Most bacteria are less than 1mm in length. Therefore hundreds of thousands of bacteria can fit into a space the size of the full stop at the end of a sentence. On the other hand, colonies of bacteria can easily be viewed without a microscope. Bacteria have been designed to be adaptable. Their surrounding layers and the genetic information for these are capable of alteration. Some alterations are reversible, disappearing when the particular pressure is lifted (Therefore “old “drugs are all of a sudden effective again).
Other alterations are maintained and can even be passed on to succeeding generations of bacteria (the problem for us). A bacterium reproduces by means of a process called binary fission, in which a copy of the DNA is made and then the outer membrane of the bacterium begins to grow inward and divides the bacterium into two identical cells. However, binary fission does not provide bacteria with a way to exchange genetic information between individuals. Bacteria transfer genetic material by means of a process called conjugation, in which one bacterium attaches itself to another bacterium and introduces DNA directly into it by means of a pilus.
The first antibiotic was discovered in 1929. Since then, huge numbers of naturally occurring and chemically synthesized antibiotics have been refined/developed/used to control bacteria. Normally, the introduction of an antibiotic is frequently followed by the development of resistance of the bacteria to the antibacterial agent by means of the adaptation. This adaption of resistance to antibiotics can develop swiftly. For example, resistance to penicillin was recognized almost immediately after introduction of the drug. With the approach of new millenium, almost 80% of all strains of Staphylococcus aureus were resistant to penicillin. Meanwhile, other bacteria remain susceptible to it.
The adaptation of bacteria to an antibacterial agent such as an antibiotic can occur in two ways. The first method is known as natural resistance. For example, gram-negative bacteria are often naturally resistant to penicillin. This natural resistance is because these bacteria have a different outer membrane and penicillin cannot penetrate it effectively.
The second category of adaptive resistance is called acquired resistance. Mostly when bacteria acquire resistance to an antibiotic, the cause is a membrane alteration that has made the passage of the molecule into the cell more difficult. This acquired resistance is almost always through a change in the genetic make-up of the bacteria. Acquired resistance occurs because of mutation or when the bacteria respond in a certain way to the effects of the antibiotic. Once resistance occurs, the genetic alteration can be passed on to subsequent generations. This acquired adaptation and resistance of bacteria is the problem that we are facing now and which will haunt us unless we can find effective alternatives to take us into the future.
Bacteria adapt to other environmental conditions as well and therefore to certain chemicals in the water.There are no need to elaborate too much on the process but some of the adaptations occur in the properties of both the interior of the organism and its surface membrane. Bacteria can also sense the chemical composition of the environment and either moves toward an attractive compound, or shifts direction and moves away from a substance sensed as being detrimental.
All the adaptations of bacteria involve some kind of memory as well as the adaptation of the genes to ensure the survival of their species. These changes can profoundly affect the ability of antibiotics to kill the bacteria. What is interesting is that a bacterial strain has the ability to generate variable offspring where some will be resistant to a new chemical, while others are not. This strategy (bet-hedging) ensures the survival of the bacterial strain under various circumstances. In fact, bet-hedging means that a generation produces offspring that is genetically identical, but differs in the ability to prosper in the current environment. Some offspring is optimally adapted to the current environment, while others thrive under completely different conditions. In case of rapid and drastic changes of the environment, the latter offspring is at an advantage and hence the species survives.
As stated above, bacteria transfer genetic material by means of a process called conjugation, in which one bacterium attaches itself to another bacterium and introduces DNA directly into it by means of a pilus. The upsetting part of this transfer of genetic material is that it can actually happen in ponds between “good” and “bad” bacteria, and even from virus to bacteria.
At least now one can understand the tremendous risks involved in mixing antibiotics in koi feed where a large percentage will be released into the water. Add to this the fact that it will be impossible to measure the dosage eventually ending op in the intestines of the fish and we are well on our way to create superbugs!
Last Updated on Tuesday, 30 November 2010 10:30