1000/1000
Hot
Most Recent
There are three concepts linked to the growing resistance to antibiotics, namely (i) the Resistome, which refers to the collection of bacterial genes that confer resistance to antibiotics, (ii) the Mobilome, which includes all the mobile genetic elements that participate in the spreading of antibiotic resistance among bacteria by horizontal gene transfer processes, and (iii) the Nichome, which refers to the set of genes that are expressed when bacteria try to colonize new niches.
Antibiotic Type: Examples | Targets | Resistance |
---|---|---|
β-Lactams: penicillins, cephalosporins | Enzymes involved in cell-wall synthesis | Breakage of the β-lactam ring by β-lactamases. Decreased uptake or increased efflux of the β-lactam. Changes in the active site of the target. |
Cationic peptides: colistin, polymyxin B | Bacterial membrane | Lipopolysaccharide modifications. Efflux pumps. Capsular polysaccharide production. |
Fluoroquinolones: ciprofloxacin | DNA gyrase and topoisomerase IV | Mutations in target enzymes. |
Rifamycins: rifampin, rifabutin, rifapentine | RNA polymerase | Mutations in the RNA polymerase (β subunit). Drug inactivation. Impeded uptake of the drug. |
Aminoglycosides: streptomycin, gentamicin | 30S ribosomal subunit | Enzymatic modification of the drug. Enzymatic modification of the target site. Efflux pumps. |
Tetracyclines: tetracycline, doxycycline, minocycline | 30S ribosomal subunit | Efflux pumps. Ribosomal protection proteins. Enzymatic inactivation of tetracycline. |
Phenicols: chloramphenicol, thiamphenicol, florfenicol | 50S ribosomal subunit | Ribosomal mutations. Enzymatic modification (methylation) of the target site. Enzymatic inactivation (acetylation) of the drug. Efflux pumps. |
Macrolides: erythromycin, azithromycin, clarithromycin | 50S ribosomal subunit | Ribosomal modification by methylation or mutation. Efflux pumps. Drug inactivation. |
Lincosamides: clindamycin | 50S ribosomal subunit | Ribosomal modification by methylation or mutation. Efflux pumps. Drug inactivation. |
Sulfonamides: sulfamethazine, sulfadiazine |
Dihydropteroate synthase in the folic acid pathway | Mutations in the target enzyme. Sulfonamide resistance mediated by HGT (genes encoding variants of the target enzyme). Drug degradation. |
Element | Main Features |
---|---|
Plasmids | DNA molecules that replicate autonomously. |
Conjugative Plasmids Mobilizable Plasmids |
Encode all elements needed for conjugation. Encode a relaxase and an origin of transfer. Need the conjugative machinery provided by ‘auxiliary’ plasmids. |
Integrative and Conjugative Elements (ICEs) | Integrated elements that can excise, replicate, and transfer by conjugation. Previously termed ‘Conjugative Transposons’. |
Integrative and Mobilizable Elements (IMEs) | Integrated elements that can excise and replicate but need conjugative machinery provided by ‘auxiliary’ elements for their transfer. Previously termed ‘Mobilizable Transposons’. |
Insertion Sequences (ISs) | Integrated elements that encode only transposition machinery. |
Prophages | Bacteriophage genomes totally or partially inserted into the host chromosome. |
Phage satellites | Elements that exploit phages for transfer between bacteria and can encode ARGs. |