Antibiotic contamination of the environment, fueled by industrial-scale use in livestock production in some countries, is a global problem that requires addressing, according to the authors of a just-published review.
The global challenge is to reduce and improve antibiotic use, Lizbeth Robles-Jimenez and her fellow researchers wrote in the journal Animals.
The review team set about examining previously published research on antibiotic drug residues, evaluating the use of these drugs in livestock production and their excretion in animal products, and in water and soil.
Antibiotics are widely used in some parts of the world for disease treatment, health protection, and as growth promoters in animal production.
The authors noted that the absorption of antibiotics in animals after administration is often poor and a significant proportion, 70 to 90%, may be excreted without being metabolized. “These residues remain unchanged in the environment.”
The authors found 165 published studies in all, reporting the concentration of antibiotic residues found in the environment, livestock (cow, sheep, pig, horse, chicken, rabbit, goat), aquatic and terrestrial animal tissues, animal products (milk and eggs), wastewater, and soil. The papers were obtained from Asia, Africa, North America, South America, Europe, and Oceania.
The largest user of veterinary antibiotics worldwide are China (45%), Brazil (7.9%), the United States (7.0%), Thailand (4.2%), India (2.2%), Iran (1.9%), Spain (1.9%), Russia (1.8%), Mexico (1.7%), and Argentina (1.5%).
The review team said the residue levels of antibiotics based on continent showed a marked variability among antimicrobial families.
The antimicrobial with the highest concentration in Asia was cephalosporins, followed by fluroquinolone.
The tetracyclines were the antibiotic family with highest residual concentration in Africa and North America. In South America, the family of antibiotics that showed the highest level of residues was fluroquinolones, followed by macrolides.
In Europe, the largest concentration of residues was shown by ß-lactam, followed by nitroimidazole.
“It is important to note,” they said, “that there is a particular distribution of antibiotic use by geographical area depending on their policies, economic/market conditions, and dietary habits.”
The authors noted that the regulation of antibiotics in animal feed, for growth promotion or therapeutic use, is a priority for the Asian region, and policies for their prohibition have been developed. However, few countries have the capacity to guarantee their application.
The Chinese government has implemented a series of policies to control the use of antibiotics in livestock, including the requirement for a prescription. However, they are still purchased without prescription and not monitored at most farms.
In Russia, farmers can use antibiotics without any restrictions, while some feed antibiotics are subject to state control.
The researchers noted that an improved standard of living in India had led to a demand for animal protein with consequent intensification of pig, poultry, and fish farming, with a resulting significant effect on the use of antibiotics.
“When talking about meat producers, one must mention the world’s leading meat producers, North and South America, which are also among the main consumers of veterinary antibiotics.
“For example, the United States uses 24.6 million pounds of antimicrobials for non-therapeutic purposes in chickens, cattle, and pigs, the most commonly used being tetracyclines, penicillins, fluroquinolones, and sulfonamides, and Brazil, being the fourth largest pork producer in the world, uses sulfonamides.
“However, although government agencies are trying to regularize the use of antibiotics, producers are not willing to stop using them, as they consider that it would be impossible to sustain current market demands without the use of antimicrobials.
“In our study, we can confirm this since most of the articles found on antibiotic residues were from the USA and Mexico. Although Brazil is one of the largest meat producers, only one article was found, which may be due to the lack of published reports and complex political barriers.”
The researchers said that although most countries have joined in the program of non-misuse of antibiotics in food animals, publication of reports, complex political, economic, and social barriers still limit the quality of data on this issue.
Data on the use of antibiotics is more readily available from countries that export a significant portion of their animal production, than those countries where most production is destined for the domestic market.
The authors said there is environmental pressure on microorganisms in soil and water when antibiotic contamination is present, forcing a selection on the reduction in the diversity and composition of the microbial community.
“Appreciating that antibiotic exposure tends to favor an increase in Gram-negative bacteria compared to Gram-positive bacteria, this will result in the disruption or loss of bacteria that play key ecological roles such as in the decomposition of matter,” they said.
They acknowledged that new international policies have limited antibiotic use as therapeutics, restricting their use as growth promoters in animal production.
“Intensive livestock production must change, as it would be impossible to sustain current market demands without the use of antimicrobials or friendlier alternatives, with a future decrease in antimicrobial resistance, so we are challenged to reduce their use.
“At present, despite the trends of increased regulations on the use of antibiotics worldwide, antibiotics are still utilized in food animal production, and are present in water and soil.”
The misuse of antibiotics continues in many countries, they said. “We need to become aware that antibiotic contamination is a global problem, and we are challenged to reduce and improve their use.”
The review team, from a range of institutions, including the Autonomous University of Mexico State, comprised Robles-Jimenez, Edgar Aranda-Aguirre, Octavio Castelan-Ortega, Beatriz Shettino-Bermudez, Rutilio Ortiz-Salinas, Marta Miranda, Xunde Li, Juan Angeles-Hernandez, Einar Vargas-Bello-Pérez, and Manuel Gonzalez-Ronquillo.
Robles-Jimenez, L.E.; Aranda-Aguirre, E.; Castelan-Ortega, O.A.; Shettino-Bermudez, B.S.; Ortiz-Salinas, R.; Miranda, M.; Li, X.; Angeles-Hernandez, J.C.; Vargas-Bello-Pérez, E.; Gonzalez-Ronquillo, M. Worldwide Traceability of Antibiotic Residues from Livestock in Wastewater and Soil: A Systematic Review. Animals 2022, 12, 60. https://doi.org/10.3390/ani12010060