Autoradiographic detection of radioactive bacteria introduced into sea water and sewage

Abstract

The agency of water in the dissemination of bacteria and viruses has long been recognized, but though measures have been taken to control this hazard, water still plays a large role in spreading pathogens such as enterovirus and salmonella. A simple and reliable method for studying dissemination of this kind would therefore be most useful.The presence in water of thermostable coli bacteria is generally considered an index offaecal contamination. Unfortunately, their detection in a water sample is a laborious procedure which requires growing cultures, often on different media, for confirmation. Furthermore, the significance of one particular source of contamination when several are present cannot be determined with current bacteriological technique. The problem has been previously attacked by using mutants of the contaminating micro-organisms, or indicator organisms such as Serratia (Robson, 1956). The tracer bacteria are added to the water at the source of contamination and water samples are taken for bacteriological examination.Radioactive substances and dyes have also been used to study the spread of contamination (Montens, 1954;Ely, 1957). Because of rapid dilution, high levels of radioactivity are necessary to follow dispersion in large volumes of water. In addition, the action of biological factors on the survival of contaminating bacteria cannot be ascertained with these materials alone.Bacteria which have been radioactively labelled can be used as tracer organisms. If they can be detected by a method which avoids the necessity of culturing water samples and if the method is sufficiently sensitive, the use of radioactive bacteria offers several advantages. In the present paper such a method is described, for use in studying the spread of bacteria in water. Water samples were filtered through a Millipore filter and an autoradiogram of the filter was prepared in which the bacteria appeared as black spots. The accuracy and sensitivity of the method were estimated and a test made under field conditions. METHODS Strain B Escherichia coli were used. The bacteria were grown overnight at 370 C. in agitated 500 ml. flasks on Andersson's synthetic medium.* The medium was modified by replacing MgSO4 with MgC12 to eliminate carrier sulphur. One micro-* MgSO4, 04 g.; Na2HPO4, 6 g.; KH2PO4, 3 g.; NaCl, 5 g.; NH4C1, 1 g.; glucose, 4 g.;H20, ad 1000 ml.; pH = 7.