| | 1. (Growth Curves) Two cultures, A and B, are made in NB (nutrient broth, which is like nutrient agar except there is no gelling agar in it). A starts out with 2x104 cfu/mL, and doubles every 28 minutes. B starts out at 8x102 cfu/mL and doubles every 23 minutes.
(a) the growth rate of A is greater than that of B
(b) the growth rate of B is greater than that of A
(c) insufficient information to compare growth rates
(d) their growth rates would be faster in GMS than in NA (GMS is glucose + mineral water)
(e) it all depends on which one reaches stationary phase first | | | 8. E. coli is a "mixed-acid" fermenter. A culture is made in NB supplemented with 0.3% glucose, and then immediately divided to make two identical flasks. E is sparged with air and F is sparged with N2
(a) neither will be fermenting
(b) E only ferments
(c) F only ferments
(d) both will be fermenting
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| | 2. Stains of the bacterial species Serratia marcesens are used: R (red) is the wild-type, and W (white) is a colorless mutant derived from R. Equal numbers of R and W are inoculated into the same flask of NB. After 3 hrs and after 10 hrs unspecified dilutions are made and plated on NA so that lots of isolated colonies grow up overnight. The 3-hr sampling produced a ratio of 25% R to 75% W.
(a) R had the higher value of g
(b) W had the higher value of g
(c) R is killing W
(d) W is killing R
(e) none of the above is necessarily true | | 9. The pH's of both E and F, above, are followed as the cultures grew. Which curve best fits Culture E? 
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| | 3. The 10-hr sampling in the previous question gave a plate with a ratio of 75% R to 25% W.
(a) R had the higher value of g
(b) W had the higher value of g
(c) R is killing W
(d) W is killing R
(e) none of the above is necessarily true | | 10. Which curve best fits Culture F?
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| | 4. Urinary tract infections - even subclinical ones - are indicated if there are more than 1x104 cfu/mL of urine. Cheryl and Mary Lou plated 10 μL of their urines and obtained 2 and 65 colonies, respectively.
(a) neither is deemed to have a urinary infection
(b) only Mary Lou is deemed to have a urinary infection
(c) only Cheryl is deemed to have a urinary infection
(d) both are deemed to have urinary infections
(e) insufficient dilutions were made | | 11. Mary Lou finds a smelly carton of out-dated milk in her refrigerator. She swabs some onto a MacConkey agar plate to culture the sour milk bacteria. Alas, no colonies grow up on the plate. Which is the most probable result?
(a) There are no E. coli in the milk.
(b) All the bacteria are dead.
(c) She should have used NA
(d) All the lactose in the old milk had been exhausted (metabolized)
(e) all of the above
(f) a and b only
(g) a and c only
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| | 5. E. coli is a facultative anaerobe (can grow either with or without O2). A culture was started in NB into which N2 was bubbled. Samples were periodically taken for plate counts. Halfway along, the N2 was replaced with air. Which graph resulted? 
| | 12. Cheryl adds 10 μL of an E. coli culture to both 5 mL of water and 5 mL of Mary Lou's soured milk. After 30 minutes, she swabs both onto MacConkey plates, and the next day she has 272 red colonies on the "water" plate, and zero colonies on the "milk" plate. Which of the following does Cheryl know for sure?
(a) the acid in the sour milk killed the E. coli
(b) the E. coli were killed in the sour milk
(c) the milk bacteria killed the E. coli
(d) a and c only
(e) nothing for sure
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| | 6. E. coli possesses a simple nutrition. A culture is started in GMS and sparged with air. Halfway along the medium is adjusted to 0.1% nutrient broth. Which curve results for periodic plate counts?
| | 13. (IMViC) You plate E. coli onto 3 different kinds of agar: NA, GMS and Simmon's Citrate Agar (citrate + diluted seawater + dye). Colonies appear the next day on... (a) NA
(b) GMS
(c) Simmon's citrate agar
(d) a and b, but not C
(e) a and c, but not b
(f) all plates
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| | 7. 100 μL of water from a small, smelly river is spread onto a MacConkey plate over the entire agar surface. Which of the following plates would indicate the river was fecally contaminated? 
(a) #1 only
(b) #1 and #2 only
(c) #1, #2, #3 and #4 only
(d) #3, #4 and #5 only
(e) #4 and #5 only
(f) #5 only | | 14. (IMViC) MacConkey agar plates are based on two reactions which few other bacterial species can BOTH perform simultaneously: (a) release NH3 from amino acids
(b) release CO2 from lactose
(c) convert lactose to various acids
(d) convert lactose to indole
(e) none of the above
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| |  15. Prof. Durham discovered that E. coli will produce gas bubbles inside of inverted tubes if the medium contains a digestible sugar. Eijkmann, who knew that lactase is rare in the microbial world, but is common in E. coli, embellished Durham's work by finding that ONLY E. coli could produce bubbles from lactose at 43°C. Which of the following Eijkmann-Durham tubes had E. coli (possibly along with other bacteria) in them? (a) all of them
(b) #1 and #5 only
(c) #3 and #4 only
(d) #2, #3 and #4 only
(e) none of the above choices
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