Antibiotic resistance can be transmitted from animals to people
Researchers from the UAB and IRTA participated in a study in which they found the same bacterial plasmid with resistance to colistin in a farmer and in his cattle. The samples were taken at the end of 2017, a year after it was recommended worldwide to reduce its use on farms.
20/04/2021
During 2015, the scientific community discovered a new gene in bacteria, called mcr-1 and distributed worldwide, which conferred resistance to colistin, an antibiotic of last resort in human health. That same year, a strain of the Escherichia coli bacteria resistant to this antibiotic was detected for the first time in Spain in a calf slaughterhouse, thanks to the Ministry of Agriculture's Antimicrobial Resistance Monitoring Program in zoonotic and commensal bacteria. Two years later, the farm where this resistant strain originated was identified and a team of researchers from the Institute of Agricultural Research and Technology (IRTA) went there to analyze faecal samples from the animals and the farmer. The sequencing and analysis of the samples, carried out by the Molecular Genetics Veterinary Service (SVGM) of the Universitat Autònoma de Barcelona (UAB), and published in the journal Antibiotics, reveal that the calves, pigs and the farmer had E. coli bacteria with the same resistance gene.
In this case, experts point out that the transmission of the resistance gene was from the animals to the person, as the calves and pigs had been treated with colistin, but the farmer had not been treated with the drug. "Bacteria are microorganisms that have two types of genetic material, chromosomal DNA and plasmids. Many antibiotic resistance genes are located on these plasmids. When there is contact between two bacteria, they can transmit this resistant "superpower", exchanging plasmids with each other. This is how the mcr-1 gene for resistance to colistin passes from one bacterium to another", explains Lourdes Migura, researcher of IRTA's Animal Health program and leader of the study.
According to experts, the farmer could have acquired colistin resistance from animal bacteria through direct contact with them, their feces or contaminated work tools. "In this case we are talking about horizontal transmission of resistance genes by plasmid exchange. In this study we clearly see that animals can be reservoirs of these genes and can transmit them to humans, which is why it is important to take extreme hygienic measures on livestock farms", explains Joaquim Viñes, researcher at the Molecular Genetics Veterinary Service (SVGM) from the Universitat Autònoma de Barcelona (UAB) and industrial PhD student at the technology-based company of the Universitat Vetgenomics.
In the future colistin may no longer be useful for treating serious infections
On farms, colistin was regularly used until 2016 mainly to treat infections such as post-weaning diarrhoea, but the finding of bacteria resistant to this antibiotic indicates its overuse. In people, it is currently only used in hospitals as a last resort in serious cases, when conventional drugs have failed to stop some bacterial infections. "Having resistant E. coli bacteria is not a direct danger to people, but it must be taken into account that this bacteria is opportunistic. This means that if a person with this resistant bacterium becomes seriously ill for another reason, the opportunistic bacterium can take advantage of the lowering of the body's defenses to infect it as well and would trigger a patient case that is very difficult to treat," he warns Migura In addition, he adds that "if this person were to enter a hospital, there would also be a risk of spreading the bacteria or its plasmid to other people".
The use of antibiotics in human and veterinary medicine has led to the emergence of resistant bacteria of critical importance to human health. At global and national level there are several initiatives to reduce the use of antibiotics and reduce the appearance of "superbugs" due to the risk it poses to global public health. In addition, IRTA is also working to reduce its use in the field of animal production and it is one of the challenges of the institution's strategic plan for the next three years.
Reference: Viñes, J., Cuscó, A., Napp, S., Alvarez, J., Saez-Llorente, J. L., Rosàs-Rodoreda, M., ... & Migura-Garcia, L. (2021). Transmission of Similar Mcr-1 Carrying Plasmids among Different Escherichia coli Lineages Isolated from Livestock and the Farmer. Antibiotics, 10(3), 313. https://doi.org/10.3390/antibiotics10030313