ABSTRACT
The behavior of wild strains in preservative efficacy tests is known to be affected by their subculture onto laboratory media. Organisms respond in different ways to changes in growth media and culture conditions, according to their various physiological states and capabilities. Microorganisms in the logarithmic phase of growth are known to be more sensitive to most types of stress compared with those in resting stag, while slowly growing cells can be particularly recalcitrant to chemical inactivation. Quality control of culture media and the assessment of its performance has been extensively discussed, particularly with reference to media used in food microbiology; few parallels have been drawn, however, in the case of media used in pharmaceutical microbiology. R. E. Leak and R. Leech suggested the use of test strains, isolated from and maintained in unpreserved product, for the detection of marginally preserved systems. Recommended challenge test inocula and wild test strains may both exhibit differing growth rates and duration times in the maximum stationary phase.
