Culture indexing for bacterial and fungal contaminants
Indexing for microbial contaminants is usually accomplished by inoculating tissue sections or intact shoots into enriched selection medium that will promote the visible growth of bacteria, filamentous fungi, yeast, or other contaminants. This chapter illustrates the indexing procedures for cultivable contaminates using a single indexing medium. It discusses the importance and limitations of culture indexing; selection of indexing media; and tissue sampling and inoculation techniques. Without specific knowledge of the actual microbial contaminants present, limitations in detecting contamination can occur if inappropriate indexing media are used. One approach is to use several highly enriched indexing media such as: Sabouraud dextrose medium; yeast extract dextrose broth; and AC broth. Sabouraud dextrose medium is formulated for the growth of fungi including yeast, filamentous fungi, and aciduric microorganisms. Yeast extract dextrose broth medium is used to stimulate bacterial growth, whereas AC broth is a sterility test medium for a variety of microorganisms.