US - In his keynote lecture at the International Poultry Scientific Forum at the IPPE event in Atlanta yesterday, Dr Randall Singer from the University of Minnesota encouraged delegates to think critically about just how much we don't know about antibiotic resistance.
His Milton L. Dendy address described many areas in which more research is needed, to help animal producers respond to public concern over antibiotic resistance in human pathogens.
Dr Singer said the dogma at the moment is that animal producers must reduce antibiotic use in order to prevent resistance developing.
Antibiotics are currently allowed to be used in the US for growth promotion in poultry, although this use will end at the start of next year when new Veterinary Feed Directive rules come into force.
Such use of the drugs at low levels does not kill off all the bacteria living in the poultry. Dr Singer said this low-level use over many decades could have caused the slow development of the resistance problems we see today.
In new regulations, legislators want producers to use a high dose of drugs as treatment when the animals become ill, rather than giving a low dose more frequently.
Since the 1910s, theorists have said that providing a high dose of antibiotics would be better, as quick, complete eradication of the bacterial population in the animal prevents the rise of bacteria with individual new resistance mutations.
However, Dr Singer said that the concern these days in animal production is the movement of existing resistance genes that are already in the environment into human pathogens, rather than new mutations arising.
He said that since a high dose will wipe out all the susceptible fraction of the bacteria, any resistant ones will become the dominant subpopulation in the flock or herd, leading to a rebalancing of the bacterial population in favour of the resistant types.
Dr Singer said that whilst wiping out the gut bacteria through treatment can often leave animals more vulnerable to another infection, studies have shown that lower doses can help the poultry gut to mature faster.
He questioned the evidence behind policies recommending high dose antibiotic treatment to wipe out the animal's colonising bacteria when disease treatment is required.
He said there are only limited studies showing resistance decreasing following reduction in animal antibiotic use, and it is not clear whether the policy changes caused the resistance effect, as resistance can vary naturally in the bacterial population anyway.
More research is needed to look into these questions, if we are to avoid unintentionally making the antibiotic resistance situation worse, Dr Singer warned.
Can poultry lead the way in resistance fight?
Despite the huge challenges faced by the industry in developing responsible antibiotic use, Dr Singer was positive about the opportunities for animal agriculture, and particularly poultry, to lead the way.
The scientist has recently joined a government panel looking into the issue, and one of his first moves has been to develop a survey to collect accurate data on antibiotic usage, which will help policy makers find out more about which methods are efficient at reducing resistance.
Whilst the US Department of Agriculture is involved with formulating the survey and examining the results, the data will be anonymous to avoid companies being identified. Dr Singer said this method would improve industry trust in the results.
A report will also be published, allowing companies to benchmark themselves against the performance of their peers. The research group aims to repeat the survey every six months.
Another opportunity that Dr Singer identified was the possibility of preventing the spreading of resistance indirectly through poultry litter.
Antibiotics can pass through the poultry gut without being fully digested, leading to contaminated litter, which may be spread on fields as fertiliser.
He said that more information is needed on how this affects the bacterial population in the environment, so that better waste management practices can be developed.
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