissue Destruction

2) Toxin Mediated – Toxic Shock Syndrome– Scalded Skin Syndrome– Staphylococcal Food Poisoning

TOXIC SHOCK SYNDROME

1978 - Todd and coworkers reported a group of children:• Acute Febrile Illness • Subsequent Development of Hypotension and Shock.• Noted association with S. aureus phage group I• Named the illness "Toxic Shock Syndrome“

1980 - Illness had been identified in 941 patients in the USA

1990 - More than 3,300 cases have been reported• 95% in women• 90% occurred during menstruation in women who

were using tampons1989 - 61 cases of TSS reported

Toxic Shock Syndrome - Epidemiology

1. Menstrual• Colonization of the

Vagina and Cervix with TSST-1 producing strains of S. aureus– Tampon Associated

• Risk proportional to the absorbancy of Tampon

– Not tampon associated

2. Non-menstrual• Post-surgical• Influenza associated• Contraceptive device

associated– Diaphragm– Sponge

• Postpartum

Pyrogenic Toxin

• Family of Proteins secreted by– S. aureus– Strep pyogenes

• Share biologic properties and Amino Acid Sequences– Molecular wgt: 20,000 30,000 daltons

• Include– TSST-1– Staphylococcal Enterotoxins A, B,C– Pyrogenic Exotoxin A & B– Streptococcal Scarlet Fever Toxins A, B,C

TSST – A Superantigen

• Able to activate large number of Tcells– Up to 20% at one time

Massive Cytokine Release

• Interacts directly with invariable region of Class II MHC molecule

• Activated T Cells Release– IL-1: pyrogen, muscle

proteolysis– IL-2– TNF: inhibit PMN function– IFN-

Physicochemical Factors that Promote TSST-1 Production

1) Protein (or amino acid) containing environment

2) Temperature 37oC - 40oC

3) Ph range 6.5 - 8

4) Presence of Oxygen

Toxic Shock Syndrome - Clinical Manifestations

1. High Fever (>39.9oC)2. Scarlatiniform Eruption3. Hypotension and Shock4. Desquamation during

convalescence

Manifestations of Specific Organ Involvement

• Mucous Membranes: hyperemia • Gastrointestinal Tract: vomiting and diarrhea • Muscle: severe myalgias • Central Nervous System: disorientation • Kidney: azotemia, pyuria urinary tract

infection• Liver: elevation of serum bilirubin and SGOT• Blood: Thrombocytopenia

Toxic Shock Syndrome -Diagnosis

• Isolation of toxin producing S. aureus from a patient with a compatible clinical illness.

Toxic Shock Syndrome - Treatment

1) Treatment of Hypotension and Shock– Vigorous Fluid Replacement

2) Attention to the Site of S. aureus Colonization– Removal of Tampons– Drainage of Staphylococcal Abscess

3) Anti-Staphylococcal Antibiotic Therapy

STAPHYLOCOCCAL SCALDED SKIN SYNDROME

• A Disease of Infants– Localized Infection with Diffuse Skin Rash

• S. aureus (Phage group II) recovered from:– Nose– Pustules– Eye – Umbilicus

• Exfoliative Toxin– Two Serologically and Biologically Distinct Proteins

• Exfoliatin A• Exfoliatin B

– Inter-Epithelial Splitting of Stratum Granulosum Layer

Staphylococcal Scalded Skin Syndrome - Clinical Features

• Starts Abruptly– Perioral erythema – Sunburn like, tender rash spreads

over entire body

• Bullae Appear Rapidly – Nikolsky sign– Flaccid bullae slough off Denuded

areas

• Exfoliated Areas Eventually Dry– Flaky desquamation lasting 3-5 days

• Within 10 days After Onset Complete Recovery – New epidermis has replaced the

denuded areas

Staphylococcal Food Poisoning• 20% of Outbreaks of Acute Food Poisoning • Toxigenic Strain of S. aureus growing in

contaminated food– Produces Enterotoxin B (Heat Stable)

• Person to Person Transmission– Responsible organism usually isolated from

person involved meal preparation • Commonly implicated foods

– Custard filled bakery good– Canned food– Potato salad – Ice cream

• Food appears normal in appearance, odor and taste

Staphylococcal Food Poisoning - Clinical Features

• Incubation period 2-6 hours• Enterotoxin stimulates intestinal peristalsis and CNS

– Abrupt onset:• Salivation• Nausea and vomiting • Abdominal cramps • Watery diarrhea

• Afebrile• Self limited, symptoms disappear in 8 hours

S. aureus Treatment

1941 – Penicillin available1945 – Penicillin resistance reported

– Plasmid mediated – 2o to beta-lactamase (penicillinase)

1960-64 Semi-synthetic pencillins produced– Methacillin, oxacillin, nafcillin

1961 Methacillin resistant S. aureus (MRSA) reported

– Resistant to all beta-lactam antibiotics

Methacillin Resistant S. aureus (MRSA)

• 2 Penicillin binding proteins (PBPs) normally have enzymatic activity responsible for cross linking peptidoglycan wall

• MRSA have acquired a chromosomal gene MecA code for alternate PBP (“PBP 2a”)– Low affinity for beta lactam– Enzymatically active generate peptidoglycan

• Treatment Vancomycin (glycopeptide AB)

Glycopeptide Resistant S. aureus

• First reported in 1997

• Increased production of cell wall precursors including PBP2a– “Soak up” antibiotic in thickened cell wall

Staphylococcus epidermidis

• Normal Flora – Virtually all humans carry S. epidermidis on the

skin and in and around body orifices

• Hospital Acquired Infection– Contamination by S. epidermidis carried by the

patient most important event in infections associated

with foreign bodies

S. epidermidis - Virulence Factors

Production of an exo-polysaccharide ("slime")

• Promotes adherence to plastic surfaces

• Increases resistance to phagocytosis

• Increases resistance to antimicrobial therapy

S. epidermidis - Patterns of Infection

• Nosocomial Bacteremia -most common cause

• Endocarditis A. Native Valve

– Uncommon- 5% of cases

B. Prosthetic Valve– Single most common cause

(40% of cases)– Probably caused by

inoculation at the time of surgery

– Indolent course

• Intravenous Catheters-Single most common cause (50-75% of cases)

• Cerebrospinal Fluid Shunts

• Peritoneal Dialysis Catheter

• Vascular Grafts

• Prosthetic Joints

Foreign Body - Mechanisms of Staphylococcal Persistence

1) Fibronectin and Fibrinogen Coating– Firm Anchor for

Staphylococci

2) Glycocalyx Production– Protects Bacteria

3) Dysfunctional Phagocyte Population– Incapable of Killing

Bacteria

S. epidermidis Infection - Treatment

1. Antimicrobial Therapy

• Usually resistant to multiple antibiotics– Beta lactams– Erythromycin, Clindamycin, Tetracycline

• Require therapy with Vancomycin

2. Removal of Foreign Body

Staphylococcus saprophyticus

• Colonizes the genitourinary mucosa of some young women

• Causes both upper and lower urinary tract disease– 95% of cases are in females 16-35 years old– Responsible for 20 of the UTI's in this age group

• Second only to E. coli

• Pathogen of young, sexually active females – 70% sexual intercourse within 24 hours preceding onset

of symptoms