The ecology and significance of the different types of coliform bacteria found in water: A Review of the Literature

Abstract

1. A review has been made of literature on the ecology of different types of coliform bacteria. The main object of the review has been to consider whether there is evidence to support the view thatBact. aerogenesand the intermediate types live normally on plants or in the soil and not in the intestines of man and other animals.2. There is ample evidence thatBact. coliis by far the most common type of coliform in normal human faeces. On the other hand, there is evidence thatBact. aerogenesor intermediate types are usually present in faeces, may sometimes be present in greater numbers thanBact. coli, and on rare occasions may be the only type present. Both quantitatively and qualitatively the coliform flora of the faeces of an individual person may vary from day to day. There is insufficient evidence on the numbers ofBact. aerogenesand intermediate types in faeces to justify any more definite statement, but limited data suggest that such types may be absent or may be present in numbers of the order of a million per gram.3. When fresh faeces are stored there is first a multiplication of such bacteria as will grow on ordinary laboratory media, including the coliform types. The rate of multiplication, as with the flora of soil, water, and milk, increases with an increase in the incubation temperature to 37° C, but the period of multiplication becomes shorter. In the literature consulted no evidence can be found to show which groups are prominent in the multiplication. Results are in agreement that on further storage the ratio of the numbers ofBact. colito those ofBact. aerogenesand intermediates decreases, the typicalBact. coliflora dying off more rapidly than other conform types. The rapidity of decrease appears to depend partially at least upon the temperature of the environment, and the decrease may be accelerated by intense sunlight.4. In urine from patients suffering from genito-urinary infections the dominant types of coliform are usually eitherBact. aerogenesor intermediates. No data on the number of such organisms in urine have been obtained from the works consulted.5. There is no-evidence that coliform bacteria multiply on fresh grasses or grains. Few quantitative data on this question have been found. In some of the older work it is doubtful whether a large proportion of the cultures isolated were actually coliform bacteria or whether they were species of other genera capable of fermenting lactose at 30° C. but not at 37° C. In the decomposition of grasses and legumes during ensilage, a process involving a considerable increase in temperature, it would appear that multiplication of conform bacteria may take place and counts may for a time equal those found in fresh faeces. No indication has been found that this multiplication is confined toBact. aerogenesor intermediates.6. Most workers who have studied the coliform bacteria in soil have ignored the quantitative aspects and no counts at intervals over long periods of coliform bacteria in any undisturbed soil appear to have been made. No evidence of any multiplication of coliform bacteria in soil has been found. Results, however, are in agreement that where pollution of the soil by animal excreta has taken place, the heavier the pollution the greater is the number of coliform bacteria; soils relatively free from human or other animal pollution either contain no coliform bacteria or only small numbers. It is generally agreed that the ratio of the numbers ofBact. colito those ofBact. aerogenesand intermediates decreases with the increase of time which has elapsed since pollution of the soil. This change is similar to that which occurs in faeces during storage.7. There is insufficient evidence to justify the definite statement often made thatBact. aerogenesand intermediates are normal inhabitants of soils, grasses, and grains.