BD Accuri News
Byron Brehm-Stecher on Food Pathogens
Byron Brehm-Stecher, PhD, heads the Brehm-Stecher Rapid Microbial Detection & Control Laboratory in the Department of Food Science and Human Nutrition at Iowa State University. Previously, he was a postdoctoral research scholar at the University of Wisconsin-Madison and a molecular biologist at a biotechnology firm in Boston, MA. Dr. Brehm-Stecher, who won an Accuri Creativity Award in 2010, spoke to us about his work developing cytometry-based assays to detect foodborne pathogens, the game-changing role of flow cytometry in food screening, and how to get peanut butter through a flow cell.
Q: Would you tell us about the research program in which you are using the BD Accuri™ C6 flow cytometer?
Dr. Brehm-Stecher: My laboratory is focused on both rapid detection of foodborne pathogens and on development of multicomponent antimicrobial systems. On the rapid detection side, we are very interested in single-cell and whole-cell approaches, including flow cytometry and image analysis. A recurring theme in our detection research is pre-analytical sample preparation—the preparative steps needed to ensure a good detection result.
On the antimicrobial side, we’re interested in both natural antimicrobials of plant or animal origin and in synthetic antimicrobials or chemical preservatives. The BD Accuri C6 system is a key basic research tool that we can leverage across our various projects—whether we’re testing the specificity and hybridization intensity of new rRNA-targeted probes or examining the inactivation kinetics or physiological impact of a new antimicrobial mixture on target pathogens.
Q: For what type of applications do you use the BD Accuri C6?
Dr. Brehm-Stecher: To date, we have used our BD Accuri C6 for development of new organism-specific probes for use in fluorescence in situ hybridization (FISH) assays, evaluation of functional food ingredients for their ability to make food spoilage yeasts permeable to natural antimicrobials, and FISH-based detection of Salmonella in complex food systems, including alfalfa sprouts and peanut butter.
How to get peanut butter through a flow cell
Q: How do you get peanut butter through a flow cell?
Dr. Brehm-Stecher: That would be quite a trick! For this work (in collaboration with Dr. Bledar Bisha, now at the University of Wyoming) we looked at overnight enrichments from Salmonella-contaminated peanut butter. Basically, we made 1:10 dilutions of peanut butter containing low levels of S. Typhimurium into non-selective growth media and incubated for 10 hours, allowing the Salmonella and anything else present to grow. Although these enrichments are easier to work with than straight peanut butter, they are still very complex systems containing fat micelles, particulate matter (peanut skin fragments), and both target and non-target flora.
To label any Salmonella cells present, we pelleted aliquots of these enrichments, fixed them in 10% buffered formalin, and resuspended them in a hybridization buffer containing Salmonella-specific FISH probes. Then, we performed short (15–20 min) hybridizations, followed by 1:10 dilution in wash buffer, then cytometry. By combining Salmonella-specific FISH labeling with analysis on our BD Accuri C6, we were able to quickly and unambiguously detect Salmonella present in the spiked samples. The method could be useful as a rapid screen for Salmonella and would deliver results much earlier than culture-based approaches.
Q: Why did you choose the BD Accuri C6?
Dr. Brehm-Stecher: Several aspects drew our interest: its pushbutton ease of operation and maintenance (simple cleaning cycle, permanently aligned optical bench), its versatility (multiple colors), its ability to analyze data using third-party software such as FlowJo™, and its small (benchtop) footprint. Although we have access to other instruments in our core facility, having a capable system right in the lab gives us an extra measure of flexibility and speeds our research considerably.
In-lab access to a cytometer makes a huge difference. Both our rapid detection and antimicrobial work involve many variables. As an example, when we’re developing new FISH probes, we need to look at the impact of probe concentration, hybridization time and temperature, salt concentration, presence or absence of denaturants, and cell fixation conditions, among other things. Then we need to screen the most promising probes against large panels of target and non-target organisms. Having a BD Accuri C6 right there on the benchtop allows us to quickly vet a large number of variables and efficiently optimize our processes.
Q: What has winning an Accuri Creativity Award meant to you and your research?
Dr. Brehm-Stecher: It’s certainly a nice accolade to have, but the best part is having a new “toy” in the lab—one that adds considerable functionality and capability to our lab and helps expand the directions we can take with our work.
The BD Accuri C6 is a potentially game-changing instrument for food safety monitoring. With its benchtop footprint, affordability, and simplicity of operation, it offers new options to food companies, regulatory agencies, and others for rapid screening of foods for bacterial pathogens.
For Research Use Only. Not for use in diagnostic or therapeutic procedures.
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