Microbiology Flashcards: Staph Aureus

Staphylococcus Aureus Overview

• Staphylococcus aureus appears as clusters resembling grapes and produces a golden color on Blood Agar.
• It is classified as Gram-positive, displaying violet coloration under a microscope.

Identification Tests

• Catalase test differentiates Staphylococcus from Streptococcus.
• Staphylococcus aureus is identified by its golden coloration on Blood Agar and a positive coagulase test which converts fibrinogen to fibrin.

Hemolytic Activity

• Staphylococcus aureus is beta-hemolytic, fully breaking down red blood cells.

Metabolism and Fermentation

• It ferments mannitol, turning the agar yellow, characteristic of mannitol fermenters.

Virulence Factors

• The primary virulence factor is Protein A, which binds to the Fc region of immunoglobulins, inhibiting complement binding and preventing opsonization and phagocytosis.

Colonization Sites

• Commonly colonizes the nares (nostrils).

Associated Inflammatory Diseases

• Causes pneumonia, particularly post-viral bacterial pneumonia, and is the most common cause of septic arthritis, bad abscesses, acute bacterial endocarditis, and osteomyelitis.

Endocarditis in Specific Populations

• Endocarditis is frequently observed in IV drug users, with the tricuspid valve being the most affected.

Osteomyelitis

• Staphylococcus aureus is the leading cause of osteomyelitis in adults.

Toxin-Mediated Diseases

• Conditions include Scalded Skin Syndrome, Toxic Shock Syndrome (TSS), and food poisoning.

Scalded Skin Syndrome

• Characterized by skin peeling due to protease activity.

Toxic Shock Syndrome Dynamics

• Most commonly caused by leaving packing in too long, TSS is mediated by the Toxic Shock Syndrome Toxin (TSST), which acts as a superantigen, causing a cytokine storm.

Food Poisoning Characteristics

• Staphylococcus aureus food poisoning features rapid onset due to pre-formed toxins, with vomiting being a more common symptom than diarrhea.

Antibiotic Resistance

• Methicillin-resistant Staphylococcus aureus (MRSA) acquires resistance by altering its penicillin-binding protein (PBP).

Treatment Protocols

• MRSA is commonly treated with Vancomycin; if methicillin-sensitive, Nafcillin is the recommended treatment.

Test your knowledge of Staphylococcus aureus with these flashcards. Learn about its appearance, gram status, and identification techniques. Perfect for microbiology students looking to reinforce their understanding of this important bacterium.