A Soy-Based Alternative to Traditional Bacterial Nutrient Media

Abstract

A vegan is an individual who does not use or consume products of any kind (Vegan Society, accessed June 15, 2008). The term animal product in a vegan context refers to any material derived from animals for human use (Stepaniak, 2000), such as meat, poultry, seafood, eggs, dairy products, honey, fur, leather, wool, and silk (Vegan Society, accessed June 15, 2008). Common by-products include gelatin, lanolin, whey, casein, and beeswax (Vegan Society, accessed June 15, 2008). Reasons cited for choosing a vegan/vegetarian lifestyle include ethical or moral convictions concerning rights, concerns for the environment, human health, and religious concerns (Time/CNN, July 7, 2002; Social Survey Division of the Office for National Statistics, 2002; Stepaniak, 2000). Various polls have reported that vegans make up anywhere from 0.2% to 1.4% of the adult U.S. population, a group that seems to be growing (Time/CNN, July 7, 2002; Stahler, 2006). Further, most people in that group fall between the ages of 16 and 34 (The Vegan Research panel, accessed June 15, 2008, an age range typical of most college students. Most complex nutrient media used in a general microbiology lab (Nutrient Broth, Luria-Bertani Broth, or Trypticase Soy Broth) contain animal-derived ingredients, such as casein, tryptone, or meat extracts. Our goal was to produce a medium that is free of all products, yet supports the growth of most non-fastidious bacteria in a manner comparable to commercially available animal-based media. To provide the growing vegan population (and anyone else uncomfortable with using products) a viable alternative in microbiology lab, we wanted to develop an equally-effective, inexpensive, animal-free substitute to conventional media. We initially tested several combinations of soy flour and other additives on eight species of bacteria, and qualitatively compared the amount of growth on these plates against standard animal-based nutrient agar plates. From these trials, we found that a mixture of toasted soy flour (SoyQuik[R]) and yeast extract powder yielded the best, most cost-effective results. Quantitative and qualitative analyses were performed to compare growth of bacterial cultures in our soy-based media to growth in the standard animal-based media. As a final assessment, we tested the soy-based medium side-by-side against animal-based media typically recommended by experimental protocol during standard microbiology labs. * Methods Nutrient Media Preparation Prospective animal-free additives were purchased in health food sections of local grocery stores or ordered online at the EnerGFoods Web site (Ener-G.com). These products (including toasted soy flour, potato flour, and rice bran) were incorporated in varying ratios into agar plates. Commercially-available Yeast Extract and Nutrient Broth (Difco[R]) powders were also used and prepared according to the manufacturer's instructions. All ingredients were dissolved in distilled water and sterilized as is typical in nutrient media preparation. When solid media was required, the preparation included 1.5% agar. Media recipes and their corresponding designations include: * SF = 3% soy flour * SP = 3% soy flour + 2% potato flour * SR = 3% soy flour + 2% rice bran * SY = 3% soy flour + 2% yeast extract * SPY = 3% soy flour + 2% potato flour + 2% yeast extract * SRY = 3% soy flour + 2% rice bran + 2% yeast extract * NB = nutrient broth (made according to manufacturer's instructions) * NBY = nutrient broth + 2% yeast extract * YE = 2% yeast extract * 2SF = 2% soy flour * MSY (modified soy media) = 2% soy flour + 0.5% yeast extract Qualitative Growth Analyses Fresh, single colonies (