Gram Positive and Negative Bacilli

Gram Positive Bacilli

  • Spore Forming Rods: Bacillus and Clostridium release potent exotoxins causing disease.

Bacillus anthracis

  • Causative agent of anthrax.

  • Unique protein capsule (antiphagocytic).

  • Aerobic growth conditions.

  • Spores resistant to heat, drying, UV; germinate and produce toxins.

  • Transmission via contact with animals or soil; potential for bio-terrorism.

Bacillus anthracis Exotoxin

  • Encoded on pXO1 plasmid (virulence factors require conditions of 37°C, increased CO2, serum proteins).

  • Composed of 3 proteins: Edema factor, Protective antigen, Lethal factor.

  • Both pXO1 and pXO2 (capsule genes) plasmids are required for virulence.

Prevention and Treatment for Anthrax

  • Rapid treatment is crucial.

  • Antibiotics: penicillin, doxycycline, ciprofloxacin, levofloxacin.

  • Vaccine available against PA protein.

Bacillus cereus

  • Causes food poisoning from spores.

  • Non-encapsulated, motile, resistant to penicillin.

  • Produces enterotoxins causing nausea and diarrhea.

  • Antibiotics ineffective due to preformed toxins.

Clostridium

  • Anaerobic, differentiating factor from other spore-forming bacilli.

  • Associated with diseases: Botulism, tetanus, gas gangrene, pseudomembranous colitis.

Clostridium botulinum

  • Causes rapidly fatal botulism from neurotoxin.

  • Neurotoxin leads to flaccid muscle paralysis.

  • Treatment involves antitoxin and respiratory support.

Infant Botulism

  • Caused by spores in honey; leads to colonization and toxin release.

Clostridium tetani

  • Tetanus caused by spores in wounds.

  • Exotoxin leads to muscle spasms (lockjaw).

  • Booster every 10 years.

Clostridium perfringens

  • Causes gas gangrene; presents as wound infection or myonecrosis, requiring prompt treatment.

Clostridium difficile

  • Causes pseudomembranous colitis after antibiotic use.

  • Symptoms: diarrhea, abdominal cramping, fever.

  • Treatment: discontinue antibiotics, use metronidazole or vancomycin.

Non-Spore Forming Rods

  • Important types: Listeria monocytogenes and Corynebacterium diphtheriae.

Listeria monocytogenes

  • Causes listeriosis, particularly in immunocompromised.

  • Found in soft cheeses, unpasteurized milk, and cold cuts.

  • Treatment: ampicillin or trimethoprim-sulfamethoxazole.

Corynebacterium diphtheriae

  • Causes diphtheria via exotoxin damaging heart and neurons.

  • Treatment includes antitoxin and antibiotics.

Gram Negative Bacilli

  • The Enterics: Part of normal flora but can cause disease.

Biochemical Classifications

  • Lactose fermentation used for identification: EMB and MacConkey media.

  • Classification includes H2S production and surface antigens (O, K, H antigens).

Diseases by Enterics

  • Can cause diarrhea (with and without systemic invasion).

  • Identifiable by type of diarrhea, symptoms include fever, abdominal pain, and bloody stool depending on causative agents.

Salmonella

  • Mostly unable to ferment lactose; primarily animal reservoirs.

  • S. enterica: Leads to enterocolitis and typhoid fever.

  • Pathogenesis involves dosage and immune status; antibiotics not recommended for enterocolitis.

Escherichia coli

  • Normal gut flora; pathogenic strains cause various infections: gastroenteritis and urinary tract infections.

  • Notable strains include E. coli O157:H7 (hemorrhagic colitis).

Shigellae

  • Causes severe acute diarrhea; transmission occurs in low numbers.

Vibrio cholerae

  • Causes cholera with severe watery diarrhea; endemic in areas lacking clean water.

Campylobacter

  • Leading cause of human enteritis, major symptoms include fever and bloody diarrhea.

Pseudomonas

  • Opportunistic pathogen; infections are resistant to many antibiotics.

Haemophilus influenzae

  • Part of nasopharyngeal flora; can cause invasive infections, particularly in children.

Helicobacter pylori

  • Chronic gastritis; linked to stomach ulcers.

  • Treatable with triple therapy (antibiotics combined with proton pump inhibitors).

Bordetella pertussis

  • Cause of whooping cough; prevention via vaccination.