Staphylococcus (Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus saprophyticus)

Staphylococcus

Kingdom: Bacteria

Phylum: Firmicutes

Class: Bacilli

Order: Bacillales

Family:Staphylococcaceae

Genus: Staphylococcus

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• Gram positive cocci in clusters or groups.

• Catalase positive

• Facultative anaerobes

• Oxidase-negative

• Medically important Organisms:• Staphylococcus aureus,

• staphylococcus epidermidis,

• staphylococcus saprophyticus.

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Catalase Test

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Staphylococcus

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Staphylococcus classification

StaphylococcusCatalase +, clusters

S.aureusβ hemolytic,

yellow on Blood

agar, Mannitol

positive.

Non-Coagulase

S.epidermidisNovobiocin sensitive,

β or γ Hemolytic

S.SaprophyticusNovobiocin resistant,

γ hemolytic

Coagulase Positive

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Staphylococcus aureus

• Coagulase positive

• Golden yellow colony on blood agar

• Nonmotile, Nonsporeforming

• Facultative anaerobe

• Fermentation of glucose produces mainly lactic acid

• Ferments mannitol (distinguishes from S. epidermidis)

Mannitol fermentation

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To perform the Slide Coagulase Test, place a 2ml of coagulase reagent (rabbit plasma) onto a clean test tube, and then add several colonies of the unknown Staphylococcus. Mix well.

If fine grains of sand or small clumps are seen, the coagulase test is positive.If the mixture remains smooth (milky looking), the coagulase test is negative. Courtesy: http://staff.um.edu.mt.

Staphylococcus aureus

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Virulent FactorsAdhesion:

Clumping factor - surface proteins

• Attaches to laminin, fibronectin, fibrin and fibrinogen, collagen (osteomyelitis)

Invasion:

alpha toxin (alpha - hemolysin)

membrane-damaging toxin (platelets and monocytes)

ß-toxin (sphingomyelinase) – β-hemolysis.

delta toxin – detergent like (produced by s. aureus and s.epidermidis)

Leukocidin – acts on PMN’s (↑ dermatonecrotic strains)

Coagulase extracellular protein binds to prothrombin → staphylothrombin → inhibits Phagocytosis

Staphylokinase, proteases, a lipase, (DNase) and a fatty acid modifying enzyme (FAME) important in abscesses

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Exotoxins

Enterotoxin – leads emesis ( food poisoning in 2-6 hrs)

TSST-1 (superantigen) – Toxic shock syndrome

Exfoliatin toxin – Scalded skin syndrome (Cadherins in desmosomes)

Pencillinase

Host Defenses escape

Capsular Polysaccharide

Protein A

Surface protein binds IgG molecules by their Fc region ↓ opsonization.

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Super antigen animation

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Virulent Factors

Courtesy : Dr.Kenneth Toder

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Epidemiology

Most opportunistic Pathogen

Nosocomial

Skin, mucus membrane and nasal areas.

Food, tampons, trauma, immune suppression etc

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Skin Infections:

Invasion: Leukocidin,

hemolysins.

Pneumonia:Invasion: hemolysins, Leukocidin and coagulase.

Endocarditis:

Invasion:

Coagulase, staphylokinase,

hemolysins and leukocidins.

Osteomyelitis & septic

arthritis:

Invasion:

Surface proteins to

collagen, hemolysins and

leukocidin

Toxic Shock Syndrome:

TSST 1, Enterotoxin.

Food Poisoning:

Enterotoxin

Scalded skin syndrome:

Exfolitin toxin

Pathogenesis

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Clinical featuresSkin conditions:

Folliculitis, Carbuncle, furuncle, Impetigo, Mastitis,Surgical infections

Opportunistic, immune suppression.

Pneumonia:Fever, chills, cough, consolidation, effusion

Hospitalized pts, post influenza infection, immune suppressed pts.

Acute Endocarditis:IV drug abuse, tricuspid valve, pneumonia

Osteomyelitis & Septic arthritis:Most common, trauma or hematogenous

Food poisoning:

2-6 hrs onset, resolve in 24-48 hrs.Mayonnaise, salads etc

Toxic shock syndrome:Tampons, sutures, Endometritis etc.

Scalded skin syndrome:Children with skin infections and umbilical cord infections.Dr.Aravind

furuncle

Impetigo Scalded skin syndrome Folliculitis

Carbuncle

Courtesy by CDC

Toxic shock syndrome

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Diagnosis Gram staining

Catalase test

Coagulase test

Yellow colonies on blood agar

PYR +

Bacitracin resistant.

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Gram Positive cocci Identification

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• Treatment:

• Resistance to penicillin

• Vancomycin drug of choice

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MRSA

Resistant to Antibiotics

HA MRSA

CA MRSA

Susceptibility – hospitalized patients, immune suppressed, improper hygiene, athletes etc.

Treatment: Vancomycin.

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Staphylococcus epidermidis • Gram +, in clusters can’t differentiate in gram stain with S.aureus.

• Coagulase negative

• Mannitol negative

• Thick polysaccharide capsule, delta toxin.

• Most common on skin flora

• Common contaminant of blood samples

• Nosocomial

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Virulent factors:

• Polysaccharide capsule

• Delta toxin

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• Clinical conditions :

• Nosocomial infections

• Catheters and prosthetic devices

• Endocarditis of prosthetic heart valves

• Infections of artificial joints

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Diagnosis

• Coagulase negative

• Mannitol negative

• Beta or gamma hemolytic on blood agar

• Novobiocin sensitive

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Treatment

• Resistant to antibiotics

• Vancomycin

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Staphylococcus saprophyticus

• Gram positive cocci inclusters

• Non hemolytic

• Coagulase negative

• Mannitol negative

• Novobiocin resistant

• UTI in sudden sexually active women (honey moon cystitis)

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Diagnosis

• Novobiocin resistant

• Coagulase negative

• Mannitol negative

Treatment

• Penicillin

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