Microbiology: Staphylococcus Aureus Overview

Questions and Answers

Which of the following is a virulence factor of Staphylococcus aureus?

Protein A

Exfoliative toxin

Enterotoxins

All of the above (correct)

Methicillin-resistant Staphylococcus aureus (MRSA) is caused by the mecA gene.

True

What syndrome is associated with the toxic shock syndrome toxin-1 (TSST-1)?

Staphylococcal toxic shock syndrome (TSS)

Staphylococcus epidermidis is coagulase ______.

negative Signup and view all the answers

What is the effect of Staphylococcus aureus food poisoning?

Short incubation period with nonbloody diarrhea and emesis Signup and view all the answers

Match the following Staphylococcus diseases with their features:

Toxic shock syndrome = Fever, vomiting, diarrhea, rash, shock Scalded skin syndrome = Exfoliative toxin leading to skin peeling Staphylococcal food poisoning = Nonbloody diarrhea and emesis Skin infections = Inflammatory disease causing abscesses Signup and view all the answers

What are common colonization sites for Staphylococcus aureus?

Nares, ears, axilla, and groin Signup and view all the answers

Staphylococcus epidermidis ferments mannitol.

False Signup and view all the answers

What type of infections does Staphylococcus epidermidis primarily cause?

Infections of prosthetic devices and IV catheters Signup and view all the answers

Study Notes

Staphylococcus aureus (S. aureus)

Gram-positive, catalase-positive, coagulase-positive cocci that form clusters.
Key virulence factor: Protein A, which binds Fc-IgG, preventing complement activation and phagocytosis.
Common colonization sites: nares, ears, axilla, and groin.

Inflammatory Diseases

Associated with skin infections, organ abscesses, pneumonia (often post-influenza), infective endocarditis, septic arthritis, and osteomyelitis.

Toxin-Mediated Diseases

Toxic shock syndrome (caused by TSST-1).
Scalded skin syndrome due to exfoliative toxins.
Rapid-onset food poisoning from enterotoxins.

Methicillin-Resistant Staphylococcus aureus (MRSA)

An important cause of serious infections in both healthcare settings and communities.
Resistance mechanism involves altered penicillin-binding proteins due to mecA gene.
Some strains produce Panton-Valentine leukocidin (PVL), which is lethal to leukocytes causing tissue necrosis.

Staphylococcal Toxic Shock Syndrome (TSS)

Symptoms: fever, vomiting, diarrhea, rash, desquamation, shock, and end-organ failure.
Laboratory findings may show elevated levels of AST, ALT, and bilirubin.
Prolonged use of vaginal tampons or nasal packing is a common association.
Differs from Streptococcus pyogenes TSS, which is linked to painful skin infections.

Food Poisoning

S. aureus food poisoning results from ingesting preformed toxins.
Characterized by a short incubation period (2–6 hours) followed by non-bloody diarrhea and vomiting.
Enterotoxins are heat-stable and survive cooking.

Abscess Formation

Coagulase production leads to fibrin clot formation around S. aureus, facilitating abscess development.

Staphylococcus epidermidis (S. epidermidis)

Gram-positive, catalase-positive, coagulase-negative cocci that form clusters.
Sensitive to novobiocin and does not ferment mannitol (differentiating it from S. aureus).
Normal skin microbiota, often contaminates blood cultures.
Known for infecting prosthetic devices (e.g., hip implants, heart valves) and IV catheters by forming adherent biofilms.

Description

This quiz covers Staphylococcus aureus, focusing on its characteristics, virulence factors like Protein A, and diseases it causes including skin infections and toxic shock syndrome. Understand the clinical significance and pathogenesis of this important pathogen.