Resistant bacteria are found all around us: in the environment, people, animals and food. Broilers have been identified as an important reservoir for resistant bacteria within the production animal sector. Especially extended-spectrum beta-lactamases (ESBL) and plasmidic AmpC-type beta-lactamases (pAmpC) are found in high numbers in many countries in broiler production. These enzymes confer resistance to many commonly used antibiotics, such as 3rd generation cephalosporins. Parent birds are usually imported as one-day old chicks or eggs from a few countries where pedigree animals are bred. ESBL/pAmpC-producing bacteria are found also in countries with limited antibiotic use in the broiler production. This raises the question of the origin of these resistant bacteria. A commonly supported theory is the transmission from top down in the production pyramid, ie. from parent animals to offspring.
In our study we sampled parent birds, their corresponding eggs and chicks to accurately study whether or not top-down transmission does occur. ESBL/pAmpC-producing Escherichia coli was isolated from the samples, and selected isolates were further whole genome sequenced to reveal resistance genes and plasmids, among others, carried by the isolates. The results show that parent birds and egg surfaces soon after lay carry resistant bacteria, but egg surfaces are free from enterobacteria after the incubation period at the hatchery. The results indicate that a direct vertical spread of resistant bacteria from parent birds to offspring is limited. Good hygiene practices probably aid in maintaining a low resistance level in the Finnish broiler production.
The study is part of the AmiFoPo - Preventing Antimicrobial Resistance in Food Production Animals project funded by the Academy of Finland 2016-2018.
The study has been finished. The published article can be found here: https://doi.org/10.1016/j.vetmic.2019.03.001