Detection of Escherichia coli in meat with an electrochemical biochip

Detection of foodborne pathogenic and spoilage bacteria by RNA-DNA hybridization is an alternative to traditional microbiological procedures. To achieve high sensitivity with RNA-DNA-based methods, efficient bacterial lysis and release of nucleic acids from bacteria are needed. Here we report the specific detection of the hygiene indicator microorganism Escherichia coli in meat by use of electrochemical biochips. We improved RNA isolation from bacteria in meat juice from pork and beef. Samples, either naturally or artificially contaminated by E. coli, were enriched by incubation in full or minimal medium. A combined treatment of the samples with lysozyme, proteinase K, and sonication resulted in efficient cell disruption and high total RNA yields. Together with optimization of enrichment time, this ensures high sensitivity of electrochemical measurements on biochips. A short enrichment period and the triple-lysis regimen in combination with electrochemical biochip measurement were tested with 25 meat samples. The lower limit of detection of the biochip was approximately 2,000 CFU of E. coli per ml. The entire analysis procedure (5 h of enrichment, triple lysis, and biochip detection) has a lower limit of detection of 1 CFU of E. coli per ml within a total time needed for analysis of 7 h.