GB1596154A

GB1596154A - Microbiological test devices

Info

Publication number: GB1596154A
Application number: GB3753276A
Authority: GB
Original assignee: Scientific Hospital Supplies Ltd
Current assignee: Scientific Hospital Supplies UK Ltd
Priority date: 1977-12-05
Filing date: 1977-12-05
Publication date: 1981-08-19

Description

(54) IMPROVEMENTS RELATING TO MICROBIOLOGICAL TEST DEVICES (71) We, SCIENTIFIC HOSPITAL SUPPLIES LIMITED, a British Company, of 38 Queensland Street, Liverpool L7 3JG, Merseyside, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to test devices which can be used for microbiological inves tigations, such as investigating the resistance of pathogenic agents or bacteria to antibioltics or similar active materials.

The testing of resistance of bacteria to antinrobial agents such as antibiotics normally involves the procedure of applying the bacteria sample onto an agar medium supported in, for example, a petri dish and placing small individual discs of filter paper on the medium, each disc of filter paper having been impregnated with measured quan- tities of different antimicrobial agents. During incubation a bacterial culture will grow on the medium and cover its surface with the exception of inhibition zones around those discs of filter paper impregnated with antimicrobial agents active against the bacteria.

The size of these zones indicates the efficiency of the antimicrobial agents used.

One disadvantage of the known discs is the time required by a user to locate a suffi aient number of these discs on the agar medium. In addition such discs are frequently not presented to the agar surface in a fiat manner, resulting in inadequate diffusion of the antibiotic into the agar with corresponding incorrect test results.

A further disadvantage is the difficulty of accurately locating the discs on the agar medium when used with the rotary plate method of sensitivity testing where the discs are to be located exactly across the border between two different cultures on the agar medium.

The purpose of the present invention is to provide an improved test device.

Accordingly the present invention provides a device for use in microbiological tests, the device comprising an elongate, substantially straight portion; and at least three test portions suitable for impregnation with a test material located on a circle or on a plurality of concentric circles and supported from the elongate, substantially straight portion by respective neck portions each of which is adapted to inhibit the passage of said test material from the test portion to the elongate, substantially straight portion.

In a preferred embodiment the elongate, substantially straight portion has projections for accurately locating the test portions in selected positions on an agar medium. The test portions and the tips of the projections may lie on arcs of concentric circles selected such that when the device is located in a petn dish with the tips of the projections touching the dish side the test portions are accurately positioned across the border or borders between different cultures, such as used in the rotary plate method.

The device is advantageously made of a porous material, for example filter paper and the neck portions are impregnated with a substance which inhibits the capillary action of the porous material. The substance is conveniently silicone which prevents the applied test material from seeping into the straight portion through the capillary system of the porous material.

At least three disc portions are provided in each device although a preferable range is from three to five disc portions. Additional dise portions may be provided by two such devices whose straight portions are joined in substantially parallel relationship by a bridge portion.

Where five or more disc portions are provided, they conveniently lie on three arcs.

Test materials such as sugars and aminoacids may be used for various diagnostic purp ses.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawings, in which: Figs. 1 to 3 show three embodiments of test devices according to the invention; and Fig. 4 shows two devices of Fig. 2 connected together to provide eight disc portions.

Fig. 1 shows a test device 10 which is made of filter paper or similar porous material and provided with three disc-shaped portions 12 each of which is supported on a straight portion 14 (preferably 2 to 3mm in width) by a respective neck portion 16; each disc portion has a diameter of 6 millimeters, this being the international standard size for discs for bacteriological determinations. A portion 18 of each neck portion, preferably where the latter joins the disc portion, is impregnated with a substance, e.g. paraffin, which breaks the capillary properties of the filter paper.

Akernatively the whole of each neck portion is impregnated with such a substance.

Each end of the straight portion 14 has a respective projection 19 positioned relative to the discs 12 to enable the latter to be accurately located on an agar medium in for example a petri dish, as described further below. Although two projections are shown, one at each end of the portion 14, only one, or more than two may be provided and they need not necessarily be at the ends of the portion 14.

The discs 12 may be either preimpregnated with different antimicrobial agents or other test materials during their manufacture and suitably stored until required or, alternatively, produced as "blanks" to be impregnated when used for a partcular test. In use the test device is placed on a culture plate such as a petri dish (not shown) containing a bacterial or other organism sample and after a period of time the antimicrobial agents produce inhibiiion zones ch are substantially cucul and concentric with the impregnated discs 12.The size of the inhibition zones provides a measure of the activity of the antimicrobial agents against the micro- organism and may be measured using, for example, a device such as disclosed in our British Patent Specification No. 1,563,088.

In, for example, the rotary plate method of sensitivity testing a first culture is applied to the agar medium on the petri dish by suitable means such as a swab which is moved outwards from the dish centre while the latter is rotated. The result is a circle (such as circle 22) of the test culture concentric with the petri dish whose side is represented by circle 26. A second, different culture is then applied in similar manner to form an annuls 24 around and adjoining the first culture. The first culture is normally a test culture whose reaction to the antimicrobial agent is precisely known and is included as an in situ comparison with the second culture which is the culture whose reaction to the agent is to be measured.It is extremely important that rhe discs 12 be placed exactly on the border 23 between the two cultures with the border lying on each disc centre. Hitherto, it has proved impossible to accurately position the known discs with any degree of consistency, partly because the border between the two cultures is difficult to discern and partly because, for obvious reasons, once a test disc is positioned on the agar medium its position cannot be altered.

However, with the present invention the tips of the projections 19 are spaced relative to the discs 12 such that when the test device is placed on the agar medium with the tips touching the side of the petri dish the discs 12 are automatically located on the border between the two cultures with complete accuracy.

The three discs 12 of the test device 10 of Fig. 1 are, of course arranged to lie on an arc of a circle od the same radius as 23 with the tips of projections 19 lying on the arc of a concentric circle whose radius is the same as that of the petri dish. Typical petri dish sizes are 8.5 cm and 15 cm diameters and a typical border 23 between cultures is arranged 5.25 cm in diameter. Thus a test device for use with such a petri dish and cultures urould have discs 12 lying on an arc of a circle 5.25 cm in diameter with the tips of projections 19 on an arc d a concentric circle 8.5 or 15 em in diameter.

Of course more than two different cultures may be formed on a petri dish with their borders forming concentric circles and the discs 12 of a suitable test device would be located on arcs of a number of corresponding circles.

The discs 12 are preferably spaced to provide for approximately 39 mm diameter inhibition zones.

Figs. 2 and 3 shows devices similar to Fig. 1 and having respectively four and five disc portions.

Fig. 4 shows how two test devices such as shown in Fig. 2 oan be interconnected by a bridging portion 20 to increase the number of discs 12 available and facilitate the location od the device on the agar medium. In Fig. 4 the neck portions 16 are 2 mm in lengrh and the straight portions 14 approximately 44 mm long. In Fig 4 all of the discs 12 conveniently lie on the same circle.

Although Fig. 4 shows test devices having four discs 12 each it is obvious that test devices having three, five or more discs 12 may be interconnected by bridge portions 20.

Conveniently one or more discs of a test device according to the invention is arranged to lie fully within a culture area.

Although the portion 14 is described and illustrated as preferably straight it may be of any suitable non-continuous elongate form.

Finally, where only one projection 19 is used it may be located at or adjacent either end of the portion 14.

Claims

WHAT WE CLAIM IS:

1. A device for use in microbiological tests, the device comprising an elongate, substantially straight portion; and at least three test portions suitable for impregnation with a test material located on a circle or on a plurality of concentric circles and supported from the elongate, substantially straight portion by respective neck portions each of which is adapted to inhibit the passage of said test material from the test portion to the elongate, substantially straight portion.

2. A device as claimed in claim 1 wherein the elongate, substantially straight portion has means for predetermining the location of the test portions relative to a culture plate when the device is mounted on the plate.

3. A device as claimed in claim 2 wherein said means comprises one projection on said elongate, substantially straight portion.

4. A device as claimed in claim 2 wherein said means comprises at least two projections on said elongate, substantially straight portion.

5. A device as claimed in claim 4 wherein said two projections are located one at or adjacent each end of said elongate, substantially straight portion.

6. A device as claimed in claim 4 or 5 wherein said circle or plurality of concentric circles is arranged concentric with a circle passing through the tips of the projections.

7. A device as claimed in any of claims 1 to 6 wherein the number of test portions is in the range three to five.

8. A device as daimed in any of claims 1 to 7 when made of porous material.

9. A device as claimed in claim 8 wherein the neck portions are impregnated with a hydrophobic barrier.

10. A device as claimed in claim 9 wherein said barrier is silicone.

11. A device as claimed in any of claims 1 to 10 wherein the test portions are disc shaped.

12. A device as daimed in any of claims 1 to 11 having its elongate, substantially straight portion joined in substantially parallel relationship by a bridge portion to an don- gate, substantially straight portion of a further device as claimed in any of claims 1 to 11.

13. A device for use in microbiological tests, substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

14. A device for use in microbiological tests, substantially as hereinbefore described with reference to any one of Figs. 2 to 4 of the accompanying drawings.