STRAIGHTERLINE MICROBIOLOGY BIO250
BOARD EVALUATION SCRIPT 2026
SOLVED QUESTIONS GRADED A+
⩥ How does McConkey agar select gram negative bacteria. Answer: it
uses blue salts and crystal violet dyes to inhibit the growth of gram
positive bacteria
⩥ What are EMB and McConkey Agar differential fo. Answer: lactose
and non-lactose fermenters
⩥ How does EMB agar differentiate between lactose and non-lactose
fermenters. Answer: it uses lactose as its medium and when the acid is
fermented, the dyes react on the colony surface, coloring it and eosin
and methylene blue inhibit gram positive bacteria
⩥ How does McConkey agar differentiate between lactose and non-
lactose fermenters. Answer: the medium contains a natural pH red dye
and lactose and when lactose is fermented, the clear colonies become
pink on the agar and crystal violet and bile salts inhibit gram positive
bacteria
⩥ How many colonies are on a countable plate. Answer: between 30-300
CFUs
, ⩥ NON-LACTOSE FERMENTERS on the EMB and McConkey agars
appear ____________________.. Answer: Colorless
⩥ On EMB agar, LACTOSE FERMENTERS appear
____________________ (small and large acid production).. Answer:
Metallic Green for large acid production Purple for small acid
production
⩥ Beta-hemolysis (complete cell lysis). Answer: Clearing around growth
⩥ Alpha-hemolysis (partial cell lysis). Answer: Greening around growth
⩥ Gamma-hemolysis (no cell lysis). Answer: No change in the medium
⩥ Positive Result For Catalase Test. Answer: Bubbles
⩥ Negative Result For Catalase Test. Answer: No Bubbles
⩥ Positive Result For Coagulase Test. Answer: Plasma forms a clot
⩥ Negative Result For Coagulase Test. Answer: Plasma remains liquid
BOARD EVALUATION SCRIPT 2026
SOLVED QUESTIONS GRADED A+
⩥ How does McConkey agar select gram negative bacteria. Answer: it
uses blue salts and crystal violet dyes to inhibit the growth of gram
positive bacteria
⩥ What are EMB and McConkey Agar differential fo. Answer: lactose
and non-lactose fermenters
⩥ How does EMB agar differentiate between lactose and non-lactose
fermenters. Answer: it uses lactose as its medium and when the acid is
fermented, the dyes react on the colony surface, coloring it and eosin
and methylene blue inhibit gram positive bacteria
⩥ How does McConkey agar differentiate between lactose and non-
lactose fermenters. Answer: the medium contains a natural pH red dye
and lactose and when lactose is fermented, the clear colonies become
pink on the agar and crystal violet and bile salts inhibit gram positive
bacteria
⩥ How many colonies are on a countable plate. Answer: between 30-300
CFUs
, ⩥ NON-LACTOSE FERMENTERS on the EMB and McConkey agars
appear ____________________.. Answer: Colorless
⩥ On EMB agar, LACTOSE FERMENTERS appear
____________________ (small and large acid production).. Answer:
Metallic Green for large acid production Purple for small acid
production
⩥ Beta-hemolysis (complete cell lysis). Answer: Clearing around growth
⩥ Alpha-hemolysis (partial cell lysis). Answer: Greening around growth
⩥ Gamma-hemolysis (no cell lysis). Answer: No change in the medium
⩥ Positive Result For Catalase Test. Answer: Bubbles
⩥ Negative Result For Catalase Test. Answer: No Bubbles
⩥ Positive Result For Coagulase Test. Answer: Plasma forms a clot
⩥ Negative Result For Coagulase Test. Answer: Plasma remains liquid
