E.coli and Shigella

Question 1

Why is E.coli considered an indicator organism?

Answer 1

It is found in the guts of humans and cows. It’s presence in the water represents possible fecal contamination.

Question 2

What is the optimum growth temperature for E.coli? Why is it this particular temperature?

Answer 2

37 C. This is the temperature of the gut from humans and other mammals

Question 3

What is the infectious dose of <i>E. coli<i> O157:H7?</i></i>

Answer 3

1-10 cells. Crazy low!

Question 4

What are the 2 antigens targeted for E. coli serotyping? Where can these antigens be found?

Answer 4

See slide 5 for discussion of O- and H- antigens

Question 5

What is an “adulterant” in food? Is E. coli O157:H7 one of these?

Answer 5

An adulterant is a zero tolerance organism (no amount is allowed in the food). Yes- it is!

Question 6

What species of Shigella produces shiga toxin?

Answer 6

S. dysentery.

Question 7

What is the reservoir of Shigella?

Answer 7

Humans

Question 8

What are “pathotypes” of E. coli, and can you name a few?

Answer 8

This word refers to the different types of E. coli that exist, that can cause different types of diseases. See slide 4 for a few examples

Question 9

What are some typical food sources of E. coli O157:H7?

Answer 9

Ground beef is still tops (>50% of outbreaks), however fresh produce is rapidly on the rise (currently about 25% of outbreaks).

Question 10

What is the purpose of the carcass washer for minimizing E. coli O157:H7?

Answer 10

See slide 9; this is an antimicrobial wash (hot water, sometimes an organic acid) for killing E. coli that is on the hide of the animals

Question 11

What were some of the new policy changes that came out of the E. coli apple cider outbreak we discussed in class?

Answer 11

See slide 12; recognition that cider could be a vehicle for E. coli, as it was previously assumed that this organism couldn’t survive in such acidic environments.

Question 12

What are the “Big Six” E. coli?

Answer 12

The six serogroups of Shiga toxin-producing E. coli other than O157 that are common human disease isolates; serogroups O26, O45, O103, O111, O121, O145

Question 13

The reservoir of the Big Six E. coli is….

Answer 13

Cattle, and other ruminants (same as O157:H7). However as discussed in class, they seem to cause problems in a wider variety of foods than O157:H7. See slide 13.

Question 14

The genus “Shigella” refers to organisms that are genetically identical to …..

Answer 14

Escherichia coli

Question 15

Two differences (one phenotypic, and the other related to the reservoir) between Shigella and most other E. coli is:

Answer 15

See slide 17