Enterobacteriacae

Gram-Negative Pathogens Overview

Gram-Negative Rods

• Aerobes: Do not ferment carbohydrates.

  • Examples:

    • Pseudomonas

    • Burkholderia

    • Bordetella

    • Francisella

    • Alcaligenes

Facultative Anaerobes

• Ferment carbohydrates:

  • Lactose fermenting:

    • Examples:

      • Escherichia

      • Klebsiella

      • Citrobacter

      • Enterobacter

Non-Lactose Fermenting

• Oxidase-negative:

  • Examples:

    • Salmonella

    • Shigella

    • Proteus

    • Providencia

    • Morganella

    • Hafnia

    • Edwardsiella

    • Serratia

    • Yersinia

Enterobacteriaceae Family

Yersinia Species

• Y. enterocolitica: Causes inflammation of the ileum and abdominal pain, mimicking appendicitis.

• Y. pestis:

  • Transmission: Carried by rat fleas.

  • Causes: Plague

    • Bubonic plague: Infection and necrosis of lymph nodes.

    • Septicemic plague: Bacterial growth in blood; causes hemorrhage and skin darkening.

    • Pneumonic plague: Infection of lungs; often fatal.

Historical Significance of Yersinia Pestis

• Major contributor to the Black Death in the 14th century, devastating Europe's population.

• Still endemic in parts of the world, particularly Africa.

Salmonella and Shigella

Salmonella

• Reservoir: Poultry.

• Causes: Typhoid fever.

  • Symptoms: Fever, headache, malaise, muscle aches, dizziness, loss of appetite, nausea, abdominal pain, diarrhea or constipation. Severe complications can include intestinal perforation and bleeding.

• Treatment: Antibiotics.

• Prevention: Typhoid vaccine.

Shigella

• Transmitted by humans, causes bacillary dysentery.

• Symptoms: Blood and mucus in stool.

E. coli and Other Gram-Negative Infections

E. coli O157:H7

• Associated with severe foodborne illnesses including bloody diarrhea and hemolytic uremic syndrome.

• Linked with fast food contamination, particularly hamburgers.

Other Enteric Bacilli

• Infections can also be caused by Proteus, Citrobacter, Enterobacter, Klebsiella, and Serratia.

Aerobic Gram-Negative Nonenteric Bacilli

General Characteristics

• Large, diverse group, mostly non-spore-forming bacteria.

• Habitats include soil, water, and the respiratory system.

• Many are opportunistic pathogens; some are true pathogens.

• All have lipopolysaccharide endotoxin in their outer membrane.

Notable Pathogens

• Pseudomonas: Opportunistic pathogen that is very resistant to antibiotics and disinfectants.

• Burkholderia: Can cause infections, environmental opportunists.

• Brucella & Francisella: Zoonotic pathogens.

• Bordetella & Legionella: Primarily affect humans.

Specific Pathogens

Pseudomonas aeruginosa

• Opportunistic pathogen, frequent nosocomial infections.

• Characteristics: Produces green pigment, highly resistant to chemicals.

• Causes infections in burn patients and swimmer's ear.

Genus Alcaligenes

• Found in soil and water, can be normal flora.

• Alcaligenes faecalis: Most common clinical species; associated with opportunistic infections.

Bordetella pertussis

• Characteristics: Minute, encapsulated coccobacillus.

• Causes: Whooping cough (pertussis).

• Transmission: Direct contact or inhalation of aerosols.

Virulence Factors

• Receptors for binding to respiratory cells, toxins that damage ciliated cells leading to mucus buildup.

• Vaccine: DTaP.

Legionnaires’ Disease

Characteristics

• Caused by Legionella pneumophila; associated with standing water sources.

• Symptoms of pneumonia vary; can lead to severe complications.

• Treatment: Levofloxacin or Azithromycin.

Other Important Bacterial Infections

Hemophilus influenzae Type B

• Causes meningitis, epiglottitis, ear infections, pneumonia, bronchitis.

• Treatment: Combination of chloramphenicol and ampicillin.

• Prevention: Hib vaccination recommended for children.

Concept Check

• Main Reservoir for Pseudomonas aeruginosa: Soil and water (Correct Answer: A)