Washington ? Dangerous bacteria are going to be a problem in America’s food for a long time as disease agents arrive in imported products and microbes already here develop in new forms, scientists say.

In a report for the Institute of Food Technologists, the scientists also say the increasing use of manure as fertilizer poses the risk of spreading harmful bacteria to food, either by contaminating irrigation water or contacting the crops.

Manure, which harbors bacteria such as E. coli O157:H7 and salmonella, is used for fertilizer on both organic and conventional crops. In some foreign countries, chicken manure is fed to farm-raised shrimp.

The report, being released today, also warns against the overuse of antibiotics in livestock, saying there is “growing body of evidence” that farm use of antibiotics is causing bacteria to become resistant to drugs.

“The job of assuring microbiological food safety is unending,” said Morris Potter, a top epidemiologist for the Food and Drug Administration who chaired the study by government and university scientists.