Question

on which of these plates should we expect to see colonies of e. coli growing after incubation? select all that apply. a. antibiotic nonresistant e. coli on streptomycin-positive plate b. antibiotic-resistant e. coli on streptomycin-negative plate c. antibiotic nonresistant e. coli on streptomycin negative plate d. antibiotic-resistant e. coli on streptomycin-positive plate

Explanation:

• For non - resistant E. coli:
• On a streptomycin - negative (no antibiotic) plate (option C), there is no antibiotic to inhibit growth, so non - resistant E. coli can grow.
• On a streptomycin - positive plate (option A), the antibiotic streptomycin will kill the non - resistant E. coli, so it cannot grow.
• For resistant E. coli:
• On a streptomycin - positive plate (option D), since the E. coli is resistant to streptomycin, it can grow.
• On a streptomycin - negative plate (option B), there is no antibiotic, so resistant E. coli can also grow as the lack of antibiotic doesn't hinder its growth (and it has the resistance trait which doesn't prevent growth in non - antibiotic environments).

Answer:

B. Antibiotic - resistant E. coli on streptomycin - negative plate
C. Antibiotic nonresistant E. coli on streptomycin - negative plate
D. Antibiotic - resistant E. coli on streptomycin - positive plate