antibiotic pills

Colistin Molecule Monday: Antibiotic Resistance

Colistin: No longer a drug of last resort?

Colistin (Polymyxin E), an antibiotic has been mentioned widely in the news recently. Colistin is not a new drug; it has actually been around for 50 years but was shelved early on due to kidney toxicity.  By reason of this market absence, it had been among the few antibiotics to which some Gram negative bacterial strains had not developed resistance. Due to its toxicity it has been limited to use in animal feed. Colistin is especially popular in China where it is made cheaply for both agricultural and veterinary use. The news of bacterial resistance to Colistin was discovered by Chinese researchers.

What does this mean? Well, first let’s look to see how antibiotics actually work…

How do antibiotics work? Antibiotic pills

Prior to antibiotics, bacterial infections were treated by either removing the infected body part, or waiting to see if the body could stave off the infection by itself. The discovery of antibiotics happened by chance in 1928 when Alexander Fleming came back to work after a weekend away from his lab and found a certain type of mold, Penicillium notatum, had halted the growth of Staphylococcus. He soon realized this would work against many other types of bacteria.

Antibiotics only work against bacterial infections. They have mistakenly been prescribed for use against viral infections, including colds, sore throats, coughs & influenza further contributing to antibiotic resistance.

There are different types of bacteria which require different antibiotics. The two main types are Gram-positive and Gram-negative. In a nutshell, Gram positive bacteria have thin permeable cell walls while Gram negative have thicker, less penetrable, two-layer cell walls.

Antibiotics kill bacteria mainly in these 3 ways:

1. Interfering with a bacterium’s ability to repair damaged DNA

2. Stopping a bacterium’s ability to make what it needs to grow & divide

3. Weakening the bacterium’s cell wall until it bursts

Why is antibiotic resistance bad?

Bacteria can become resistant to the effects of antibiotic drugs to which they were previously vulnerable. Over time through natural selection and selective pressure, bacteria accumulate gene variants that allow them to become resistant. When we overuse or improperly administer antibiotics, we give bacteria the opportunity to adapt and grow antibiotic resistance. Given enough time, all our antibiotics could become obsolete. This is why the discovery of a Colistin resistant bacterial strain is worrisome, as it was seen as a “last resort” antibiotic.


Colistin Molecule Structure

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