Microbiology 101: Why antibiotics don't kill viruses

Originally published in The Ottawa Citizen January 28, 2003
Original Title: Oh I do so like squeezing bubblewrap

The problem of bacterial resistance to antibiotics remains a major public health concern. Last week’s column reviewed several measures to reverse this trend. Yet despite public education, there remains an expectation at times that antibiotics will eliminate that nagging week-long cold or flu. Viral infections do not get better with antibiotics but bacterial infection do.

It is important to understand the differences between viruses and bacteria in order to appreciate how antibiotics work.

A bacterium functions analogous to a house. Within the protective walls of the house reside the machinery, pipes, ductwork and appliances necessary to maintain a normal living environment.

At the house’s centre sits a table upon which lie the blueprints or plans for its construction and maintenance. Let us call these plans “Designs ‘N Architecture” or DNA.

Sitting around the table are Readers ‘N Administrators or RNA, the contractor. They will interpret the plans in order to instruct the subcontractors (the Ribo crew or ribosomes) what they must build or repair. In addition, the Ribo crew manufactures the materials for each task.

Using the DNA the contractor will build replicas of the house within the development. However, suppose someone thinks of a better way to build the walls, wants more energy efficient windows, a high efficiency furnace, automation among other changes. The contractor can incorporate these ideas into the DNA to improve future homes.

In fact, one house can share its improvements with a neighbour. The neighbour will incorporate these changes into the DNA because it affords them greater protection and resiliency.

Bacteria use, genetically speaking, DNA, RNA and ribosomes to help it carry out basic life sustaining functions: eliminate waste, feed, grow and reproduce.

Antibiotics can exploit these functions. It is no different than damaging a house. There are different types of antibiotics. Each either prevents bacterial growth (bacteriostatic) or kills them outright (bacteriocidal). The choice of antibiotic depends upon the type of infectious bacteria. For example, penicillin will cure Strep throat but will do nothing to clear up common pneumonias or bladder infections.

Antibiotics work by:

  • interfering with the construction of the wall, weakening it. The immune system can penetrate the bacterial wall and destroy its contents, literally blowing them up.
  • preventing the RNA from accurately reading the DNA. This kink in the assembly line leads to defective or inferior construction materials. Plans go awry. The ribosomes are unable to perform their tasks.
  • attacking the ribosomes halting all construction and repair. The remaining few cannot meet the demands of the job and produce defective walls or repairs.
  • poking holes in an existing wall breaking down the protective barriers. Antibodies and special immune system cells enter through these holes destroying the bacterium.

Bacteria can fight back by fortifying their walls, prevent the antibiotic from attaching to their walls and produce enzymes that inactivate the antibiotic. Other antibiotic-resistant bacteria can transfer pieces of their DNA to less resistant bacteria. In effect, they provide to their weaker brethren the secret of their antibiotic resistance.

Viruses are hundreds to thousands of time smaller than bacteria. They contain the plans to reproduce themselves but do not have the ability to carry them out on their own. They are the plans sitting on the table surrounded by four walls; simple strands of genetic material in a box.

Indeed, with respect to human disease, they are wanderers looking for a place to live. By inserting their genetic material into a human cell’s DNA, they take control of its day-to-day operations. They hijack the cell’s own machinery in order to reproduce. When the cell fills with viral particles, it ruptures. The virus spreads to other cells and the process begins anew.

Antibiotics cannot destroy viruses because they specifically target the machinery found in bacteria. Since viruses do not contain any of this machinery, the antibiotic does not have a target to attack.

Anti-viral medications and vaccines are can disrupt the reproductive cycle of the virus. These medications are not antibiotics. Vaccines stimulate the immune system to produce antibodies. The army of antibodies will mobilize and eradicate specific viruses before they cause harm.

Antibiotics can stop pain and suffering and save lives. As with all prescriptions, feel free to ask why this treatment is indicated. Your doctor should be willing to provide the answer.


© Dr. Barry Dworkin 2003

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