Staphylococcus aureus Toxins Quiz

Medical Bacteriology

• Gram-positive cocci are a diverse group of bacteria
• Include Staphylococcus, Streptococcus, and Enterococcus species

Staphylococcus spp.

• Staphylococcus is a genus of Gram-positive bacteria in the family Staphylococcaceae
• Currently comprises 49 species
• Gram-positive cocci, typically arranged in clusters (1 µm)
• Do not form spores and are non-motile
• Produce exotoxins
• Ubiquitous in animals and humans
• Survive on dry surfaces for extended periods
• Includes species like Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus saprophyticus, Staphylococcus haemolyticus, and Staphylococcus lugdunensis

Staphylococcus aureus

• Gram-positive cocci, appear in clusters
• Can grow in aerobic and anaerobic conditions
• Can grow in high salt concentrations
• Colonies often display a characteristic yellow or gold color due to carotenoid pigments
• Produces coagulase, a key virulence factor distinguishing it from other staphylococci
• Coagulase-negative staphylococci (CoNS) are a group of staphylococcal species that do not produce coagulase
• Humans are the reservoir for S. aureus, colonizing the skin and nasopharynx
• Transmission to susceptible hosts can occur via direct contact or fomites (e.g. contaminated clothing/bed linens)

S. aureus: Virulence Factors

• Adhesins: Bind to cell surface receptors on host tissues, host cells, and soluble factors in the blood, inhibiting complement activation cascade
• Autolysins: Highly immunogenic cell wall transglycosylases that facilitate invasion of non-professional phagocytes
• Leukocidins: Secreted toxins and peptides that target and kill key immune cells
• Immunoglobulin Binding Proteins: Inhibit engagement of host immune factors and bind IgGs via Fc regions, thus inhibiting host immune factors
• Superantigens: Potent immunostimulatory exotoxins, activating T cells and triggering cytokine release
• MSCRAMM Proteins (adhesins): Adhere to host matrix proteins like fibronectin and collagen.
• Polysaccharide Capsule: Protects bacteria by inhibiting phagocytosis
• Protein A: Binds to the Fc region of IgGs, preventing phagocytosis and inducing B-cell death, decreasing antibodies specific for S. aureus

S. aureus: Secreted Proteins Involved in Pathogenesis

• Enzymes: Coagulase (converts fibrinogen to fibrin), Hyaluronidase (hydrolyzes hyaluronic acids), Fibrinolysin (dissolves fibrin clots), Lipases (hydrolyze lipids), Nucleases (hydrolyze DNA)
• Toxins: Cytotoxins (toxic to various cells including erythrocytes, leukocytes, macrophages, and platelets), Exfoliative toxins (ETA, ETB: proteins that split the intercellular bridges), Enterotoxins (A-E, G-I: stimulate proliferation of T cells and trigger cytokine release), Toxic shock syndrome toxin-1 (TSST-1: induces cytokine release and endothelial cell damage).

Cytotoxins of S. aureus

• α-toxin: Disrupts smooth muscle in blood vessels and is toxic to many cells (erythrocytes, leukocytes, hepatocytes and platelets)
• β-toxin (or sphingomyelinase C): Specific for sphingomyelin and lysophosphatidylcholine, toxic to erythrocytes, fibroblasts, leukocytes and macrophages
• δ-toxin: Wide spectrum of cytolytic activity affecting erythrocytes, many other mammalian cells and intracellular membranes
• γ-toxin: Bicomponent toxin inducing cell lysis mediated by pore formation and subsequent increased permeability to cations and osmotic instability
• PV (Pantom-Valentine leukocidin) toxin: Bicomponent toxin acting on leukocytes by forming pores

Staphylococcal Scalded Skin Syndrome

• Mediated by exfoliative toxins, which are proteases that split desmoglein-1
• Responsible for the intercellular bridges in the stratum granulosum epidermis

Enterotoxins and Food Poisoning

• Numerous staphylococcal enterotoxins have been identified
• Stable to heating
• Resistant to gastric enzymes
• Food contamination leads to rapid onset of vomiting, diarrhea, and abdominal cramping, resolving within 24 hours

Coagulase-negative Staphylococci (CoNS)

• Group of non-coagulase-producing staphylococci
• Includes Staphylococcus epidermidis, Staphylococcus saprophyticus, Staphylococcus haemolyticus and Staphylococcus lugdunensis
• Can infect prosthetic heart valves, and less frequently, native heart valves
• Can lead to persistent bacteremia in patients with shunts or catheters.

Streptococcus spp.

• Streptococcus is a gram-positive genus in the family Streptococcaceae

• 100 species

• Gram-positive cocci, arranged in pairs or chains
• Strictly facultative anaerobes
• Catalase-negative
• Do not produce spores and are not motile
• Produce exotoxins
• Wide variety of species exist that cause different illnesses

Hemolytic Patterns

• α-hemolysis (partially breaks down hemoglobin)
• β-hemolysis (completely breaks down hemoglobin)
• γ-hemolysis (no breakdown of hemoglobin)

Streptococcus pyogenes

• Gram-positive, β-hemolytic bacteria
• Lancefield group A
• Antigenic structures include peptidoglycan, group-specific carbohydrate, type-specific antigen (M protein), M-like surface proteins, lipoteichoic acid, and F protein.
• Some strains have a hyaluronic acid capsule
• Produce various toxins and enzymes (streptolysin S and O, pyrogenic exotoxins, streptokinase, DNases, and hyaluronidase) crucial for pathogenesis.
• Cause various diseases like pharyngitis, scarlet fever, impetigo, erysipelas, necrotizing fasciitis, scarlet fever, and rheumatic fever.

Streptococcus agalactiae

• Group B streptococci
• Large colonies with a narrow zone of beta hemolysis
• Polysaccharide capsule with antiphagocytic properties
• Major cause of neonatal infections, including sepsis, pneumonia, and meningitis.
• Diagnosed frequently via laboratory tests (Gram stain, culture, and susceptibility testing).

Streptococcus pneumoniae

• Gram-positive, lancet-shaped coccus, often appearing in pairs (diplococci)
• α-hemolytic on blood agar (aerobic)
• β-hemolytic if grown anaerobically
• Encapsulated strains are large, round, and mucoid; non-encapsulated strains are smaller and flat
• Undergoes autolysis with aging, dissolving the central portion of the colony.
• Causes pneumococcal pneumonia and meningitis.

Enterococcus spp.

• Gram-positive cocci arranged in pairs or short chains
• Grow under various conditions (aerobic/anaerobic)
• Found in the large intestine and genitourinary tract.
• Often associated with urinary tract infections (especially with catheterization)
• Some strains are resistant to various antibiotics; making diagnosis and treatment challenging
• Possible complications include endocarditis, which can be lethal.

Laboratory Diagnosis

• Techniques for diagnosing the various bacteria discussed, including microscopy, culture, biochemical tests, and antigen/antibody detection, and susceptibility tests.

MRSA Strains

• Methicillin-resistant Staphylococcus aureus, showing resistance to methicillin and other related penicillins
• Due to the presence of a new penicillin-binding protein that has a low affinity for methicillin.
• Some strains have also shown resistance to vancomycin (VRSA)

Treatment and Prevention

• Information on treatment methods including antibiotic selection, and prophylactic measures.

Test your knowledge on the various toxins produced by Staphylococcus aureus, including their mechanisms of action and effects on human tissues. This quiz covers topics such as α-toxin, Panton-Valentine leukocidin, and Toxic Shock Syndrome Toxin-1, and explores the characteristics that distinguish S. aureus from other staphylococcal species.