Bacillus, Clostridium, Listeria

Medically Important Gram- Positive Bacilli

  • can be subdivided into 3 general groups, based on presence or absence of endospores and acid-fastness

  • 3 general groups:

    1. endospore-formers: bacillus, clostridium

    2. non-endospore-formers: listeria, erysipelothrix

    3. irregular shaped and staining properties: actinomyces, nocardia, corynebacterium

Spore-Forming Bacilli

  • genus bacillus

  • genus clostridium

  • genus sporolactobacillus

General Characteristics of the Genus Bacillus

  • gram- positive, endospore-forming, motile rods

  • mostly saprobes, habitat: soil

  • obligate aerobic or facultative and catalase positive

  • versatile in degrading complex macromolecules

  • source of antibiotics

  • primary habitat is soil

  • 2 species of medical importance:

    • bacillus anthracis

    • bacillus cereus

Bacillus Anthracis

  • virulence factors - capsule and 3 exotoxin combination

    • protective Ag- entry pore

    • edema factor - increase cAMP

    • lethal factor - cleave host MAPK

  • 3 types of anthrax:

    • cutaneous- spores enter through skin, black sore- eschar; least dangerous

    • pulmonary- inhalation of spores

    • gastrointestinal- ingested spores

both pulmonary and GI- exotoxins lead to cardiovascular shock and death (40-45% mortality with current treatments)

Control and Treatment

  • diagnosis - use phage or DFA = direct fluorescent Ab

  • treated with pencillin, tetracycline, or ciprofloxacin

  • burn or decontaminate animal carcasses, gas sterilize imported materials

  • vaccines

    • live spores and toxoid to protect livestock

    • purified toxoid; for high risk occupations and military personnel; toxoid 6 inoculations over 1.5 years; annual boosters

Bacillus Cereus

  • common airborne and dustborne; usual methods of disinfection and antisepsis are ineffective; facultative

  • grows in foods, spores survive cooking and reheating

  • ingestion of heat stable enterotoxin-containing food causes nausea, vomiting, abdominal cramps, and diarrhea; 24-hour duration

  • heat labile enterotoxin, bacterial growth-diarrheal, lasts longer

  • no treatment

    • increasingly reported in immunosuppressed- severe pneumonia, wound infections

    • eye infections- rapid blindness, drug resistance

The Genus Clostridium

  • gram-positive, spore-forming rods

  • anaerobic and catalase negative- spores produced only under anaerobic conditions

  • 120 species

  • oval or spherical spores produced only under anaerobic conditions

  • synthesize organic acids, alcohols, and exotoxins

  • cause wound infections, tissue infections, and food intoxications

Gas Gangrene

  • clostridium perfringens most frequent clostridia involved in soft tissue and wound infections

  • spores found in soil, human skin, intestine, and vagina

  • predisposing factors - surgical incisions, compound fractures, diabetic ulcers, septic abortions, puncture wounds, gunshot wounds

    • soft tissue/ wound infections

    • gas gangrene- 2 forms

      • anaerobic cellulitis - localized to damaged area

      • myonecrosis - toxins cause damage to spread

    • damaged /dead tissue + anaerobic conditions - germination, vegetative growth and release f toxins, fermentation of muscle carbohydrates - formation of gas and further destruction of tissue

      • 25% mortality; if treatment delayed, or septicemia near 100%

      • gas gangrene diagnostic for clostridial wound infection

  • Virulence Factors

    • factors

      • alpha toxin - causes RBC rupture, edema, and tissue destruction

    • collagenase

    • hyaluronidase

    • DNase

Treatment and Prevention

  • immediate cleansing of dirty wounds, deep wounds, compound fractures, and infected incisions

  • debridement of disease tissue

  • large doses of cephalosoporin or penicillin; protein synthesis inhibitors- inhibit toxin production

  • hyperbaric oxygen therapy

  • no vaccines available

Tetanus

  • clostridium tetani

  • common resident of soil and GI tracts of animals

  • causes tetanus or lockjaw, a neuromuscular disease

  • most commonly among geratric patients and IV drug abusers; neonates in developing countries

Pathology

  • spores usually enter through accidental puncture wounds, burns, umbilical stumps, frostbite, and crushed body parts

  • anaerobic environment is required for vegetative cells to grow and release toxin

  • tetanospasmin - neurotoxin causes paralysis by binding to motor nerve endings; blocking the release of neurotransmitter for muscular contraction inhibition; muscles contract uncontrollably

  • death most often due to paralysis of respiratory muscles

Neonatal Tetanus

Treatment and Prevention

  • treatment aimed at deterring degree of toxemia and infection and maintaining homeostasis

  • antitoxin therapy with human tetanus immune globulin; antibodies inactivates circulating toxin but not counteract that which is already bound

  • metronidazole drug of choice (efficient penetration into wounds and abcesses); and muscle relaxants

  • tetanus toxoid vaccine available; booster needed every 10 years

Clostridium difficile- associated disease (CDAD)

  • normal resident of colon, in low numbers

  • causes antibiotic-associated colitis

    • relatively non-invasive; treatment with broad-spectrum antibiotics kills the other bacteria, allowing C. difficile to overgrow

  • produces enterotoxins that damage intestines

  • major cause of diarrhea in hospitals

  • increasingly common in community-acquired diarrhea

  • ELISA of stool for diagnosis

Treatment and Prevention

  • mild uncomplicated cases respond to fluid and electrolyte replacement and withdrawal of antimicrobials

  • severe infections treated with oral vancomycin or metronidazole and replacement cultures

  • increased precautions to prevent spread

  • mild uncomplicated cases respond to fluid and electrolyte replacement nd withdrawal of antimicrobials

  • severe infections treated with oral vancomycin or metronidazole and replacement cultures

  • increased precautions to prevent spread

Clostridial Food Poisoning

  • clostridium botulinum - rare but severe intoxication usually from home canned food

  • clostridium perfringens - mild intestinal illness; second most common form of food poisoning worldwide

Botulinum Food Poisoning

  • botulism - intoxication associated with inadequate food preservation

  • clostridium botulinum - spore-forming anaerobe; commonly inhabitats soil and water

Pathogenesis

  • spores are present on soil, water, food when gathered and processed

  • if reliable temperature and pressure are not achieved (anaerobic) air will be evacuated but spores will remain

  • anaerobic conditions favor spore germination and vegetative growth

  • potent toxin, botulin, is released

  • botulin toxin is carried to neuromuscular junctions and blocks the release of acetylcholine, necessary for muscle contraction to occur

  • double or blurred vision, difficulty swallowing, neuromuscular symptoms

Infant and Wound Botulism

  • infant botulism - caused by ingested spores that germinate and release toxin; flaccid paralysis

  • wound botulism - spores enter wound, germinate, release toxin and cause food poisoning symptoms

Treatment and Prevention

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

  • administer antitoxin; cardiac and respiratory support

  • infectious botulism treated with penicillin

  • practice proper methods of preserving and handling canned foods; addition of preservatives

Clostridium Gastroenteritis

  • clostrium perfringens

  • spores contaminate food that has not been cooked thoroughly enough to destroy spores

  • spores germinate and multiply (especially if unrefrigerated)

  • when consumed, exotoxin is produced in the intestine; acts on epithelial cells, acute abdominal pain, diarrhea, and nausea

  • rapid recovery

Spore-Forming Pathogens

Gram- Positive Regular Non-Spore-Forming Bacilli

  • regular: stain uniformly and do not assume pleomorphic shapes

  • medically important:

    • Listeria monocytogenes

    • Erysipelothrix rhusiopathiae

Listeria monocytogenes

  • non-spore forming gram-positive

  • ranging from coccobacilli to long filaments

  • 1-4 flagella and lack capsules

  • resistant to cold, heat, salt, pH extremes, and bile

  • virulence attributed to ability to replicate in the cytoplasm of cells after inducing phagocytosis; low pH triggers listeriolysin O; creates pore ion phagosome; bacteria released in cytosol; avoids humoral immune system

Epidemiology and Pathology

  • primary reservoir in soil and water; animal intestines

  • can contaminate foods and grow during refrigeration

  • listeriosis- most cases associated with dairy products, poultry, and meat

  • often mild or subclinical in normal adults; dangerous for pregnant women

  • immunocompromised patients, fetuses, and neonates; affects brain and meninges

    • 20% death rate

Diagnosis and Control

  • culture requires lengthy cold enrichment process

  • rapid diagnostic tests using ELISA, immunofluorescence, and DNA analysis

  • ampicillin and trimethoprim/sulfamethoxazole

  • prevention - pasteurization and cooking

Erysipelothrix rhusiopathiae

  • gram - positive rod widely distributed in animals and the environment

  • primary reservoir - tonsils of healthy pigs

  • enters through skin abrasion, multiplies to produce erysipeloid, dark red lesions, fever, joint pain, rarely septicemia

  • penicillin or erythromycin and vaccine for pigs

Gram- Positive Irregular Non-Spore-Forming Bacilli

  • irregular: pleomorphic, stain unevenly

  • medically important genera:

    • Corynebacterium

    • Propionibacterium

    • Mycobacterium

    • Actinomyces

    • Nocardia

Filamentous Bacilli

  • Genera Actinomyces & Nocardia nonmotile filamentous bacteria

  • Actinomyces

    • many normal flora, opportunistic, non motile

    • role in plaque and dental caries

    • Actinomycoses - chronic infection of skin and soft tissues - associated oral care

    • rarely associated with > 4 yrs non-copper IUDs

Nocardia

  • soil organisms

    • N. brasiliensis - pulmonary like TB and brain abscesses

  • N. asteroids - mycetoma, slow destructive infection of tissue and bone

Corynebacterium diptheriae

  • gram-positive irregular bacilli, pleomorphic, catalase positive

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

  • sporadic in adults - immunity wanes

Pathology

  • 2 stages of disease:

    1. local infection - upper respiratory tract inflammation (primary infection)

      • sore throat, nausea, vomiting, swollen lymph nodes;

        • pseudomembrane

          • formation can cause asphyxiation

      • cutaneous (secondary infection)

    2. diptherotoxin production and toxemia

      • target organs - primarily heart and nerves; death rate: 5-10%; from bacteriophage

Diphtherotoxin

  • cleavage of leader during secretion

  • B-bind heparin- binding EGF (high surface heart and liver cells) translocate A domain

  • A- inactivate EF-2 (1/ribosome)

Diagnostic Methods

  • gray pseudomembrane and swelling indicative

  • stain, serology - culture

    • slow, biochemistry required

  • Elek test - antitoxin binding

Treatment and Prevention

  • antitoxin

  • penicillin or erythromycin

  • prevented by toxoid vaccine series and boosters