In making a smear of bacteria for viewing with the microscope a. The thicker the
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In making a smear of bacteria for viewing with the microscope a. The thicker the smear, the better b. The smear should be dried by passing it through a flame to boil off the water c. Several colonies should be picked onto the slide d. All of the above are true e. None of the above is true Which of the following stains is/are considered differential? a. capsule stain b. stain c. acid fast stain. d. Gram stain. e. c and d Media such as nutrient agar or trypticase soy are sterilized in an autoclave a. At 15 lbs per square inch () pressure for 24 hours b. At 100 psi and 121.60 C for 10-12 minutes c. At 15 psi and 121.60C for 15-20 minutes d. At 100 psi and 121.60C for 10-12 overnight e. None of the above agar must be filter sterilized. Which of the following is/are true of coli? a. Is gram positive b. Is never pathogenic c. Forms spores under adverse conditions d. Is motile e. All of the above are true. Which statement is false about the acid fast stain? a. It reveals the causative bacteria in a sputum sample from a person with presumptive tuberculosis b. It is useful for distinguishing a small group of organisms, for example, Mycobacterium. c. It uses crystal violet and safranin. d. It uses carbol and methylene blue. e. It is heated to overcome the wax in the wall and stain certain bacteria The main reason why boiling of liquid media is not reliable for sterilization is a. Heat sensitive instruments may be destroyed. b. Heat resistant endospores are unaffected. c. Water boils at a higher temperature at lower altitudes. d. Viruses are more sensitive to heat than bacteria. A phenol red glucose broth with a Durham tube is inoculated with bacterial culture that is an example of respiration. Which of the following will be the result? a. There will be no growth and the broth will be yellow. b. There will be growth and the broth will be yellow with no gas in the Durham tube. c. There will be growth and the broth will be yellow with gas in the Durham tube. d. There will be growth and the broth will be red with gas in the Durham tube. Which of the following is not an example of a multi-test medium? a. Litmus milk agar b. Triple Sugar Iron agar (TSI) c. Sulfide indole motility agar (SIM) d. Tyrpticase soy agar (TSA) e. Eosin Methylene Blue agar (EMB)Explanation / Answer
13. The smear should be thin, but not thicker. If the smear is too thick, it is imposiible to clearlyb see the bacterial
cells. The bacterial sample is air dried , but not dried under flame. the air dried sample slide is then passed
through the flame of bunsen burner to heat fix. Once the slide is heat fixed, it can be stained. Several colonies of
bcateria are not picked, instead only few colonies of bacteria are picked to clearly see individual bacterial cells.
Therefore, none of the above is true.
Hence, the correct option is (E).
14. Differential stains are often used for general identification of bacteria but it doesnt allow for identification
of exact species.
Examples of differential stains include gram stain and acid fast stain.
Gram Stain
+ controls: Staphylococcus, Bacillus, Streptococcus
- controls: Escherichia, Salmonella, Enterobacter
Acid-fast Stain
+ controls: Mycobacteria, Nocardia
- controls: any type of bacteria that does not have a waxy cell wall
Hence, the correct option is (E).
15.Nutrient agar is a general purpose medium supporting growth of a wide range of non-fastidious organisms.Trypticase soy medium is recommended for use as a general growth medium in the isolation and cultivation of microorganisms.
This medium is also recommended for use in the cultivation, storage, maintenance and transportation of pure cultures of microorganisms.
These media are sterilised in an autoclave at 15psi and 120.6 degrees for 15-20min. These are the minimum readings set for sterilisingmedia. If the medium is exposed to temperatures in excess of 121°C, it may not properly gel or may result in poor cell growth.
Hence, the correct option is (C).
16. Escherichia coli is motile. It possess peritrichous flagellae. it swims or crawls by rotating this flagellae.
E.coli is a gram negative bacteria. It is a non -spore forming bacteria. Some strains of E.coli are pathogenic.
Hence, the correct option is (D).
17. Both crystal violet and safranin are basic stains and may be used to do simple stains on gram positive and gram negative cells.
For Gram-negative- they have a higher lipid content and thinner peptidoglycan layer than Gram-positive & the alcohol extracts the lipid,
making wall more porous and incapable of retaining crystal violet-iodine complex.
For Gram-positive- they have a thicker peptidoglycan layer and high degree of cross-linking (due to teichoic acids) which traps crystal
violet-iodine complex more effectively.
Acid-fast stain does not use crystal violet and saffranin. This statement is false/incorrect.
Hence, the correct option is (C).
18. Boiling is not reliable for sterilization because heat resistant endospores are unaffected.
Hence, the correct option is (B).
19. A phenol red glucose broth with a Durham tube inoculated with bacterial culture results in the following.
There willbe growth and the broth will be red with gas in the Durham tube.
Gases are released from the cell and asvolume of gas increases, it displaces an equal volume in media, bubbles will appear at the top of tube.
When the organism is able to use the carbohydrate, a gas by-product may be produced. If it is, an air bubble will be trapped inside the Durham tube.
If the organism is unable to utilize the carbohydrate, gas will not be produced, and no air bubble will be formed.
Hence, the correct option is (D).
20.Trypticase soy (TSA) medium is recommended for use as a general growth medium in the isolation and cultivation of microorganisms.
This medium is also recommended for use in the cultivation, storage, maintenance and transportation of pure cultures of microorganisms.It is not an example of a multi-test medium.
Hence, the correct option is (D).
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