STRAIGHTERLINE MICROBIOLOGY BIO250 BOARD EVALUATION SCRIPT 2026 SOLVED QUESTIONS GRADED A+

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