Lecture on Nonsporeforming Bacilli and Spore-Forming Pathogens

NONSPOREFORMING BACILLI

• Listeria monocytogenes

  • Psychrophile capable of growing 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; may lead to stillbirth

  • Most cases linked to dairy products, poultry, and meat

  • Often mild or subclinical in healthy adults

  • Severe impact on immunocompromised patients, fetuses, and neonates, including brain and meninges infections

  • Mortality Rate: 20% in severe cases

  • Treatment: Ampicillin and trimethoprim/sulfamethoxazole

• Streptomyces

  • Soil bacteria, nonpathogenic

  • Source of antibiotics

• Lactobacillus

  • Commonly found in yogurt

• Propionibacterium

  • Skin anaerobe; associated with acne

CORNYBACTERIUM

• General Characteristics

  • Nonspore forming bacillus

  • Stains unevenly and is pleomorphic

  • Most species are skin diphtheroids

  • Can cause deep, erosive ulcers that heal slowly

• Corynebacterium diphtheriae

  • Causes inflammation of upper respiratory tract: tonsils, larynx, pharynx, trachea

  • Produces diphtherotoxin

  • Main complication: formation of pseudomembrane

  • Greenish-gray film in pharynx from inflammation fluid solidification

  • Pseudomembrane can lead to airway bleeding and asphyxiation

• Prevention:

  • DPT vaccine (Diphtheria, Pertussis, Tetanus)

  • Schedule: Starts at 6-8 months, booster at 15 months, additional at school age

TREATMENT AND PREVENTION OF DIPHTHERIA

• Diphtheria Antitoxin

• Antibiotics: Penicillin or erythromycin

• Prevention via the toxoid vaccine series and booster shots

GRAM-POSITIVE SPORE-FORMING BACILLI

Overview

• Endospore:

  • Dense survival unit that develops within a vegetative cell due to nutrient deprivation

  • Most endospore-forming bacteria are Gram-positive, motile, rod-shaped (e.g., Bacillus, Clostridium)

  • Resistant to heat, drying, radiation, and chemicals, aiding survival, longevity, and ecological viability

BACILLUS

• General Characteristics

  • Aerobic and catalase positive

  • Primary habitat: soil

  • Bacillus anthracis - causes anthrax:

  • Transmission: Endemic via livestock

  • Virulence Factors: Polypeptide capsule, exotoxins (e.g., edema, cell death)

Types of Anthrax

• Cutaneous Anthrax:

  • Production of papule in skin, becomes necrotic and forms black eschar

• Pulmonary Anthrax (Woolsorters disease):

  • Inhalation of spores leads to growth in lungs, toxin release, capillary thrombosis, cardiovascular shock

  • Diagnosis: Widened mediastinum observed in X-ray

• Gastrointestinal Anthrax:

  • Symptoms: nausea, vomiting, loss of appetite, fever, followed by abdominal pain, blood vomiting, severe diarrhea

  • Mortality Rate: May exceed 50%, even with treatment

  • Treatment: Clindamycin, doxycycline, or ciprofloxacin combined with Raxibacumab (monoclonal antibodies against one of the toxins)

• Vaccines:

  • Live spores and toxoid for livestock; Purified toxoid (Biothrax) for high-risk occupations and military

  • Schedule: 6 inoculations over 1.5 years, then annual boosters

BACILLUS CEREUS

• Airborne and dust-borne; disinfectants may be ineffective

• Grows in foods, spores can survive cooking/reheating

• Symptoms: Ingestion of toxin-containing food leads to nausea, vomiting, abdominal cramps, diarrhea lasting approximately 24 hours

• Treatment: No specific treatment; condition is usually self-limiting

GAS GANGRENE / MYONECROSIS

• Clostridium perfringens

  • Most common clostridia in soft tissue and wound infections

  • Spores found in soil, human skin, intestine, vagina

• Predisposing Factors: Surgical incisions, compound fractures, diabetic ulcers, septic abortions, puncture wounds, gunshot wounds

• Virulence Factors:

  • Alpha toxin (causes RBC rupture, edema, and tissue destruction)

  • Collagenase, hyaluronidase, DNase

CLostridium Characteristics

• Gram-positive, spore-forming rods, anaerobic and catalase-negative

• C. perfringens:

  • Produces cytotoxins: Lecithinase, collagenase, hyaluronidase, and DNAse

  • Causes gas gangrene in diabetes; gas formed via fermentation of muscle carbohydrates

  • Treatment: Hyperbaric oxygen therapy to reduce infection severity

CLOSTRIDIUM TETANI

• Tetanospasmin:

  • Neurotoxin causing uncontrollable muscle contraction leading to tetanus

• Mechanism: Inhibition of γ-aminobutyric acid (GABA) release causes symptoms such as muscle spasms, rigidity, lockjaw, and respiratory difficulty

• Infection Pathway: Typically occurs when bacterium enters injured tissue

• Treatment: Tetanus immunoglobulin (TIG)

• Prevention: DTP vaccine—3 doses at 2 months apart, boosters at 1 and 4 years

  • Vaccine provides protection for 10 years

CLOSTRIDIAL FOOD POISONING

• Involved species:

  • Clostridium botulinum: Rare but severe intoxication, usually from home-canned food

  • Clostridium perfringens: Causes mild intestinal illness; second most common form of food poisoning globally

C. BOTULINUM

• Causes botulism, linked to poorly preserved food

• Produces botulin toxin:

  • Interferes with neurotransmitter acetylcholine release, resulting in muscle paralysis

  • Used in cosmetics as Botox to inhibit muscle contraction and reduce wrinkles

Treatment and Prevention of Botulism

• Detection of toxin presence in food, intestinal contents, or feces

• Administer antitoxin and provide cardiac, respiratory support

• Infectious botulism: Treated with penicillin

• Recommendations for proper canning and preserving food and the addition of preservatives

C. DIFFICILE

• Often a normal intestinal resident

• Causes antibiotic-associated colitis when normal flora disrupted, resulting in necrosis of colon

• Mild cases: Respond to fluid and electrolyte replacement

• Severe cases: Treated with oral vancomycin or metronidazole and cultures for replacement

SPORE-FORMING PATHOGENS DIFFERENTIATION

Table 19.2: Differentiation of Important Spore-Forming Species

MYCOBACTERIA

• General Characteristics

  • Gram-positive

  • Acid-fast due to mycolic acid

  • Not spore-forming

  • Slow-growing

  • Resistant to many antibiotics

  • Significant pathogens: M. tuberculosis and M. leprae

M. TUBERCULOSIS

• Infects primarily the lungs (primary tuberculosis), can affect other organs (extrapulmonary tuberculosis)

• Transmission through respiratory contact, particularly in AIDS patients

• Detected via Mantoux test:

  • Purified protein derivative (PPD) injected; thick red patch indicates infection

Mycobacterium tuberculosis

• Morphology: Long, thin rod; forms cords

• Lacks exotoxins or enzymes contributing to infectiousness

• Virulence Factors: Complex waxes and cord factor that prevent lysosomal destruction

Latent and Recurrent TB

• If primary tuberculosis does not resolve, reactivation can occur, leading to severe symptoms:

  • Violent coughing, greenish/bloody sputum, fever, anorexia, weight loss, fatigue

• Untreated, mortality rate may reach 60%

Infection Pathway

• 10%-20% of cases result in no infection

• Inhaled bacilli engulfed by macrophages results in infection in 80%-90% of cases (+TB test)

• 90%-95% may clear infection via immune action (-TB test)

• Progression may lead to latent TB (dormant bacilli), consistent symptoms after 2 years (+TB test)

• Recurrent disease involves the breakdown of tubercles and more systemic spread (+TB test)

Clinical Methods for Detecting TB

• In Vitro tests: Blood tests like QuantiFERON-TB Gold, T-SPOT TB test

• Chest X-rays: Non-diagnostic, rules out pulmonary TB

• Acid-fast Staining: Ziehl-Neelsen stain and fluorescence staining

• Cultural isolation and Biochemical testing: Most accurate for diagnosing TB

Management and Prevention of TB

• 6-24 months on at least two drugs from a list of 11

• Resistance common; initial treatment phase with four drugs:

  • isoniazid (INH), rifampin (RIF), ethambutol (EMB), pyrazinamide (PZA) for 8 weeks

  • Continuation phase: Daily doses of INH and RIF for 18 weeks

• Rifater: Combination of INH, RIF, and PZA simplified into one pill regimen

• BCG Vaccine: Based on attenuated M. bovis, used in some countries

MYCOBACTERIUM LEPRAE

• Causes Hansen’s bacillus/Hansen’s disease

• Strict parasite; cannot grow in artificial media

• Slowest-growing species, multiplies in host cells as globi

Leprosy

• Transmitted via direct contact

• Living conditions significantly influence transmission

• Two types of leprosy:

  • Tuberculoid leprosy: Superficial with discoloration and skin growth

  • Lepromatous leprosy: Causes severe disfigurement

Symptoms of Hansen’s Disease

• Skin lesions: faded/discolored growths

• Thick, dry, or stiff skin

• Severe pain and numbness in affected areas

• Muscle weakness or paralysis, especially in extremities

• Vision issues that can lead to blindness

• Enlarged nerves (e.g., elbows, knees)

• Stuffy nose, nosebleeds, ulcers on feet

Diagnosis, Treatment, and Prevention of Leprosy

• Treatment involves long-term combined therapy

• Constant surveillance of high-risk populations needed for prevention

• No definitive vaccine currently available

• Diagnosis: Combination of symptomology, microscopic examination, and patient history

  • Symptoms to look for: Numbness, loss of sensitivity, thickened earlobes, chronic stuffy nose

  • Detection of acid-fast bacilli in lesions and nasal discharges

MYCOBACTERIUM AVIUM COMPLEX (MAC)

• Opportunistic and nosocomial agent, non-tuberculous mycobacteria

• Leading cause of AIDS-related death

CONCEPTS CHECK

1. Mode of transmission for Bacillus cereus: Ingestion

2. Botulinum toxin action affects: Neuromuscular junction (Answer: C)

3. Corynebacterium diphtheriae causes pseudomembrane respiratory distress and can be prevented with vaccine: True

4. Tuberculosis is spread via: Respiratory droplets