Enterobacteriaceae PART1

Question 1

Sites where members of the enterobaacteriaceae are considered “usual flora”

Answer 1

GI tract, uncommon normal flora of other areas

Question 2

Sites where members of the enterobacteriaceae are considered always pathogenic

Answer 2

Normally sterile areas

Question 3

Characteristics that are common among all members of Enterobacteriaceae

Answer 3

1. GNR - straight
2. Facultative anaerobes
3. Peritrichous flagella (if motile)
4. Ferment glucose
5. Nitrates reduced to nitrites
6. Oxidase negative
7. Grow well on Mac agar

Question 4

What Enterobacteriaceae generally look like on a SBA

Answer 4

Large, smooth, grey colonies on SBA

Question 5

Factors which contribute to pathogenicity of Enterobacteriaceae (8)

Answer 5

1. Endotoxins
2. Exotoxins
3. Invasiveness
4. Adherence to epithelial cells
5. Capsules
6. Colonization
7. Certain antigens
8. Hemolysins/ Enzymes

Question 6

When trying to isolate from areas with normal flora you may need to….?

Answer 6

Add several types of differential and selective media

- stool- MAC, HECK, XLD for example

Question 7

5 identification schemes of identifying Enterobacteriaceae

Answer 7

1. Crosshatch/checkerboard
2. Grouping systems
3. Branching Flow Diagrams
4. Numerical coding systems

Question 8

Problem with crosshatch/ checkerboard methods

Answer 8

Accurate but tedious

Question 9

Problem with Grouping Systems (Edwards and Ewing)

Answer 9

Quicker but additional material may be needed

Question 10

Problem with Branching Flow Diagrams

Answer 10

Simple but dangerous

-atypical organisms may be misidentified

Question 11

Problem with coding systems

Answer 11

Need to use your brain not rely strictly on the number identification

Question 12

Purpose of serologic typing

Answer 12

• identification of isolate

- Epidemiologic “fingerprinting” (helps trace where its coming from)

Question 13

Most frequently serotyped GNRs

Answer 13

Salmonella
Shigella
Escherichia coli (selective isolates)

Question 14

Serologic Typing Antigenic Structure

- K (name and 3 facts)

Answer 14

Capsular antigen

• polysaccharide
• heat labile
• may block O antigen

Question 15

Serologic Typing Antigenic Structure

- H (name and two facts)

Answer 15

Flagellar antigen

• protein
• heat labile

Question 16

Serologic Typing Antigenic Structure

- O ( name and two facts)

Answer 16

Somatic antigen

• part of cell wall
• heat stable

Question 17

Serologic Typing

• what media
• what antisera
• what to do if O group is blocked

Answer 17

• non-sugar containing and non-selective media (tsoy, sea)
• Polyvalent antisera
• boil organism and retype (because of capsule present)

Question 18

Problems involved with the treatment of infections from Enterobacteriacea

Answer 18

• High mortality rate for GN septicemia
• antimicrobial resistance due to not taking all of antibiotics
• Potentially harmful effects of antimicrobials used for treatment