Chapter XI Actinomycetes

Publisher Summary Difficulties encountered when isolating actinomycetes have probably contributed to the comparative neglect of these micro-organisms in certain fields of research. In comparison with their main competitors—, bacteria and fungi— they have certain deficiencies. Their rate of radial growth on culture media is lower than that of fungi, and their rate of cell production is generally lower than that of bacteria. Therefore, methods for their isolation must be designed to compensate, at least partially, for their generally poor competitive ability under laboratory conditions. Many of the methods for isolating actinomycetes may also be employed for enumerating them in their various natural habits. Many workers isolate Aactinomycetes as a group from soil, but unless specialized techniques are used, these isolates consist of a very high percentage of Streptomyces strains, which are the most numerous group in soil. Soil may be pre-treated in various ways to increase the numbers and/or proportion of actinomycetes in it before dilutions are prepared. Simply air-drying the sample will reduce the numbers of vegetative bacterial cells while allowing many actinomycete spores to survive. The procedure used to incorporate the diluted soil suspensions into agar medium can also influence the efficiency of the dilution-plate technique. Actinomycetes are an integral part of the microflora of fresh water, and have been isolated from lakes, rivers and water supplies where they have been implicated in the production of unpleasant flavors, odors, and colors.