GB2302549A - Seal for hermetically closing a Petri dish - Google Patents

Description

2302549 1 PETRI DISHES AND THEIR USE IN THE PRODUCTION OF LONG LIFE

CULTURE PLATES The present invention relates to a removable ring seal for a culture plate or petri dish, to a sterile pack containing the ring seal, to a petri dish fitted with the ring seal, and to a process for making long life culture plates using the ring seal.

Known petri dishes generally comprise a bottom container and a mating cover member. The bottom container takes the form of a shallow truncated cylinder. The cover member takes a similar complementary form but has a larger diameter and has a depending peripheral wall which is a loose fit over the peripheral wall of the cover so that the cover can be lowered onto and rest on the peripheral wall of the container. Petri dishes are traditionally made of glass, but more recently disposable petri dishes have become available which are of thin plastics material and are provided in pre-sterilised packs.

Petri dishes can be used to make culture plates e.g. agar plates in which a layer of culture agar medium (CAM) lines the bottom of the container. The agar plates can be prepared by pouring melted CAM into the container to form a layer of thickness 2-5mm, after which the agar is 2 allowed to cool and set with the cover in place. After the agar has set, but before use, the agar plates are tested for bacterial sterility. Such agar plates provide a commonplace and convenient culture medium.

However, the CAM or other culture medium in an agar plate is subject to dehydration, oxidation and contamination. Agar plates therefore have a limited shelf life, generally not more than about two to three weeks, and have to be prepared afresh periodically. They are generally stored in refrigerators until they are used.

A problem with which the present invention is concerned is to provide a means for producing agar plates having an extended shelf life.

In one aspect the present invention provides a ring seal which can produce a hermetic closure for a petri dish comprising a container and cover. The ring seal comprises a closed length of resilient material which is shaped to be a releasable f it onto a rim of the container so as to form a cap. The cover which would otherwise be a loose f it on the container when pushed into place forms an air tight seal by compression of part of the ring seal between the wall of the container and a depending rim of the cover.

3 In a further aspect the invention provides a pack comprising one or more sterilised ring seals as aforesaid. This also provides a process of sterilising a ring seal as aforesaid by the use of a sterilising liquid or gas or by means of UV light.

In a further aspect the invention provides a petri dish fitted with a ring seal as aforesaid, which dish may be filled with a sterile culture medium.

In a further aspect the invention relates to the use of a ring seal as aforesaid for providing a generally occlusive or hermetic closure for a petri dish to moderate or eliminate the ingress of air and bacterial contaminants and thus increase the shelf life of the culture medium in the dish. Thus the invention also provides a process for making a long life culture plate, said process comprising providing a sterile petri dish comprising a container and a cover, filling the petri dish with a culture medium under sterile conditions, allowing the culture medium to set, fitting to the container a ring seal as aforesaid, and applying the cover so as to compress part of the ring seal between the container and the cover and form a hermetic closure for the petri dish.

The provision of an air tight or air resistant seal as 4 aforesaid reduces or prevents dehydration, oxidation or contamination of the CAM within the petri dish.

The ring seal may be of a simple inverted U-shape, or it may have a central septum between its two sides walls. It may be used in association with an inner lid for the petri dish which comprises a planar base shaped to fit within the container and a peripheral wall upstanding from the base which fits within but has a smaller diameter than the peripheral wall of the container. The lid may be fitted into the container to displace the air over the CAM, after which the ring seal is capped over the rims and peripheral walls of the lid and container to f orm a hermetic seal. A handle may be provided on the base of the lid to facilitate manipulation.

In a further form of the petri dish, there is provided an inner lid as aforesaid which is combined with a ring seal of inverted U-shape to form a single or integral component. The ring seal is formed at the rim of the lid with an inner side wall thereof forming an integral part of the peripheral wall of the composite lid. Again the composite lid fits into the container to displace air over the CAM, and the lid fits over the rim and peripheral wall of the container to form a hermetic seal as aforesaid. A handle is provided to facilitate manipulation. Such a composite lid and its use for extending the shelf life of agar plates also forms an aspect of the invention.

is When preparing a long life agar plate, melted culture agar medium is poured into the container to a thickness of 2-5mm and allowed to set. The ring seal/lid and ring seal/composite lid are fitted into the container. The cover is replaced and capped over the ring seal/composite lid to complete the air tight petri dish.

According to the present invention there is also provided a method for preparing long life agar plates incorporating a ring seal/lid and a ring seal/composite lid into a petri dish to form an air tight container.

Prior to use the cover is taken off and after the removal of the ring seal/lid or ring seal/composite lid, the cover is replaced on the container. The agar plate is similar to a conventional agar plate except in terms of its shelf life and can be used in a conventional manner.

The ring seal/lid and ring seal/composite lid may be made of any suitable deformable resilient material, for example deformable plastic or rubber. The material is desirably readily sterilised e.g. by the action of a sterilising gas or liquid or by UV light.

6 Various embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which; Figure 1 is a view in vertical section of a petri dish containing CAM, with a ring seal capped over the rim and peripheral wall of the container, and the cover f itted over the ring seal to form a hermetic seal for the container; Figure 2 is a view in enlarged vertical section similar to Figure 1, but showing the use of a ring seal having a septum; Figure 3 is a view in vertical section of a third form is of the container, in which there is provided an inner lid that fits closely against the CAM layer; Figure 4 is a view in enlarged vertical section, similar to Figure 3 but showing the use of a ring seal having a septum; Figure 5 is a view in vertical section of a further form of the petri dish having a combined inner lid and ring seal; and Figure 6 is a view in enlarged vertical section similar to Figure 5 but showing the use of a combined inner lid 7 and ring seal provided with a central septum.

In figures 1 and 2 there is shown a petri dish comprising a container 2 and a lid 10, both of thin plastics material. The container 2 may typically be of external diameter 9cm and wall height about 1.4cm. The lid 10 is a loose fit on the container 2 with an internal diameter of about 9.1cm and wall height of about 0.7cm. Such petri dishes are disposable and cannot be heat sterilised because of the material in which they are made. They are typically provided in packs of 50, in pre-sterilised form. However, the invention is also applicable to glass petri dishes. The flat base of the container 2 carries a thin layer 20 of CAM. The top edge of the container wall carries ring seal 9 which is of inverted U-shape in cross section and is a push fit onto the wall to form a deformable cap therefore. The lid 10 is now a push f it onto the ring seal 9, which is of deformable plastics material, and the outer portion of the ring seal 9 becomes compressed between the wall of the container 2 and the depending rim of the lid 10 to provide an air-tight seal.

The above petri dish structure enables a conventional petri dish to be used to make a long-life agar plate which may have an extended shelf life, typically about three weeks to four months. Because of its air 8 tightness, the petri dish can protect its contents from dehydration, oxidation and other contamination during long term storage. In order to make a long life plate, the agar medium is prepared in advance and sterilised in an autoclave e.g by heating to 12WC for 15 to 20 minutes at a pressure of 115 lbs. The plastic petri dishes are available presterilised, the sterilisation typically being carried out by means of a sterilising gas or by means of UV light. In order to prepare petri dishes, the pack in which they are supplied is opened in a sterile room, and subsequent operations are carried out while maintaining sterile procedures. The lid of each container is removed, the container is filled with agar at a temperature of about 60T to provide the layer 20, and the layer is allowed to set, after which the filled container portions 2 are inverted. The ring seals 9 are also pre-sterilised, by sterilising gas, by UV light or by other suitable means. With the container containing the set agar layer facing downwardly, the ring seal 9 is fitted to its peripheral wall. The downward attitude of the container has the advantage that contamination of the culture medium is minimised. The container 2 and ring seal 9 are then pushed into the lid 10 which is upwardly facing to produce a hermetically sealed long life agar plate.

The plates can be prepared by the above method in 1 9 batches, and samples may be tested for bacterial sterility by incubation at 370C for 48 to 72 hours. if the culture medium has become contaminated, colonies will appear on it.

The above procedure provides a simple way of converting conventional petri dish for forming agar plates into dish which will provide long life agar plates. No alteration to the structure of the petri dish is required, and the ring seal may be removed after it has been fitted to return the agar plate to its previous condition and enable it to be used in the usual way.

Figure 2 shows on an enlarged scale the edge region of a petri dish fitted with a ring seal 9 having a central septum 7 between its two depending side walls.

Figure 3 shows a further form of the present petri dish in which the container 2 and layer of CAM 20 are as previously described, but there is provided an inner lid 8 having a handle 6 which fits tightly within the walls of the container 2 as shown so as to be in contact or in close proximity with the CAM layer 20 and impede the contact of air with the CAM layer. The ring seal 9 now caps the upper ends of both the container wall and the cylindrical side wall of the inner lid 8 and prevents air ingress to the CAM layer. The cover 10 f its onto the ring seal 9 to provide an additional hermetic seal for the petri dish as previously described.

The arrangement of Figure 4 is similar to that of Figure 3 except that the ring seal 9 again has a central septum 7.

In Figure 5, a container 2 and a CAM layer 20 are covered by a combined inner lid and ring seal 8', 9'. This is made of deformable plastics material, and comprises diskshaped base portion which covers the CAM layer 20, an upstanding cylindrical wall which fits closely within the side wall of the container 2, and an integral ring seal 9 which fits over the end of the container side wall to provide a first air tight seal and to provide a portion which becomes jammed between the side wall and the lid 10 to provide a further hermetic seal as aforesaid. The structure of Figure 6 is similar, except that the side wall 41 of the inner lid 81 is now spaced within the side wall of the container 2, and there is provided a septum 7 which fits against the inner surface of the container side wall as shown.

Various changes and modifications may be made to the embodiment described above without departing f rom the invention, the scope of which is defined in the accompanying claims.

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Claims (1)

1. CLAIMS - UK

   1. A ring seal for providing a hermetic closure for a petri dish comprising a container and a cover, said ring seal comprising a closed length of resilient material which is shaped to be releasably fitted to a rim of the container to f orm a cap thereof so that in use an air tight seal is formed when the mating cover is f itted to the container and/or when a lid is fitted within the container.

   2. The seal of claim 1 which is arranged to seal a petri dish having an inner lid for displacing air from above the culture medium and provided with an inner peripheral wall which fits closely against the inner wall of the container, said seal being arranged to cap an inner peripheral wall of the lid and the peripheral wall of the container.

   3. The seal of claim 1, which is integral with a lid for displacing air from above the culture medium.

   4. The seal of any preceding claim, comprising a central septum located between the side walls of said seal, which septum in use contacts the rim of the petri dish.

   12 A sterile pack comprising a ring seal as claimed in any preceding claim.

   8.

   A petri dish including a ring seal as claimed in any preceding claim.

   A petri dish as claimed in claim 6 and filled with a sterile culture medium.

   A process for making a long life culture plate, which comprises providing a sterile petri dish comprising a container and a cover, filling the petri dish with culture medium under sterile conditions, allowing the culture medium to set, fitting to the container a ring seal as claimed in any of claims 1 to 4 and applying the cover so as to compress the ring seal between the container and the cover and form a hermetic closure for the petri dish.

   A petri dish ring seal substantially as hereinbefore described with reference to or as illustrated in any of the accompanying drawings.

   10. A petri dish fitted with a ring seal as claimed in claim 9.