Microbiology Lab Practical Exam 2
Questions and Answers 100% Correct
What is the role of the inoculating loop in microbiological techniques?
✔✔To transfer small amounts of bacterial culture onto a medium for streaking or sub-culturing.
What is the appearance of a Gram-positive bacterium after a Gram stain?
✔✔Purple coloration due to a thick peptidoglycan layer.
What is the characteristic appearance of a positive catalase test result?
✔✔Bubbling or fizzing when hydrogen peroxide is added, indicating the presence of catalase.
What does a positive coagulase test indicate about a bacterium?
✔✔It produces coagulase, which causes blood plasma to clot.
What is the appearance of a positive starch hydrolysis test?
✔✔A clear zone around the bacterial growth after iodine is added, indicating the breakdown of
starch.
1
,What is the primary purpose of an EMB (Eosin Methylene Blue) agar?
✔✔To isolate and differentiate Gram-negative enteric bacteria based on lactose fermentation.
What is the purpose of a motility test?
✔✔To determine if a bacterium is capable of moving in a semi-solid medium.
What is the result of a positive urease test?
✔✔A pink color change, indicating the production of ammonia from urea.
What is the appearance of a positive phenylalanine deaminase test?
✔✔A green color develops after the addition of ferric chloride.
What does a positive indole test indicate?
✔✔The production of indole from tryptophan metabolism.
What is the purpose of a phenol red broth test?
✔✔To detect the fermentation of specific sugars, with acid and/or gas production.
2
, What does a positive hydrogen sulfide (H2S) test look like?
✔✔Blackening in the medium, indicating the production of hydrogen sulfide gas.
What is the result of a positive methyl red test?
✔✔A red color indicates mixed-acid fermentation.
What does a positive Voges-Proskauer (VP) test result look like?
✔✔A red or pink color develops, indicating acetoin production.
What is the term for a bacterium that uses oxygen for respiration but can also grow in the
absence of oxygen?
✔✔Facultative anaerobe.
What is the appearance of a positive mannitol salt agar test?
✔✔A yellow color change around bacterial growth, indicating mannitol fermentation.
What is the role of the selective medium in microbiology?
✔✔To promote the growth of specific organisms while inhibiting others.
3
Questions and Answers 100% Correct
What is the role of the inoculating loop in microbiological techniques?
✔✔To transfer small amounts of bacterial culture onto a medium for streaking or sub-culturing.
What is the appearance of a Gram-positive bacterium after a Gram stain?
✔✔Purple coloration due to a thick peptidoglycan layer.
What is the characteristic appearance of a positive catalase test result?
✔✔Bubbling or fizzing when hydrogen peroxide is added, indicating the presence of catalase.
What does a positive coagulase test indicate about a bacterium?
✔✔It produces coagulase, which causes blood plasma to clot.
What is the appearance of a positive starch hydrolysis test?
✔✔A clear zone around the bacterial growth after iodine is added, indicating the breakdown of
starch.
1
,What is the primary purpose of an EMB (Eosin Methylene Blue) agar?
✔✔To isolate and differentiate Gram-negative enteric bacteria based on lactose fermentation.
What is the purpose of a motility test?
✔✔To determine if a bacterium is capable of moving in a semi-solid medium.
What is the result of a positive urease test?
✔✔A pink color change, indicating the production of ammonia from urea.
What is the appearance of a positive phenylalanine deaminase test?
✔✔A green color develops after the addition of ferric chloride.
What does a positive indole test indicate?
✔✔The production of indole from tryptophan metabolism.
What is the purpose of a phenol red broth test?
✔✔To detect the fermentation of specific sugars, with acid and/or gas production.
2
, What does a positive hydrogen sulfide (H2S) test look like?
✔✔Blackening in the medium, indicating the production of hydrogen sulfide gas.
What is the result of a positive methyl red test?
✔✔A red color indicates mixed-acid fermentation.
What does a positive Voges-Proskauer (VP) test result look like?
✔✔A red or pink color develops, indicating acetoin production.
What is the term for a bacterium that uses oxygen for respiration but can also grow in the
absence of oxygen?
✔✔Facultative anaerobe.
What is the appearance of a positive mannitol salt agar test?
✔✔A yellow color change around bacterial growth, indicating mannitol fermentation.
What is the role of the selective medium in microbiology?
✔✔To promote the growth of specific organisms while inhibiting others.
3
