Culture medium for microorganisms

Details Culture medium for microorganisms Culture medium for microorganisms

1999-01-06

2001-12-18

Wityshyn, Michael G. (Department: 1651)

Chemistry: molecular biology and microbiology

Micro-organism, per se ; compositions thereof; proces of...

C435S004000, C435S029000, C435S030000, C435S252100, C435S253600

Reexamination Certificate

active

06331429

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a material for culture media and a culture medium. More specifically, the present invention relates to a material for culture media and a culture medium for culture and detection of microorganisms present in foods and environment.
PRIOR ART
The conventional method for culturing and detecting microorganisms will be described below, while taking the determination of standard plate count in the food test by way of example. First, a dehydrated agar culture medium is dissolved and sterilized and then stored at a temperature of about 45° C. A predetermined amount of the agar medium is dispensed in a sterilized Petri dish to which a predetermined amount of a sample to be examined such as a food suspension has previously been added, followed by pour culture, solidification of the agar, culture at a predetermined temperature and then determination of the number of colonies formed. As has been described above, the conventional method for culturing microorganisms requires much labor and time since it requires the preliminary preparation of a culture medium and the sterilization thereof and the agar media should be maintained at a temperature at which it is not solidified. To carry out the microbial test rapidly and more simply, it is desirable that such preparation of a culture medium, which requires much labor and time, can be eliminated. In addition, the conventional method also suffers from a problem in that a large number of plastic Petri dishes must generally be used for the preparation of the medium and this in turn results in the generation of a large quantity of plastic waste after the culture of microorganisms.
The environmental microbial test has in general been carried out by wiping a subject to be examined with a swab, rinsing the swab with sterilized water or sterilized physiological saline to thus form a suspension of the bacterial cell bodies adhered to the swab, smearing the suspension onto an agar medium previously prepared or culturing them through pour culture by the same method described above and finally determining the number of colonies formed thereon.
On the other hand, there has been put on the market a simplified culture medium capable of eliminating the labor required for the preparation thereof. The simplified culture may be classified, for convenience, into stamp-type (Japanese Un-Examined Patent Publication (hereinafter referred to as “J. P. KOKAI”) No. Hei 4-117299), filter-type, film-type (Japanese Examined Patent Publication (hereinafter referred to as “J. P. KOKOKU”) No. Hei 2-49705; and J. P. KOKAI No. Hei 3-15379) and test paper-type ones. The stamp-type simplified medium is one in which an agar medium is dispensed in a plastic container to above the rim and the surface of which can be brought into direct contact with a subject upon test. The simplified medium of this type is easily used and is favorable for simple environmental test for microbial contamination, but the medium is insufficient in the ability of quantitative analysis because of a small area thereof Therefore, it is difficult to examine subjects having curvatures or uneven surfaces and the culture medium of this type cannot be used in the usual food test and environmental test. Moreover, the medium requires the use of a plastic container and this accordingly leads to the generation of a large quantity of plastic waste after the culture like the aforementioned conventional methods. The filter-type simplified culture medium is favorable for the test of liquid samples, but is unfavorable for the test of samples other than liquid ones. In the test paper-type one, colonies are formed within the test paper or the like and therefore, the media suffers from a problem in that the colonies formed are not easily observed and the medium does not ensure good quantitative properties. The film-type simplified culture medium permits quantitative test of foods and can easily be used, but the medium of this type cannot be brought into direct contact with a subject to be tested, unlike the stamp-type one, when examining, for instance, environments. In addition, the number of bacterial cells or colonies cannot always be determined because of the presence of bacterial cells capable of dissolving gels.
There have been put on the market several types of simplified culture media that are designed in such a manner that they can easily be used depending on various purposes. However, there has not yet been developed any simplified culture medium that can, in itself, be used in various applications such as the food test and direct test of subjects.
On the other hand, a color-developing agent such as a tetrazolium salt and/or a color former such as a fluorescent substrate (hereunder simply referred to as “color former”) are sometimes added to a culture medium so that the growth of microorganisms can easily be confirmed. However, these color formers may sometimes inhibit the growth of microorganisms and there has often been observed a low correlation between the results obtained in the presence or absence of these color formers depending on the kinds of sample microbial florae. Moreover, a selecting agent is often added to a culture medium to control the growth of the microorganisms other than those which should be detected, but it is common that the selecting agent also serves to inhibit the growth of the latter and to thus often retard the growth thereof.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide material for culture media and a culture medium which permit easy test of bacterial cells present in a variety of subjects to be tested. More specifically, an object of the present invention is to provide material for culture media and a culture medium which permit quantitative test of microorganisms present in foods or environments by wiping, with a swab or the like, a food suspension or a subject to be tested in an environment, dispersing the bacterial cells adhered to the swab in water to give a suspension and then adding the suspension to a culture medium prepared from the material. These material for culture media and culture medium also permit the direct contact test wherein they are brought into contact with a subject to be tested, directly if the subject is in a wet condition or after wetting them through addition of sterilized water if it is in a dry state. Moreover, these material for culture media and culture medium also permit the inhibition of any direct contact between the microorganisms and a color former and/or a selecting agent at the initial stage of the culture and in turn permit the reduction of the influence of these agents on the growth of the microorganisms to be tested.
According to the present invention, there are provided the following material for culture media and culture media:
(1) Material for culture media comprising a fiber layer, a layer A of a polymeric compound free of a color former and a selecting agent and a layer B of a polymeric compound containing a color former and/or a selecting agent, which are laminated together in this order.
(2) The material for culture media according to the foregoing item (1) wherein a polymeric compound whose 4% by weight aqueous solution has a viscosity, as determined at 20° C., of 10 cps is used as the polymeric compound for forming the layers A and B.
(3) A medium for culturing microorganisms comprising nutrients required for the growth of microorganisms, which are incorporated into at least one of the layer A, the layer B and the fiber layer of the material for culture media according to the foregoing item (1) or (2).
The culture medium of the present invention is one prepared by incorporating nutrients into the material for culture media according to the present invention. The material for culture media and the culture medium of the present invention are a dry material for culture media and a dry culture medium which can be converted into a culture medium to which water or nutrient-containing water is added to give a culture medium capable of growing microo

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