Representatives Edward J. Markey and Louise Slaughter ae concerned that corn-based livestock feed could be linked to a sharp rise in antibiotic resistance.

They say that the same antibiotics that are used in animal agriculture, such as penicillin and erythromycin, are also used by ethanol producers to prevent bacterial growth during the corn-based ethanol fermentation process.

Producers then sell the byproduct of ethanol production as livestock and poultry feed, a use that the lawmakers say appears to be sliding under the regulatory radar.

In the letter sent to FDA Commissioner Margaret Hamburg, the lawmakers ask the agency about its recent effort to reduce the use of antibiotics for animal growth promotion in food-animals, as well as what the FDA is doing to ensure that ethanol producers comply with regulations for food additives.

Currently, about 80 per cent of antibiotics sold in the United States are used in animals and have the potential to make their way into our food stream, they claim.

A study by the FDA found that levels of certain antibiotics remaining in the byproducts of ethanol production have the potential to cause antibiotic resistant bacteria.

"Antibiotic resistant strains of bacteria are a grave public health threat that is growing worldwide," write Reps. Markey and Slaughter in the letter to the FDA.

"As the threat of antibiotic resistance expands, we must ensure that the unnecessary use of antibiotics in agricultural animals is minimized and FDA has the ability to limit their use if it serves to protect public health."