ABSTRACT
An important reason for lack of reproducibility and relevance is the plasticity of the microbial cell and especially the envelope. The cell envelope is remarkably flexible in both structure and composition and constantly interacts with its environment. The variation in the growth environment of a challenge inoculum will influence not only the reproducibility of a testing procedure but also its sensitivity and relevance. Variation may be inadvertent, through poor specification of the media, or it may be intrinsic to a particular technique, such as the use of cultures on solid media. Biofilm microorganisms in the form of solid cultures have traditionally been used by microbiologists as a means of recognizing contaminant organisms and maintaining pure stock cultures. If conventional microbial challenge test procedures are to be made more relevant, then attention must be paid to the nutrient environment from which the inocula are drawn.
