Resistência antimicrobiana de escherichia coli isolada de fezes de bezerros alimentados ou não com leite de descarte

Abstract

One of the foremost concerns within the One Health framework is the presence of bacterial strains displaying multidrug resistance to antimicrobials. While the emergence and establishment of resistance are natural, inevitable, and irreversible phenomena, the indiscriminate use of antimicrobials can expedite the process through selective pressure. Antimicrobial use in the bovine production chain, particularly in mastitis treatment, can generate residues excreted in milk, rendering it unsuitable for human consumption. Consequently, milk from animals undergoing antimicrobial treatment is deemed non-marketable, constituting "waste milk." To mitigate losses on the farm, many producers opt to provide this milk to young animals, replacing milk replacers in calf nutrition. However, antimicrobial residues in this feed can impact the intestinal microflora of the animals, leading to the selection of resistant isolates. Therefore, the aim of this study was to identify whether there is a correlation between the isolation of multidrug-resistant Escherichia coli recovered from calf feces and the ingestion of waste milk containing antimicrobial residues. For this purpose, fecal samples were collected from 70 lactating animals, up to 90 days old, from different properties located in seven municipalities in Rio Grande do Sul, Brazil. The animals were divided into four groups: calves with diarrhea consuming waste milk (n=15, G1S), without diarrhea consuming waste milk (n=20, G1N), with diarrhea without consumption of waste milk (n=15, G2S), and without diarrhea without consumption of waste milk (n=20, G2N). The samples were inoculated on culture media, and E. coli isolates underwent antimicrobial susceptibility testing and PCR for the detection of fimbriae and toxin genes. Isolates were classified as multidrug-resistant (MDR) if they exhibited resistance to at least one antimicrobial from three or more different classes. In the G1S group, all animals presented isolates of MDR E. coli in feces (15/15, 100%). In the G2S group, 6 samples showed MDR isolates (6/15, 40%). When analyzing groups of animals without diarrhea, the frequency of animals harboring MDR isolates was also higher in those that received waste milk (G1N: 12/20, 60%) compared to those that received milk replacer or bulk tank milk (G2N: 2/20, 10%). There was a significant relationship (p<0.05) between the isolation of MDR E. coli and the consumption of waste milk, both in animals with diarrhea and healthy ones. A positive relationship was also observed when evaluating waste milk supply and the presence of MDR E. coli in feces, regardless of the clinical condition of the animals. These results indicate that the provision of milk containing antimicrobial residues promotes the maintenance and spread of MDR E. coli isolates in the fecal microbiota of calves. Considering that MDR E. coli isolates will be excreted in the animals' feces, it is likely that these bacteria will contaminate the environment and eventually cause challenging-to-treat infections in both animals and humans, posing a serious One Health issue.