Enterobacterales

Question 1

Identify sites where Enterobacterales members are considered “usual flora” and where they would be considered always pathogenic.

Answer 1

“Normal flora” of intestinal tract
Relatively uncommon “normal flora” of other areas
*May be found in any anatomical site
Found in nosomical infections
Soil, water, plants, etc
Resistant to multiple antimicrobials

Question 2

Recognize the biochemical and phenotypic characteristics that are common among all Enterobacterales members.

Answer 2

Straight GNRs
Facultative anaerobes
Peritrichous flagella (if motile)
Ferment glucose
Nitrates reduced to nitrites
Oxidase negative
Grows well on MAC

Question 3

Phenotypic characteristics of Enterobacterales, more specifically

Answer 3

Large, smooth, grey colonies on SBA – rather non-specific
May/may not be hemolytic
GS not helpful in ID
Smell!!!

Question 4

List the factors which contribute to the pathogenicity of Enterobacterales organisms.

Answer 4

Endotoxins
Exotoxins, including enterotoxins
Adherence to epithelial cells
Capsules
Colonization
Invasiveness
Antigens
Hemolysins & enzymes

Question 5

Explain the reasons for serotyping enteric pathogens and list which pathogens require typing.

Answer 5

1. ID of isolate – the need to differentiate between closely related organisms
2. Epidemiologic “fingerprinting”: able to track an infection or identify where it was acquired

Enteric pathogens:
1. Salmonella
2. Shigella
3. Enterohemorrhagic E. coli (EHEC/STEC)

Question 6

Discuss the major properties of the somatic, flagellar and capsular antigens.

Answer 6

Somatic antigen (O)
*Part of cell wall
*Heat stable
Flagellar antigen (H)
*Proteins
*Heat stable
Capsular antigen (K)
*Polysaccharide
*Heat labile
*May block O antigen