Lab 5: Ecoli and coliforms

Question 1

Describe characteristics of coliforms

Answer 1

1) motile
2) facultive anaerobes
3) used to predict the presence of fecal contamination
4) Rod shaped
5) Used to ferment lactose

Question 2

What are the characteristics of Ecoli?

Answer 2

1) One of the most widely studied microbes in the world
2) Located in the gut microflora of cattle, and sheep
3) Prone to contaiminating meats
4) CDC recommends that you cook beef to 14 degrees celsius before eating
5) Serotypes of ecoli are distinguished based on surface antigens such as:
O-lipopolysaccaride
H-Flagella
K-Capsule

Question 3

What are the Ecoli Subgroups

Answer 3

1) Shiga toxin producing Ecoli (STEC)
Subspecies:Enterhemmoragic Ecoli (EHEC): Causes hemolytic uremic syndrome
does not ferment sorbitol
Ex: O157 ecoli
2) Enteropathogenic ecoli
causes lesions in cells and invades them
causes severe diareah in infants especially in developing countries
3)Enterotoxigenic ecoli
causes diareah in travelers known as travelers diareah
toxin is resistant to heat
4) Enteroinvasive Ecoli
can pass through intestinal epilitheal wall of intestine leading to nonbloody diareah and dysentry

Question 4

List the public health concerns

Answer 4

Shiga toxin producing Ecoli causes 265000 illnesses each year and 36 percent is caused by Ecoli. 5- 10 percent of these illnesses develop hemolytic uremic syndrome (especially children).

Question 5

Describe features of food borne infection:

Answer 5

Takes 3-4 days to colonize and 5-7 day to disappear.

Question 6

What is mackonkey agar and what are it’s features? What type of organisams can grow in it?

Answer 6

1) can be used to select and diffrentiate microorganisams such as Gram - bacteria which ferment lactose
2) Crystal violet dye and bile salts are used to prevent growth of gram + bacteria (Competing bacteria)
3) lactose used for fermentation
4) Neutral red (pH 7) and the pink color is less than 6.8

Organisams that ferment lactose can grow in this media which include
klebisella species, escherichia coli, and citrobacter species

Question 7

Describe what the three modifications to maconkey agar are:

Answer 7

Sorbitol mackonkey agar:
Mackonkey agar containing sorbitol instead of lactose, Ecoli -O157 will produce colorless colonies in this type of agar
Mackonkey agar without crystal violet: This does not contain any crystal violet to prevent gram positive bacteria from forming so it’s a less selective media for microbes
Mackonkey agar with without salt to control swarming or clusters of the bacteria proteus from forming

Question 8

Describe the advantages and disadvantages of using petri films

Answer 8

Advantages: light, easy to use, don’t need to autoclave, and you don’t need to spread plate
Disadvantage: Much more expensive than conventional plating, using petri dishes and autoclaving procedures.
This is why they are not always used in the lab

Question 9

What is the purpose of the experiment?

Answer 9

Purpose of experiment is to seperate Escerichia Ecoli and colforms form beef, lettuce and sprouts using Mackonkey agar and petri films.

Question 10

Materials

Answer 10

1) petrifilms
2) mackonkey agar petri dish plates
3) lettuce
4) beef
5) Sprouts
6) Peptone water
7) Micropipettes
8) Loop

Question 11

Describe the procedure of the experiment:

Answer 11

1) collect 25 gram sample of beef, sporuts and lettuce and 1)homogenize it to 100ul of peptone water for 60 seconds.
2) Make 3 1:10 dilutions of peptone water and from 10^0 to 10^-3 and and 100ul of peptone water to three mackonkey agar petri dishes and spread plate them. Duplicate each one of them
3) Pour solution from 10^-2 and 10^-3 tubes onto petri film plates. Duplicate each one of these
4) Incubate samples at 37 degrees celsius for 24 hours and then refrigerate them for 1 week.