Gram Negative Bacteria

Gram Negative Unique Features

red/pink, endotoxin/LPS, outer membrane & inner membrane

E. Coli 

Gram Stain: Red/Pink

Shape: Rods/Bacilli

Clinical Manifestations:

• Gastroenteritis (diarrhea)

• Neonatal Meningitis 

• UTIs (causes >80% of all UTIs) → usually we pee out E. Coli but some persist in the bladder if P-pili on bacteria binds gal-gal receptor in bladder so when it contracts it is not pushed out and immune response (WBCs) causes the irritation

  Toxins:

• ENDOtoxin = LPS → sepsis 

• EXOtoxins: 

  • Cholera Toxin = Traveler’s Diarrhea (watery diarrhea) → ETEC → stimulates adenylate cyclase which secretes electrolytes to bowel lumen & water follows

  • Shiga Toxin = Bloody Diarrhea (0157:H7) & Hemolytic Uremic Syndrome → EHEC → targets tRNA, disrupts protein synthesis = cell death and blood released

Notes: Fast Growth (20-30 min doubling time); Normal gut flora

Salmonella

Gram Stain: Red/Pink

Shape: Rods/Bacilli

Pseudomonas

Gram Stain: Red/Pink

Shape: Rods/Bacilli

Clinical Manifestations:

• Burn/Wound Infections

• Lungs in Cystic Fibrosis patients 

• Otitis Externa (swimmers ear) 

• UTI w/ catheter

Toxins:

• ENDOtoxin = LPS → sepsis → Ecthyma Gangrenosum (a rare skin infection that causes rapidly progressing lesions that lead to necrotic ulcers)

• EXOtoxin A = cell death (halts protein synthesis via ADP ribosylation of EF-2 which is part of translation)

Notes: CGD patients are susceptible b/c it is Catalase +; From Environment; Fast growth; Biofilm formation (antibiotic choice based on this); Green color b/c it produces pyocyanin

Haemophilus

Gram Stain: Red/Pink

Shape: Rods/Coccobacilli

Neisseria

Gram Stain: Red/Pink

Shape: Diplococci

Types: N gonorrhoeae & N meningitidis

Campylobacter

Gram Stain: Red/Pink

Shape: Curved Rods/Vibrio