Gram Negative Bacteria Flashcards Preview

• Gram negative
• Facultative anaerobes
• Form Bacilli and Cocobacilli
• Many are commensals of the human colon that cause disease under certain circumstances
• Most can ferment glucose
• Oxidase (-) 

Salmonella

Shigella

Proteus

Escherichia coli are gram negative, facultative aneroibic bacilli that are typically part of the normal flora of the human colon. 

They are catalase (+) and ferment lactose

ETEC = Enterotoxigenic

EHEC = Enterohermorrhagic

EPEC = Enteropathogenic

EIEC = Enteroinvasive

EAEC = Enteroaggregative

The organism ferments lactose

• Alpha-heymolysin: Pore-forming
• Aerobactin: Iron siderophore
• Polysaccharide capsulse: Inhibits phagocytosis
• Pili/fimbriae: Forms attachments 

Meningitis

UTI

Septic Shock

Nosocomial infections

Diarrhea (5 types)

Culturable on routine media

EMB agar: appears metallic green

MacConkey agar: turns the agar pink due to ability to ferment lactose

Trimethoprim/sulfamethoxazol

nitrofuratoin

fosfomycin

2 toxins that are plasmid encoded and act on gut epithelial cells

• Heat labile (LT): An A-B Toxin, increases cAMP 
  • Similar to cholera toxin
• Heat stable (ST): Increases cGMP

Enterotoxigenic diarrhea

• "traveller's diarrhea"
• Watery stools
• 24-72 hr incubation period
• Spread through food and water contaminated with human wasta

ETEC grows cultures from stools

ELISA PCR available for ST and LT, but is not commonly used

ETEC

• Causes enterotoxigenic diarrhea
• "Traveler's diarrhea"
• Watery stools

Rehydration

Ciprofloxacin or other fluroquinolone

Avoid raw veggies, pre-peeled fruit, unpasturized dairy, lukewarm cooked foods 

Type III secretion systems...

• Form attachment and effacement lesions
• Replace normal microvilli with pedastals at the point of attachment
• Inject bacterial proteins into the cytoplasm of host cells by... 

1. Secretion apparatus is embedded into the host cell membrane
   -> Secretes toxins to the exterior of the bacterium
    
2. Several secreted proteins insert into the host cell membrane and form a translocation complex
   -> Translocates toxins into the host cytoplasm
    
3. Toxins have enzymatic activity, act as effector proteins

• Type III Secretion Systems
  • Injects toxin into host cell
• Shiga-like toxin
  • Inhibits 60s unit of the human ribosome
• Fimbriae
  • Forms attachment and effacement lesions

Enterohemorrhagic diarrhea E. coli

• Bloody diarrhea
• Crampy
• Absent or low-grade fever
• May lead to hemolytic-uremic syndrome (10% of case)

Accompanies ~10% of cases of EHEC; a result of shiga-like toxin

• Decrease in platelets
• Renal failure
  • Toxin damages endothelial cells in glomerulus -> Clumps of platelets form -> Causes lysis of RBCs
• CNS dysfunction

• Cannot ferment sorbitol
• Immunoassay for shiga-like toxin in stool
• O157:H7 serotype causes massive outbreaks

Rehydration

(do NOT use antibiotics)

Avoid undercooked meat and unpasteurized diary or juice

EHEC (enterohemorrhagic)

Cattle

Avoid infection by avoiding consumption of raw meat, unpasteurized dairy/juice

Enteropathogenic E. coli

• Associated wtih childhood diarrhea in developing countries
• Fever, bloody diarrhea

Enteropathogenic E. coli

• Bundle-forming pili
  • Responsible for initial attachment to intestinal epithelium
• Type III secretion system
  • Injects Tir into cell membrane
  • Acts as a receptor for intimin (an adhesin)

• Bacteria bind to intestinal epithelial cells using bundle-forming pili
  • Disruption of the overlying mucosa
    • Fever, bloody diarrhea

Outside of the United states

Causative agents of diarrhea in developing countries

Diarrhea in developing countries 

(Rarely seen in the USA)

LPS