Question

List four ways in which a microorganism can be resistant to an antimicrobial agent and explain why they can or can’t be transferred to other microorganisms.

Answer 1

The four methods by which a microorganism can develop resistance to antibiotics:

1) Resistance due to altered receptors:

Penicillin resistance can be obtained due to alteration of penicillin binding proteins. ?-lactams induce synthesis of a new penicillin-binding protein, PBP2a. PBP2a does not bind any ?-lactam. There may also be less affinity of the penicillin binding proteins to penicillins.

Acquisition of transposons leads to synthesis of special cell wall-synthesizing enzymes that change the normal D-Ala-D-Ala side chain in the peptidoglycan assembly pathway. This will prevent vancomycin binding to peptidoglycan. Methylation of two adenine nucleotides in the 23S component of 50S RNA leads to macrolide resistance.

2) Resistance due to decrease entry of drug:

Less binding of drugs to plasma membrane and entry into the cell will cause resistance. Tetracycline bind to plasma membrane and diffuse through outer layer of cell. If the drug doesn’t not bind to plasma membrane they will not be effective. Fosfomycin and fosmidomycin inhibit cell wall synthesis. They enter bacteria by means of a glycerol-phosphate or glucose-6-phosphate transport system. If this system is inhibited, resistance will occur.

3) Resistance Due to Destruction or Inactivation of a Drug:

Micororganisms have the enzyme chloramphenicol transacetylate. It acetylates hydroxyl groups on the chloramphenicol structure, thereby inducing resistance to chloramphenicol. Presence of penicillinase enzyme will give resistance to penicillin. Penicillinase breaks down penicillin.

4) Synthesis of Resistant Metabolic Pathway:

Some streptococci lack hydrolytic enzymes to form cell wall. These organisms are therefore resistance to beta lactam antibiotics. An altered hydrolytic system can convert a bactericidal agent to bacteriostatic agent. Flucytosine resistance in yeast is because they cannot convert it to its active component, fluorouracil.

Bacterial antibiotic resistance can be transferred to other microorganism by various methods. When a bacteria that has acquired antibiotic resistance grows and divides, it transfer the resistance to the new bacteria formed. This is known as vertical transfer. In horizontal transfer, bacteria can transfer resistance by conjugation, transformation, and transduction. Environmentally resistance can be transferred when bacteria move from place to place and host to host in different places. People can transfer antibiotic resistance via coughing sneezing etc.