Pathogenic Gram Positive Bacteria Study Notes

Definition: Gram positive bacteria are characterized by their thick peptidoglycan cell wall which retains crystal violet dye used in Gram staining, appearing purple under a microscope.
Types: This category includes various pathogenic species that lead to human infections.

List of Pathogenic Species:
- Staphylococcus epidermidis
- Staphylococcus aureus
- Streptococcus pyogenes
- Streptococcus mutans
- Streptococcus pneumoniae
- Listeria monocytogenes
- Clostridium difficile
- Clostridium tetani
- Clostridium botulinum
- Bacillus anthracis
- Mycoplasma pneumoniae
- Corynebacterium diphtheriae
- Mycobacterium tuberculosis

Characteristics:
- Structure: Cocci arranged in clusters resembling bunches of grapes.
- Oxygen Requirement: Facultative anaerobes, able to survive with or without oxygen.
- Growth Tolerance: Salt tolerant up to 28% NaCl, heat resistant (60°C for 30 minutes).
- Virulence: S. aureus (high virulence) & S. epidermidis (opportunistic pathogen).
- Transmission: Via direct contact or contaminated surfaces (fomites).
Pathogenicity/Virulence Factors:
- Protein A: Binds to IgG, protecting against opsonization.
- Coagulase: Enzyme that coagulates blood, assisting in evading immune response by forming blood clots.
- Enzymes produced:
- Hyaluronidase (breaks down hyaluronan).
- Lipases (grow in oily skin areas).
- Toxins produced:
- Cytolytic toxins (e.g., Panton-Valentine Leukocidin, α-toxin).
- Superantigens (cause toxic shock syndrome).
- Enterotoxins (cause food poisoning).
- b-lactamases (make strains resistant to antibiotics).

Gastrointestinal Diseases:
- Food Poisoning: Caused by enterotoxins; often results from skin contamination during food prep. Symptoms include nausea, vomiting, diarrhea, and abdominal pain that resolve in approximately 24 hours. Toxins are heat-stable.
Cutaneous Diseases:
- Staphylococcal Scalded Skin Syndrome (SSSS): Caused by epidermolytic toxins; manifests as redness and blisters primarily in children. Complications from secondary infections are common.
- Impetigo: Caused by S. aureus (mostly) and Streptococcus spp.; characterized by pus-filled blisters.
- Folliculitis: Infection of hair follicles.
Generalized Diseases:
- Toxic Shock Syndrome (TSS): A severe condition caused by TSS toxin-1. Symptoms include fever, rash, and multiple organ failure. Originally noted in tampon-using women, prompting regulatory changes.
- Bacteremia: Presence of bacteria in the blood associated with procedures or infections.
- Endocarditis: Infection of heart lining with severe complications.
- Pneumonia: Lung infection secondary to bacteremia.
- Osteomyelitis: Bone infection with localized pain and fever.

Characteristics:
- Cocci found in pairs or chains, facultative anaerobes, and diverse species (~50).
- Classified based on colony morphology, hemolysis patterns (alpha and beta), and serological specificity via antibody reactions.
Disease Associations:
- Streptococcus pyogenes (Group A):
- Common causes include strep throat, scarlet fever, and skin infections. Pathogenic strains can produce several hazardous factors including M protein, streptolysins, and superantigens (leading to Streptococcal Toxic Shock Syndrome).
- Streptococcus pneumoniae:
- Causes pneumonia, meningitis, and sinusitis; possesses virulence factors such as polysaccharide capsule and pneumolysin.
- Streptococcus mutans:
- Known for dental plaque formation via dextran production, leading to dental caries.

Characteristics:
- Gram positive bacilli, facultative anaerobe, grows at low temperatures (0°C to 45°C).
- Opportunistic pathogen primarily affecting vulnerable populations (elderly, pregnant).
Pathogenesis:
- Transmission usually via contaminated food. Can result in severe conditions like meningitis. Virulence factors include internalins, listeriolysin O, and the ActA protein.

Characteristics:
- Gram positive bacilli, obligate anaerobes, endospore-forming, found in soil and gastrointestinal tracts.
Disease Associations:
- C. difficile: Causes antibiotic-associated diarrhea when normal flora is disrupted; toxins destroy tissue. Symptoms include diarrhea and abdominal pain.
- C. tetani: Causes tetanus via tetanospasmin toxin, leading to muscle spasms.
- C. botulinum: Causes botulism via botulinum toxin, leading to muscle paralysis.

Characteristics:
- Gram positive bacilli, facultative anaerobe, endospore-forming, found in soil.
Pathogenesis and Treatment:
- Main route of infection is through endospores. Disease forms include inhalation anthrax (high mortality), GI anthrax (rare), and cutaneous anthrax.

Characteristics:
- Lacks a cell wall, resistant to cell wall inhibitors; pleomorphic forms.
Pathogenesis and Symptoms:
- Causes atypical pneumonia, spreads via airborne droplets. Symptoms include fever and cough. No vaccine is available.

Characteristics:
- Gram positive bacilli, can change shapes under different environmental conditions.
Pathogenesis:
- Produces diphtheria toxin that inhibits protein synthesis. Diphtheria presents with upper respiratory symptoms capable of occluding the airway if untreated.

Epidemiology:
- Affects ¼ of the global population, prominent in areas like Indonesia and China. A leading cause of death related to infectious diseases.
Pathogenesis:
- Characterized by slow growth, resistance to many antibiotics. Transmission occurs via inhalation, leading to pulmonary symptoms primarily.
Treatment:
- Involves a combination therapy including isoniazid and rifampin; multi-drug resistant strains pose a challenge.

Figure 3.44: Overview of cytoskeletal proteins in eukaryotic cells.
Figure 26.10: Electron micrograph of Listeria monocytogenes in host.
Figure 15.16: Comparison of botulinum and tetanus toxin mechanisms.
Tuberculosis Testing:
- Figure 22.14: Mantoux Tuberculin Skin Test explained.