Question

71. A simple stain                                                                                                                                         

A. requires one stain and one decolorizing agent                                                                                                                                    

B. requires multiple staining steps                                                                                                                     

C. allows visualization of bacterial motility                                                                                                   

D. increases the contrast between the cell and the background                                                              

E. differentiates one bacterial group from another

72. Which of the following statements about the Kirby-Bauer technique for measuring the effectiveness of antimicrobial chemicals is INCORRECT?                                                                                                         

A. Either Gram-positive or Gram-negative bacteria may be used as the test organism.                          

B. The size of the inhibition zone helps to determine the effectiveness of the chemical                        

C. Effectiveness of the chemical is usually determined two hours after preparing the plate.   

D. Rate of diffusion may influence the size of the inhibition zone.                                                                 

E. This method can be used to test antibiotics, antiseptics, or disinfectants.

73. It was found that the causative agent of a food poisoning case to be an endospore-forming Gram positive bacterium, how does an endospore appear when Gram stained?                                                                                                                                                                 

A. violet          

B. red             

C. colorless         

D. a color in between violet and red

Answer 1

 

71.) A

Simple staining requires one stain and a decolourizing agent.Its value lies in its simplicity and ease of use.After prepartion of the smear followed by heat fixing,it is covered with stain for a particular length of time.Excess of the stain is washed away with water and blots the slide dry. simple staining helps in observing the size,shape and arrangement of bacteria. Some stains that are used in simple staining procedure are crystal violet,methylene blue..etc.

72.) C

In Kirby-Bauer method,bothe types ,that is ,gram negative and gram positive bacterias can be used as test organism,eg:Staphylococcus which is gram positive and Pseudomonas which is gram negative.The zone width is the function of initial concentration of the antibiotic ,its soluabilityand also its diffusion rate through agar.after the plates has been prepared, appropriate antibiotic disks are placed on it.then the plates are immediately kept for incubation at 35 degree celsius .the width of the zone is measured after 16 to 18 hours.

73.) C

After gram staining the endospore remain colourless since they are impermeable to stains. But, endospores can be stained with some special methods ,like staining with malachite green(strong dye) ,then the excess dye is washed off and the cell is counterstained with safranin dye.This technique yield a green endospore resting in a pink to red cell.