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This pioneering work suggested that different bacteria were unique species, since the colour of the pigmented bacteria was consistent when transferred to another potato slice, and inspired the development of solid nutrient media by Robert Koch and his co-workers. The transitional step between liquid and solid culture was the work of Schroeter in 1872, who isolated pigmented bacterial colonies of the now-described red Serratia marcescens and violet Chromobacterium violaceum on thin slices of heat-treated potato. However, before isolation on solid media became a standard practice, it can be said that Pasteur did not truly obtain pure cultures of microorganisms. Pasteur used a medium consisting of 100 parts water, 10 parts dextrose, one part ammonium tartrate and one part the ash of yeast cells to grow bacteria. The method of growing bacteria in a transparent liquid nutrient medium and inoculating fresh medium from turbid medium to isolate a pure culture of the bacterium was commonly employed by the French pioneering microbiologist Louis Pasteur, beginning in 1861. The development of classical microbial methods, broth culture, plate count, serial dilution, enrichment and microbial identification over time has been described in the literature. From Pasteur’s discoveries to the Petri dish
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Questions that can be asked include: what does this understanding mean to the pharmaceutical microbiologist responsible for testing and releasing drug products? How does this apply to the challenge of evaluating, validating and implementing alternative methods to the compendial microbiological test methods? As a background to a general discussion of these questions amongst microbiologists, it is useful to review the history of the development of microbiological testing methods. This cultivability could range from 0.1 to 0.01% in oceanic microbiota to around 80% for the microbiota on the human forearm. The advent of ribosomal RNA gene sequence analysis thirty years ago has significantly expanded our awareness of microbial diversity in water, air, soil and the human body and reemphasised that, overall, cultivable microorganisms represent less than 1% of the microorganisms observed by direct microscopic examination.