The Gram-positive Bacilli of Medical Importance

Chapter 19: The Gram-positive Bacilli of Medical Importance

Bacillus Overview

  • Structure: Gram-positive, facultative anaerobes, form endospores.

  • Pathogenicity: Pathogenic strains produce anthrax toxins.

  • Transmission: Inhalation, inoculation, or ingestion of spores from infected animals.

Bacillus anthracis Disease Manifestations

  • Gastrointestinal Anthrax: Rare in humans.

  • Inhalation Anthrax: Requires inhalation of spores; high mortality.

  • Cutaneous Anthrax: Produces ulcer (eschar); fatality rate ~20% untreated.

Diagnosis, Treatment, and Prevention for Bacillus anthracis

  • Diagnosis: Nonmotile, large Gram-positive bacilli in samples.

  • Treatment: Effective antimicrobials.

  • Prevention: Control in animals; vaccines require multiple doses.

Clostridium species Overview

  • Anaerobic, endospore-forming, found in soil and GI tracts.

  • Pathogenicity: Produces toxins causing irreversible damage.

Disease Caused by Clostridium perfringens

  • Food Poisoning: Abdominal cramps, diarrhea.

  • Gas Gangrene: Trauma introduces spores; necrosis results.

Diagnosis, Treatment, and Prevention for Clostridium perfringens

  • Diagnosis: Minimal bacterial load in food/feces.

  • Treatment: Self-limiting for food poisoning; gas gangrene requires removal of tissue, antitoxin, and penicillin.

  • Prevention: Food refrigeration; wound cleaning.

Clostridium tetani Overview

  • Motile, obligate anaerobes; causes tetanus via tetanospasmin toxin.

Pathogenesis and Effects of Tetanospasmin

  • Tetanospasmin: Potent neurotoxin causing muscle contractions; prevents release of inhibitory neurotransmitters.

Epidemiology and Disease of Clostridium tetani

  • Symptoms: Lockjaw, spasms, contractions spread, high mortality (~50%).

  • Recurrence due to lack of vaccinations, prevalent in underdeveloped countries.

Diagnosis, Treatment, and Prevention for Clostridium tetani

  • Diagnosis: Characteristic muscle contractions.

  • Treatment: Clean wounds, immunoglobulin, and antimicrobial drugs, immunization with toxoid.

Clostridium difficile Overview

  • Anaerobic, motile bacterium; produces toxins, opportunistic pathogen.

Disease Caused by Clostridium difficile

  • Mild infections: Self-limiting diarrhea.

  • Serious infections: Pseudomembranous colitis, life-threatening.

Diagnosis, Treatment, and Prevention for Clostridium difficile

  • Diagnosis: Isolation from feces; toxin presence via immunoassay.

  • Treatment: Discontinue antibiotic; antibiotics for serious cases.

  • Prevention: Hygiene to limit nosocomial infections.

Clostridium botulinum Overview

  • Anaerobic, endospore-forming; produces botulism toxins causing paralysis.

Botulism Overview

  • Symptoms: Three forms - foodborne, infant, wound botulism.

  • Causes asphyxiation and slow nerve recovery.

Diagnosis, Treatment, and Prevention for Clostridium botulinum

  • Diagnosis: Symptoms are diagnostic.

  • Treatment: Intestinal wash, neutralizing antibodies; antimicrobial drugs in severe cases.

  • Prevention: Proper canning, no honey for infants.

Listeria monocytogenes Overview

  • Non-endospore-forming, intracellular pathogen; found in food and drink.

Pathogenesis, Epidemiology, and Disease of Listeria monocytogenes

  • Can cause meningitis; serious complications for pregnant women.

Diagnosis, Treatment, and Prevention for Listeria monocytogenes

  • Diagnosis: Bacteria in cerebrospinal fluid.

  • Treatment: Ampicillin; other antibiotics for allergies.

  • Prevention: High-risk groups avoid contaminated foods.

Corynebacterium diphtheriae Overview

  • Pleomorphic, non-endospore-forming; colonizes various body tracts.

Pathogenesis and Disease of Corynebacterium diphtheriae

  • Causes diphtheria; transmitted via droplets.

  • Toxic affects protein synthesis; non-toxigenic strains nonpathogenic.

Diagnosis, Treatment, and Prevention for Corynebacterium diphtheriae

  • Diagnosis: Presence of pseudomembrane, Elek test for confirmation.

  • Treatment: Antitoxin, antibiotics, possible surgery.

  • Prevention: Vaccination is key.

Mycobacterium Overview

  • Non-endospore-forming; contains mycolic acid, contributing to resistance.

Mycobacterium tuberculosis Overview

  • Causes tuberculosis; three types: primary, secondary, disseminated.

Epidemiology of Mycobacterium tuberculosis

  • Cases declining in the U.S; worldwide prevalence, development of resistant strains.

Diagnosis, Treatment, and Prevention for Mycobacterium tuberculosis

  • Diagnosis: Tuberculin skin test, chest X-rays.

  • Treatment: Combination therapy; multiple months of treatment.

  • Prevention: BCG vaccine; avoid contact with infected individuals.

Mycobacterium leprae Overview

  • Also known as Hansen’s disease; cooler body regions preferred.

Pathogenesis and Disease of Mycobacterium leprae

  • Two forms: tuberculoid (non-progressive) and lepromatous (virulent).

  • Transmission through person-to-person contact.

Diagnosis, Treatment, and Prevention for Mycobacterium leprae

  • Diagnosis: Based on clinical signs.

  • Treatment: Combination of antimicrobials.

  • Prevention: Limit exposure; BCG vaccine offers partial protection.