Suggested Grouping of Slow Lactose Fermenting Coliform Organisms

The detection of acetyl-methyl-carbinol in bacterial cultures: A comparative study of the methods of O'Meara and of Barritt

The early work on the chemistry of the Voges-Proskauer reaction is too well known to need consideration here. Several workers tried to hasten and strengthen the reaction by the addition of various oxidizing agents, but with little success. O'Meara (1931) made the first real advance when he investigated anew the chemistry of the reaction and found the accepted views incorrect in several respects. As a result he added creatine to the culture, used a much stronger alkaline solution than had hitherto been customary, and so achieved a marked improvement in the rapidity of development and intensity of the colour. He recommended the use of 24 hr. cultures.

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 effect of temperature of incubation on the results of tests for differentiating species of coliform bacteria

1. A study has been made of different types of coliform bacteria with particular reference to (a) their ability to ferment lactose in MacConkey broth at different temperatures, and (b) the effect of using different temperatures of incubation for the indol, methyl-red, V.P., and citrate tests.

2. It was found that 97% of the cultures ofBact. coli(indol positive, methyl-red positive, V.P. negative, citrate negative) examined could ferment lactose with production of acid and gas between 40 and 44° C. The number was not appreciably reduced at 45° C. but was markedly reduced at 46° C. 28% of the cultures ofBact. coli(indol negative, methyl-red positive, V.P. negative, citrate negative) and 15% ofBact. aerogenes(indol negative, methyl-red negative, V.P. positive, citrate positive) were found to be positive at 44° C.

3. The adoption of a temperature of incubation of 30°C. for the V.P. test as advocated by Levine (1941) and the use of O'Meara's test showed that many cultures previously regarded as unable to produce acetylmethylcarbinol were in fact able to do so. Employing a temperature of 30°C. for 5, or in some cases 7, days for the methyl-red test, it was found that with nearly all the cultures tested there was an inverse correlation between the results of the methyl-red test and those of the V.P. test. With these modifications in technique some cultures originally designated as Intermediate type I were found to have reactions corresponding with those ofBact. aerogenestype I. Similarly, many cultures originally classified as Intermediate type II should have been typed asBact. aerogenestype II.

4. It was found that all cultures of Intermediate type I classified as such by the new technique were incapable of using the nitrogen of uric acid for growth, but that the majority produced hydrogen sulphide. Cultures ofBact. aerogenestype II, on the other hand, grew well in uric acid medium, but produced no hydrogen sulphide.

The investigation described in this paper was carried out by the Freshwater Biological Association, as part of the programme of the Water Pollution Research Board of the Department of Scientific and Industrial Research. The paper is published by permission of the Department.

Erwinia -Like Microorganisms Isolated from Animal and Human Hosts

Erwinia -like microorganisms were isolated from the vital organs of more than 40% of a large deer population examined as well as from 13% of a small random sampling. Over a brief period of observation, a similar isolate was recovered from throat cultures of two children and one adolescent. There is no obvious explanation of the presence of the plant pathogen or its significance under these circumstances.

COLIFORM BACTERIA IN SEA WATER AND SHELLFISH: I. LACTOSE FERMENTATION AT 35.5° AND 44 °C

Of 6452 coliform strains isolated from sea water and shellfish specimens by membrane filtration (MF) and Violet Red Bile (VRB) agar techniques, 4728 (73.3 per cent) fermented lactose with the production of acid and gas within 48 hours at 35.5 °C; these cultures were incubated in Eijkman medium, in a water-bath at 44 °C, for 48 hours. Gas-positive tests were recorded for 94.6 per cent of Escherichia coli type I strains and 37.7 per cent of E. coli type II strains; 6.7 per cent of the "non-faecal" strains (represented by 10 coliform biotypes) were also gas-positive at 44 °C. The capacity of selected strains to ferment lactose at higher temperatures (44.5° to 46.0 °C) was also studied.A total of 1724 (26.7 per cent) of the cultures produced completely typical coliform colonies on MF membranes or VRB agar plates but were incapable of rapid lactose fermentation at 35.5 °C on subsequent isolation. Aerobacter biotypes were predominant (77 per cent), and 47.4 per cent of the cultures liquefied gelatin. The probable effect of lactose-degraded coliform bacteria on coliform density estimates made by the MF technique is discussed.