Physical-Chemical Properties of MRSA Fighting Agents


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MRSA treatments have changed over the years, as the staph bacteria have become more resistant to various antibiotics. Image by Decoded Science

MRSA treatments have changed over the years, as the staph bacteria have become more resistant to various antibiotics. Image by Decoded Science

MRSA poses a significant problem for the medical community and human population during the 21st century, as it becomes more and more resistant to common antibiotics.

Doctors now use a next- generation antibiotic that is recently FDA-approved to cure this drug-resistant staph infection. The new-generation antibiotic, Dalbavancin, differs from the original effective medicine of 1950, Penicillin, by many orders of magnitude.

Dalbavancin ‘out weighs’ Penicillin by approximately 2/3 and examination of the two structures reveals a level of complexity that is mind boggling. The two molecules are shown here, side-by-side.

MRSA Antibiotics: Molecular Overview

Looking at the two antibiotics, it can be difficult to grasp the biochemical properties of the molecules. You can easily see the red, blue, green, and yellow colored letters (elements) in the structures. These ‘hotspots’ are the points of discrete, molecular recognition for the antibiotics.

How can two molecules that are clearly so different function in the same way?  Easy answer: They do not function in the same manner. The aforementioned hotspots are points of chemical functionality for the molecules – it is the functionalities that allow the body to either completely metabolize the molecule, or let pass from the gut into the bloodstream.

After the drug/antibiotic has entered the bloodstream, the molecule is distributed throughout the body. Because antibiotics act indiscriminately, they aim to remove all bacteria from the body.

When a molecule ‘approaches’ the targeted-enzyme, physical-chemical properties guide the molecule. We can state these in terms of electronics and energetics: The electronic properties determine how a molecule is recognized, while the energetics determine whether the recognition is the ‘best fit.’

Properties of Bio-Molecular Interaction

Water allows our bodies to transport bio-molecules such as penicillin to the targeted areas of our bodies. Once dissolved, the molecule is buffeted by ‘solvent molecules’ – at this point, we can’t see it as we could have earlier. The solvent molecules are ‘pseudo-electronic’ forces that act upon the molecule—bending the once-stiff geometry in the crystalline phase to a geometry that flows with the fluid environment.

Looking at these particular molecules, the variations in size allow for an understanding in how the number of  variables in the molecular geometry give rise to molecular ‘best fit.’

Penicillin vs. Dalbavancin

Penicillin, the original ‘best molecule,’ had a fairly compact geometry that allowed for fewer degrees of freedom or less propensity to be buffeted by the surrounding environment. Once the molecule reached its destination, it disrupted the bacterial cell walls and prevented the infection from progressing.

Dalbavancin, the new drug, is large, and contains multiple functionalities (or molecular groups) and this is why it is effective. The colored elements within the drug allow it to fold-or bend towards the watery solvent. The grey areas of the molecule do not solvate well in bodily fluids. So, as the drug is buffeted within the water, it will adapt by exposing the parts of the molecule that are able to protect sensitive parts of the drug.

This happens day-in-and-out as the drugs we ingest flow in and out of different environments in the body. In regions where water dissolution is not as important (fatty tissue, cell membranes or disrupting the biosynthesis of a bacterial cell wall), the grey portions of the molecule act to protect (or carry) the other sensitive areas of the molecule towards the target.

Fighting Bacteria With Chemistry

The history of fighting bacterial infections is one of adaptation. Nature evolves as humanity works on the artificial evolution of medications to combat infections such as MRSA, and chemistry is at work on both sides of the equation.

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