Gram Negative Bacteria Flashcards Preview

FDN3 By Nathan and Minnie > Gram Negative Bacteria > Flashcards

Flashcards in Gram Negative Bacteria Deck (201)
Loading flashcards...
1

What are some of the distinctive characteristics of the Enterobacteriaceae family?

  • 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 (-) 

2

Which members of the enterobacteriaceae family cannot ferment glucose? 

Salmonella

Shigella

Proteus

3

Escherichia coli are... [Gram stain, metabolism, shape distinctive morphology]

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

4

List the 5 subtypes of E. coli

ETEC = Enterotoxigenic

EHEC = Enterohermorrhagic

EPEC = Enteropathogenic

EIEC = Enteroinvasive

EAEC = Enteroaggregative

5

What is significant about an organism that turns MacConkey agar pink?

The organism ferments lactose

6

List the determinants of pathogenicity that apply to all E. coli subtypes

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

7

What dieseases are commonly associated with E. coli infection?

Meningitis

UTI

Septic Shock

Nosocomial infections

Diarrhea (5 types)

8

How is an E. coli infection diagnosed?

Culturable on routine media

EMB agar: appears metallic green

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

9

How are UTI and kidney infections caused by E. coli treated?

Trimethoprim/sulfamethoxazol

nitrofuratoin

fosfomycin

10

What are the determinants of pathogenicity of ETEC?

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

 

11

Describe an ETEC infection

Enterotoxigenic diarrhea

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

12

How is ETEC infection diagnosed?

ETEC grows cultures from stools

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

13

An E. coli strain positive for ST and LT is most likely.. 

ETEC

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

14

How is ETEC infection treated?

Rehydration

Ciprofloxacin or other fluroquinolone

15

How can ETEC infection be prevented?

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

16

Describe the Type III Secretion System

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

17

What are the determinants of pathogenicity of EHEC?

  • 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

18

Describe an EHEC infection

Enterohemorrhagic diarrhea E. coli

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

19

What is hemolytic-uremic syndrome?

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

20

What distinguises EHEC from other E. coli strains?

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

21

How is EHEC infection treated?

Rehydration

(do NOT use antibiotics)

22

How can EHEC infection be prevented?

Avoid undercooked meat and unpasteurized diary or juice

23

Infection with which E. coli subfamily is associated with consumption of raw meat?

EHEC (enterohemorrhagic)

24

Where is the reservoir for EHEC?

Cattle

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

25

Describe an EPEC infection

Enteropathogenic E. coli

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

26

What are the determinants of pathogenicity of EPEC?

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)

27

Describe the mechanism of action of EPEC infection

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

28

Where are EPEC and EIEC most commonly found?

Outside of the United states

Causative agents of diarrhea in developing countries

29

Describe EAEC infection

Diarrhea in developing countries 

(Rarely seen in the USA)

30

Which E. coli determinant of pathogenicity is associated with sepsis?

LPS