Question

cuse u grunt pleyenire bullial cell 3) Suppose that you place some bacterial cells on an LB agar plate containing ampicillin. One of these bacterial cells is resistant to ampicillin; the other bacterial cells are not resistant to ampicillin (see far left plate on the picture below). After incubating the plate for 24 hours, only the ampicillin-resistant cell is able to form a colony. However, if the plate is incubated for an additional 48 hours, the other nearby bacterial cells (which are not resistant to ampicillin) are somehow able to grown and form colonies also (see picture below) Single bacterial cell that's Colony of bacterial cells that's resistant to ampicillin Colonies of bacterial cells that are not resistant to ampicillin 24 hre 48 hre (a) Recall from your warmup assignment that there are several ways that bacteria may resist the effects of antibiotics. In which one of these ways does the bacterium above the one in the middle of the plate) seem to resist the effects of ampicillin? Explain your answer. Hint: Assume that gene transfer cannot happen on/through the agar plate.

Answer 1

Q.3 a) Answer-

1. Bacteria can acquire antibiotic resistance by horizontal gene transfer where resistance strain transfers plasmid that has antibiotic resistance to the antibiotic sensitive strain. But in this experiment information is given that gene transfer cannot occur on/through agar plate.

2. As gene transfer cannot happen then another way is there by which bacteria gain antibiotic resistance is genetic mutation which is associated with mechanism of action of antibiotic ampicillin which is present in LB agar.

3. The bacterium at the middle of the plate which shows formation of colony after 24 hours of incubation that bacterium is resistant to ampicillin. This bacterium resist the effect of ampicillin by producing plasmid mediated beta lactamase enzyme that cleaves beta lactam ring of ampicillin. Due to cleavage of beta lactamase ring ampicillin no longer bound to bacterial transpeptidase enzyme so that bacteria can synthesize its cell wall properly. Due to plasmid containing gene that codes for beta lactamase enzyme bacteria can grow in presence of ampicillin antibiotic.

4. After 48hours other nearby bacterial cells forms colony this indicates that these bacteria has acquired antibiotic resistance by mutation in gene that may work by modifying antimicrobial target or by decreasing drug uptake or by activation of efflux mechanism through which antibiotic is removed from cell etc. As gene transfer cannot happen on/through the agar plate.