Antibiotic and antimicrobial feed additives

Since their discovery, antibiotics have been widely used in animals to prevent or treat diseases and, after the 1950s, as feed proficiency enhancers and growth promoters in animal farming (livestock and fish), although in smaller amounts. For instance, antibiotics such as oxytetracycline (OTC), aureomycin, bacitracin, penicillin, and streptomycin have been used in a quantity of 1 20 ppm (mg kg21) in combination with animal feed. If, on one side, such a “broadening” use of antibiotics allowed an improvement in animal production, on the other side, it raised several controversial environmental and ethical concerns. A typical example is the drawback derived from the antibiotics used in intensive fish farming for disease prevention and treatment, which is related to water pollution due to drug residue diffusion. It is worth noting that since the banning of antibiotics as growth promoters in the European Union and USA, with the only exception of metaphylactic and prophylactic purposes, their use in food-producing animals strongly decreased, suggesting that the control measures taken at country level were effective. However, there have been different pictures of these drugs’ use across countries. For instance, polymyxins (e.g., colistin) are halved in food-producing animals in the USA, positively impacting human hospitalizations where such drugs are the elective treatment for multidrug-resistant bacteria. On the other hand, in the European Union, polymyxins are used more in food-producing animals than in humans. In contrast, aminopenicillins, third- and fourth-generation cephalosporins, and quinolones are used more in humans than in food-producing animals. Despite the aforementioned considerations, antibiotic use increased in developing countries and is expected to rise by 67% by 2030 worldwide. Therefore, it is reasonable to hypothesize that such perpetrated use of antibiotics in animals is one of the leading causes of antibiotic resistance spread in the last 20 years among humans and pets. If antibiotic withdrawal times are not respected, or the drugs are administered through injection in food-producing animals, drug residues in foodstuffs (e.g., milk, eggs, and meat) can occur with consequent harmful effects on consumers’ and animals’ health. Many literature reports evidenced the presence of antibiotics in foods of animal origin [milk, cheese, honey, and meat] and pet food, shading the light also on their toxic effects in vitro and in vivo as a consequence of their use as feed additives.