Concepts and Examples
By Jay Garland, Dynamac Corp, Kennedy Space Center

Dr. Garland described Competitive Exclusion–the use of harmless or beneficial organisms to control undesirable organisms–as a possible approach to assuring the microbial safety of sprouts.

To date, efforts to reduce or eliminate potential microbial risk with sprouts have centered almost entirely on sanitization methods. The most effective method that has gotten formal recognition is the use of very strong chlorine seed treatments. But it has been observed that this treatment is of limited effectiveness, as well as being a workplace hazard, and is inconsistent with organic production methods.

In 2005, Jay and co-researcher Anabelle Matos published a report in the Journal of Food Protection. In this report they showed greater reduction of pathogens by inoculation with mixed communities of non-pathogenic organisms commonly found on sprouts than from inoculation with a single organism, P. Fluorescens, which is a significant part of the normal flora on sprouts.

Jay began his presentation with two questions: Is the sum safer than the parts? Do the strangers in the room matter?

These questions can be roughly paraphrased as: Is some combination of organisms more effective for CE than any single organism or simple combination of organisms? And do organisms we haven’t identified, perhaps because they are difficult or impossible to culture in a lab, contribute significantly to the CE effect?

Jay described the “Competitive Exclusion Principle” proposed by G.F. Gausse which basically states that when two organisms are competing in a given environment for the same resources, one will prevail over the other.

But the overall natural environment consists of many niches: hence no single organism eliminates all the others. Furthermore, a diversity of organisms can work together to enhance their survival within a given niche.

A drawback in using mixed populations of organisms to reduce or eliminate pathogens is that unless you know exactly what’s in the mix, you may be inadvertently introducing organisms that you don’t want. So the challenge is to rationally assemble effective communities.

The good news in this effort is that sprouts are a very useful medium for CE research, given the simple equipment and short time frame involved. The bad news is that it’s a complicated and time-consuming process to identify and culture and combine microorganisms.

Jay concluded his presentation by suggesting proposed work in the direction of developing an effective and workable CE procedure. This work includescontinuing to identify and isolate organisms from sprouts, looking for a “star,” i.e. a particularly effective CE organism; investigating the effectiveness of mixed microbial communities across different sprout types, and working toward a minimum complexity<>maximum effectiveness cocktail.

Presentation Summarized by Bob Sanderson