DETECTION AND SIGNIFICANCE OF THE COLIFORM GROUP IN MILK¹²

Abstract

Comparatively few reports on the types of the coliform group present in milk have been published and in most instances the species have not been determined. It is diBcult to compare earlier work with more recent investigations because of differences in classifications employed. Earlier work is summarized by Yale (1933). This investigator isolated 63 per cent EsclzeAchia, 26 per cent Aerobacter, and 11 per cent intermediates from raw milk and 57, 10, and 33 per cent respectively from pasteurized milk. Ten species of Escherichia and three of Aerobacter were isolated by Pale, who found Escherichia COG, Eschwichia pseudocoloides, and Escherichia commzcnior, in this order, the most prevalent in the first genus, and Aerobacter aerogenes and Aerobacter cloame most frequent in the latter. The results of more recent investigations will be included in the discussion. EXPERINENTAL WORKThe organisms identified in this report were isolated by inoculating 275 samples of raw milk in groups of 50 samples into a total of 12 media; 25 samples of raw milk into 10 media; and 31 samples of raw milk, 34 samples of pasteurized milk, and 25 samples of "certified" milk into five media as discussed in a previous paper, Bartram and Black (1936). The cultures were identified as Escher'ichiia, Aerobacter, or intermediate according to their reaction on Methyl Red-Voges Proskauer medium, Simmon's citrate agar, and the indol reaction. The species in the Esclterichiu-Aerobacter genera were classified in accordance with the descriptions given in Bergey 's Manual (1934). The species of the intermediate o r Citrobactw genus were identified according to the classification of Werkman and Gillem (1932).The technique and media employed in physiological tests were those recommended by the Committee on Bacteriological Technic of Approved for publieation by the Director of the Maryland Agricultural Experiment Station.' A portion of a

Productivity of Media Containing Milk for Recently Isolated Strains of the Coliform Group

“…As far as is known, the productivity of the various solid media has not been reported so that no comparison is possible. However, the results in general confirm those obtained in previous work by us, (Bartram and Black, 1936) although desoxycholate agar fell below the results that might have been expected. This was accounted for by its low productivity with the strains of the intermediate group and may be characteristic of the medium, although this has not been determined with additional intermediate strains.…”

“…The media employed were selected from those used by us in a I Based on a portion of a thesis submitted by the senior author to the Graduate School of the University of Maryland in partial fulfillment of the requirements for the degree of Doctor of Philosophy. previous study (Bartram and Black, 1936) and were prepared from dehydrated products or according to the methods described by their proponents. Both the liquid and solid media were made up in such strengths that the addition of the 1 cc.…”

Coliform Organisms in Certified Milk

“…Numerous mediums, both liquid and solid, have been recommended for the isolation and enumeration of coliform bacteria in milk. The merits of a large number of these have been studied and discussed extensively by Bartram and Black (1936) and Yale (1937a). Granted a suitable medium the major objection to the use of liquid mediums is the large number of tubes which must be used if the determination is to be quantitative.…”

“…(Chilson et al, 1936, Yale, 1937a In certified milk, however, the conditions are such as led Ayers and Clemmer (1918) and Sherman and Wing (1933) to suggest that the coliform count may serve as a supplementary index of sanitary quality. If, as Bartram and Black (1937) suggest, the tendency to regard all coliform organisms as of possible fecal origin is valid, then the presence of any members of the group would indicate a highly undesirable condition. Parr (1936Parr ( , 1937 has noted a "succes-sion of forms" in stored feces where the Escherichia types found in fresh samples soon disappeared and were replaced by intermediates and members of the Aerobacter group.…”

The Presumptive Enumeration of Lactose Negative as well as Lactose Positive Enterobacteriaceae in Foods

“…It is preferred generally in diagnostic bacteriology to use solid instead of liquid media because, in the former, competition phenomena play virtually no role, while the result that isolation of primary cultures is a far more reliable procedure. This consideration led to using the well-established crystal violet neutral red bile agar (violet red bile agar of Bartram and Black, (1936)) for the present purpose. Though in this formula lactose could have been replaced by mannitol, the complete medium supplemented with mannitol is preferred to allow laboratories, who so far have used the dehydrated culture medium for the enumeration of coliform bacteria, to continue to do so.…”