Ionophore resistance and potential risk of ionophore driven co-selection of clinically relevant antimicrobial resistance in poultry
Today’s intensive broiler production is highly dependent on ionophore coccidiostats. These antiparasitic agents are applied as feed additives. The most important group, the ionophores, not only exhibit antiparasitic activity but are also antimicrobial against Gram-positive bacteria. Because these ionophores are not used in humans, it is widely assumed their use does not impact human health. However, recent Swedish and Norwegian research shows that ionophores can cause the co-selection of vancomycin resistance in enterococci. Vancomycin is a critically important antimicrobial for human medicine. Because of its limited relevance for human medicine, monitoring of antimicrobial resistance against ionophores, in particular salinomycin (SAL), was discontinued several years ago. From historical data, however, it can be retrieved that a fair percentage of the Enterococcus faecium and Enterococcus faecalis isolates from poultry origin show SAL resistance. The current research was initiated to determine whether ionophore resistance in enterococci from poultry co-occurs with other clinically relevant types of antimicrobial resistance. A set of 137 E. faecium and E. faecalis isolates from poultry products from conventional and organic origin was phenotypically characterized. The resistance profiles were statistically analysed and subsequently a selection of 20 isolates was DNA sequenced and analysed for the presence of resistance genes. Almost 40% of the isolates appeared to have a SAL resistant phenotype. Results of the statistical analysis showed a significant correlation between the presence of SAL resistance and erythromycin (ERY) resistance in E. faecium from conventional farming. The same correlation was also observed in E. faecalis from both conventional and organic origin. Besides this, both E. faecium and E. faecalis show significant correlation between the presence of SAL and tetracycline (TET) resistance and SAL and ampicillin (AMP) resistance. DNA sequencing results show good agreement between the observed phenotypic resistance and the identified resistance genes. In all of the isolates showing phenotypic SAL resistance the narAB genes could be identified. Moreover, in most isolates narAB is found to be located on a plasmid carrying additional genes for other types of antibiotic resistance. This is an alarming observation, since it implies that the use of ionophores may drive the transfer and dissemination of other, clinically relevant types of antimicrobial resistance by co-selection. These results question the sustainability of the prophylactic use of ionophores in broiler production. More research is needed to determine the extent and the impact of this issue. It is unknown whether ionophore resistance also occurs in other Gram-positive bacteria, like Staphylococcus aureus. It is plausible that ionophore resistance genes other than narAB will be present in poultry associated bacteria. E. faecium and E. faecalis are an important cause of hospital-acquired infections. Analysis of human enterococcal isolates should reveal whether transmission from the poultry reservoir is occurring and thus whether the use of ionophores in poultry impacts human healthcare.
| Main Authors: | , , , , |
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| Format: | External research report biblioteca |
| Language: | English |
| Published: |
Wageningen Food Safety Research
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| Subjects: | Life Science, |
| Online Access: | https://research.wur.nl/en/publications/ionophore-resistance-and-potential-risk-of-ionophore-driven-co-se |
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