Match the three views with the sites that undergo modification to produce resistance.
|i - Scientist 1||a – Enzymes|
|ii - Scientist 2||b – Cytolemma|
|iii - Scientist 3||c – Antibiotic|
|d – Cell wall|
Penicillin is an antibiotic that has been used to treat various infections. But lately there has been a steep rise in the number
of penicillin resistant cases. Various mechanisms have been proposed to explain the development of this resistance.
The antibiotic action of penicillin is related to its ability to inhibit the synthesis of bacterial cell wall. An enzyme
transpeptidase is required for the linking of muramic acid residues during the formation of bacterial cell wall. Penicillin
binds to transpeptidase and renders it inactive.
Bacteria undergo transformation over the course of time, and due to the ensuing recombinational events, the homologous
segments of the genes coding for the normal transpeptidase are replaced by genes that code for a modified transpeptidase.
The modified transpeptidase is not recognized by Penicillin and the antibiotic fails to act. These genes may be inherited and
lead to transfer of resistance down the generations. Various types of transpeptidases are known. A recombinational change
in type P transpeptidase is responsible for a low level resistance while an intermediate level resistance occurs with changes
in type Q transpeptidase. A change affecting the homogenous segments coding for both P and Q type transpeptidases
accounts for a high degree of resistance. Indiscretion in prescribing penicillin has led to development of high level
A β-lactam ring is central to the structure of Penicillin. Some bacteria produce an enzyme β-lactamase which digests
components of this ring. This process breaks open the ring and renders the antibiotic ineffective. The genes that code for
this enzyme may be present in the chromosome or may be acquired by plasmid transfer. These genes generally remain
dormant but their expression is triggered by overexposure of the bacteria to β-lactam antibiotics like Penicillin. Patients on
penicillin should complete the full course of the antibiotic. Non-compliance leads to persistence of bacteria in the body and
these bacteria acquire genes that code for β-lactamase. The resistance however does not rule out the use of penicillin
completely. Penicillin can be combined with an enzyme inhibitor that impairs the functioning of the bacterial enzyme.
Penetration into the bacteria is the first step in the mechanism of action of an antibiotic. In certain groups of bacteria,
alteration in a gene leads to modifications in Porins - outer membrane proteins. This modification makes the bacterial cell
membrane impermeable to penicillin. The bacteria may inherit this gene or acquire it as the result of a mutation.