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Dr. Manal El SaidHead of M icrobiology Department

Staphylococc i

Staphylococcus aureus

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Staphylococcus aureus

Diseases

-lactamase

Toxic shock syndrome

Abscesses of many organs

Endocarditis

Gastroenteritis (food poisoning)

Hospital-acquired pneumonia

Surgical wound infections

Sepsis.

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Staphylococcus aureus

Habitat and Transmission

Characteristics Gram-positive cocci in clusters.

Coagulase-positive.

Catalase-positive.

Most isolates produce-lactamase

-lactamase.

Main habitat is human nose & skin.

Transmission is via the hands.

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Pathogenesis

Staphylococcus aureus

Three exotoxins:

1-Toxic shock syndrome toxin

-Superantigen helper T cells release of

lymphokines ( IL-2).

2- Enterotoxin

- Superantigen

- Food poisoning (has a short incubation period because it

is preformed in food).3-Scalded skin syndrome toxin:

- Protease cleaves desmoglein in tight junctions in skin.

- Protein A binds to heavy chain of IgG & prevents

activation of complement.

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Pathogenesis

Staphylococcus aureus

Abscesscontaining pusis the most common lesion.

Predisposing factors to infection

- Breaks in the skin

- Foreign bodies such as sutures

- Neutrophil levels below 500/ml

- Intravenous drug use right-sided endocarditis

- Tampon use toxic shock syndrome

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Laboratory Diagnosis

Staphylococcus aureus

Gram-stained smear and culture.

Yellow or gold colonies on blood agar.

Coagulase-positive

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Laboratory Diagnosis

Staphylococcus aureus

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Staphylococcus aureus

Treatment

;

Penicillin G for sensitive isolates

Nafcillin(-lactamaseresistant penicillins) for resistant

isolates

Vancomycinfor isolates resistant to nafcillin (changes in

binding proteins).

About 85% are resistant to penicillin G (tolerant to penicillin)

Plasmid-encoded -lactamasemediates most resistance.

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S. aureus methicillin-resistant (MRSA) is due to altered

penicillin-binding proteins.

MRSA can produce outbreaks of disease, especially in

hospitals.

The drug of choice is vancomycin, to which gentamicin is

sometimes added.

Daptomycinis also useful.

S. aureusmethicillin-resistant

(MRSA)

Treatment

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Trimethoprim-sulfamethoxazole or clindamycin can be used

to treat nonlife-threatening infections caused by these

organisms.

MRSA strains are resistant to all -lactam drugs, including

both penicillins & cephalosporins.

Treatment

S. aureusmethicillin-resistant

(MRSA)

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S. aureuswith intermediate

resistance to vancomycin

Treatment Strains of S. aureus with intermediate resistance to

vancomycin (VISA) & with complete resistance to

vancomycin (VRSA) isolated from patients.

These strains are methicillin-resistantas well, which makes

them very difficult to treat.

Daptomycin can be used to treat these infections

Quinupristin-dalfopristin is another useful choice.

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Staphylococcus aureus

Prevention

;

Cefazolinis used to prevent surgical wound infections.

No vaccine is available.

Handwashing reduces spread.

B j M di l C ll

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Diseases

Characteristics

Staphylococcus epiderm id is

Endocarditison prosthetic heart valves

Prosthetic hip infection

Intravascular catheter infection

Cerebrospinal fluid shunt infection

Neonatal sepsis.

Gram-positive cocci in clusters.

Coagulase-negative.

Catalase-positive.

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Pathogenesis

Habitat and Transmission

Staphylococcus epiderm idis

Normal flora of human skin & mucous membranes.

Patient's own strains cause infection

Transmission from person to person via hands.

Glycocalyx-producing strains adhere well to foreign bodies

such as prosthetic implants & catheters. It is low-virulence organism that causes disease:

- Immunocompromised patients

- Those with implants.

It is a major cause of hospital-acquired infections.

B tt j M di l C ll

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Laboratory Diagnosis

Staphylococcus epiderm idis

Gram-stained smear and culture.

Whitish, nonhemolytic colonies on blood agar.

Coagulase-negative.

Itis sensitive to novobiocin (S. saprophyt icus,is resistant).

B tt j M di l C ll

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Laboratory Diagnosis

Staphylococcus epiderm idis

Batterjee Medical College

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Treatment

Staphylococcus epiderm idis

Vancomycinplus either rifampinor aminoglycoside.

It produces -lactamases & is resistant to many antibiotics.

Prevention

There is no drug or vaccine.

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