Gram Positive Rods

Gram Positive Rods (GPR)

• Clostrifium botulinum

• Clostridium difficile

• Clostridium perfringens

• Clostridium tetani

• Literia monocytogenes

• Bacillus anthracis

• Corynebacterium diphtheriae

Anarobes

• Require anaerobic conditions for growth

  • Low redox potential

  • Oxgen toxicity

  • Bacteria that grow in <10% oxygen (as low as .5%)

  • Solely Fermentation (as opposed to faculatative anaerobes)

• Generally lack catalase and superoxide dismutase (SOD)

• But many of the human pathogens are aerotolerant and some produce catalase and/or SOD

• Growing anaerobes

  • Protect from oxygen

  • Anaerobic atmosphere

  • Selective media (mixed cultures)

    • Aminoglycoside antibiotics in media

Anaerobes: Classification

• Gram-Positive Cocci - Peptostreptococcus

• Gram-Negative Cocci - Veillonella

• Gram-Positive Rods

  • Clostridium - C. perfringens, C. tetani, C. botulinum, C. difficile

    • All spore-forming (opposite of Bacillus sp.)

• Gram-Negative Rods

  • Bacteriodes

    • B. fragilis - β lactamase producer

    • Other Bacteriodes species

  • Other genera (Fusobacterium, Prevotella, etc.)

Anaerobes: Epidemiology

• Microbiota contains abundant anaerobes

• Most infections endogenous (O2 is most everywhere else)
  Environmental - trauma and spores

Anaerobes: Pathogenesis

• A Traumatic Event + Anaerobic Environment + Organism Virulence Factors

• The Event 1: Displacement of microbiota

  • Trauma

  • Surgery

  • Disease - diverticulitis (inflammation in the intestines)

• The Event 2: Environmental contamination

  • Trauma

  • Spore-forming — Clostridia

• The Environment

  • Tissues → anaerobic

    • Dead tissue

    • Vascular compromise

    • Mixed infection is typical

      • Multiple organisms displaced

      • Synergy

• The Organism

  • Microbiota Composition - poor match with organisms isolated from infections

  • Virulence Factors

    • Oxygen tolerance - SOD, catalase

    • Capsules

    • Toxins

Pseudomembranous Colitis

• 1950s-70s

  • Newborns given tetracyline

  • Stool overgrowth with tetracycline-resistant S. aureus

  • More antibiotics, no Staph or enteric pathogens

  • Anaerobes not considered

C. diff Colitis: Pathogenesis

• C. difficile small part (2-15%) of stool microbiota

• Antimicrobial administration

  • Intestinal microbiota broadly suppressed

  • C. difficle sporulation readily occurs in vivo

    • Spores protective against antibiotics

  • Spore germination triggered by bile salts

  • Highest cause of antimicrobial-associated diarrhea (AAD)

    • 5-10 days into antibiotic course

• Exotoxin Production

  • A & B toxins (TcdA, TcdB), usually borh

    • Some of the largest bacterial toxins known

    • Disrupts GCPR (actin polymerization)

  • Makes toxins in vegetative state

  • Disrupt cytoplasmic transduction proteins

• Enhanced Virulence Recently

  • Produce more TcdA &/or TcdB

  • New 3rd detected (C. difficile transferase, CDT)

• Toxic Megacolon

  • Acute toxic colitis

  • Dilation of the colon

C. diff Colitis - Clinical Aspects

• Diagnosis

  • C. difficile toxin detected in stool

  • Antibiotic-associated diarrhea 30-50%

  • NAA - gene not toxin

• Treatment

  • Oral metronidazole or vanomycin

    • Vanomycin not absorbed

  • Colectomy - toxic megacolon, lifesaving

C. diff Colitis - Relapses

• Can survive in environment

• Treatment

  • Metronidazole/vanomycin/others

  • Pulsed vanomycin (allows for vegetative bacteria to emerge from spores)

  • Colectomy for toxic megacolon

• Prevention

  • Probiotics - “do no harm” - ? Primary prevention

  • Fecal transplant >90% success

  • Future: block spore germination - competitive inhibitors of bile salts ($$$)

C. diff

• The leading cause of fatal diarrhea in the U.S.

• Big concern with chemotherapy

• The leading cause of death related to “antibiotic use”

• Smells SUPER BAD

• Strains without toxins outcompete strains with toxins

• Unknown how the toxins are exported (Recall, the toxins are HUGE)

Listeria monocytogenes

• Common in animals

• Sporadic human cases

  • Elderly

  • Newborns

  • Immunocompromised

• Fast facts

  • GPR

  • Motile via flagella <30 C

  • β-hemolytic

  • Catalase positive

  • Grows at below freezing temperatures and above 37 C

  • Wide spread in nature (soil, water, decay)

  • Forms biofilms

Listeria: Epidemiology

• Foodborne Transmission

• Grows at refrigerator temps

• Uncooked foods

  • Cole slaw, cured salami, cantaloupe

• Pasteurization failures

  • Soft (nacho) cheese

  • “Natural” milk

• Transplacental transmission

  • 1000 cases and 200 deaths each year (active surveillance keeps this at bay

Listeria: Pathogenesis

• Invasion and Spread

  • Internalin - attachment, cytoskeleton reorganization

  • Literiolysin O (LLO) - lyse endocytotic vacuole

• Purposely gets engulfed → Escaped endosome using LLO (before lysosome can fuse) → Uses actin to make tail to propel organism through the membrane

Listeria: Clinical Aspects

• Primary Infection

  • Gastroenteritis

• Bacteremia, meningitis

  • Immunocompromised, also newborn, older age)

• Intraterine, postpartum

• Diagnosis: Routine blood culture

• Treatment: Not reported often due to low # of cases, but if it is, penicillin

• Prevention: Public health measures (cook meat, careful with lunch meat and hot dogs, wash raw veggies, proper cutting board technique)

Bacillus

• Large Gram-positive rods

• Aerobic

• Spore-forming

• Found in soil (rich in organic matter) and animals

Bacillus anthracis

• Structure

  • Polypeptide capsule

• Products

  • Exotoxin(s) — 3 protein complex

• Other attributes

  • Long chains

  • Non-motile

  • Nonhemolytic

  • Capsule

  • Spore forming (VERY stable and lightweight)

  • One of the first vaccines

    • Pasture vaccinated with attenuated strain for farm animals

Bacillus anthracis: Epidemiology

• Animal disease

  • Humans accidental host

  • Eradicated in developed countries

• Human disease

  • Imported spores in animal products (hides, wool, etc.)

  • Bioterrorism

• Skin - Direct contact (low spread)

• GI - Ingestion

• Pulmonary - Inhalation

  • Woolsorter’s disease

  • Natural - Imported animal hides

  • Bioterrorism

  • Inhalation anthrax is not spread from person to person

• Bioterrorism

  • Spores are stable

  • Soviet accident

    • Explosion of 20 lbs of spores

    • 60 deaths

  • Special preparations produce “clouds”

  • Anthrax clouds

    • Accidents - Russia

    • U.S. mail

    • Missile warheads

Anthrax: Pathogenesis

• Spores germinate to vegetative form in rich environment

• Polypeptide capsule is antiphagocytic

• Exotoxin complex causes injury

  • Edema factor (EF)

  • Lethal factor (LF)

  • Protective antigen (PA)

• PA binds to either EF or LF to make a pore site on cell

• Malignant pustule

Anthrax: Clinical Aspects

• Diagnosis

  • G+ rods in sputum, CSF

  • Culture routine but laboratory identification difficult

  • Notify lab immediately of anthrax suspicion

Anthrax: Prevention

• Eradication of animal anthrax

• Chemoprophylaxis

  • Cirprofloxacin

• Vaccines

  • Live, attenuated (Pasteur)

    • Animals

    • Russia, China

  • Inactivated toxin

    • US military