Micro L7

Medical Bacteriology Overview

• Presented by: Kamyar Motavaze, Ph.D., Oxford College

• Focus: Gram-negative bacteria

Key Terms

• Fusospirochetal infections

• Cancrum oris

• Axial filaments

• Oral treponemes

• Lyme disease

• Granulomatous

• Caseation

• Scrofuloderma

• Leprosy

• Legionnaires’ disease

• Trachoma

• Typhus

Fusobacteria

• Characteristics:

  • Gram-negative, anaerobic, fusiform (cigar-shaped) bacilli

  • Non-motile and non-sporing

• Normal habitats: Oral cavity, large intestine, and female genital tract

• Key species:

  • F. nucleatum, F. periodontium, and F. simiae (associated with periodontal diseases)

Fusobacterium Nucleatum

• Habitat: Oral cavity (healthy gingival crevice and periodontal pockets)

• Associated infections:

  • Fusospirochetal infections, which include:

    • Acute ulcerative gingivitis (trench mouth)

    • Vincent’s angina (ulcerative tonsillitis from acute ulcerative gingivitis)

    • Cancrum oris (noma), a consequence of necrotizing ulcerative gingivitis leading to facial tissue loss

• Virulence factors:

  • I. Endotoxin

  • II. Adhesin A

• Drugs of choice (DOCs): Penicillin, metronidazole

Spirochetes

• Characteristics:

  • Motile, helical microorganisms

  • Have a central protoplasmic cylinder encircled by a cytoplasmic membrane

  • Cell wall is similar to gram-negative

  • Contain three to five axial filaments beneath the cell wall contributing to movement

• Key Genera:

  • Borrelia

  • Treponema: important for dental infections

  • Leptospira

Treponema

• Treponema pallidum

  • Normal habitats: Oral cavity and genital tract

  • Transmission: Sexual intercourse, blood, saliva, placenta

  • Morphology: Thin, helical cells with spaced coils (visible via dark-field microscopy)

  • Causative agent: Syphilis

  • DOC: Penicillin (tetracycline for allergic patients)

• Treponema pallidum subsp. pertenue: Causative agent of yaws (skin lesions, transmissible via direct contact)

• Treponema carateum: Causative agent of pinta (depigmented skin)

Oral Treponemes

• E.g. T. denticola

• Habitat: Oral cavity (crevices and gingival margins)

• Characteristics: Spiral cells with fewer coils than T. pallidum

• Virulence factors:

  • I. Collagenase

  • II. Endotoxin

• DOCs: Penicillin, metronidazole

Borrelia

• Borrelia burgdorferi

  • Habitat: Tick and small mammals

  • Transmission: Tick vector

  • Causative agent: Lyme disease (arthritis, cardiac, and neurological disorders)

  • DOCs: Tetracycline, amoxicillin

• Borrelia recurrentis: Causative agent of relapsing fever (transmitted via louse vector)

Leptospira

• Species: Leptospira biflexa & Leptospira interrogans

• Habitat: Water, wet soils, kidneys of some animals

• Transmission: Urine from animals

• Causative agent: Leptospirosis (symptoms: fever, jaundice, renal failure)

Mycobacteria

• Characteristics:

  • Slim, aerobic, and acid-fast bacilli (high mycolic acid content in cell wall)

  • Non-motile and non-sporing

• Important species:

  • Mycobacterium tuberculosis

    • Habitat: Human lung

    • Transmission: Respiratory droplets

    • Causative agent: Tuberculosis

    • Symptoms: Chronic, granulomatous, caseation, more severe in HIV-positive individuals

    • Treatment: Long-lasting combination therapy of antituberculous drugs (pyrazinamide, ethambutol, rifampin, isoniazid)

    • MDR-TB: Multidrug-resistant is a global issue

    • BCG vaccine: Preventive vaccine

• Mycobacterium bovis:

  • Habitat: Cattle

  • Transmission: Contaminated milk

  • Causative agent: Scrofuloderma in children (enlargement and caseation of cervical lymph nodes)

• Mycobacterium leprae

  • Habitats: Human skin and nerves

  • Transmission: Long-term contact

  • Causative agent: Leprosy (chronic, progressive infection)

  • Forms:

    1. Lepromatous leprosy (disfigurement)

    2. Tuberculoid leprosy (anesthesia and paresthesia)

  • Treatment: Combination therapy (dapsone, rifampin, clofazimine)

MOTT (Mycobacteria Other Than Tuberculosis)

• Large group of mycobacteria with lower pathogenicity for humans

• Examples: M. avium and M. intracellulare

• Habitats: Soil, water, animals

• Causative agents: Pulmonary infections often with TB (more common in immunocompromised patients)

• Response: Sensitive to antituberculous drugs

Legionella

• Characteristics:

  • Gram-negative, aerobic bacilli

  • Habitats: Soil, water supplies, dental units, air conditioners

  • Key species: L. pneumophila

• Infections:

  • Legionnaires’ disease: Severe pneumonia with diarrhea, hematuria, proteinuria

  • Pontiac fever: Mild pneumonia

• DOCs: Erythromycin, rifampin, ciprofloxacin

Chlamydia

• Characteristics:

  • Gram-negative coccobacilli, obligate intracellular parasites

  • Different from viruses: size, genome, antibiotic sensitivity, growth cycle complexity

• Key species:

  • Chlamydia trachomatis:

    • Causes: A. Ocular infections (neonatal conjunctivitis, keratoconjunctivitis, trachoma leading to blindness) B. Genital infections (urethritis, lymphogranuloma venereum) C. Pneumonia in neonates

    • DOCs: Tetracyclines, erythromycin, sulfonamides

  • Chlamydia pneumoniae: Causative agent of mild pneumonia and sore throat

  • Chlamydia psittaci: Causative agent of psittacosis (ornithosis in taxidermists)

Rickettsia

• Characteristics:

  • Gram-negative coccobacilli, obligate intracellular parasites

• Infections:

  • Typhus (febrile illness with maculopapular rashes, transmitted by fleas)

  • Rocky Mountain spotted fever (transmitted by ticks)

  • DOCs: Tetracyclines, chloramphenicol

• Coxiella burnetii: Causative agent of Q fever (atypical pneumonia affecting brain and heart)

Mycoplasma

• Characteristics:

  • Obligate intracellular parasites, smallest prokaryotes, cell wall-deficient, sterols in plasma membrane

• Prototype: Mycoplasma pneumoniae

• Infections:

  • Atypical pneumonia

  • Mucocutaneous eruptions (with skin rashes and oral/vaginal ulcers)

  • Stevens-Johnson syndrome: oral ulceration associated with skin rash and conjunctivitis

  • Hemolytic anemia

• DOCs: Tetracyclines, erythromycin

References

• Samaranayake L. (2024). Essential Microbiology for Dentistry (6th edition). Churchill Livingstone Inc., London, United Kingdom. 424 p.

• evolve.elsevier.com