Flies, already blamed for spreading disease, may help spread drug-resistant superbugs from chicken droppings, researchers reported on Monday.

They matched antibiotic-resistant enterococci and staphylococci bacteria from houseflies and the litter found in intensive poultry-farming barns in the Delmarva Peninsula region of Delaware, Maryland and Virginia.

The findings, reported in the journal Science of the Total Environment, may help explain some of the spread of drug-resistant bacteria.

"Flies are well-known vectors of disease and have been implicated in the spread of various viral and bacterial infections affecting humans, including enteric fever, cholera, salmonellosis, campylobacteriosis and shigellosis," said Jay Graham of Johns Hopkins University in Baltimore, who led the research.

"Our study found similarities in the antibiotic-resistant bacteria in both the flies and poultry litter we sampled. The evidence is another example of the risks associated with the inadequate treatment of animal wastes," Graham said in a statement.

As many as 30,000 flies can fly in and out of a poultry house over six weeks, the researchers said, citing a recent Danish study.

"Although we did not directly quantify the contribution of flies to human exposure, our results suggest that flies in intensive production areas could efficiently spread resistant organisms over large distances," said Ellen Silbergeld, another of the researchers.