Antibiotics, Resistome and Resistance Mechanisms: A Bacterial Perspective

Abstract

History of mankind is regarded as struggle against infectious diseases. Rather than observing the withering away of bacterial diseases, antibiotic resistance has emerged as a serious global health concern. Medium of antibiotic resistance in bacteria varies greatly and comprises of target protection, target substitution, antibiotic detoxification and block of intracellular antibiotic accumulation. Further aggravation to prevailing situation arose on observing bacteria gradually becoming resistant to different classes of antibiotics through acquisition of resistance genes from same and different genera of bacteria. Attributing bacteria with feature of better adaptability, dispersal of antibiotic resistance genes to minimize effects of antibiotics by various means including horizontal gene transfer (conjugation, transformation, and transduction), Mobile genetic elements (plasmids, transposons, insertion sequences, integrons, and integrative-conjugative elements) and bacterial toxin-antitoxin system led to speedy bloom of antibiotic resistance amongst bacteria. Proficiency of bacteria to obtain resistance genes generated an unpleasant situation; a grave, but a lot unacknowledged, feature of resistance gene transfer.

Keywords: antibiotics; bacteria; bacterial resistance; diseases; health care.

Figure 1

Various ways of resistance mechanisms to counteract effect of antibiotics. Horizontal Gene transfer facilitates transfer and exchange of genetic material among bacterial cells. Transformation involves direct uptake of genetic material from the surrounding by competent recipient having chromosomal set of proteins. Transduction involves DNA insertion into chromosome as prophage which then replicates, packages host DNA alone or in combination with the host cell chromosome. Conjugative plasmids utilize a protein structure pilus to make a link with the recipient cell so as to move them into the recipient cell that ultimately transfers the copy of entire bacterial chromosome, multicopy plasmid or a small portion to a recipient cell, where these genetic elements insert into the chromosome or replicate independently if compatible with the inhabitant plasmids. Integrons use site specific recombination mechanism where it provides a promoter for gene cassettes to exchange and disseminate. Transposons and insertion sequences insert into new sites on the chromosome or plasmids by non-homologous recombination and increase the copy number of transferred genes giving rise to chromosomal mutations, deletions and rearrangements.