Gamma Proteobacteria

Gram Negative Bacteria

Overview

  • Gram-negative bacteria are characterized by their thin peptidoglycan layer and outer membrane.

  • Includes both pathogenic and non-pathogenic species.

Non-Pathogenic Example

  • Thiomargaria: Not pathogenic.

Pathogenic Examples

  • Pseudomonas spp.

  • Shigella spp.

  • Legionella spp.

  • Escherichia spp.

  • Vibrio spp.

  • Proteus spp.

  • Haemophilus spp.

  • Yersinia spp.

  • Salmonella spp.

  • Klebsiella spp.

  • U-proteobacteria

Key Pathogen Characteristics

  • Pseudomonas:

    • CFTR Mutation affects water release in lung cells, allowing colonization.

  • Thiomargarita spp.:

    • Very large cells (>100mm).

Legionella spp.

Overview

  • Legionella pneumophila:

    • Most frequently isolated species causing legionellosis.

  • Fastidious organism requiring specific conditions.

Habitat

  • Lives in close association with amoebas for nutrients and moisture, helping form biofilm.

Vibro spp.

Overview

  • Transmission through the fecal-oral route.

Haemophilus spp.

Characteristics

  • Known as 'blood-loving' bacteria:

    • Inhabit mucous membranes of the upper respiratory tract, mouth, vagina, and intestines.

  • Require specific factors for growth:

    • X Factor (Hemo = blood, Filia = love)

    • NAD+ (V Factor)

Pathogenic Member

  • H. influenzae:

    • Causes acute bacterial conjunctivitis.

    • Not the causative agent of influenza.

Proteus spp.

Characteristics

  • Highly motile, exhibits a swarming growth pattern on agar plates.

  • Associated with:

    • Urinary tract infections (UTIs).

    • Wound infections.

    • Infant diarrhea.

  • Improper catheter installation can lead to UTI.

Salmonella spp.

Overview

  • Almost all members are pathogenic.

  • Common inhabitants of the intestinal tract.

    • Salmonella typhimurium causes typhoid fever.

Pathogenic Mechanism

  • Utilizes type III secretion system to inject effector proteins into host cells.

Transmission Sources

  • Reservoirs include:

    • Companion animals, wild animals, and birds.

  • Indirect transmission through fecal contamination of food, water, and environmental sources.

Virulence Factors

  • Virulence plasmids

  • Type 3 and Type 1 secretion systems

  • Superoxide dismutase

  • Fimbriae

  • Flagella

  • Vi antigen

  • Toxins

  • Lipopolysaccharides (LPS)

  • Biofilms

Shigella spp.

Overview

  • Causes dysentery; can obtain Shiga toxin gene from Shigella, leading to serious damage.

Yersinia spp.

Pathogenic Forms

  • Septicemic Plague: Infects circulatory system.

  • Pneumonic Plague: Infects lungs.

  • Does not infect the intestinal tract.

Klebsiella spp.

Characteristics

  • Commonly found in soil and water.

  • Produces a capsule, leading to secondary nosocomial infections.

    • Klebsiella pneumoniae: Causes severe pneumonia in humans.