The Distribution and Sanitary Significance of B. coli, B. lactis aerogenes and Intermediate Types of Coliform Bacilli in Water, Soil, Faeces, and Ice-Cream

The bacterial content of ice-cream in relation to manufacture, storage and standards of purity

Ice-Cream has occasionally been proved to be the carrier of disease, and therefore a study of the ingredients used, the processes of manufacture and the bacterial content of the final product is an important branch of modern hygiene.

A comparison of two methods of assessing the number of different types of coliform organisms in water

1. A bacteriological examination was made of 1108 samples of water submitted to the laboratory for routine analysis. Of these, 550 contained coliform bacilli and were examined by two different methods. The first method, referred to as method I and officially recommended by the Ministry of Health, involves enrichment in MacConkey broth at 37°C., followed by plating and subsequent identification of selected colonies. The second method, described by G. S. Wilson and his colleagues in their report on milk and referred to as method IV, consists in subculturing every positive 37°C. MacConkey tube into MacConkey broth at 44°C. for Bact. coli I and into Koser's citrate at 37°C. for organisms of the iritermediate-aerogrenes-cloacae group (I.A.C.). In both methods the absolute numbers of coliform bacilli and of the different types are calculated from probability tables.

2. From every fermented tube of MacConkey broth at 37°C. that was plated coliform organisms were isolated. In not a single instance was a false positive, due to non-coliform bacilli, encountered. This merely confirms the general experience in this country of the high degree of specificity of MacConkey broth for members of the conform group. Altogether 2840 strains were isolated by method I and classified according to the scheme given in Table I (p. 310).

3. In the 550 samples Bact. coli I was demonstrated 417 times by method I and 446 times by method IV. The corresponding numbers for I.A.C. were 213 and 449. Method IV therefore proved rather more delicate for the detection of Bact. coli I, and very much more delicate for the detection of I.A.C.

4. Evidence is brought to show that the frequent failure of method I to detect I.A.C. is due partly to a dilution effect and partly to the overgrowth of I.A.C. by Bact. coli I. The chances of demonstrating I.A.C. by method I are remarkably small unless these organisms are present alone, or in numbers greater than or approximately equal to those of coli I.

5. The specificity of the 44°C. MacConkey test for Bact. coli I, and for the infrequent Irregular II which closely resembles it, is very high. For instance, among 2840 strains tested, only fifteen produced gas in MacConkey at 44°C. which could not be classified as Bact. coli I or Irregular II. Only six out of a total of 1086 I.A.C. strains reacted positively to this test. Finally not a single strain, other than Bact. coli I, isolated from 100 samples of human faeces was found capable of producing gas in MacConkey broth at 44°C.

6. The specificity of the citrate test for I.A.C. is not so high as that of the 44° C. MacConkey test for Bact. coli I. In eight out of eighty-one samples of water a positive citrate test was given by organisms other than I.A.C. Examination showed that these consisted of Bact. coli I, non-lactose-fermenters, or of irregular types. Since neither Bact. coli I nor the non-lactose-fermenters grew in citrate in pure culture, and since they were found in citrate tubes that had been subcultured from fermented MacConkey broths inoculated with relatively large quantities of polluted water, it seems possible that their growth was due to the carrying over of small amounts of organic matter into the citrate medium.

7. Observations on the association of Bact. coli II, Irregular I and Irregular II with other coliform types render it probable that Bact. coli II is not mainly of faecal origin, that Irregular I is almost certainly of faecal origin, and that Irregular II may be of faecal origin, but that further evidence will be required to establish this definitively.

8. Owing to the fact that Irregular I does not produce gas in MacConkey broth at 44°C., the faecal coli count by method IV is underestimated, and owing to the fact that Irregular II does produce gas at 44°C., the faecal coli count is overestimated. In this series of examinations the faecal coli count was falsely estimated owing to the presence of Irregular I in 0·4% and owing to the presence of Irregular II in 0·5 % of samples. The combined error of 0·9 % is insignificant in relation to the experimental error of the technique as a whole.

9. By the use of method IV it is possible to demonstrate that (a) I.A.C. is nearly as frequently present in polluted water as Bact. coli I, and when the pollution is only slight may exceed it; (b) I.A.C. tends to be the dominant organism in polluted water that has been subjected to chlorination; and (c) I.A.C. is often present in human faeces (61% of 100 samples), and may sometimes constitute the dominant coliform type. In view of these facts it would seem unwise to neglect organisms of the I.A.C. type in the interpretation of water analyses in this country. Their presence is likely to be of most significance in water of a fairly high degree of purity in which, owing to chlorination or other causes, Bact. coli I can no longer be detected.

10. It is therefore concluded that it would be advisable in future to adopt a method of analysis, such as method IV, which affords a more delicate index of the presence of Bact. coli I, and particularly of I.A.C., in water than the method officially recommended at the present time. The fact that method IV is both simpler, quicker, and cheaper than Method I provides an additional recommendation for this change.

The classification of coliform bacteria

A study of the biological characters of 1636 cultures of coliform bacteria, isolated from milk and bovine faeces, shows that the coliform group consists of a large number of different types. These types are so closely interlinked in characters and in relations to environment as to justify their inclusion in one genus. Nevertheless, to facilitate the identification of types, the group may be subdivided into subgroups, the Voges-Proskauer, Koser, inositol and indole reactions being reliable and outstanding criteria for this purpose. These characters show almost perfect correlations with various other characters. Thus Voges-Proskauer-negative types have a low CO2to H2ratio and are methyl-red-positive; Voges-Proskauer-positive types have a high CO2to H2ratio, are methyl-red-negative and Koser-positive. Koser-negative types are not highly resistant to brilliant green, are non-capsulated, do not form thick mucoid colonies and are Voges-Proskauer-negative, inositol-negative and indole-positive. Koser-positive types are highly resistant to brilliant green, and with the exception of group 2 and certain members of group 3, are frequently encapsulated and form thick, mucoid colonies. Non-inositol-fermenters are as a rule motile and adonitol-negative. Inositol-fermenters are Koser-positive, adonitol-positive, sucrose-positive and raffinose-positive; are frequently encapsulated and form thick, mucoid colonies; and as a rule are non-motile. Indole-negative types are Koser-positive, while indole-positive types are generally Koser-positive or negative according to whether the inositol reactions are positive or negative.

The Viability of Bact. coli and Bact. aerogenes in Water. A Method for the Rapid Enumeration of these Organisms

1. The survival of coliform organisms was studied in river water, either raw or sterilised, kept at different temperatures.

2. For determining the coliform count and the differentialcoli-aerogenescount in sterilised river water, direct plating of the water on agar, with subsequent study of a number of colonies picked at random, was used. For raw river water the rapid method described by Wilson and his colleagues (1935) was used, which obviates the necessity of plating and of colonial examination.

3. WhenBact. coliandBact. aerogeneswere held in stored river water, which was protected from agitation, they underwent a gradual decrease in numbers and finally disappeared. At 37°C. they died out rapidly, but survived for a much longer time at temperatures in the neighbourhood of 0°C. They were able to survive longer in sterile water than in raw water.

4. Observations, however, made on water kept at room temperature and subjected to gentle aeration showed that not only did the organisms not die out, but that they actually multiplied, so that their numbers were considerably higher at the end of two months than at the beginning of the experiment.

5. In raw river water coliform bacilli survived longer at room temperature when kept in the dark than in daylight.

6. On the whole,aerogenes1proved more resistant thanBact. colito the environmental conditions provided. This was particularly noticeable in samples kept at room temperature (18°C.). In samples of raw water kept at 37°C.aerogenesproved slightly more resistant thancoli, while at 0–2°C. the reverse was true.

7. The general conclusion seems to be that, except at very low temperatures,aerogenesis likely to survive longer in raw river water thanBact. coli.

8. This conclusion is clearly of importance in the interpretation of thecoli-aerogenesresults in water analysis.

The ecology and significance of the different types of coliform bacteria found in water: A review of the literature

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.

235. The enrichment ofaerogenes-cloacaetypes in milk held at low temperatures: with observations on the relative rates of growth ofaerogenes-cloacaeandb. colitypes in milk at different temperatures

1. Seventy-five pure cultures of various types of coliform bacteria were grown in sterilized or partially sterilized milk for 24 hr. at 17° C. The cultures ofB. aerogenes, B. oxytocusandB. cloacaetypes as a rule multiplied much more rapidly than those of theB. colitypes. Similar results were obtained when twenty-nine cultures of various coliform types were grown in raw milk for 24 hr. at 17° C. There was generally little or no tendency to clumping of the organisms in the milk, even after 3 days' incubation at 17° C.

2. Forty mixed cultures, each consisting of anaerogenes-cloacaetype and aB. coli, were grown in milk for 24 hr. at 17° C. In thirty-four instances theaerogenes-cloacaetype multiplied more rapidly than theB. coli.

3. Twenty-one of these mixed cultures were also grown in milk for 24 hr. at 22, 30 and 37° C. At 22, as at 17° C, theaerogenes-cloacaetype multiplied as a rule more rapidly than theB. coli, while at 30 and 37°C. the reverse was the case.

4. Twelve specimens of bovine faeces were inoculated into raw milk and the cultures kept at 17° C. for 36 hr.Aerogenes-cloacaetypes occurring in the faeces became enriched in the milk, the coliform flora of the milk at the end of the incubation period frequently consisting chiefly of these types.

5. The greater incidence ofaerogenes-cloacaetypes in summer milk in Scotland as compared with winter milk, found in a previous investigation, may be explained by the fact that when milk is contaminated directly or indirectly with faeces, these types become enriched at the temperatures of holding commonly employed in summer. Such enrichment does not occur in winter, the holding temperature of the milk being as a rule so low that there is little or no proliferation of any coliform types. Consequently, the relative proportions of the various coliform types in winter milk tend to remain similar to those in the faeces.

Biochemical characteristics and identification of Enterobacteriaceae isolated from meats

The isolation and identification of 2,220 Enterobacteriaceae from meats indicated that Escherichia coli biotype I, Enterobacter agglomerans, and Serratia liquefaciens were the principal types to be differentiated in meats. Citrobacter freundii, Klebsiella pneumoniae, Enterobacter cloacae, and Enterobacter hafniae were also commonly identified. Identification of isolates by the Encise II (Roche Diagnostics Inc., Nutley, N.J.) and Minitek (BBL Microbiology Systems, Cockeysville, Md.) coding systems gave similar results with only 255 (11.5%) discrepancies in identity, but both systems required large numbers of supplementary tests for identification of the isolates. Not only the distribution of Enterobacteriaceae types isolated from meats but also some of the biochemical reactions of the isolates differed from those of clinical isolates. The Minitek technique is recommended because of its versatility. However, with the addition of cellobiose and salicin disks and the inclusion of methyl red to the Minitek test and the use of the Voges-Proskauer test and gas production in EC medium at elevated temperature as standard tests, the identification of these Enterobacteriaceae from meats would be greatly facilitated. The inclusion of the motility test, for example, using nitrate motility agar, would also be of value to Enterobacteriaceae identification.

Formate lactose glutamate: a chemically defined medium as a possible substitute for MacConkey broth in the presumptive coliform examination of water

During a period of 13 months, 1273 consecutive samples of water received at this laboratory were submitted to a modified presumptive coliform test which included single tubes of four different media. These were: (1) MacConkey broth, (2) formate lactose glutamate medium (pH 7·5), (3) lactose glutamate medium (pH 7·5), and (4) Folpmers's glucose glutamic acid (pH 6·0). 955 samples gave exactly the same results in all four media, but the remaining 318 samples produced differences which enabled comparisons to be made between the media.

As compared with MacConkey broth, the three glutamic-acid media produced between 24–30% more isolations ofEsch. coli, and the formate and the glucose media produced at least the same total number of true coliform organisms (includingEsch. coli) with appreciably fewer false positive reactions. The lactose glutamate medium gave no false positive reactions but, through the suppression of coliform organisms other thanEsch. coli, reduced by 16% the total coliform yield. MacConkey broth gave the largest early (18 and 24 hr.) yield of positive reactions, but the results at the end of 24 hr. showed the formate medium to be not far behind MacConkey broth and appreciably ahead of the glucose medium.

Further experiments with the formate lactose glutamate medium adjusted to different pH's, ranging from 6·0–7·5, indicated that a medium of pH 6·7 provided optimal conditions for the early development of both acid and gas. It was therefore decided to test this observation more fully with routine samples. During a period of 4 months, 279 unselected consecutive samples of water (of which 78 gave positive results) and 57 consecutive unchlorinated water samples (56 of which gave positive results) were examined by a multiple-tube technique in both MacConkey broth and formate lactose glutamate medium (pH 6·7). In the former series the MacConkey broth contained the inhibitory bile salt previously used; in the latter series this was replaced by a relatively non-inhibitory bile salt. In both series the formate medium yielded an appreciably increased total of coliform organisms (12 and 17%) including an increased total ofEsch. coli(27% in the former and 13% in the latter series), and in both series also the results at 18 hr. were abreast with, and at 24 hr. ahead of, those obtained in MacConkey broth.

With certain reservations, it is considered that formate lactose glutamate medium (pH 6·7) can be offered as a suitable alternative to MacConkey broth for the presumptive coliform test of water. Wider trials of this medium would be required before this claim could be fully substantiated.

My thanks are gratefully accorded to Drs W. H. H. Jebb and A. H. Tomlinson of the Oxford Public Health Laboratory for invaluable advice during the investigation and to Dr Ian Sutherland of the M.R.C. Statistical Research Unit for statistic appraisal of the results. I am also greatly indebted to my technicians Mr J. H. Evans, F.I.M.L.T., and Mr G. H. Lowe, F.I.M.L.T., for their unstinting help.

EFFECT of anaerobic spore-bearing organisms on the validity of the presumptive coliform test as used in the bacteriological examination of water

The investigation of 10,436 fermented tubes arising in the presumptive coliform examination of samples of water at six laboratories in England and Wales has shown that, with unchlorinated supplies, the unconfirmed presumptive test gives sufficiently accurate results. Full confirmation of all presumptive positive tubes of these waters is impracticable as a routine and ‘colony-confirmation’ gives a correction of only 0·5%. With chlorinated waters, however, ‘colony-confirmation’ discloses an error of 5·5%, largely due to the presence of anaerobes. This error can also affect the faecal coli (44° C.) count and may be so large in individual samples that assessment of chlorinated supplies should not be based on the presumptive test until this has been checked at least by plating.

Bacteriology of fresh water: II. The distribution and types of coliform bacteria in lakes and streams

1. The distribution of coliform bacteria in lakes and streams has been studied. Weekly samples have been collected from different depths from the north and south basins of Windermere, from Thirlmere, and Bsthwaite Water, dnd from streams flowing into these lakes. Nearly 300 cultures have been isolated from positive tubes of MacConkey broth and their relationship to the coliform group has been studied and considered.

2. In relatively unpolluted streams the counts of coliform bacteria and the plate counts on sodium casemate agar tended to fluctuate in the same direction as river level, but in polluted streams the increased flow of water accompanying a higher river level reduced the numbers of bacteria per unit volume. Counts of coliform bacteria were, in general, much higher in summer than in winter, despite the lower rainfall in summer.

3. During the winter period of circulation of the water, samples of water from different depths in the lakes gave approximately the same count for coliform bacteria. When stratification of the water became established numbers of coliform bacteria in the hypolimnion (the lower stratum) dropped to very low figures and remained fairly constant; much higher counts were found in the epilimnion (the upper stratum).

Large fluctuations in numbers of coliform bacteria which occurred from week to week in the lakes were related to fluctuations in plate counts at only one of the seven sampling points, and were not related to previous rainfall. The count of coliform bacteria was greatest in summer and autumn, a phenomenon that was by no means entirely a result of the bacteria which were washed in being concentrated in the epilimnion. It is suggested that temperature may have affected viability and proliferation.

4. Of the total number of coliform organisms producing acid and gas from lactose at 37° C, approximately 70% wereBact. colitypes I and II, and the remainder were members of the I.A.C. group. In the relatively pure waters of Thirlmere and its inflowsBact. coli, type I, made up 86 and 98% respectively of the total coliform cultures isolated, whereas in the relatively impure waters of Windermere and Esthwaite Water the percentages were 39 and 37 respectively. The differences were due to the greater proportions ofBact. aerogenes, type I, and of intermediate and irregular types in the impure waters. The significance of greater proportions of the I.A.C. group in polluted rather than in unpolluted water is discussed. The actual counts of coliform bacteria were very much lower in Thirlmere than in the other lakes examined.

5. Of the total cultures isolated from positive tubes of MacConkey broth 27% did not produce acid and gas in MacConkey broth at 37° C. Approximately one-half of these cultures, however, fermented lactose at 30° C, and gave varied results with the standard differential tests. The majority of these cultures could, by gradually increasing the incubation temperatures of successive inoculations, be “trained” to ferment lactose at 37° C but not at 40° C. They were more frequently isolated from the polluted lakes and inflows than from unpolluted waters. The remaining organisms isolated proved to be non-lactose-fermenting species belonging to the generaProteus, Salmonella, EberthellaandAlkaligenes(Bergey).

A comparative study of coliform organisms found in chlorinated and in non-chlorinated swimming bath water

The investigation deals with the bacteriological examination of 386 samples of water from Manchester swimming baths where the method of purification could be studied.

There were 339 samples from chlorinated pools of which 160 gave acid and gas in MacConkey broth at 37° C. and 2130 strains were isolated. The remaining forty-seven samples were from untreated open-air pools. Thirty of these samples were positive and 270 strains were isolated. The strains were classified according to Wilson's method into thecoli, intermediate,aerogenesand irregular groups, and only 1·78% of the total were found to be irregular. Both series of samples included more than 72% which containedcoli, and among the chlorinated samples no less than 70% yieldedaerogenesand nearly 49% intermediate type, while among the non-chlorinated baths there were 43% withaerogenesand 40% with intermediate type. There was a similar difference in the proportions ofcoli, aerogenesand intermediate type in chlorinated and in non-chlorinated baths when the results were considered on the basis of strains (Table II).

Since these differences in proportion were considered significant, and since the chief variation in conditions between outdoor and indoor baths consists of chlorination, a series of experiments was devised to test the effect of chlorine on pure cultures ofcoli, aerogenes, and intermediate type. There was very little change after adding 0·1 part of chlorine per million, but the addition of 0·3 and 0·5 part was followed by very rapid reduction in numbers with diminution in free chlorine. This reduction was on the whole least withaerogenes. The numbers continued to fall for about 48 hr. until all trace of chlorine had disappeared and then regrowth occurred. This regrowth was most vigorous and most rapid withaerogenes(see figures) but was very slow in all cases.