Streptomycin is an aminoglycoside antibiotic that inhibits bacterial protein synthesis by binding the 30S ribosomal subunit. Resistance is commonly mediated by the aadA gene, which encodes aminoglycoside adenyltransferase. This enzyme modifies streptomycin and spectinomycin, rendering them inactive. The aadA gene is frequently found on class 1 integrons and plasmids, making it a key marker for horizontal gene transfer and antibiotic resistance surveillance in environmental and clinical settings.
Gentamicin is a broad-spectrum aminoglycoside antibiotic that disrupts bacterial protein synthesis by binding the 30S ribosomal subunit. Resistance is often mediated by the aadB gene, which encodes an aminoglycoside adenyltransferase that inactivates gentamicin (as well as tobramycin and kanamycin). The aadB gene is typically found on class 1 integrons and plasmids, facilitating its horizontal transfer across bacterial populations in clinical and environmental settings.
Cephalosporins are B-lactam antibiotics that inhibit bacterial cell wall synthesis by targeting penicillin-binding proteins (PBPs). Resistance is commonly mediated by the ampC gene, which encodes a class C B-lactamase capable of hydrolyzing cephalosporins, especially second- and third-generation drugs. Unlike other B-lactamases, AmpC enzymes are often chromosomally encoded but can also be plasmid-borne, enhancing their mobility and contributing to multidrug resistance in both clinical and environmental bacterial populations.
Macrolides (e.g., erythromycin, azithromycin) are antibiotics that inhibit bacterial protein synthesis by targeting the 50S ribosomal subunit. Resistance is commonly conferred by the ermB gene, which encodes an rRNA methyltransferase that modifies the 23S rRNA, reducing macrolide binding. The ermB gene is widely distributed among Gram-positive and Gram-negative bacteria and is often located on mobile genetic elements, making it a key marker for monitoring antibiotic resistance in both clinical and environmental microbiomes.
