Lab 7 Flashcards
Normally, food products contain members of the genus Salmonella.
True or False?
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.
Normally, food products do not contain members of the genus Salmonella.
True or False?
True.
When such bacteria are found, they are considered a public health hazard since they may cause severe gastrointestinal disorders.
Not all Salmonella strains are potentially pathogenic.
True or False?
False.
Although certain strains of the genus are considered more virulent than others, all species should be treated as potential pathogens.
All Salmonella strains are potentially pathogenic.
True or False?
True.
Although certain strains of the genus are considered more virulent than others, all species should be treated as potential pathogens.
How are Salmonella mainly distributed?
Either directly or indirectly by fecal contamination.
They are frequently associated with other bacteria that inhabit the intestinal tract of humans and other animals.
Why are the procedures for the isolation and identification of Salmonella complex?
Because they share characteristics to bacteria of the following genera: Escherichia, Enterobacter, Proteus, Serratia, and Shigella.
What do the procedures for the isolation and identification of Salmonella and E. coli involve? [4]
- Pre-enrichment (of processed foods)
- Enrichment
- Plating on selective agar media
- Biochemical and serological tests
Why is the enrichment process carried out in Salmonella isolation and identification?
To encourage the growth of Salmonella and eliminate or inhibit the growth of competitive organisms that would normally outgrow Salmonella.
Name 3 options of enrichment broths and/or selective media that have been suggested for use in the isolation of Salmonella.
- Tetrathionate broth
- Brilliant green agar
- Salmonella-Shigella agar
What is a differential medium commonly used for Salmonella?
Triple sugar iron agar (TSI)
What is TSI agar used for?
To differentiate between members of the Enterobacteriaceae.
How are bacteria differentiated by TSI? [2]
- The ability to ferment glucose and either lactose or sucrose
- The abilty to produce hydrogen sulfide (H2S)
How can a positive confirmation of Salmonella be obtained?
Serological testing (e.g., agglutination tests and fluorescent microscopy)
Standard methods for identifying Salmonella require a minimum of […].
Standard methods for identifying Salmonella require a minimum of 4 days.
What are coliforms?
- 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.
What has been recommended as an indicator organism since 1905 by the American Public Health Association?
- E. coli
- A normal inhabitant of the intestinal tract of birds and animals who may excrete as many as 10^10 organisms/day.
Describe how E. coli colonies appear on EMB plates.
- Nucleated with or without a metallic sheen
How are typical E. coli colonies (on EMB) confirmed?
- Gram staining
- IMViC reactions (biochemical tests including: indole production, methyl red, voges proskauer, and citrate utiliztaion)
What organism is recognized as a cause of hemorrhagic colitis and hemolytic uremic syndrome?
E. coli 0157:H7
How is presence of E. coli 0157:H7 confirmed?
- 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.
What is TSB?
- Tryptic soy broth enrichment broth
- A nutritious media that supports the growth of a variety of microbes.
- E. coli enrichment
What is buffered peptone water?
- 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.
What is tetrathionate broth with added iodine and brilliant green used for?
- Selective medium for the isolation of Salmonella.
- The salts, iodine and brilliant green inhibit most other bacteria.
