Penicillin
- I am Martin
- Nov 21, 2023
- 2 min read
An antibiotic is a type of antimicrobial substance active against bacteria.
Antimicrobials could be bactericidal or bacteriostatic.
There are 4 different approaches to achieving antibacterial activities,
by Inhibiting bacterial cell wall biosynthesis, bacterial protein synthesis, bacterial metabolism, or bacterial nucleic acid synthesis.
Penicillins are the oldest and still the most widely used of all antibiotics.
It is a narrow-spectrum antibiotic.
It has a B-lactam ring, the integrity of which is required for antibacterial activity.
Penicillins are bactericidal for growing cells.
It inactivates bacterial transpeptidases and prevents the cross-linking of peptidoglycan polymers which is essential for bacterial cell wall integrity.
Penicillins also bind to and inactivate, penicillin-binding proteins (PBPs) involved in cell wall synthesis. The action of autolysin in the presence of penicillin further weakens the cell wall. These agents exert bactericidal activity by interfering with the last step of bacterial cell wall synthesis, which causes rapid cell lysis.
Natural penicillins(such as Penicillin G and Penicillin V) target gram-positive and gram-negative cocci, gram-positive bacilli, oral anaerobes, and spirochetes, one of the commonly known bacteria in this class is treponema pallidum, which causes syphilis.
Penicillin G and penicillin V have similar spectra of activity,
Penicillin V is more acid-stable and thus better absorbed by the oral route, whereas penicillin G is administered via injection.
The main mechanisms of drug resistance are lower permeability of the antibiotic through the cell wall.
A gram-positive bacterium has a thick, multilayered cell wall consisting mainly of peptidoglycan surrounding the cytoplasmic membrane.
Also, the resistance of the drug can contribute to the presence of antibiotic-inactivating enzymes, such as β lactamases.
After years of exposure to β-lactam antibiotics,
a large number of bacterial organisms have developed resistance to the drugs by producing β lactamase, an enzyme that hydrolyzes the β-lactam ring and inactivates the antibiotics.
Targeting those β lactamases–producing organisms, β-lactam antibiotics are combined with β-lactamase inhibitors to exert bactericidal activity.
Clavulanic acid is one of the β-Lactamase inhibitors, and structurally related to penicillin, but have no antimicrobial properties of its own.
it irreversibly inhibits B-lactamase.
Clavulanic acid is used in combination with amoxicillin, and it is under the brand name Augmentin.
Also, modifications of the R-group side-chain (attached to the β-lactam ring) alter the pharmacologic properties and resistance to β-lactamase.
Last but not least, the resistance of the drug can also contribute to
the lack of drug-binding sites. Vancomycin was the last-resort drug for S. aureus strains resistant to β-lactam antibiotics and it is used to treat possible MRSA cases.
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