Bacterial control strains are a critical component in microbiological methods, ensuring the media, reagents and related components of a test method are performing in a manner to ensure the quality of the analytical results. The use of naturally occurring bacterial strains as positive controls during testing is counter-indicated due to the risk of sample cross-contamination. Taking advantage of the target site specificity of transposon Tn7, we developed a collection of strains which express Green Fluorescent Protein (GFP) at high-levels, permitting the rapid screening of the following species on selective or non-selective agar plates: Escherichia coli O157:H7, Shigella sonnei, S. flexneri, Salmonella enterica subsp. enterica serovar Gaminara, S. Mbandaka, S. Tennessee, S. Minnesota, S. Senftenberg and S. Typhimurium. These new engineered strains that fluoresce when irradiated with Ultraviolet light, are easily identified and differentiated from naturally occurring pathogens. Importantly, performance testing in our laboratory and several FDA field laboratories showed that none of those strains containing the GFP marker displayed the potential of becoming a mixed population of fluorescent and non-fluorescent cells, making them suitable laboratory control strains for food microbiologists. We are employing the same approach to engineer additional reference strains for the FDAs’ Compendium of Microbiological Methods, the Bacteriological Analytical Manual (BAM), to exhibit the same stable fluorescent phenotype. Having a suite of control strains with stable, easily identifiable phenotypes like fluorescence eliminates the need to perform the time consuming and expensive confirmatory testing required when naturally occurring bacterial strains are used in microbial methods.
Dr. Rachel Binet has been with the U.S. Food and Drug Administration’s Center for Food Safety and Applied Nutrition (CFSAN) since 2009 and currently serves as a Research Microbiologist in the Microbiological Methods Development Branch, within the Division of Microbiology.
Dr. Binet was trained as a microbiologist at the Institute Pasteur in France and received her M.Sc. in Microbiology in 1994 and her Ph.D. in Microbiology in 1998. She began her career using Genetics strategies to explore the physiology of various Gram-negative bacteria, including Escherichia coli, Serratia marcescens, Shigella and Chlamydia. At FDA her research continues to concentrate on Microbial Genetics and Physiology, with the addition of Genomics and Metagenomics as tools to improve the recovery yield of pathogenic E. coli, Shigella and Salmonella from contaminated food products.
Dr. Binet serves as expert in committees related to laboratory biosafety and security at FDA and on microbial methods for CFSAN and for the International Organization for Standardization (ISO).