Microbiology Lab Practical – Final Exam 2025
UPDATE/PRACTICE QUESTIONS AND CORRECT VERIFIED
ANSWERS (complete solutions) ASSURED
SUCCESS/GRADED A+!!!
Selective Media - CORRECT ANSWER-Media used to isolate particular groups of
organisms while suppressing the growth of others. (Ex: gram + gram-)
Differential Media - CORRECT ANSWER-Media that allows the differentiation of
colonies of desired organisms from other that grow on the same plate.
Enriched Media - CORRECT ANSWER-Media that allow metabolically fastidious
microorganisms to grow because of the addition of specific growth factors
Colistin-Nalidixic Acid (CNA) Agar - CORRECT ANSWER-What is an example of
selective media?
MacConkey Agar or Mannitol Salt Agar - CORRECT ANSWER-What is an example
of differential media?
Blood Agar - CORRECT ANSWER-What is an example of enriched media?
,4-Quadrant Streak - CORRECT ANSWER-Which inoculation technique leads to
isolated colonies?
Colistin-Nalidixic Acid - CORRECT ANSWER-What does CNA stand for?
Gram positive - CORRECT ANSWER-What type of organism is CNA agar selective
for?
Colistin, nalidixic acid - CORRECT ANSWER-What is the inhibitor for CNA agar?
No - CORRECT ANSWER-Does CNA agar have an indicator?
Gram negative - CORRECT ANSWER-What type of organism is MacConkey agar
selective for?
Bile salts, gram + - CORRECT ANSWER-What is the inhibitor for MacConkey agar
and what does it inhibit?
Neutral Red - CORRECT ANSWER-What is the indicator for MacConkey agar?
A pH drop around colonies - CORRECT ANSWER-What causes the color change
in neutral red with MacConkey agar?
,Lactose fermenting, gram - - CORRECT ANSWER-For what type of organisms
does the neutral red indicator in MacConkey agar appear pink to brick red?
Lactose non-fermenting, gram - - CORRECT ANSWER-For what type of
organisms does the neutral red indicator in MacConkey agar appear clear?
Aseptic technique - CORRECT ANSWER-A combination of lab methods which are
used to keep the worker and work area free of bacterial contamination as well as
insure that culture media are inoculated only with the organism of interest.
1) Always work near a flame in the aseptic zone
2) Keep all sterile containers closed except during use
3) Never lay caps on bench
4) Keep all tubes in racks and perform all procedures in a quick, orderly fashion -
CORRECT ANSWER-What are some ways you can insure good aseptic
technique?
Pure culture - CORRECT ANSWER-A culture that contains only one type of
bacteria
Mixed culture - CORRECT ANSWER-Culture containing two or more kinds of
organisms.
Mannitol Salt Agar - CORRECT ANSWER-What does MSA stand for?
, Staphylococcus spp - CORRECT ANSWER-What organisms is MSA selective for?
Sodium Chloride 7.5% - CORRECT ANSWER-What is the inhibitor for MSA?
Phenol Red - CORRECT ANSWER-What is the indicator for MSA?
saprophyticus - CORRECT ANSWER-For what species of Staphylococcus does the
phenol red indicator in MSA turn yellow?
It ferments the mannitol - CORRECT ANSWER-Why does the phenol red
indicator in MSA turn yellow with S. saprophyticus?
epidermidis - CORRECT ANSWER-For which species of Staphlyococcus does the
phenol red indicator in MSA stay red?
Tryptic Soy Agar - CORRECT ANSWER-What does TSA stand for?
Blood (of hemolysis) - CORRECT ANSWER-What is the indicator of Blood Agar?
To see if an organism has any hemolytic patterns - CORRECT ANSWER-What is
the purpose of blood agar plates?
UPDATE/PRACTICE QUESTIONS AND CORRECT VERIFIED
ANSWERS (complete solutions) ASSURED
SUCCESS/GRADED A+!!!
Selective Media - CORRECT ANSWER-Media used to isolate particular groups of
organisms while suppressing the growth of others. (Ex: gram + gram-)
Differential Media - CORRECT ANSWER-Media that allows the differentiation of
colonies of desired organisms from other that grow on the same plate.
Enriched Media - CORRECT ANSWER-Media that allow metabolically fastidious
microorganisms to grow because of the addition of specific growth factors
Colistin-Nalidixic Acid (CNA) Agar - CORRECT ANSWER-What is an example of
selective media?
MacConkey Agar or Mannitol Salt Agar - CORRECT ANSWER-What is an example
of differential media?
Blood Agar - CORRECT ANSWER-What is an example of enriched media?
,4-Quadrant Streak - CORRECT ANSWER-Which inoculation technique leads to
isolated colonies?
Colistin-Nalidixic Acid - CORRECT ANSWER-What does CNA stand for?
Gram positive - CORRECT ANSWER-What type of organism is CNA agar selective
for?
Colistin, nalidixic acid - CORRECT ANSWER-What is the inhibitor for CNA agar?
No - CORRECT ANSWER-Does CNA agar have an indicator?
Gram negative - CORRECT ANSWER-What type of organism is MacConkey agar
selective for?
Bile salts, gram + - CORRECT ANSWER-What is the inhibitor for MacConkey agar
and what does it inhibit?
Neutral Red - CORRECT ANSWER-What is the indicator for MacConkey agar?
A pH drop around colonies - CORRECT ANSWER-What causes the color change
in neutral red with MacConkey agar?
,Lactose fermenting, gram - - CORRECT ANSWER-For what type of organisms
does the neutral red indicator in MacConkey agar appear pink to brick red?
Lactose non-fermenting, gram - - CORRECT ANSWER-For what type of
organisms does the neutral red indicator in MacConkey agar appear clear?
Aseptic technique - CORRECT ANSWER-A combination of lab methods which are
used to keep the worker and work area free of bacterial contamination as well as
insure that culture media are inoculated only with the organism of interest.
1) Always work near a flame in the aseptic zone
2) Keep all sterile containers closed except during use
3) Never lay caps on bench
4) Keep all tubes in racks and perform all procedures in a quick, orderly fashion -
CORRECT ANSWER-What are some ways you can insure good aseptic
technique?
Pure culture - CORRECT ANSWER-A culture that contains only one type of
bacteria
Mixed culture - CORRECT ANSWER-Culture containing two or more kinds of
organisms.
Mannitol Salt Agar - CORRECT ANSWER-What does MSA stand for?
, Staphylococcus spp - CORRECT ANSWER-What organisms is MSA selective for?
Sodium Chloride 7.5% - CORRECT ANSWER-What is the inhibitor for MSA?
Phenol Red - CORRECT ANSWER-What is the indicator for MSA?
saprophyticus - CORRECT ANSWER-For what species of Staphylococcus does the
phenol red indicator in MSA turn yellow?
It ferments the mannitol - CORRECT ANSWER-Why does the phenol red
indicator in MSA turn yellow with S. saprophyticus?
epidermidis - CORRECT ANSWER-For which species of Staphlyococcus does the
phenol red indicator in MSA stay red?
Tryptic Soy Agar - CORRECT ANSWER-What does TSA stand for?
Blood (of hemolysis) - CORRECT ANSWER-What is the indicator of Blood Agar?
To see if an organism has any hemolytic patterns - CORRECT ANSWER-What is
the purpose of blood agar plates?
