畜産食品に含まれる腸球菌群に関する衛生学的研究特に汚染指標としての意義について

橋本 秀夫

広島大学水畜産学部紀要

Journal of the Faculty of Fisheries and Animal Husbandry, Hiroshima University

Studies on enterococcus group as an indicator of pollution in water, soil, foods and others have been recently reported by many investigators. Though the presence and significance of enterococcus group in various food materials, especially in fish and other marine products had been investigated, there are a few investigations on enterococcus group in milk, meat and their products.

Therefore, this investigation was undertaken to ascertain the significance of enterococcus group as an indicator of pollution in milk, meat and their products. First, the screening media for enterococcus group were examined and the best was determined. Then, using this screening medium, the qualitative and quantitative examinations for enterococcus group in milk, meet and their products and feces of human and various animals were made, on the other hand the counts of coliform bacteria and all living bacteria too were done. Next, the identification, the relationship between the materials inspected and the species of strains detected, the thermoresistance test and the longevity of enterococcus group were studied respectively.

The results obtained are summarized as follows:

1. When the screening medium for enterococcus group is used, the content of sodium azide (NaN3) in the medium must be adjusted from 0.002% to 0025% according as the grade of contamination in the inspected materials. But, according as the concentration of NaN3 become thick, it is necessary to notice that growth of enterococcus group is inhibited (Tables3 and 4).
2. In the distribution of enterococcus group and coliforms in milk, meat and their products, both organisms are detected at nearly 100% and the number of coliform bacteria was predominant in raw materials, but in the heat-treated milk products enterococcus group bacteria was dominant. Enterococcus group are positive in all samples of milk powder, whereas coliforms are negative (Tables 6, 7 ,9-17).
3. Distribution of enterococcus group was 100% in 60 human and 75 animal feces (Tables 20,23 and 24).
4. Of 968 streptococcal strains isolated from milk, meat and their products and feces, 101 were classified as Str. faecalis, 100 as Str. faecalis var. liquefaciens, 3 as Str. faecalis var. zymogenes, 438 as Str. faecium, 93 as Str. durans, 138 as unidentified enterococci, 21 as Str. bovisand 74 as unidentified streptococci (Table 30).
5. Of 873 strains of enterococcus group, 438 strains were Str. faecium; Str. faecium occupied the half of strains of enterococcus group.
6. The frequency of detection of Str. faecalis and its varieties was greater than the one of Str. faecium in raw milk and meat, but in heat-treated foods Str. faecium was superior (Table 32).
7. The strains of Str. faecium originated from powdered milk were divided into 7 subtypes by their fermentative reaction to carbohydrates. Moreover, it is noted that a definite subtype was detected in the milk powder obtained from a definite dairy plant (Tables 34 and 35).
8. In human and animal feces, the M.P.N. of coliform bacteria was generally greater than the one of enterococcus group bacteria without reference to individual or race or species of human and animals (Tables 20-22). The M.P.N. of enterococcus group bacteria in human feces was far greater than the one of bovine (Tables 23 and 24).
9. In comparison the species of enterococci detected from human feces with the one from animal feces, Str. faecium was highly positive in the latter, especially in bovine. In the case of human feces, however, Str. faecalis and its varieties as well as Str. faecium were isolated to the same grade (Table 33).
10. When the thermoresistance tests of Str. faecalis, Str. faecalis var. liquefaciens and Str. faecium were tested under the various conditions, the thermoresistance of Str. faecium was the most stable, Str. faecalis var. /iquefaciens was the most labile and Str. faeca/is was in the midst of these two. From these results, it was experimentally proved that there is a difference of species of enterococci detected between raw and heat-treated foods (Tables 36 and 37).
11. When the longevities of enterococcus group and coliforms were compared with samples of butter, feces and inoculated skim milk being preserved at various temperature, it was found that the longevity of enterococcus group was longer than the one of coliforms. Such result was always obtained without reference to the number
of enterococcus group bacteria or coliform bacteria included (Tables 38-40 and 42).
12. Enterococcus group in powdered milk preserved at room temperature survived at least for 15-17 months after manufacture (Table 41).
13. It is the most suitable measure to know how food materials are contaminative that the estimations of number of living bacteria, coliforms and enterococcus group in food materials are performed at the same time.
14. In such milk products as the positive rate of enterococcus group is higher than the one of coliforms, it will be found that the inspection of enterococcus group is better than the one of coliforms for ascertaining the grade of cleanliness of food materials.
15. If the enterococcus group was detected from dairy products such as condensed milk and processed cheese, an insufficient pasteurization or a recontamination after pasteurization are suspected.
16. In preservative foods, for example in certain milk products, it is worthy to survey the presence of enterococcus group as an indicator of pollution, because enterococcus group is usally survival longer than coliforms in foods preserved.
17. In such heat-treated foods as milk powder, it may be possible that the grade of heating or the recontamination after pasteurization is presumed by typing of enterococci detected.
18. As there is a difference of species between the strains derived from human feces and the strains from animal feces, when the typing of enterococci isolated from various foods is made, it may be presumed which the contamination of food originated from human or animal feces.
19. In rats' feces, theM.P.N. of enterococcus group bacteria was generally larger than the M.P.N. of coliform bacteria (Table 20).
20. Both M.P.N. of enterococcus group bacteria and coliform bacteria in dogs' feces were found to be the highest in all II kinds of human and animal feces surveyed (Text-fig. I).
From the above-mentioned results, it was found that the significance of enterococcus group as an indicator of pollution is equal to the one of coliforms, in some instances the significance of enterococcus group is even superior to the coliforms. Also, the author believe that Str. faecium is worthy to be shared one species among enterococcus group.

医学 [ 490 ]

英語

広島大学水畜産学部

[ISSN] 0440-8756

[NCID] AN00213563