enterobactecteria

Gram-Negative Pathogens Overview

Table of Gram-Negative Pathogens

1. Gram-Negative Rods
  • Aerobes (Do not ferment carbohydrates):
    • Pseudomonas
    • Burkholderia
    • Bordetella
    • Francisella
    • Alcaligenes
2. Facultative Anaerobes (Ferment carbohydrates)
  • Lactose Fermenting:
    • Escherichia
    • Klebsiella
    • Citrobacter
    • Enterobacter
3. Non-Lactose Fermenting
  • Oxidase-Negative:
    • Salmonella
    • Shigella
    • Proteus
    • Providencia
    • Morganella
    • Hafnia
    • Edwardsiella
    • Serratia
    • Yersinia

Details on Key Pathogens

Enterobacteriaceae Family

Yersinia Species
  • Yersinia enterocolitica:
    • Causes inflammation of the ileum and abdominal pain that mimics appendicitis.
  • Yersinia pestis:
    • Transmission: Carried by rat fleas.
    • Disease caused: Plague
    • Bubonic plague: Infection and necrosis of lymph nodes.
    • Septicemic plague: Also known as the “Black Death,” involves bacterial growth in the blood, leading to subcutaneous hemorrhage and skin darkening.
    • Pneumonic plague: Infection of the lungs; can be fatal.
Yersinia Pestis Characteristics
  • Gram-negative Enterobacteriaceae.
  • Spread throughout Europe in the 14th century causing high mortality (approximately one-third of Europe’s population).
  • Still endemic in various regions, particularly in Africa.

Salmonella and Shigella

  • Associated with foodborne illnesses and fever due to lipid A endotoxin.
Salmonella
  • Reservoir: Poultry.
  • Causes: Typhoid fever.
  • Symptoms:
    • Headache
    • Malaise
    • Muscle aches
    • Dizziness
    • Loss of appetite
    • Nausea
    • Abdominal pain.
    • Diarrhea or constipation may occur.
  • Complications: Possible intestinal perforation, intestinal bleeding, confusion, delirium, or rarely coma.
  • Treatment: Antibiotics.
  • Prevention: Typhoid vaccine.
Shigella
  • Transmission: Carried by humans causing bacillary dysentery.
  • Symptoms:
    • Patches of blood and mucus in the small intestine lining.

Escherichia coli

  • Nosocomial Pathogen: Causes infections while hospitalized.
  • Lactose Fermenting
  • Coliform Bacteria: Involved in various infections.
  • Key Strain: E. coli O157:H7
    • Causes bloody diarrhea, hemolytic uremic syndrome (HUS), kidney failure, and death.
    • Particularly associated with fast food and hamburgers.

Aerobic Gram-Negative Nonenteric Bacilli

  • Characteristics:
    • Large group of non-spore-forming bacteria.
    • Live in diverse habitats: large intestines, zoonotic sources, respiratory tracts, soil, and water.
  • Medical Significance:
    • Most are non-pathogenic; some act as true pathogens or opportunists.
    • Outer Membrane Lipopolysaccharide: Functions as an endotoxin.
    • Pseudomonas and Burkholderia: Opportunistic pathogens.
    • Brucella and Francisella: Zoonotic pathogens.
    • Bordetella and Legionella: Primarily human pathogens.
Pseudomonas aeruginosa
  • Environmental Presence: Frequently nosocomial, very resistant to disinfectants and drugs.
  • Characteristics:
    • Contaminates ventilators, IV solutions, and anesthesia equipment.
  • Opportunistic Pathogen: Common in 10% of normal human intestinal flora.
  • Notable Feature: Produces green pigment (pyocyanin) and exhibits UV fluorescence.
  • Infection Risks: Causes dermatitis, especially in burn patients and swimmer’s ear.
Genus Alcaligenes
  • Location: Soil and water, may become normal flora.
  • Common Species: Alcaligenes faecalis, associated with pneumonia, septicemia, and meningitis.

Bordetella pertussis

  • Description: Minute, encapsulated coccobacillus.
  • Causes: Pertussis or whooping cough.
  • Complications: Severe, life-threatening in infants.
  • Reservoir: Asymptomatic carriers.
  • Transmission: Direct contact or inhalation of aerosolized droplets.
Virulence Factors
  • Mechanisms of Action:
    • Receptors that recognize and bind to ciliated respiratory epithelial cells.
    • Toxins destroy and dislodge ciliated cells, leading to mucus buildup and airway blockage.
  • Prevention: Vaccination with DTaP (acellular).

Legionella pneumophila

  • Description: Causes Legionnaire's disease and Pontiac fever.
  • Environment: Found in sources of standing water such as cooling towers and HVAC systems.
Clinical Distinctions
  • Legionnaires' Disease (More Severe):
    • Affects primarily males over 50; nosocomial disease in elderly patients.
    • Symptoms include fever, cough, diarrhea, abdominal pain.
    • Pneumonia Fatality Rate: Ranges from 3-30%.
    • Treatment: Levofloxacin or Azithromycin.

Hemophilus influenza Type b

  • Causes: Meningitis, epiglottitis, ear infection, pneumonia, and bronchitis.
    • Treatment: Combination of chloramphenicol and ampicillin.
    • Prevention: Routine Hib vaccination recommended for children.

Concept Check

Question

  • The main reservoir for Pseudomonas aeruginosa is:
    • A. Soil and water
    • B. Infected individuals
    • C. Asymptomatic carriers
    • D. Wild animals

Answer

  • Answer: A