Relation between Food Concentration and Surface for Bacterial Growth

Abstract

Storage of waters, underground, surface, sea and sewage, removed from their natural environment results in an initial multiplication of bacteria. The initial increase is reflected in the total plate counts as well as in the numbers of coliform organisms. The increase cannot be attributed to the change in temperature, as incubation of the waters at the same temper-atures as in their natural environment does not prevent it. This phenomenon is the more puzzling because the waters in their natural environment do not undergo similar increases. Zobell and Anderson (1936) obtained greater increases of bac-teria in sea water stored in small volumes. This was attributed to the contact of the water with the proportionate larger solid surface area in small receptacles. The solid surfaces provide a resting place for periphytes as well as concentrating the nutrients in a film thereupon. The bacteria may multiply upon the solid surface without necessarily being firmly attached to it. Stark, Stadler and McCoy (1938) found that in support of Zobell's results, measurable amounts of organic matter accumu-lated over a period of hours on the surface of chemically clean glass slides suspended in sterile lake water, indicating that the accumulation of organic matter is independent of and precedes bacterial growth. Butterfield (1933) on the other hand, found that size of container does not make any difference in the increase of bacteria in stored river water. That volume-surface ratio does not influence bacterial growth curves obtained in culture media was indicated by Rahn (1932), but all the waters which manifest an initial increase in bacteria are poor in nutritive value for bacterial growth. Even sewage is poor in nutrients in rela-tion to culture media. Zobell and Anderson (1936) state that the effect of surface area on bacterial multiplication is manifest only in dilute solutions. When 100 mgm. of peptone and 1 mgm. of KNO2 were added per liter of sea water, there was no difference between small and large receptacles in the rate of nitrite reduction. There is little information available in regard to limiting con-centration of food materials on the growth of different bacteria. Butterfield (1929) found that 0.5 mgm. each of glucose and peptone per liter, though not optimum for the growth of Aero-bacter aerogenes was by no means a limiting concentration as the organisms multiplied after an extended lag period. Friedlein (1928) reported that Escherichia coli did not grow in a sodium lactate medium at concentrations lower than 0.1 per cent (1000 p.p.m.) and in a glucose medium in concentrations below 0.016 per cent (160 p.p.m.). Bacterial growth was determined by tur-bidity measurements and it is a question whether the failure to obtain increases in turbidity at these low food concentrations can be taken as a positive proof of the absence of growth. Expeiments reported below were therefore undertaken to