A use-dilution test was used to evaluate two disinfectants against Salmonella choleraesuis. The results were as follows:

Time of Exposure (min)	Bacterial Growth after Exposures Disinfectant A	Bacterial Growth after Exposures Disinfectant B Diluted with Distilled Water	Bacterial Growth after Exposures Disinfectant B Diluted with Tap water
10	G	NG	G
20	5mm	NG	NG
30	10mm	NG	NG

a. Which disinfectant was the most effective? b. Which disinfectant should be used against Staphylococcus?

Devise an experiment that will differentiate between bactericidal and bacteriostatic effects.

The disk-diffusion method was used to evaluate three disinfectants. The results were as follows:

a. Which disinfectant was the most effective against the organism? b. Can you determine whether compound Y was bactericidal or bacteriostatic?

Entamoeba histolytica and Giardia lamblia were isolated from the stool sample of a 45-year-old man, and Shigella sonnei was isolated from the stool sample of an 18-year-old woman. Both patients experienced diarrhea and severe abdominal cramps, and prior to onset of digestive symptoms both had been treated by the same chiropractor. The chiropractor had administered colonic irrigations (enemas) to these patients. The device used for this treatment was a gravity-dependent apparatus using 12 liters of tap water. There were no check valves to prevent backflow, so all parts of the apparatus could have become contaminated with feces during each colonic treatment. The chiropractor provided colonic treatment to four or five patients per day. Between patients, the adaptor piece that is inserted into the rectum was placed in a “hot-water sterilizer.”What two errors were made by the chiropractor?

The antimicrobial effect of gamma radiation is due to (a) ______. The antimicrobial effect of ultraviolet radiation is due to (b) ________.

Most laboratory media contain a fermentable carbohydrate and peptone because the majority of bacteria require carbon, nitrogen, and energy sources in these forms. How are these three needs met by glucose–minimal salts medium? (Hint: See Table 6.2.)

For each of the following bacteria, explain why it is often resistant to disinfectants.
a. Mycobacterium
b. Pseudomonas
c. Bacillus

Which of the following elements is NOT correctly matched with its cellular function?

A. magnesium and potassium – required as cofactors for enzymes

B. phosphorus – incorporated into nucleic acids

C. phosphorus – used for the production of carbohydrates.

D. sulfur - used for the synthesis of amino acids

E. nitrogen – needed for amino acid synthesis

What happens in lactic acid fermentation?

Explain how enzymes increase the speed of chemical reactions.

Differentiate between narrow-spectrum and broad-spectrum antibiotics.

Some bacteria become resistant to tetracycline because they don’t make porins. Why can a porin-deficient mutant be detected by its inability to grow on a medium containing a single carbon source such as succinic acid?

How is a plastic filtration apparatus presterilized? (Assume the plastic cannot be heat sterilized.)

Describe the use of a DNA probe and PCR for:
a. rapid identification of an unknown bacterium.
b. determining which of a group of bacteria are most closely related.