Enterobacteriaceae: Media & Identification Tests
Enterobacteriaceae: Media & Identification Tests (9831-11)
Continue your study of this challenging family of organisms by considering the differential properties of selective media and other identification techniques. MacConkey, Xylose, Lysine, Deoxycholate, Salmonella-Shigella, Hektoen Enteric, Bismuth Sulfite agars (and many more) are discussed. Learn what results to expect when various biochemical tests such as carbohydrate fermentation, triple sugar iron, ONPG, Voges Proskauer, IMViC Series, and Urea Motility Indole are used, and describe the appearance of those organisms that do grow.
| Code |
9831-11 |
| Niveau |
Fondamental |
Prix membres
$0
Prix non-membres
$135
Renseignements additionnels
PEP hours: 7
CPS/ART credits: 0
Learning Outcomes:
Media for Isolation of Enterobacteriaceae
· List the four groups of media used for isolation of enteric pathogens from fecal cultures.
· Name the medium from group 1 most commonly used in clinical laboratories.
· List the three media included in group 2 in order of selectivity.
· List the three media included in group 3 and why a medium of this group would be used.
· List the three media included in group 4.
MacConkey Agar
· Name the selective ingredients and state what bacteria will grow on this medium.
· Describe the differential properties.
Xylose-Lysine-Deoxycholate Agar
· Describe the use of XLD in isolation of Salmonella and Shigella.
· Describe the differential properties under the headings:
· carbohydrates present and pH indicator
· Appearance of colonies that do not ferment any of the carbohydrates (Shigella)
· Appearance of colonies fermenting xylose and decarboxylating lysine (Salmonella)
· Appearance of most normal flora Enterobacteriaceae
· Appearance of colonies producing H2S
Salmonella-Shigella Agar
· Name the three selective ingredients and describe the selectivity.
· Describe the differential properties and state the appearance of:
· Lactose fermenters
· Nonlactose fermenters
· H2S positive colonies
Hektoen Enteric Agar
· Name the inhibitory agent and describe the selectivity.
· Describe the differential properties under the headings:
· Carbohydrates and pH indicators
· Appearance of colonies that ferment carbohydrate(s)
· Appearance of colonies that do not ferment any of the three carbohydrates (Salmonella and Shigella)
· Appearance of H2S positive colonies
Bismuth Sulfite Agar
· Name the selective ingredients and describe the selectivity.
· Describe the appearance of Salmonella colonies.
Selenite
· Describe the principle and explain why subculture should not be delayed beyond 24 hours.
Tetrathionate
· Explain why iodine must be added to the medium just before use.
Gram Negative Broth
· Describe the selective properties.
· Compare the three enrichment media under the following headings:
· Inhibition of normal fecal flora
· Ability to isolate Salmonella and Shigella
· List a suitable selection of media for fecal cultures.
Identification Tests for Enterobacteriaceae
· List three reasons for using conventional tests.
Carbohydrate Fermentation Tests
· State what information may be obtained from carbohydrate fermentation tests.
· Explain what may happen when test media are overheated during preparation and how this can be avoided.
· Using phenol red broth base, describe results for:
· No growth
· Negative test
· Aerogenic fermentation
· Anaerogenic fermentation
· Describe the appearance and explain the cause of reversion.
Triple Sugar Iron Agar
· List the following ingredients:
· Sugars and pH indicator
· H2S detection system
· Describe the following results and give a suitable code for recording:
· Glucose only fermented
· Lactose and/or sucrose fermented
· Aerogenic and anaerogenic fermentation
· H2S production
· No fermentation
· State how the following may affect results:
· Shallow butt
· Tight cap
· Over incubation
· Under incubation
· State how Kligler’s iron agar differs.
Orthonitrophenyl-Beta-D-Galactosidase Test
· Name the two enzymes required in the initial stage of lactose fermentation and state which is detected in the ONPG test.
· Describe the three categories of lactose fermentation for Enterobacteriaceae and state the enzymes involved and the ONPG result for each.
· Name the end product detected and appearance of a positive and negative test.
Indole Test
· State suitable media for the test.
· Name the two reagents used for detection of indole, state how each is used, the appearance of a positive test and the advantage of each reagent.
· Describe the procedure for the spot indole test.
Voges-Proskauer Test
· State the end products of the two main carbohydrate fermentation pathways and state which is detected by the VP test.
· Name the test medium, reagents used and describe appearance of a positive and negative test.
· Outline the procedure for rapid detection of acetoin.
Citrate Test
· Describe the principle of the test to include:
· Test medium
· pH indicator
· Appearance of positive and negative tests
· Effect of oxygen on results
Malonate Test
· Describe the principle of the test and results indicating positive and negative results.
Urease Test
· Describe the principle of the test including:
· Test medium
· pH indicator
· Results indicating positive and negative results
· Describe the difference in sensitivity of urea broth and Christensen’s urea agar.
Phenylalanine Deaminase Test
· Describe the principle of the test to include:
· Test medium
· Reagent
· Results indicating positive and negative tests
· State how results correlate with tryptophan deaminase results.
Decarboxylase Tests
· Describe the principle of the test including:
· Test medium
· Results indicating positive and negative tests
· Explain what the control tube is and state expected results for Enterobacteriaceae.
· Explain why the tests are layered with oil and how over incubation affects results.
Lysine Iron Agar
· Describe the use and interpretation.
Urea Motility Indole Medium
· Describe the use and interpretation.
Instructor: Helen Smith, MLT
Prerequisites: Enterobacteriaceae (9830-11)
Textbook: N/A
Equipment: Computer with Internet is required
Start Date: Upon registration
Completion: Up to 52 weeks
Version Date: December 2011