Stable isotope ratios as a tool in microbial forensics--Part 2. Isotopic variation among different growth media as a tool for sourcing origins of bacterial cells or spores

Since the anthrax attacks of 2001 the need for methods to trace the origins of microbial agents has become urgent. The stable isotope ratios of bacteria record information from both the nutrients and the water used to make their culture media and could potentially be used to provide information about their growth environment. We present a survey of carbon (C), nitrogen (N), and hydrogen (H) stable isotope ratios in 516 samples of bacteriological culture media. The observed variation was consistent with expected isotopic variation in the plant and animal products upon which the media are based. The variation is sufficient to translate into substantial isotope variation in cultures grown on different batches of media, and thus to allow investigators to determine whether seized media could have been used to produce seized bioweapons agents.