Bacteria 4 Other gram pos MID 2029

Learning Objectives

• Describe the medically pertinent anatomy of gram-positive organisms:
    - Membrane
    - Cell wall
    - Gram-stain

• Outline the classification of Gram-positive organisms:
    - Distinguishing features

• Outline the various exotoxins:
    - By type
    - Target
    - Mechanism
    - Organism

• Outline unique virulence factors/characteristics.

• Outline various diseases by organism and by disease:
    - GI
    - Intoxication
    - Cellulitis
    - Sepsis

Gram Positive Vocabulary

• Listeria monocytogenes:
    - Gram-positive rod
    - Flagella motility
    - Intracellular; cell-mediated immunity

• Relevant diseases:
    - Sepsis
    - Meningitis
    - Pneumococcus
    - Group B strep
    - E. coli (related to placenta)

• Sources of Listeria:
    - Foodborne (cheese, vegetables, fruits, meats)

• Corynebacterium diphtheroids:
    - Corynebacterium diphtheriae:
      - Causes diphtheria
      - Vaccination (DPT and TDAP immunizations)
      - Respiratory distress due to Diphtheria Toxin (an AB toxin)
      - Affects elongation factor 2 (EF-2) in ribosomes

• Pseudomembrane formation
    - Respiratory distress
    - Affects heart and CNS
    - Requires immunization (toxoid, tetanus)

• Gardnerella vaginalis:
    - Associated with clue cell formation in bacterial vaginosis
    - Treatment: Metronidazole

• Anaerobic gram-positive cocci:
    - Include Peptococcus and Peptostreptococcus

Anecdotal Reflections

• Personal reflections on a cemetery visit related to diphtheria deaths.

• Highlighting Listeria contamination in food as a public health concern.

• Mention of various gram-positive cocci and their capacity to cause abscesses.

Listeria monocytogenes Overview

• Characteristics:
    - Small gram-positive bacilli; may appear in chains
    - Beta-hemolytic
    - Catalase-positive
    - Facultative anaerobe
    - Exhibit tumbling motility at room temperature via 1-5 flagella

• Habitat:
    - Found in animals and soil

• Pathogenesis:
    - Intracellular Parasite: Listeriolysin O allows it to survive in phagolysosome
    - Capable of polymerizing host cell actin, aiding in cell-to-cell spread

• Transmission:
    - Ingested through contaminated food (e.g., hot dogs, deli meats, raw vegetables)
    - Can lead to:
      - Sepsis in neonates and immunocompromised individuals
      - Meningitis in most vulnerable populations (elderly, pregnant women, infants)
    - Pregnancy Risks:
      - Can cause amnionitis, miscarriage, stillbirth, or neonatal sepsis (granulomatosis infantiseptica)

• Diagnosis and Treatment:
    - Diagnosed via cultures from blood or CSF; cold-enrichment techniques required
    - Treatment typically includes ampicillin or trimethoprim-sulfamethoxazole

Corynebacteria Overview

• Corynebacterium diphtheriae:
    - Gram-positive rod-like to filamentous bacterium
    - Aerobic to facultative anaerobic, non-motile, non-spore forming

• Pathogenicity:
    - Colonizes respiratory tract
    - Produces neuraminidase, stimulating growth by pyruvate production
    - Some strains produce diphtheria toxin (toxigenic strains):
      - Toxin mechanism involves ADP-ribosylation of EF-2, blocking protein synthesis

• Diagnosis:
    - Diagnosis via clinical symptoms (muscle weakness, edema, pseudomembrane in respiratory tract) and isolation from Tellurite media (producing jet-black colonies)
    - Schick test recognizes previous immunity

• Prevention and Treatment:
    - DPT vaccine (toxoid)
    - Treatment includes antitoxin and antibiotics (penicillin, erythromycin, gentamicin)

Gardnerella vaginalis Overview

• Characteristics:
    - Small gram-variable coccobacilli (diptheroid);
    - Cell wall is essentially gram-positive
    - Facultative anaerobic, non-spore forming, non-motile

• Clinical Associations:
    - Involved in bacterial vaginosis due to decreased Lactobacillus flora, leading to overgrowth of anaerobes
    - Characterized by formation of clue cells and fishy odor

• Diagnosis and Treatment:
    - Diagnosed by identification of clue cells or culture
    - Treated with metronidazole or clindamycin

Anaerobic Gram Positive Cocci

• Classification:
    - Members of Clostridiaceae family (anaerobic, gram-positive cocci)
    - Non-spore forming, divided into:
      - Peptostreptococcus (chains)
      - Peptococcus (clusters; some reclassified)

• Pathogenesis:
    - Commensals in skin, GI, and urinary tracts, but can become pathogenic in immunosuppressed or trauma cases

• Species of Note:
    - Peptostreptococcus magnus (formerly Peptococcus magnus)
    - Peptococcus niger (human commensal, not typically pathogenic)
    - Peptoniphilus asaccharolyticus (formerly a species of Peptostreptococcus)

• Clinical Infections:
    - Cause a variety of infections including oral, respiratory, skin, deep organ abscesses, and GU infections

• Diagnosis and Treatment:
    - Diagnosis via anaerobic culture and gram staining;
    - Treatment typically involves beta-lactam antibiotics

Gram Positive Cocci and Rods Overview

• Gram Positive Cell Structure:
    - Characterized by a thick peptidoglycan cell wall, differentiating them from negative counterparts
    - Single cell membrane, contrasting with the double layers seen in gram-negative organisms

• Bacillus and Clostridia Families:
    - Bacillus = aerobic, Clostridia = anaerobic

• Listeria and Corynebacteria Characteristics:
    - Non-spore forming, notable pathogenic profiles