Samples of freshly-ground beef and pre-packaged beef were purchased from three different stores. One-tenth of a gram of each sample was placed in Thio broth, from which serial dilutions were made. Samples from each dilution were inoculated onto two sets of blood and McConkey agars and incubated for 24 hours. Colonies were then counted.
Colonies were counted for each set of cultures at each dilution and the absolute number of bacteria were calculated. Freshly-ground beef had less bacteria than pre-packaged beef. Surprisingly there was one brand of pre-packaged beef that had minimal growth on all plates tested. It was later discovered that this brand was irradiated prior to shipping.
Freshly-ground beef had less bacteria than pre-packaged beef, unless the pre-packaged beef had been irradiated. Based upon my results, the FDA should require that all ground beef be irradiated, in order to minimize the number of cases of bacteria-related foodborne illness.
Freshly-ground beef has less bacteria than pre-packaged beef, unless the pre-packaged beef has been irradiated.
Science Fair Project done By Michael P. Hartman