organisms of this type, it seems probable that they have also

Transcription

1 II. ANAEROBIC BACTERIA IN DAIRY PRODUCTS RELATIONSHIP OF ANAEROBIC BACTERIA TO CERTAIN ABNORMAL FERMENTATIONS Department of Dairy Industry, Iowa State College, Ames, Iowa Received for publication, July 5, 1929 INTRODUCTION Abnormal changes occurring in dairy products under practical conditions are occasionally found to be due to anaerobic bacteria, Because of the difficulties involved in isolating and studying organisms of this type, it seems probable that they have also been of importance in fermentations in which they have been missed, especially when aerobic or facultative orgamsms capable of producing the same general change were also present. A number of objectionable fermentations in dairy products due to anaerobes have been encountered at the Iowa Agricultural Experiment Station; some of these are reported herein. HISTORICAL Burri (1923), in discussing the relationship of silage to contamination of cheese, reported that motile butyric acid bacteria and Clostridium putrificm were responsible for abnormal conditions in Emmental cheese. He found the spores of C. putrificum regularly in Emmental cheese, but in small numbers. Burri concluded that the stinker type of cheese is caused by a combination of C. putrificum and butyric acid bacteria and that the numerous defective products found in American cheese factories as the result of the action of butyric acid bacteria and other spore forming organisms may be due to the use of unsuitable silage on certain farms. Matheson (1923) isolated a spore-forming anaerobe from 95

2 96 typical niszler cheese and found that it could reproduce the condition in experimental cheese. An anaerobe similar to Clostridium butyricum was secured from a pimento cheese of the Neufchatel type by Warren (1926). The cheese became bitter and sharply acid. Albus (1927) isolated a spore forming anaerobe from gassy Swiss cheese containing pimentos. He concluded that the organism developed because of the carbohydrate supplied by the pimento. Later, Albus (1928) obtained a non-pathogenic strain of Clostridium welchii from a Swiss cheese which had developed an abnormal gassy fermentation. The organism reproduced the condition when experimental cheese was made from milk inoculated with it. EXAMPLES OF ABNORMAL CONDITIONS DUE TO ANAEROBES 1. An abnormalfermentation in acidophilus milk prepared in flasiks A method at one time used in preparing acidophilus milk was to sterilize skim milk in 2-liter Erlenmeyer flasks and, after inoculation, incubate at 37 C. Occasionally a flask. of milk treated in this manner would become very gassy; if the milk had not coagulated it would show considerable foam which was greatly increased by shaking, while, if it had coagulated, the curd would be full of gas holes that conspicuously increased the volume of the material. Microscopic examination of the abnormal fermented material revealed the presence of considerable numbers of short, thick, Gram-positive rods among the Lactobacillus acidophilus cells. The numbers of these rods and the absence of other contaminating types indicated that they were responsible for the abnormal condition, while the general morphology suggested that they were anaerobes. Isolations were made by means of agar shake cultures and only the one contaminant was found. It possessed morphological and cultural characters which classed it as C. welchii.

3 ANAEROBIC BACTERIA IN DAIRY PRODUCTS 2. An abnormal fermentation in acidophilus milk prepared in a tank Acidophilus milk was also prepared by heating milk in a 20- gallon, glass-lined, insulated tank under about 6 pounds steam pressure for one hour, after which it was cooled to 370C. and inoculated through a small opening in the top of the tank. Usually, twenty-four hours were required to develop the desired acidity. On one occasion, when the tank was opened for examination about twenty hours after inoculation, a floating curd full of gas holes was found. A microscopic examination of this material showed that along with the L. acidophilus cells there were a number of short, thick, gram positive rods. When inoculations were made from the fermented milk into brain medium containing 0.1 per cent glucose there was pronounced gas formation and microscopic observations showed that the thick Gram-positive rods had become very numerous. Although detailed studies of the contaminating organism were not made, the general characters indicated that it was C. welchii. S. Coagulation and gas development in pasteurized milk During a study of the changes occurring in pasteurized milk at different temperatures, two samples held at room temperature coagulated and became very gassy. Each of these was examined microscopically and numerous Gram-variable rods were found. Shake cultures of the samples were made in glucose agar and, after incubation for twenty-four hours at 370C., colonies were visible. Some of these were picked into freshly boiled and cooled litmus milk and the tubes sealed with a mixture of paraffin and vaseline. Upon incubation at 37 C., coagulation and gas production occurred. The microscopic and cultural characters of the organisms isolated indicated that they were of one type and that they belonged to the group of anaerobic organisms of which C. butyricum is a member. Until more work has been done on this group of organisms, it will be impossible to identify the isolated cultures definitely. 2),AOZC 97

4 no 4. Gas production in pasteuriwed milk During later work on the changes taking place in pasteurized milk held at room temperature, a considerable number of samples showed gas development in from three to four days. Usually coagulation did not occur until several days after the beginning of the gas production. The samples of milk showing the gassy condition generally had a rather pronounced rancid odor. Microscopic examination of material from the samples showed the presence of streptococci, Gram-negative rods and Grampositive rods. The Gram-positive rods were of various sizes and appeared to include different species. Some of them were large and thick and had terminal to subterminal oval spores; what was believed to be this type was isolated by means of liver infusion glucose agar shake cultures. In pure culture, the organism appeared as a fairly long, thick, motile rod that stained Gram-variable with most of the rods negative, even in twenty-four-hour cultures. Spores were formed in twenty-four hours in 0.1 per cent glucose brain medium; they were oval and occurred in terminal to subterminal positions. The rods carrying spores were swollen. Litmus milk under a seal was reduced, gas was formed and a soft curd furrowed by escaping gas developed. In 0.1 per cent glucose brain medium, gas was produced but there was no blackening or softening. The organism undoubtedly belongs to the group of butyric acid organisms. 5. Rancid odor in pasteurized cream A number of samples of pasteurized table cream, which had been held over-night in a comparatively warm cellar because ice was not available, developed a rancid odor. Following this, the cream coagulated and, with a curd present, gas production was evident. In each instance where this rancid condition was noted, an anaerobe that was believed to be the cause was isolated. The cultures were of two types. One type possessed characters identifying it as C. welchii, while the other was the same as the organism described under example 4.

5 ANAEROBIC BACTERIA IN DAIRY PRODUCTS 99 SUMMARY Instances of abnormal conditions in dairy products caused by the growth of anaerobic bacteria are reported. The organisms involved were C. welchii and types belonging to the group of butyric acid organisms. REFERENCES ALBUS, W. R Gassy fermentation in processed Swiss cheese containing pimentos. Jour. Bacteriol., 13, 66. ALBus, W. R A strain of Clostridium welchii causing abnormal gassy fermentation in Emmenthal or Swiss cheese. Jour. Bacteriol., 15, BURRI, ROBERT 1923 The relation of ensilage to cheese making. Proc. World's Dairy Cong., 1, MATHESON, KENNETH JEsBE 1923 New developments in the manufacture of Swiss cheese. Proc. World's Dairy Cong., 1, WARREN, D. H A defect of pimento cheese. Jour. Dairy Sci., 9, Downloaded from on October 26, 2018 by guest