Ciprofloxacin is an antibiotic. Medical professionals use antibiotics to kill bacteria, but bacteria tend to be very adaptable to their environment and can develop resistance to the previously lethal effects of ciprofloxacin. Ciprofloxacin resistance is important in medicine as the bacteria that the drug can combat include several significant species that cause disease, such as Klebsiella, E. coli, and Salmonella.
Bacteria are single-celled organisms. Each cell contains genetic material that act as an instruction booklet for the cell to read. All the functions and products of the cell are encoded by the genetic material. As well as the genes, the cell contains internal machinery that make the products the cell needs to stay alive and to grow. Finally, the cell has structural components that keep the cell safe from the outside environment as much as possible. In the external wall of the cell, channels exist that allow useful substances inside while keeping most of the detrimental substances outside.
Any substance that can kill one of these cells, when it infects a person, is called an antibiotic. Cell death can occur if the chemical breaks it up from the outside or if it makes its way inside and breaks its machinery. Ciprofloxacin works from the inside of the bacterial cell and targets one specific enzyme inside.
Antibiotic resistance arises because bacteria can mutate, or change their genes. The new gene form can code for a product that is better than the previous version at surviving attack by the antibiotic. As bacteria commonly occur in large numbers, if a course of antibiotics does not kill all the bacteria present, then the surviving bacteria, with the new version of the gene, can multiply back out of control.
As ciprofloxacin works against the bacterium from the inside of the cell, in order to work, it needs the bacterium to allow it in. One form of ciprofloxacin resistance appears to be that resistant bacteria have versions of genes that instruct the cell to build channels in the wall that keep some of the antibiotic out. Another avenue of ciprofloxacin resistance is that cells produce new forms of pump mechanisms, which pick up the antibiotic molecules inside the cell and throw them outside.
Inside the cell, ciprofloxacin targets an enzyme called DNA gyrase, which helps the cell to divide and grow. If the DNA gyrase cannot work properly, then the bacterium cannot multiply, and the old cell eventually dies of old age. For the ciprofloxacin to work properly, it needs to be able to recognize the enzyme in order to bind to it. An important mode of ciprofloxacin resistance, therefore, is that bacteria change the gene that codes for the enzyme and make a version of the enzyme that ciprofloxacin does not recognize. Resistant bacteria can then divide and multiply as normal.
Resistance to antibiotics is an ongoing process, and bacteria, as long as they can mutate, can develop new ways of becoming immune to a chemical. Doctors can, however, slow down the process by restricting the types of infections that ciprofloxacin can be used to treat. Patients are also required to finish an entire course of ciprofloxacin to ensure that all the susceptible bacteria are dead and do not have time to develop drug resistance.