Spore forming and Non-spore forming bacilli

NONSPOREFORMING BACILLI

• Listeria monocytogenes

  • Psychrophile: Can grow during refrigeration.

  • Resistant to cold, heat, salt, and pH extremes.

  • Transmission: Contaminated dairy products, poultry, and meat.

  • Causes Listeriosis:

    • Nonspecific symptoms: fever, diarrhea, sore throat.

    • Pregnant women are particularly susceptible to infection, leading to stillbirth.

    • Most cases associated with dairy products, poultry, and meat.

    • Often mild or subclinical in healthy adults.

  • High-risk groups: Immunocompromised patients, fetuses, neonates; affects brain and meninges with a 20% death rate.

  • Treatment: Ampicillin and trimethoprim/sulfamethoxazole.

• Streptomyces

  • Soil bacteria; nonpathogenic source of antibiotics.

• Lactobacillus

  • Commonly found in yogurt.

• Propionibacterium

  • Skin anaerobe; associated with acne.

Cornybacterium

• Nonspore-forming bacillus; stains unevenly and is pleomorphic.

• Most are skin diptheroids causing deep, erosive ulcers that heal slowly.

• Corynebacterium diphtheriae

  • Causes inflammation of the upper respiratory tract, specifically tonsils, larynx, pharynx, and trachea.

  • Produces diphtherotoxin.

  • Main complication: pseudomembrane formation in the pharynx, which can cause airway bleeding and asphyxiation.

  • Prevention: DPT vaccine starting at 6-8 months, booster at 15 months, and school age.

Corynebacterium diphtheriae

• Characteristics: Nonspore-forming bacillus, pleomorphic, shows a gray coating, especially noted in diphtheria-related pseudomembrane in the posterior pharynx, which can become large and obstruct the airway.

Treatment and Prevention of Diphtheria

• Antitoxins and antibiotics (Penicillin or erythromycin).

• Prevention through toxoid vaccine series and boosters.

Gram-Positive Spore-Forming Bacilli 1

• Endospore: Dense survival unit that forms in response to nutrient deprivation.

  • Most endospore-forming bacteria are gram-positive, motile, rod-shaped (genera Bacillus and Clostridium).

  • Resistant to: heat, drying, radiation, and chemicals, enhancing their survival and ecological niche.

Gram-Positive Spore-Forming Bacilli 2

• Spore and vegetative cell transformations, resistant to adverse environmental conditions.

Sporeforming Bacilli

• Environmental opportunists; can be carried as normal flora.

• Bacillus

  • Aerobic, catalase positive; primary habitat is soil.

  • Bacillus anthracis: Causes anthrax.

    • Endemic; transmitted by livestock.

    • Virulence factors include polypeptide capsule and exotoxins (e.g., edema, cell death).

  • Cutaneous anthrax: Characterized by skin papules that can become necrotic (black eschar).

  • Pulmonary anthrax (Woolsorters disease): Inhaled spores lead to lung growth and release toxins, resulting in cardiovascular shock.

  • Gastrointestinal anthrax: Symptoms include nausea, vomiting, loss of appetite, abdominal pain, fever, and can exceed 50% mortality despite treatment.

  • Treatment: Clindamycin, doxycycline, or ciprofloxacin with Raxibacumab.

  • Vaccines available for livestock and high-risk individuals.

Bacillus cereus

• Common airborne and dust-borne; resistant to normal disinfectants.

• Spores survive cooking and reheating, leading to gastrointestinal distress through toxin consumption, typically with a 24-hour duration.

Gas Gangrene/Myonecrosis 1

• Clostridium perfringens: Major clostridia in soft tissue and wound infections.

  • Spores present in soil, human skin, intestine, vagina.

  • Predisposition: Surgical incisions, fractures, ulcers, septic abortions, puncture wounds.

  • Virulence factors: Alpha toxin, collagenase, hyaluronidase, DNase.

Clostridium

• Gram-positive, spore-forming rods; anaerobic, catalase negative.

• C. perfringens: Produces cytotoxins causing gas gangrene and tissue destruction, particularly in diabetic patients.

  • Treatment options: Hyperbaric oxygen therapy to escalate recovery.

C.tetani

• Produces tetanospasmin neurotoxin, causing uncontrolled muscle contractions (tetanus).

  • Neurotoxin inhibits GABA release, leading to muscle spasms and rigidity.

  • Treatment: Tetanus immunoglobulin (TIG).

  • Prevention through DTP vaccine.

Clostridial Food Poisoning

• Clostridium botulinum: Severe intoxication; often from home-canned food.

• Clostridium perfringens: Causes mild intestinal illness, being the second most common cause of food poisoning.

C.botulinum

• Causes botulism linked to poorly preserved food.

  • Produces neurotoxin botulin, blocking acetylcholine release; leads to muscle paralysis.

  • Botox uses this toxin for cosmetic applications.

Treatment and Prevention of Botulism

• Test for toxin presence in food/intestines.

• Administer antitoxin; provide cardiac and respiratory support.

• Infectious botulism: treated with penicillin.

• Proper canning and food handling methods are critical.

C.difficile

• Normal gut resident.

• Causes antibiotic-associated colitis when antibiotics disrupt normal flora.

  • Treatment for mild cases: fluid and electrolyte replacement; severe infections treated with oral vancomycin or metronidazole.

Spore-Forming Pathogens Differentiation

Mycobacteria

• Gram-positive, acid-fast due to mycolic acid; non-spore forming.

• Notable pathogens: M.tuberculosis and M.leprae.

M.tuberculosis

• Infects lungs (primary tuberculosis) and organs (extrapulmonary tuberculosis).

• Transmission: Respiratory contact, especially in AIDS patients.

• Detected by Mantoux test (PPD).

Mycobacterium tuberculosis 1

• Tubercle bacillus, long and thin; grows in cords.

• No exotoxins or enzymes contributing to its infectiousness.

• Virulence: Complex waxes prevent destruction by lysosomes or macrophages.

Latent and Recurrent TB 1

• Non-recovery from primary TB can lead to reactivation.

• Symptoms: violent coughing, sputum changes, fever, weight loss; untreated mortality rate is 60%.

Latent and Recurrent TB 2

• Inhalation of TB droplets can lead to infection.

• The immune system often clears infection.

• Latency can last for years without symptoms, but reactivation can occur.

Clinical Methods of Detecting TB 1

• In vitro methods: QuantiFERON-TB Gold test, T-SPOT TB test.

• Chest X-rays: used to rule out pulmonary TB.

• Acid-fast staining; cultural isolation for accurate diagnosis.

Management and Prevention of TB

• Long-term treatment (6-24 months) with at least two drugs from a specific list.

• Common initial treatment: isoniazid, rifampin, ethambutol, pyrazinamide (first 8 weeks).

• Follow-up: INH and RIF for 18 weeks.

Mycobacterium leprae

• Hansen’s bacillus; strict parasite, slow-growing, multiplies within host cells as globi.

• Causes leprosy, chronic disease affecting skin and nerves.

M.Leprae

• Transmission: Direct contact; conditions affect risk.

• Two types:

  • Tuberculoid leprosy: superficial skin changes.

  • Lepromatous leprosy: significant disfigurement.

Symptoms of Hansen’s Disease

• Skin lesions, pain, numbness, muscle weakness, eye problems, enlarged nerves; chronic nasal issues.

Course of Infection and Disease 2

• Two major forms of leprosy:

  • Tuberculoid (paucibacillary): few lesions, good immune response.

  • Lepromatous (multibacillary): many bacilli, poor response.

Diagnosis, Treatment and Prevention of Leprosy

• Long-term combined therapy; no definitive vaccine currently.

• Diagnosis through symptoms, examinations, and patient history.

Mycobacterium avium complex (MAC)

• Opportunistic, non-tuberculous mycobacteria; major cause of AIDS-related death.

Concepts Check

1. Bacillus cereus transmission mode: Ingestion.

2. Botulinum toxin acts on: Neuromuscular junction.

3. Corynebacterium diphtheriae infection can be prevented with a vaccine: True.

4. Tuberculosis spreads via: Respiratory droplets.