Bacteriology/Food Science 324:
1999 QUIZ NO. 2

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I. MULTIPLE TRUE/FALSE (15 points). In the blank by each statement, place a + for a true statement or a O for a false statement. There can be any number of + or O statements. Do not change or qualify the wording of any statement in any way. Each is either true or false as stated. (1/2 point for each blank.)

EXAMPLES:

  O     Slides of stained smears must be discarded into the disinfectant.
  +     One always italicizes or underlines genus and species names when writing them in formal communications.

1.  Aseptic technique

        only applies when one is working with pathogenic organisms.
        allows one to drop the caps and plugs of the tubes onto the table as one transfers organisms from one tube to another.
        is followed when only the tip of the loop or needle is sterilized in the flame.

2.  The following are characteristics of all lactic acid bacteria:

        They are gram-positive organisms.
        They are strict anaerobes.
        They are very easy to cultivate in the laboratory by the use of simple media without the inclusion of many growth factors.
        They characteristically ferment glucose and lactose.

3.  Pseudocatalase is indicated by the following reactions when the benzidine and catalase tests are run at the same time:

        a positive benzidine reaction
        a negative benzidine reaction
        a positive catalase reaction
        a negative catalase reaction

4.  The addition of nitrate in the manufacture of sausage

        is done with the understanding that there will be organisms that will reduce it.
        requires the activity of lactic acid bacteria to assist in the ultimate adjustment of the color of the meat.
        always leads to "nitrite burn."
        is done to reduce the amount of NaCl which is added.

5.  Fecal coliforms

        and true coliforms are mutually exclusive (i.e., non-overlapping) groups of bacteria.
        are among the lactose-fermenting members of the Family Enterobacteriaceae.
        include Pseudomonas.

6.  The following are characteristics of all "enteric" bacteria:

        They are gram-negative organisms.
        Their natural habitat is the enteric (intestinal) canal of mammals.
        They are strict aerobes.
        They tend to deaminate amino acids and thereby cause an alkaline product to be formed aerobically in media containing peptones.
        They are positive in the tests for methyl red, hydrogen sulfide (H₂S), lysine decarboxylation and lactose fermentation.

7.  In the isolation procedure for Salmonella, the use of plating media containing neither lactose nor a pH indicator can assist in the detection and isolation of one or more of the following:

        typical non-lactose-fermenting strains of Salmonella
        atypical lactose-fermenting strains of Salmonella
        gram-positive bacteria

8.  The following are anaerobic reactions which can occur within colonies that are growing on plates which are incubated aerobically:

        amino acid deamination
        amino acid decarboxylation
        lactose fermentation
        hydrogen sulfide (H₂S) production

II. MATCHING (10 points).

1. In the blank by each item in column a, place the letter of the best-associated item from column b. Only one letter per blank. Any letter may be used any number of times or not at all. (One-half point for each blank.)

2. In the blank by each item in column a, place the letter of the best-associated item from column b. Only one letter per blank. Any letter may be used any number of times or not at all. (One-half point for each blank.)

III.  SHORT ANSWER (8 points).

1.  DEFINITIONS (3 points). Briefly define each of the of the following three terms. Please do not give examples as the only answers. Make sure your definitions apply specifically to these terms!

•  Indicator organism (In the general sense, not specifically referring to coliforms.)
  
  
•  Psychrotroph
  
  
•  Sherman Criteria (Just what is it and what's it for? You need not list all the specific "criteria.")
  

2.  (3 points) Briefly indicate a possible problem associated with each of the following procedures:

•  Testing the methyl red reaction in MR-VP Broth at 24 hours of incubation instead of after a longer incubation of 48 hours or more.
  
  
•  Utilizing a loop instead of a needle when picking colonies off a petri dish.
  
  
•  Beginning the test for coliforms by skipping the presumptive test and jumping straight to the confirmatory test.
  

3.  (2 points) In the fermentation of ground meat to produce sausage:

•  Besides as a flavoring agent, why is salt (NaCl) added to the meat product prior to fermentation?
  
  
•  What causes the meat to develop the characteristic firm and "bouncy" texture that is associated with fermented sausage?
  

IV.  PROBLEM (3 points)..

1.  (1 point) If you inoculated 0.1 ml of a 10^–5 dilution of your sample onto a plate of the appropriate medium and then counted 160 colonies after incubation, you must then multiply 160 by 10^–6 to obtain the CFUs per ml or gram of your sample. True or false?

2.  (2 points) A sample of food was analyzed for Salmonella and the following results were ultimately obtained from the analysis of nine enrichments. Each enrichment was set up with a certain size of sample as shown below:

What was the MPN of Salmonella per gram of the sample?

1.  Note the TSI tube in front of you. Indicate its letter and number here:        

•  Reaction for glucose fermentation:
  
  
•  Reaction for hydrogen sulfide production:
  

2.  Note the LIA tube in front of you. Indicate its letter and number here:        

•  Reaction for lysine decarboxylation:
  
  
•  Reaction for lysine deamination:
  

NOTE: For TSI, yellow=acid and red=alkaline. For LIA, yellow=acid and blue/purple=alkaline.

VI.  EXTRA CREDIT (4 points).  You are in an enteric lab out in the real world, and you are picking colonies off plates of selective-differential isolation media for further testing. These plates had been inoculated with environmental samples, and we expect a variety of enterics to be present. We also expect some colonies of that pesky Pseudomonas to be present also.

Now, the organism you are specifically after is Sorgobacter, an enteric with one or more characteristics that allow it to be differentiated from all other enterics – as seen by the reactions in the following table:

As part of the enteric isolation routine, you plan on picking colonies into a screening medium, such as Kligler Iron Agar (KIA) before doing a lot of specific tests. Before you do that, you decide you have time to make a modification of KIA that will allow you to decide whether or not you have Sorgobacter, just from the appearance of the modified KIA after incubation.

•  You know that KIA already has two sugars in it – lactose and glucose – and the glucose is present in a relatively small amount. Which one of the following sugars would you add to the ingredients in KIA (in a relatively fairly large amount) such that Sorgobacter will look different from all of the other enterics and also Pseudomonas? Fructose, galactose or mannitol?
  
  
•  Briefly describe the appearance of Sorgobacter growing in this modified KIA. That is, would you expect an acid or alkaline reaction in the aerobic (slant) region? And what about the anaerobic region (i.e., the "butt")?
  
  
•  What would be the pH reaction in the aerobic (slant) region for all of the other enterics? Acid or alkaline?
  
  
•  If (for whatever reason) you were to add one of the amino acids to the medium, which onecould allow Sorgobacter to show an alkaline reaction in the anaerobic (butt) region? Arginine or lysine?