Question

You are observing a slide. When you look through the eyepieces, all you see is complete darkness. What should you check before calling your instructor to ask why nothing is visible? make sure that the light source is turned on and the microscope is plugged in. adjust the intensity of the light source. make sure that the diaphragm is open. check to see that an objective lens is fully set into place over the slide. all the above (answer) The level of microbial contamination on an agar plate is measured as the ______ of colonies. distribution pattern number (answer) color size Which is the correct definition of sterile. Completely free of all lifeforms, including spores and viruses (answer) Completely free of all viruses Completely free of all endospores Completely free of all vegetative forms of bacteria and viruses Growth in Different Types of Media: You have a nutrient broth, an agar slant, and an agar plate with bacterial growth in or on each. If you wanted to evaluate the macroscopic appearance of the bacteria growing in or on the medium, which of the cultures would be the best choice? agar plate agar slant broth none of the above You are interested in studying the gram-negative bacteria that may be found in ground meat. You would like to use a medium that will enable the growth of most species of gram-negative bacteria, while inhibiting gram-positive bacteria. This would be a ______ medium. defined complex selective differential MacConkey (MAC) agar isolates gram (-) bacteria by inhibiting the growth of gram (+) bacteria. T or F Staphylococcus aureus can be identified on mannitol salt agar (MSA) because it ferments the mannitol, changing the color of the agar from pink to yellow. T or F

Answer 1

Question 1 :- Darkness while viewing through microscope

The right option is "All of the above"

Explanation :- There can be multiple reasons for seeing complete darkness while looking through a light microscope. One reason can be absence of light due light source being off or microscope being not plugged in. Diaphragm of the lens could be blocking the view of lens or lens may not be placed over the slide properly.

Question 2:- Level of contamination :-

The right option is "Number"

Explanation :- Microbial contamination is calculated as Cfu per ml which means colony forming unit. Through this, we can determine how many viable bacterial cells are present in a sample. Cfu is calculated by counting Colony numbers on an agar plate.

Question 3 :- Definition of Sterile :-

The right option is "Completely free of all life forms including spores and viruses

Explanation :- Sterile refers to not only the vegetative forms but also reproductive forms of life which includes spores. Thus, Sterilization techniques should be able to kill spores too effectively in order to be useful.

Question 4:- Macroscopic evaluation culture:

The right option is " Agar Plate."

Explanation :- Macroscopic evaluation of Bacteria includes colony morphology like color, texture and size of colonies, their elevation too. These can be Best viewed when bacteria are grown over an Agar Plate.

Question 5:- Media for only Gram negative bacteria growth :

The right option is "Selective media"

Explanation :- Selective media are used to grow only one type of bacteria while inhibiting other types bacterial growth. Since they select for only one type of bacteria they are called Selective media. Differential media are different than Selective media in the sense that differential media may support growth of different types of bacteria but will provide a visual aid like colour change to distinguish in between them.

Question 6:- Macconkey Agar

The statement is TRUE

Explanation :- Macconkey Agar contain different types of salt from biles and these salts inhibit the growth of Gram positive bacteria as they are toxic to them while Gram negative and especially enteric bacteria can utilise them and grow on this. Thus it selects for Gram negative bacteria.

Question 7:- MSA media and Staphylococcus aureus :

This statement is TRUE

Explanation : MSA media is used to grow Gram negative bacteria and some Gram positive bacteria can also grow on it. This can differentiate between those which can ferment Mannitol from those who can not.

Fermentation of Mannitol leads to formation of acids in the media and these acids change the color media from pink to Yellow as we also add a pH indicator (Phenol red) in it.