TABLE 1.

The most commonly used antibiotics and the relative ARGs in livestock production (DHPS, dihydropteroate synthase; DHPR, dihydropyridine-resistant).

Antibiotic family	Most used	Animal Farming	Use	Contrasted bacteria and recognized main targets	Resistance mechanism	Main ARGs
Macrolides	Tylosin	Cattle	Gastrointestinal and respiratory infections	Gram-positive bacteria.	Interference with protein synthesis (sequestration of mRNA ribosome-binding site)	erm, msr, mef genes
	Erytromycin	Pig		Main target: Lawsonia intracellularis
	Clarithromycin	Poultry		Staphylococcus aureus
Sulfonamides	Sulfamethazine	Cattle	Urinary tract infections	Gram-positive and Gram-negative bacteria. Main target: Enterobacteriaceae, Pasteurellaceae	Interference with folic acid synthesis competing for the enzyme DHPS	sulI, sulII genes
		Pig	Respiratory infections
		Poultry
Tetracyclines	Chlortetracycline	Cattle	Systemic and local infections	Gram-positive and Gram-negative bacteria	Interference with efflux pump systems	tet genes
	Oxytetracyclines	Pig	Gastrointestinal and respiratory infections
	Doxycycline	Poultry
Quinolones	Fluoroquinolones (Enrofloxacin, Danofloxacin, Marbofloxacine)	Pig	Intestinal infections	Gram-positive and Gram-negative bacteria, including mycobacteria, and anaerobes	Mutations in the genes encoding quinolone target DNA gyrase and topoisomerase IV, interference with efflux pump systems	qnr genes
		Cattle
β-lactams	Penicillins (Amoxycilline, Ampicillines) Cephalosporins, Carbapenems	Pig	Respiratory diseases	Gram-positive and Gram-negative bacteria	Interference with cell wall synthesis and permeability, inactivation through β-Lactamase enzyme	bla, amp, pen genes,
		Cattle	Necrotic enteritis
		Poultry
		Dog
		Cat
Aminoglycosides	Streptomycin, Spectinomycin, Neomycin, Aspramycin, Gentamycin, Lincomycin	Pig	Intestinal infections	Gram-positive, and Gram-negative bacteria, if aerobic	Inhibition of protein synthesis (rhibosome interference)	aac, aad, aad aph genes
		Poultry
Phenicols	Chloramphenicol	Pig	Respiratory disease, foot rot	Broad spectrum. Main target: Photobacterium, Salmonella, E. coli	Enzymatic modification of antibiotic molecules	cat, pp-flo, flo genes
	Thiamphenicols (thiamphenicol, florfenicol)
Diaminopyrimidines	Trimethoprim	Horse	Post-weaning scours	Gram-positive and many Gram-negative bacteria. Main target: Enterobacteriaceae	Interference with folic acid synthesis by binding the enzyme DHFR	dfr genes
		Pig
Polypeptides	Bacitracin, Colistin	Pig	Intestinal diseases	Gram-positive (Bacitracin) or Gram negative (Colistin) bacteria. Main Gram negative target: E. coli Salmonela spp. Pseudomonas aeruginosa, Klebsiella pneumoniae, or Acinetobacter.	LPS modification, efflux pump systems regulation	pmr,pho, mcr, kpn genes
		Poultry		Main Gram positive target: Campylobacter
Lincosamides	Lincomycin	Pig	Respiratory and Intestinal infections	Gram positive bacteria, most anaerobic and some mycolpasma species. Main target: Staphylococcus aureus	Alteration of the antibiotic target site	lnu, lin, erm genes
		Poultry
		Cattle
Pleuromutilins	Tiamulin	Pig	Respiratory and Intestinal infections	Pasteurellaceae, Brachyspira, Micoplasma	Alteration/protection of the antibiotic target site	vga, sal, lsa genes
	Valnemulin	Poultry

References: (Schwarz et al., 2001; Petinaki et al., 2008; Guardabassi et al., 2009; Abbas et al., 2011; Van Hoek et al., 2011; Li et al., 2013; Shang et al., 2013; Tasho and Cho, 2016; Deng et al., 2017; Aghapour et al., 2019; https://www.msdvetmanual.com/pharmacology/antibacterial-agents).