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Picture credit : University of Queensland


The organisms living on planet earth are widespread in many categories based on the level of organization, complexity of functions, and size. Those organisms which can be seen with the help of microscope are called microorganism, having Size range of 1 millimeter or less in diameter. There are some microbes which are visible to naked eye: bread mold, filamentous photosynthetic microbe, and bacteria like thiomargsrits namibiensis, their individual cell can grow up to 0.7 mm wide.

These tiny creatures play a pivoted role in human metabolism, and regulation of life sustaining cycles. However some of them are pathogenic, can cause lethal infections ranging from mild to chronic disorders. To combat such harmful flora , Laboratory made medicines are used , and in some cases the immune system of living organism are trained with the help of external regulators to prevent infection. These are called anti-microbial agents. Alongside, due to frequent exposure to these anti-microbial agents, some of them show resistance.

The phenomena through which the microbe show resistance to any anti-microbial agent is coined as Anti-microbial resistivity.

The opposition shown by microbes to antibiotics, antiviral, and antifungal agents is called anti-microbial resistance. The adoptability of microbe to show resistivity is due to the mutation with the passage of time and this change in behavior depend upon the level of exposure to these anti agents.

Antibiotics are the class of anti-microbial agent which are specialized in provoking the immune system of living organism to fight back. What happened is? , the recurrent exposure to these antibiotics substantial fluctuate the DNA of the microbe and it developed the mechanism to combat. In some cases the resistance gene present in plasmid of some bacteria functioned in the same fashion and with subsequent exposure and generation, the bacteria became resistant to such antibiotics.

When bacteria enter the body, they multiply inside the body and make its progeny and cause an infection. So antibiotic act against bacteria. Either to inhibit the growth of bacteria or to kill bacteria, to prevent infection antibiotic are use. Antibiotics which inhibit the growth of bacteria are called bacteriostatic or unlikely those who are act to kill bacteria are called bactericidal.  Antibiotics are functionless when it comes to viral infection.




  1. Modification in physical structure

Bacteria modify its outer membrane so that less antibiotic enter the bacterial cell. Example: Gram negative bacteria.

  1. Unload the antibiotics

Bacteria have pumps (Efflux) in their membrane which pump out the antibiotics out of the cell. Example: Pseudomonas aeruginosa pumps out the beta lactam and trimethoprim etc.

  1. Alter/change or destroy the antibiotics

Bacteria release the enzyme, protein and chemical which alter the bonding of antibiotics. Example: Beta lactamase, an enzyme produce by the bacteria to break ring in beta lactam antibiotics.

  1. Mutate targets for the antibiotics

The target of the antibiotic is modified either mutating the gene responsible for that target or code an enzyme which alter the target. Example: resistance to vancomycin. Genes of bacteria which synthesized protein that changes the Penta peptide of peptidoglycans. The bacterium which produce antibiotics must have resistance gene .The antibiotic resistance gene are present on the chromosomes, resistance plasmid, and transposable elements. Thus, resistance encoding genes are transmissible from one bacterium to another through horizontal gene transfer. Bacterium which are not producing antibiotics are called non-producer. So in such cases chromosomal mutation occurs and it makes a difference in the drugs target.


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