Lab 7

Question 1

Normally, food products contain members of the genus Salmonella.
True or False?

Answer 1

False.
Normally, food products do not contain members of the genus Salmonella. When such bacteria are found, they are considered a public health hazard since they may cause severe gastrointestinal disorders.

Question 2

Normally, food products do not contain members of the genus Salmonella.
True or False?

Answer 2

True.
When such bacteria are found, they are considered a public health hazard since they may cause severe gastrointestinal disorders.

Question 3

Not all Salmonella strains are potentially pathogenic.
True or False?

Answer 3

False.
Although certain strains of the genus are considered more virulent than others, all species should be treated as potential pathogens.

Question 4

All Salmonella strains are potentially pathogenic.
True or False?

Answer 4

True.
Although certain strains of the genus are considered more virulent than others, all species should be treated as potential pathogens.

Question 5

How are Salmonella mainly distributed?

Answer 5

Either directly or indirectly by fecal contamination.

They are frequently associated with other bacteria that inhabit the intestinal tract of humans and other animals.

Question 6

Why are the procedures for the isolation and identification of Salmonella complex?

Answer 6

Because they share characteristics to bacteria of the following genera: Escherichia, Enterobacter, Proteus, Serratia, and Shigella.

Question 7

What do the procedures for the isolation and identification of Salmonella and E. coli involve? [4]

Answer 7

• Pre-enrichment (of processed foods)
• Enrichment
• Plating on selective agar media
• Biochemical and serological tests

Question 8

Why is the enrichment process carried out in Salmonella isolation and identification?

Answer 8

To encourage the growth of Salmonella and eliminate or inhibit the growth of competitive organisms that would normally outgrow Salmonella.

Question 9

Name 3 options of enrichment broths and/or selective media that have been suggested for use in the isolation of Salmonella.

Answer 9

• Tetrathionate broth
• Brilliant green agar
• Salmonella-Shigella agar

Question 10

What is a differential medium commonly used for Salmonella?

Answer 10

Triple sugar iron agar (TSI)

Question 11

What is TSI agar used for?

Answer 11

To differentiate between members of the Enterobacteriaceae.

Question 12

How are bacteria differentiated by TSI? [2]

Answer 12

• The ability to ferment glucose and either lactose or sucrose
• The abilty to produce hydrogen sulfide (H2S)

Question 13

How can a positive confirmation of Salmonella be obtained?

Answer 13

Serological testing (e.g., agglutination tests and fluorescent microscopy)

Question 14

Standard methods for identifying Salmonella require a minimum of […].

Answer 14

Standard methods for identifying Salmonella require a minimum of 4 days.

Question 15

What are coliforms?

Answer 15

• Includes E. coli
• Gram-negative rods
• Typically reside in intestines of humans and animals
• May be associated with enteric pathogens
• Their presence in a food sample may be indicative of fecal contamination and a potential health risk to consumers.

Question 16

What has been recommended as an indicator organism since 1905 by the American Public Health Association?

Answer 16

• E. coli
• A normal inhabitant of the intestinal tract of birds and animals who may excrete as many as 10^10 organisms/day.

Question 17

Describe how E. coli colonies appear on EMB plates.

Answer 17

• Nucleated with or without a metallic sheen

Question 18

How are typical E. coli colonies (on EMB) confirmed?

Answer 18

• Gram staining
• IMViC reactions (biochemical tests including: indole production, methyl red, voges proskauer, and citrate utiliztaion)

Question 19

What organism is recognized as a cause of hemorrhagic colitis and hemolytic uremic syndrome?

Answer 19

E. coli 0157:H7

Question 20

How is presence of E. coli 0157:H7 confirmed?

Answer 20

• Biochemical attribute - lack of the enzyme beta-glucoronidase
• Interference by other enteric organisms prevents complete identification, so immunological tests must be performed on suspect colonies for confirmation.

Question 21

What is TSB?

Answer 21

• Tryptic soy broth enrichment broth
• A nutritious media that supports the growth of a variety of microbes.
• E. coli enrichment

Question 22

What is buffered peptone water?

Answer 22

• Buffered peptone water is used as a pre-enrichment broth for the isolation of Salmonella from foods.
• The conditions of the media allows for resuscitation of injured or stressed cells (low numbers and/or sub-lethally injured Salmonella spp. cells may be present in a test food sample.
• It is a non-selective pre-enrichment media.

Question 23

What is tetrathionate broth with added iodine and brilliant green used for?

Answer 23

• Selective medium for the isolation of Salmonella.
• The salts, iodine and brilliant green inhibit most other bacteria.