Cipro Overview

Because of all of the news about Anthrax recently, the drug Cipro is being discussed daily. Cipro, the Bayer brand name for the drug ciprofloxacin, is one of the antibiotics that is effective against the anthrax bacteria.

In this edition of HowStuffWorks, we'll take a quick look at Cipro so that you can understand how it works against Anthrax.

How Bacteria Work: DNA and Enzymes

If you have read How Cells Work, then you are familiar with the inner workings of a typical bacterium and might want to skip this section. Here's a quick summary to highlight the most important points in How Cells Work -- we'll use the common E. coli cell as an example:

  • A bacterium is a small, single-celled organism. In the case of E. coli, the bacteria are about one-hundredth the size of a typical human cell. You can think of the bacterium as a cell wall (think of the cell wall as a tiny plastic bag) filled with various proteins, enzymes and other molecules, plus a long strand of DNA, all floating in water.
  • The DNA strand in E. coli contains about four million base pairs, and these base pairs are organized into about 1,000 genes. A gene is simply a template for a protein, and often these proteins are enzymes.
  • An enzyme is a protein that speeds up a particular chemical reaction. For example, one of the 1,000 enzymes in an E. coli's DNA might know how to break a maltose molecule (a simple sugar) into its two glucose molecules. That is all that that particular enzyme can do, but that action is important when an E. coli is eating maltose. Once the maltose is broken into glucose, other enzymes act on the glucose molecules to turn them into energy for the cell to use. Any cell has enzymes that help it digest food, add to the cell wall, duplicate DNA strands, produce energy molecules, and so on. The E. coli might have thousands of copies of some enzymes floating around inside it, and only a few copies of others. The collection of 1,000 or so different types of enzymes floating in the cell makes all of the cell's chemistry possible. This chemistry makes the cell "alive" -- it allows the E. coli to sense food, move around, eat and reproduce. See How Cells Work for more details.
  • To make an enzyme that it needs, the chemical mechanisms inside an E. coli cell make a copy of a gene from the DNA strand and use this template to form the enzyme. The DNA strand contains the templates for all 1,000 enzymes that the bacterium needs to live its life. A section of the DNA strand, called a gene, tells the cell how to manufacture one enzyme. That enzyme, once manufactured, then floats freely inside the cell and does its thing -- it helps the cell perform one of the chemical reactions that the cell needs to live. The process of manufacturing an enzyme from a gene on the DNA strand is amazing -- see How Cells Work for details.

You can see that, in any living cell, DNA helps create enzymes, and enzymes create the chemical reactions that are "life."

How Antibiotics Work

You can now see that the life of a cell is dependent on a rich soup of enzymes that float in the cell's cytoplasm.

An antibiotic is a poison that works to destroy bacterial cells while leaving human cells unharmed. All antibiotics take advantage of the fact that there are many differences between the enzymes inside a human cell and the enzymes inside a bacterium. If a toxin is found, for example, that affects a particular E. coli enzyme that does not even exist in human cells, then it may be an effective antibiotic. Streptomycin, for example, is an antibiotic that can gum up the ribosome in a bacterium but leaves human ribosomes unharmed (a ribosome is a large enzyme that helps to turn DNA information into new enzymes).

Penicillin was one of the first antibiotics. It gums up certain bacteria's ability to build cell walls. Since bacterial cell walls and human cell walls are very different, penicillin has a big effect on certain species of bacteria but no effect on human cells. The sulfa drugs work by disabling an enzyme that manages the creation of nucleotides in bacteria but not in humans. Without nucleotides, the bacteria cannot reproduce.

Antibiotics only work on living cells. Bacteria are living cells. Antibiotics have no effect on viruses. See How Viruses Work for details.

You can see that the search for new antibiotics occurs down at the enzyme level, hunting for differences between the enzymes in human and bacterial cells that can be exploited to kill bacteria without affecting human cells.

The problem with any antibiotic is that it becomes ineffective over time. Bacteria reproduce so quickly that the probability for mutations is high. In your body, there may be millions of bacteria that the antibiotic kills. But if just one of them has a mutation that makes it immune to the antibiotic, that one cell can reproduce quickly and then spread to other people. Most bacterial diseases have become resistant to some of the antibiotics used against them through this process.

How Cipro Works

Anthrax bacteria (Bacillus anthracis)
Anthrax bacteria (Bacillus anthracis)

Cipro is an antibiotic that happens to be effective against anthrax bacteria, as well as many other types of bacteria. For example, it will kill E. coli bacteria. It is helpful in treating bacterial infections that cause everything from bronchitis to gonorrhea.

According to the Bayer site, Cipro works in the following way: inhibits bacterial nuclear DNA synthesis, so that bacteria rapidly die. The target is the enzyme DNA gyrase (topoisomerase II), which is responsible for the supercoiling and uncoiling of the DNA. Supercoiling of the DNA allows the long DNA molecule to fit into the cell. Uncoiling of the structure is the initiative step for replication, transcription and repair of the DNA. Thus, prolonged inhibition will eventually lead to the death of the cell.

In other words, inside E. Coli bacteria and anthrax bacteria is an enzyme, called topoisomerase II, that helps the cell to wind DNA into a compact structure and then unwind it when needed. Cipro blocks topoisomerase II and prevents it from doing its job. A bacterial cell that has Cipro in it can no longer uncoil its DNA in order to create enzymes or reproduce. The bacteria containing Cipro eventually die.

There are reports that Soviet scientists created antibiotic-resistant strains of anthrax. One easy way to accomplish this would be to grow large quantities of anthrax and then treat it with Cipro to see if any of the cells lived. Then you would allow those few living cells to reproduce. These would be Cipro-resistant cells. However, they would not be resistant to other antibiotics that happen to work against anthrax.

For more information on Cipro, anthrax and related topics, check out the links on the next page.

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