Ionophores in relation to antibiotic resistance in humans.

Discipline: antibiotics; Keywords: gram positive bacteria, altered fermentation, propionate, Streptomyces cinnamonensis, health concerns.

In last month’s column I argued that pressure groups and uninformed health conscious consumers sometimes hamper development of innovative technologies which could increase efficiency and lower the cost of production to the farmer. I used the example of r-bST as so elegantly discussed by Erasmus and Webb in Volume 43, No 3 of the SA Journal of Animal Science of 2013. Another example they referred to in their review is the ionophores, with the most work being done on monensin (Rumensin). I used their information and also other evidence in discussing the issue below.

Ionophores are classified as antibiotics although their mode of action is somewhat different to the classical definition. They are widely used in the poultry, beef, sheep and dairy industries of many countries, also in South Africa. However, because of perceived implications to human health of pathogens becoming resistant to antibiotics, the use of ionophores as other antibiotics has been banned in the EU and pressure is building up in many other countries to do the same. The question is whether banning is justified.

Ionophores in the rumen inhibit gram positive bacteria, thereby altering fermentation patterns resulting in more propionate and less methane production (an environmental advantage), which is favourable for milk production, more protein and a net gain of energy to the cow, usually reflecting in a better condition score and reconception, and less incidence of ketosis. Production increases range from 0.7 to 1.5kg per day and because feed intake is slightly depressed, efficiency of production may be increased to the extent of 2.5%. Thus, there is unequivocal evidence that the use of ionophores in dairy cow feeding, as in other species, is beneficial and which will be given up if ionophores are disallowed.

Scientifically, there is very little evidence to support the banning by the EU or the pressure by activists in other parts of the world to do so, for the following reasons: (1) monensin is a naturally occurring compound produced by the bacterium Streptomyces cinnamonensis; (2) ionophores have never been and is unlikely to be used as antibiotics in humans, since their function is not of relevance to human medicine; (3) as mentioned above, ionophores have a distinctly different mode of action from therapeutic antibiotics; (4) ionophore resistance appears to be an adaptation rather than a mutation or acquisition of foreign genes, the latter which is one of the reasons for the concern, and (5), there is no metabolic or physical pathway for ionophore residues to pass from the animal body to the milk.

Ionophores are still extensively used as feed additives in the country. The scientific results to keep on doing so are convincing and there is no justification for the health concerns raised. In addition, we should keep on fighting the trend of activists that mislead the public and support the development of new technologies and products which could be to the benefit of the farmer. Because of the genuine concern of the public (which includes me) for pathogenic organisms becoming resistant to the therapeutic antibiotics in use, the development of new, safe products to replace suspect in-feed growth promoters should be encouraged. This may involve GMO technologies and products with similar characteristics as ionophores, and if proven safe by controlling bodies, we as administrators, scientists and farmers have an obligation to make sure that consumers accept such innovations.