Researchers have identified factors associated with the global trend in antimicrobial resistance in livestock animals in low- to middle-income countries, according to study findings published in Science.

A total of 901 point prevalence surveys of pathogens in developing countries were analyzed to map antibiotic resistance in animals. The analysis retained its focus on animal resistance to Escherichia coli, Campylobacter spp., nontyphoidal Salmonella spp., and Staphylococcus aureus resistance.

The percentage of antimicrobial compounds demonstrating resistance of >50% in chickens increased from 0.15 to 0.41 and increased in pigs from 0.13 to 0.34 in low- and middle-income countries between 2000 and 2018. The most frequently used classes of antimicrobial drugs also demonstrated the highest resistance rates in animal production. These included tetracyclines, sulfonamides, and penicillins. The antimicrobial agents critical to human health that displayed the highest rates of resistance were ciprofloxacin and erythromycin (20% to 60%), as well as third- and fourth-generation cephalosporins (10% to 40%). Lower rates of resistance were found for linezolid and gentamicin (<20%).

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There were similar rates of resistance in low- to -middle-income countries and Europe for quinolone in both E. coli and Salmonella spp. (20% to 60% vs 59.8% to 64%, respectively). Resistance to gentamycin was higher in low- to middle-income countries than in Europe (5% to 38% vs 2.4% to 8.9%, respectively). Also, low- to middle-income countries had highest resistance rates for tetracycline (60%) and quinolones (60%) in Campylobacter spp. Rates of resistance to antimicrobials for S. aureus were higher in Asia, particularly for penicillin (40% to 80%), erythromycin (20% to 60%), tetracycline (20% to 60%), and oxacillin (20% to 60%).

With regard to study limitations, the researchers suggest that the lack of sufficient geographic coverage may have resulted in “inaccurate spatial predictions, and local variations in antimicrobial resistance may not reflect ‘ground truth.’”

The finding that antimicrobial resistance was higher in Asia prompted the researchers to suggest that countries in this region “should take immediate actions to preserve antimicrobials that are essential in human medicine by restricting their use in animal production.”


Boeckel TPV, Pires J, Silvester R, et al. Global trends in antimicrobial resistance in animals in low- and middle-income countries [published online Sep 20, 2019]. Science. doi:10.1126/science.aaw1944