Table 1.

Mechanism of antibiotic resistance.

S. No.	Kind of antibiotic resistance	Mechanism involved in resistance
1	Restricting entry of antibiotics	Antibiotics spread out in the cell through the occurrence of mutations in the gene which specifically encodes the outer membrane porin protein, and this results in the change in OMPK36 variant porin which shows less permeability for the antibiotics in Klebsiella pneumonia [159]. Because of the downregulation of the main porin protein or refilling the cell membrane with some another selected protein channel, the permeability of membrane for antibiotics in some bacteria such as E. coli and Acinetobacter is decreased [160].
2	Accession of various efflux pump genes related to chromosomal and plasmid	Through strong efflux pumping, the numbers of antimicrobials are launched out of the cell. Their overexpression allows resistance to formerly effective antibiotics example—MDR efflux pump in Pseudomonas aeruginosa and E. coli [161].
3	Moderation and defense of antibiotic target	By changing the arrangement of the targets, the binding affinity of antibiotics can be reduced. Klebsiella pneumonia and Staphylococcus aureus are found to be resistant to linezolid, and this is achieved by the mutation in allele which encodes the 23 s rRNA ribosomal subunit [162]. Development of resistance to the certain drugs such as macrolids, lincosamines, and streptograminscan be attained by doing methylation of their binding site and the 16 s rRNA by the action of enzyme called erythromycin ribosomal methylase and family. Resistance to the several other group of drugs such as penicillin, pleuromutilins, lincosamides, and oxazolidons can be achieved with the help of enzyme chloramphenicol florfenicol resistance methyltransferase through the incorporation of CH3 to A2503 in the 23 s rRNA [163]. Resistance to methicillin in S. aureus is because of the genetic discovery of chromosomal mec A which records a single binding protein for extra penicillin, PBP2a, with a less affinity for all β-lactam [164].
4	Antibiotic opposition via hydrolytic enzymes	The resistance is achieved by chromosomal detection, and plasmid-mediated encoding genetic enzyme degrades with antibiotics, for example, β-lactamase which includes penicillinase only degrading penicillin, cephalosporinases deactivate cephalosporins and aminopenicillins, and expanded beta-lactamases, which play an important role in digesting all β-lactam, but carbapenemase and carbapenem disabled the whole β-lactamase [165].
5	Moderation of antibiotic resistance	Detection of gene enzymes is deactivated by antibiotics with the addition of an active functional group. For instance, resistance to aminoglycolides in Campylobacter coli (C. coli) that is microaerophilic Gram-negative bacteria is caused by nucleotidylation, acetylation, and phosphorylation of its -OH and CO-NH groups by acetyl transferases, phosphotransferases, and nucleotidyltransferases [166].