The Classification of the Colon-Aerogenes Group of Bacteria in Relation to their Habitat and its Application to the Sanitary Examination of Water Supplies in the Tropics and in Temperate Climates: A Comparative Study of 2500 Cultures

The utility of Escherichia coli as a contamination indicator for rural drinking water: Evidence from whole genome sequencing

Across the water sector, Escherichia coli is the preferred microbial water quality indicator and current guidance upholds that it indicates recent faecal contamination. This has been challenged, however, by research demonstrating growth of E. coli in the environment. In this study, we used whole genome sequencing to investigate the links between E. coli and recent faecal contamination in drinking water. We sequenced 103 E. coli isolates sampled from 9 water supplies in rural Kitui County, Kenya, including points of collection (n = 14) and use (n = 30). Biomarkers for definitive source tracking remain elusive, so we analysed the phylogenetic grouping, multi-locus sequence types (MLSTs), allelic diversity, and virulence and antimicrobial resistance (AMR) genes of the isolates for insight into their likely source. Phylogroup B1, which is generally better adapted to water environments, is dominant in our samples (n = 69) and allelic diversity differences (z = 2.12, p = 0.03) suggest that naturalised populations may be particularly relevant at collection points with lower E. coli concentrations (<50 / 100mL). The strains that are more likely to have originated from human and/or recent faecal contamination (n = 50), were found at poorly protected collection points (4 sites) or at points of use (12 sites). We discuss the difficulty of interpreting health risk from E. coli grab samples, especially at household level, and our findings support the use of E. coli risk categories and encourage monitoring that accounts for sanitary conditions and temporal variability.

An examination of the modified Eijkman method applied to pure coliform cultures obtained from waters in Singapore

Since the original definition of the coli-aerogenes group of organisms by MacConkey (1905,1909), research has been continually directed in an endeavour to find a more rapid and definite distinction between its respective members.

In general, for the purposes of water analysis, the conform organisms can be divided into two main groups: faecal coli, of which Bact. colitype I can be considered the typical member, and the non-faecal organisms comprising the intermediate-aerogenes-cloacae (I.A.C.) organisms. All available evidence tends to show that Bact. colitype I is by far the most frequent organism in the human and animal intestine. Levine (1921) has summarized the figures of various workers and obtained a percentage ratio of 93·4:6·6 as the ratio of coli:aerogenes in faeces, while Bardsley (1938) has shown that in only a very few cases does the number of I.A.C. organisms exceed the faecal coli in faeces.

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 Eijkman test for faecal coli in the bacteriological examination of water supplies: A survey and discussion of the experimental work from 1929 to the present day with a study of 104 water samples and of 602 cultures

1. A historical survey is given of work upon the Eijkman method.

2. A total of 104 water samples were examined by methods I and III. These yielded 602 cultures obtained from the 44 and 37° C. presumptive series, and of these 357 were 44° C.-positive. The only types capable of fermenting lactose at 44° C. wereBact. colitype I and Irregular type II, with the addition of three cultures of intermediate type I and two ofaerogenestype I.

3. The relative efficiencies in the detection ofBact. coliof the 44° C. method by direct inoculation and of the 37° C. presumptive test with plating and differentiation were compared. Out of 104 samples, sixty-eight were shown to contain faecalBact. coli, and in 19% of these the 44° C. method detectedBact. coliwhen it was not recovered at 37° C. The converse was true in only 13% of samples.

4. The results obtained by other workers in regard to the specificity of incubation at 44° C. and to the various methods hitherto proposed for employing it have been collected and discussed; technical advantages and disadvantages have also been considered.

5. It is concluded: (1) That false positives at 44° C. are a negligible quantity for practical purposes. (2) That the best all-round method to use is Wilson's method IV. (3) That 48 hr. incubation should be given, but that 24 hr. is sufficient when rapidity is desired. (4) That the test should be officially recognized and standards laid down for use with it.

6. Cellobiose was found to be inferior to citrate for the identification of the I.A.C. group.

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

This section of the work deals with the routine bacteriological examination of 2144 samples of water, of which 1102 contained lactose-fermenting bacilli, 4333 strains being isolated. Twelve strains which liquefied gelatine and 24 which gave anomalous MR and VP reactions were excluded from the coliform group; the remaining 4297 cultures were classified on the basis of the MR, VP, indol, citrate and uric acid tests.

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.

412. Coliform bacteria in New Zealand butter

1. The limitations have been explored of a simplified form of Grimes's litmus milk method, as used for a presumptive test for coliform organisms in butter.

2. To improve on this test, the merits and demerits of renneted litmus milk and litmus milk agar have been investigated, and the latter found preferable.

3. Of 719 samples of export salted butter tested for coliform contamination, only 19·1% gave confirmed positive results using MacConkey broth as the presumptive medium, 21·9% were positive using a litmus milk agar medium, and 30·2% (on 434 samples only) were positive using renneted milk.

4. The coliform organisms isolated were classified into the usual types and a seasonal variation in the coli to aerogenes ratio noted.

5. An observation is made on what appears to be the inhibitory effect of bile salt on the gas production of several strains of the aerogenes-cloacae group isolated in this investigation.

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.

The Bacteriological Examination of Mussels

1. This paper reports the results obtained by the cultivation of the bacteria of ten batches each of ten mussels, 100 mussels in all, in lactose bile broth.

2. From these mussels 371 cultures of bacteria were obtained. 30·7 per cent, of these were not Gram-negative bacilli, 10·0 per cent. were Gram-negative bacilli which did not ferment lactose and glucose, 59·3 per cent. were coliform bacilli.

3. By reading the results in lactose bile broth after 24 hours' incubation, and by regarding as positive those tubes which show strong acid and good gas production the most reliable results were obtained. 93·0 per cent. of all typical, and 83·8 per cent. of all typical and atypicalB. colifound gave this reaction. 37·6 per cent. of the organisms giving this reaction were typicalB. coli, 61·1 per cent. of them were typical or atypicalB. coli, and 97·2 per cent. of them were coliform bacilli.

4. The writer's method is described in detail. Its essentials are the rejection of shell fluid, the standardisation of the volume of each mussel at 25 c.c. by the addition of saline, the inoculation of three volumes of mussel mince into lactose bile broth—0·5, 0·1 and 0·02 cc., each in duplicate, and the regarding as positive each of these amounts only when acid and gas are produced in 24 hours in both tubes.

5. It is suggested that a batch of mussels showing more than seven positives in the tubes inoculated with 0·5 cc.. of mince, or more than three in the tubes inoculated with 0·1 c.c. or more than one in the tubes inoculated with 0·02 c.c. should be considered as contaminated to an undesirable extent.

6. Three types of solid media—Salle's, MacConkey's and Burke-Gaffney's— were tested. None were considered suitable for the bacteriological examination of mussels.

7. Reasons are given for considering any solid medium inferior to fluid medium for the bacteriological examination of mussels.

The Type of Coliform Bacilli Prevalent in Urine and their Significance, with Special Reference to the Sanitary Aspects

1. 1000 urinary and 500 faecal cultures of coliform bacteria were studied by means of the methyl-red, citrate and indol tests and also by their fermentation reactions upon saccharose and dulcite.

2. 8 per cent, of the faecal strains and 52 per cent, of the urinary strains were of theaerogenestype,i.e.methyl-red negative and citrate positive. Indol was produced in 94 per cent, and 43 per cent, of cases respectively.

3. This would suggest additional evidence that thecoligroup are quickly outnumbered by theaerogenesgroup once they leave the faeces, and also that the presence of theaerogenestype is not confined even in large numbers to an extra-corporeal habitat.

4. In water bacteriology the constancy or change in the relative proportions ofcoliandaerogenesstrains present is the goal at which to aim. Theaerogenesvariety cannot of itself be regarded as non-excretal or even non-faecal.

5. From a sanitary standpoint, the classification of coliform bacteria by means of the methyl-red and citrate tests cannot be regarded as entirely free from error so long as (a) theaerogenesstrains are found in faeces, in however small numbers, (b) these strains occur as the predominant type in urine, and (c) intermediate strains are found in the faeces, urine, soil and water.

6. The principal value of these tests lies in their comparative specificity in identifyingB. coliof immediate faecal origin. The presence of such an organism, interpreted together with the indol test, may be said to suggest dangerous faecal pollution if found prominently in a water sample. The presence of other types identified by the same tests cannot be regarded as having the same significant value in regard to a negative opinion.

7. A plea is made for a further study of coliform bacteria by means of the tests described in relation to the biological behaviour of the bacteria under different environmental conditions.

The Utilisation of Citrates and the Fermentation of Cellobiose by Strains of Bacterium coli Isolated from Human Faeces

1. Of 585 strains of lactose-fermenting aerobes each isolated from faeces of a different person, 501 did not utilise citrate or ferment cellobiose; 20 were citrate negative and cellobiose positive; 27 were cellobiose negative and citrate positive; and 37 were positive to both tests.

2. Almost 10 per cent, of the strains isolated were indol negative.

3. One culture was methyl-red negative and Voges-Proskauer positive. Two were positive to both tests. The rest were methyl-red positive and Voges-Proskauer negative.

4. It is concluded that the results are not favourable to the use of the citrate or the cellobiose test in routine water analysis.

5. A discussion of the taxonomy of the lactose-fermenting aerobes is given. Only two species,Bacterium coli(Escherich) L. and N., andBacterium aerogenes(Escherich) Chester, are recognised.