Staphylococcal Toxins and Their Effects

Medical Bacteriology

• Gram-positive cocci are a bacterial classification
• Staphylococcus, Streptococcus, and Enterococcus are examples of gram-positive cocci
• Staphylococcus is a genus of Gram-positive bacteria in the Staphylococcaceae family, currently containing 49 species
• Staphylococcus are Gram-positive cocci that are arranged in clusters and do not produce spores; they are not motile but produce exotoxins
• Staphylococcus aureus is a species of Staphylococcus
• Staphylococcus epidermidis is another species within Staphylococcus.
• Staphylococcus saprophyticus and other species exist.

Staphylococcus spp.

• Staphylococcus aureus colonies can appear yellow or gold due to carotenoid pigments
• Staphylococcus aureus produces coagulase, a key characteristic used for identification
• Coagulase-negative staphylococci (CoNS) represents a group that do not produce coagulase

Epidemiology of S. aureus

• Humans are the reservoir of S. aureus, with 15-50% of healthy individuals carrying the bacteria
• S. aureus colonizes the skin and nasopharynx
• Transmission can occur through direct contact or contact with fomites (contaminated objects)

S. aureus: Virulence Factors

• Adhesins (MSCRAMM proteins) help bacteria adhere to host cells and tissues
• Autolysins aid in the invasion of non-professional phagocytes
• Leukocidins kill host immune cells, like white blood cells
• Superantigens activate immune cells, contributing to significant inflammation
• Immunoglobulin binding proteins inhibit the host immune response
• Capsule: protection from phagocytes
• Protein A: prevents phagocytosis and decreases antibody production

S. aureus: Secreted Proteins

• Enzymes like coagulase, hyaluronidase, fibrinolysin, lipases, and nucleases participate in pathogenesis
• Toxins like cytotoxins, exfoliative toxins, enterotoxins, and toxic shock syndrome toxin-1 disrupt host cells, tissues, or lead to a systemic response

Cytotoxins of S. aureus

• Alpha-toxin damages blood vessels and cells
• Beta-toxin targets a variety of cells (erythrocytes, fibroblasts, leukocytes, and macrophages) that are sensitive to it
• Delta-toxin is a broad-spectrum cytolytic substance
• Gamma-toxin causes lysis in cells by pore formation
• PV toxin causes lysis in leukocytes

Superantigens of S. aureus

• Exfoliative toxin A splits intercellular bridges
• Enterotoxins trigger an inflammatory response in the intestines
• Toxic shock syndrome toxin-1 (TSST-1) has a large systemic effect; causing a widespread inflammatory response.

Pathogenesis of S. aureus

• Diseases caused by S. aureus manifest as a result of toxins or direct tissue invasion and destruction
• Some diseases, often skin-related, result from toxin activity like scaled skin syndrome and food poisoning Other infections result from S. aureus proliferation in tissues, leading to inflammation and abscess formation, including cutaneous infections, endocarditis, pneumonia, osteomyelitis, and septic arthritis

Staphylococcal Scalded Skin Syndrome (SSSS)

• Exfoliative toxins (proteases) cause the separation of the outer layers of the skin
• Causes in infants
• Results in blisters

Enterotoxins and food poisoning

• Enterotoxins are heat-stable and resistant to gastric enzymes
• Bacteria contaminate food and release enterotoxins
• Symptoms: usually vomit, diarrhea, and abdominal cramping
• Resolution typically within 24 hours

Staphylococcus species

• Coagulase-negative Staphylococci are divided into other species
• Can cause infection in prosthetic heart valves and native heart valves

Staphylococcus epidermidis

• Gram-positive, facultative aerobe
• Found on skin
• Can form biofilms, causing infections (like catheter infections)

Streptococcus spp.

• Gram-positive cocci in pairs or chains
• In the Streptococcus family
• Do not produce spores
• Fastidious growth requirements

Streptolysin S (SLS) & O (SLO)

• SLS: oxygen-stable, lyses cells (erythrocytes, leukocytes, and platelets)
• SLO: oxygen-labile, lyses cells (erythrocytes, leukocytes, and platelets)

Enzymes (Streptococcus)

• Streptokinase (A and B): break down blood clots
• DNases (A to D): reduce the viscosity of fluid in infected areas
• Hyaluronidase: helps bacteria spread in tissues

Clinical Diseases (Streptococcus pyogenes)

• Pharyngitis: sore throat, fever, possible scarlet fever
• Scarlet fever: rash, fever, and inflamed tongue
• Skin infections: such as impetigo and erysipelas
• Necrotizing fasciitis: severe tissue destruction (flesh-eating)
• Streptococcal toxic shock syndrome (STSS): life-threatening systemic illness
• Rheumatic fever: inflammatory condition affecting the heart, joints and tissues
• Acute glomerulonephritis: kidney inflammation

Streptococcus agalactiae

• Gram-positive cocci, Beta-hemolytic, Lancefield group B
• Can colonize the vaginal tract, causing neonatal infections
• Often associated with serious neonatal sepsis or meningitis, or other infections in adults

Streptococcus pneumoniae

• Encapsulated gram-positive diplococci
• Can cause pneumonia, sinusitis, otitis media, and meningitis
• Often resistant to antibiotics

Laboratory Diagnosis (general)

• Gram staining: identification of Gram-positive cocci (pairs or chains) is a routine step
• Culture
• Microscopic examination
• Biochemical tests for species identification

Enterococcus

• Gram-positive cocci (pairs or short chains)
• Found in the intestines
• Often associated with urinary tract infections in hospitalized patients or those with catheters
• Also can cause endocarditis under certain conditions.

Treatment (general)

• Antibiotics are often used to treat these infections, however resistance is evolving in some bacterial species, including to most beta-lactam antibiotics.

This quiz covers various toxins produced by Staphylococcus species, including their mechanisms, associated conditions, and effects on the human body. Test your knowledge on staphylococcal enterotoxins, TSST-1, and the implications of these toxins in food poisoning and toxic shock syndrome.