Eight formulas of plating medium have been studied to determine their comparative abilities in satisfying the cultural requirements of the bacterial population in materials of marine origin. Five series of experiments comprising a total of 56 trials have been performed. The procedure and technique employed are thoroughly discussed. Media prepared with “aged” sea water as menstruum were found to be definitely superior to those prepared with distilled water, alone or with NaCl.
The effect of different diluents, various plating temperatures of the medium and various incubation temperatures on the total bacterial colony counts were also investigated.
The principal problem which arises when planning any bacteriological investigation requiring quantitative bacterial determination in materials of marine source is the selection of a medium that gives the most nearly accurate picture of their bacterial population. Such a medium should satisfy the cultural requirements of a great number of microorganisms in the material under study.
The large number of nutrient media recommended for this purpose attests to the basic importance of an appropriate medium for enumerating marine bacteria. Comparative studies conducted by the Scripps Institution of Oceanography, on a large number of media which have been recommended by various workers show that medium 2216 (vide infra) is one of the best for supporting the growth of a maximum number of bacteria and for ability to reproduce the plate counts on marine material (ZoBell, 1946).
Fischer (cited by ZoBell, 1942) recommended a medium which differs slightly from 2216. This medium contains 1.0 per cent peptone and 0.5 per cent fish extract in sea water. ZoBell (1941), however, failed to produce any increase in plate counts by fortifying Medium 2216 with various fish extracts.
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