Bacteria: Irregular Bacilli

Gram +, Irregular Non-Spore-Forming Bacilli

• Irregular: Pleomorphic, stain unevenly

• Medically Important:

• Corynebacterium

• Propionibacterium

• Mycobacterium

• Actinomyces

• Norcardia

Corynebacterium Diphtheriae

• Gram + irregular bacilli

Epidemiology

• Reservoir of healthy carriers, potential for diphtheria is always present

• Most cases occur in non-immunized children living in crowded, unsanitary conditions

• Acquired via respiratory droplets from carriers or actively infected individuals

Pathology

• 2 Stages of Disease:

• Local Infection: Upper respiratory tract inflammation (primary infection), pseudomembrane formation can cause asphyxiation

• Diptherotoxin production and toxemia, target organs primarily heart and nerves

Treatment and Prevention

• Antitoxin

• Penicillin or erythromycin

• Prevented by toxoid vaccine series and boosters

Mycobacteria: Acid Fast Bacilli

• Gram positive irregular bacilli

• Acid Fast Staining

• Strict Aerobes

• Produce catalase

• Possess mycotic acids and a unique type of peptidoglycan

• Do not form capsules, flagella, or spores

• Grow slowly

Mycobacterium Tuberculosis

• Tubercle Bacillus

• Produce no exotoxins or enzymes

• Virulence Factors: Contain complex waxes and cord factor that prevent destruction by lysosomes or macrophages

Epidemiology of Tuberculosis

• Predisposing factors include: inadequate nutrition, debilitation of the immune system, poor access to medical care, lung damage, and genetics

• Estimate 1/3 rd of world population and 15 million in U.S. carry tubercle bacillus; highest rate in U.S. occurring in recent immigrants

• Bacillus very resistant; transmitted by airborne respiratory droplets

Course of Infection and Disease

• 5% to 10% of infected people develop clinical disease

• Untreated, the disease progresses slowly, majority of TB cases contained in lungs

• Clinical tuberculosis divided into:

  • Primary tuberculosis

  • Secondary tuberculosis (reactivation or reinfection)

  • Disseminated (extra pulmonary) tuberculosis

• Primary TB: infectious dose 10 cells

Diagnosis

• In vivo or tuberculin testing

• Mantoux test: Local intradermal injection of purified protein derivative (PPD), look for red wheal to form in 48-72 hours

• Induration: established guidelines to indicate interpretation of result based on size or wheal and specific population factors

Diagnosis (2)

• In vivo or tuberculin testing

• X-rays

• Direct identification of acid-fast bacilli in specimen

• Cultural isolation and biochemical testing