How do microorganisms become resistant to antibiotics?
A chemotherapeutic agent is defined as a chemical substance used for the treatment of infectious diseases or diseases caused by the proliferation of malignant cells. A special group of chemotherapeutic agents, which are usually derived from microorganisms, are called antibiotics. In fact, antibiotics have come to refer to metabolic products of certain microorganisms that are inhibitory or obviously harmful to other microorganisms in very small amounts.
Although there are about a hundred different drugs classified as antibiotics, all of them fall into one of two categories: the narrow-spectrum antibiotics and the broad-spectrum antibiotics. Drugs in the former category (example, penicillin) target specific strains of bacteria, while those in the latter category (example, streptomycin) are capable of inhibiting or killing a wide range of different microorganisms that cause diseases.
Is it safe to say then that a person has to take antibiotics for every ailment or disease he contracts? The answer is no. We have to understand that taking antibiotics excessively can lead to microorganisms acquiring antibiotic resistance. The more a person takes antibiotics, the more often disease-causing microorganisms may mutate into forms that are resistant to antibiotics.
The instance of microorganisms developing antibiotic resistance seems to be a never-ending process. There are several reasons why microorganisms develop a tolerance to antibiotics. For one, antibiotic resistance may be due to a preexisting factor in the microorganism, or it may be because of some acquired factors. Resistance to penicillin, for example, may be due to the production by resistant microorganisms of penicillinase, an enzyme that inactivates penicillin by hydrolyzing it.
Some normally unresistant strains of bacteria, on the other hand, may acquire resistance to penicillin. Acquired resistance in this case may also be due to the production of penicillinase in the different types of genetically adapted microorganisms. Still, a lot of microorganisms which do not produce penicillinase are also resistant to penicillin. This implies the possibility of an alternative metabolic pathway or enzyme-catalyzed reaction that is not susceptible to inhibition by penicillin.
Besides the production of penicillinase by microorganisms, there are other reasons for antibiotic resistance. One reason is that It may be due to the production of an enzyme altered in such a way that it works in support of the cell but is not affected by the antibiotic. Alteration of ribosomal protein structure is another reason. In other cases, antibiotic resistance may be due to the development of an alternative metabolic pathway which bypasses some reaction that would normally be restrained by the antibiotic.
Three other possible reasons for antibiotic resistance must be mentioned here: synthesis of excess enzyme that is more than the amount that can be made inactive by the antibiotic; competitive inhibition between a substance that is essential to the metabolism of a particular microorganism and a particular antibiotic; and the lack of sufficient power or capacity of the antibiotic to penetrate the cell because of some alteration of the cell membrane.