Tag Archives: Bacterium

Dr. C’s Journal: MRSA- Methicillin Resistant Staphylococcus Aureus

Staphylococcus aureus is a highly successful – eg.BAD – disease producing bacterium, or “pathogen”. From the standpoint of the bacterium, it didn’t know it was so bad, and was merely producing factors that break down its surroundings to produce food for multiplication. Unfortunately, the proteins-ENZYMES- produced by the staphylococcus, In its effort to survive, can cause anything from diarrhea, abscesses, high fevers, shock, and kidney failure to death.

The staphylococcus was very successful for thousands of years, until slowed down by penicillin.

Penicillin attached itself to a critical part of the staphylococcal cell wall, which stopped the bacterium from functioning. The staphylococcus retaliated by producing an enzyme, penicillinase, that destroys penicillin. Humans responded by producing methicillin, which resisted destruction by the penicillinase. The Staph responded again by a genetic change in the target of penicillin, PBP, so that the Methicillin wouldn’t attach, hence the term methicillin resistant staphylococcus aureus, MRSA.

Interestingly, the MRSA can send little packets of genes called “plasmids” to other bacteria, even other species, which take in the packets and allow them to resist methecillin also. This is called horizontal transfer of resistance.

The staphylococcus aureus has many other ways of protecting itself, and is a good example of the various ways a bacterium can deal with antibiotics.

It can prevent the antibiotic from gaining entrance, or pump it out of the cell faster. It can destroy the antibiotic, as with penicillinase. It can modify the bacterial target of the antibiotic, as in the PBP that protects from penicillin. It can also develop an alternative metabolic pathway or structure to bypass the effect of the antibiotic.

THIS IS WAR, similar to the human kind. The offense develops the sword. The defense develops the shield. The offense develops mounted archery. The defense develops the castle and so on.

We’re not so very different from the bacteria, and in fact every single cell of our bodies has descended from an ancestral  bacterial cell that engulfed another bacterium, which became the mitochondrion, a “slave cell” dedicated to producing thousands of times more energy than the simple bacterium, and leading to multicellular organisms.

Each organism develops appropriate defenses. Penicillium molds developed penicillin to protect themselves from bacteria and we took advantage of this. But it is a dynamic process, with both offense and defense having to adapt repeatedly over time.

In the next article, I will be discussing the bacterium Pseudomonas aeruginosa which is not as dynamic as the staph aureus; It specializes in people with problems, and is called a “facultative pathogen”.

However Pseudomonas is particularly good at exploiting its specialized habitat, which is increasing with the popularity of immunosuppressants and insertion of surgical hardware.

—Dr. C.

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