Radiometric Detection of Some Food-Borne Bacteria

Abstract

Studies on detection of bacteria by radiometric techniques have been concerned primarily with aerobic species in clinical specimens. The data presented here are related to detection of aerobic and anaerobic species that are of significance in foods, by measurement of 14 CO 2 evolved from the metabolism of 14 C-glucose. Salmonella typhimurium and Staphylococcus aureus were inoculated into tryptic soy broth containing 0.0139 μCi of 14 C glucose/ml of medium. Detection times ranged from 10 to 3 hr for inocula of 10 0 to 10 4 cells/ml of broth. Heat-shocked spores of Clostridium sporogenes or C. botulinum were incubated in tryptic soy broth supplemented with Thiotone and NaHCO 3 . The medium was rendered anaerobic with N 2 . Spores were detected when 0.0833 μCi of labeled glucose was available/ml of medium but not when 0.0139 μCi of glucose was present/ml. The spores required 3 to 4 hr longer for detection than did comparable numbers of aerobic vegetative cells. The results demonstrate the importance of availability of sufficient label in the media and the potential of the application of this technique for sterility testing of foods.