Question

5. Look up the chemical formulas for bleach, isopropyl alcohol, and chlorhexidine gluconate (the active ingredient in Hibiclens). How does each chemical achieve its germicidal properties?”

“3. If a population of bacteria evolves resistance to penicillin, are these bacteria more likely to be also resistant to ampicillin or kanamycin? Explain your reasoning.”

“2. What is the mechanism of action for each of the antibiotics used in this experiment?” (ampicillin, kanamycin, and penicillin)

Answer 1

5. Sodium hypochlorite present in bleach, is responsible for it's antimicrobial activity. It causes denaturation of proteins, that are essential for the survival of microorganisms.

Isopropyl alcohol is another substance that targets cellular proteins. It also damages membrane lipids, which altogether leads to disruption of the bacterial cell membrane.

The positively charged chlorhexidin, present in chlorhexidin gluconate, interacts with negatively charged bacterial cell wall. This disrupts the cell wall, which causes osmotic instability, ultimately leading to death.

6. Ampicillin is an anti-microbial drug that is different from natural penicillin. It is a modified form of natural penicillin, made by introducing an amino group. Natural penicillin is not able to cross the outer membrane of gram negative bacteria (intrinsic resistance), whereas, presence of amino group allows ampicillin to cross the outer membrane of gram negative bacteria, as a result of which, ampicillin has a wider activity than penicillin, being active against both gram positive and some gram negative bacteria.

Kanamycin is a drug belonging to the group of aminoglycosides. It targets the 30S ribosomal subunit, which is different from the site recognized by penicillin.

Thus, a penicillin resistant bacteria will not be resistant to kanamycin. However, it can be possible that it is resistant to ampicillin, if it produces the enzyme beta-lactamase, which is responsible for cleaving beta lactam rings present in ampicillin and penicillin.