GB2346893A

GB2346893A - Microbiological illuminating apparatus

Info

Publication number: GB2346893A
Application number: GB9928381A
Authority: GB
Inventors: Simon Snowden
Original assignee: Mast Group Ltd
Current assignee: Mast Group Ltd
Priority date: 1998-12-03
Filing date: 1999-12-01
Publication date: 2000-08-23
Anticipated expiration: 2019-12-01
Also published as: GB9928381D0; GB9826482D0; GB2346893B

Abstract

Apparatus for illuminating and examining microbiological tests, comprising an openable enclosure containing a platform for supporting a test dish, the enclosure including a support for at least one light source which has disposed to provide a respective collimated light beam towards a viewing region that includes the location or expected location of the test dish, whereby the region is evenly but not diffusely illuminated, and a mounting for a video camera such that the video camera is directed at the viewing region.

Description

ILLUMINATING SYSTEM This invention relates to a system for the illumination and examination of microbiological tests, particularly tests for the susceptibility of micro-organisms to other substances particularly antibiotics. In its preferred form it relates to an arrangement of lamps and filters, for use in conjunction with a video camera and associated processing means for producing a pixel map of a susceptibility test Background of the Invention It is customary at the present time to conduct tests for the susceptibility of a micro-organism to another substance such as an antibiotic or more generally an antimicrobial substance or a variety of such substances. Typically a petri dish containing a nutrient gel receives a sample of a micro-organism, which is deposited in or on the gel. Then a carrier containing an antimicrobial substance (or a multiplicity of such substances) is placed on or in the gel. The effectiveness of the various substances, for example antibiotics, may be gauged by the radius of a circular region around the original location of each sample, the micro-organism having been affected by the antibiotic within this region but remaining as yet unaffected outside it.

Obviously, the greater the radius of this generally circular region the greater the susceptibility of the micro-organism to the respective antibiotic.

Although in traditional practice the radius of the region of susceptance has been measured humanly, it is generally desirable to automate the process of measurement. For this purpose one may employ a video camera disposed above the test dish to produce a pixel map of the dish and its contents and to make measurements using the image or pixel map produced by the camera. Typically for example the pixel map may be composed of pixels each representing a square of which a side is 0.22 millimetres (4.5 pixels per millimetre) so that the pixel map may, with appropriate data processing, potentially provide an accurate measure of the regions of susceptance. A preferred method of processing a pixel map to provide a measure of the various regions is set out in our co-pending application No. 9826484. 9, entitled'Image Analysis of Microbiological Tests'However, the present invention is not intended to be limited to use in that method and it may have a more general utility, as exemplified hereinafter.

It is generally found that the surface of the nutrient medium where the micro-organism has been affected by the antimicrobial substance is generally flat or at least more even than the surrounding region where in the micro-organism is not so affected due to growth of the micro-organism on or in the gel. Furthermore, the nutrient gel is normally translucent.

Although the transition from the susceptible region to the surrounding region may therefore be indicated by a change in the surface condition, there is not normally any significant colour or density change which would facilitate the discrimination between the susceptible region and the surrounding region Though various image enhancement techniques are available to emphasize the differences between the regions and thereby to enable an accurate estimate or measurement of the position of a transition between them, it is difficult to obtain an optical image of the test which differentiates the regions sufficiently to enable such image enhancement techniques to be of value.

It is customary in circumstances similar to those which have been described to employ diffuse lighting. However, it is has been found that diffuse illumination does not enable good optical distinction between the regions of interest.

Summare of the Invention The invention is based on the provision of a plurality of collimated light sources disposed to illuminate a region. The test dish will be located in this region. A video camera will be disposed to have a field of view generally looking down on the test dish. There are one or more and preferably at least four light sources which provide respective, defined (preferably collimated) illumination of respective parts of a region in which the test dish is located, the illumination being substantial even in intensity over said region. Preferably the sources are symmetrically and obliquely disposed relative to a viewing axis of the camera. The angles of incidence of the light beams produced by the sources are such that there is no or substantially no reflection into the camera. Each of the light sources is provided with a filter, such as IDF (image directing film) II. Preferably an optical filter attenuating daylight is disposed in a location under the test dish.

In the drawings: Figure I is a simplifie elevation view of an apparatus according to the invention ; Figure 2 is a plan view of the apparatus, and Figure 3 is a detail of the apparatus.

Detailed Description The preferred apparatus comprises an enclosure (not shown) which has frame members, a top panel and side panels. Adjacent a side panel in suitable enclosures may be processing circuits coupled to a video camera mentioned below. The enclosure will normally have a rear panel and an openable front panel which may have a window though which the interior of the enclosure may be viewed.

Mounted in the top panel, for example by means of skew cut-out tabs, are four light sources 1-4 constituted by halogen lamps each of which has reflectors disposed to provide a substantially collimated beam towards the expected location of the petri dish. Each lamp has in front of it a filter 5 constituted by image directing film to further collimate the respective light beam. The lamps I to 4 are arranged in approximately the same plane and symmetrically about the viewing axis of the video camera 6, each being disposed to illuminate a respective quadrant of a circular region of which the centre is disposed on the viewing axis of the video camera. The camera may produce a composite output and be arranged to provide a pixel map of the viewing region, typically at a scale of 4 to 5 pixels per millimetre.

The apparatus includes a platform 7 for a test (petri) dish. This platform may be constituted by or include an optical filter which severely attenuates visible light and thereby provides a dark background against which the test dish is viewed. The filter may have a pass-band in the infra-red region of the optical spectrum.

The apparatus can be used to distinguish between regions of different surface roughness caused by microbial growth on the basis that the collimated light will be more scattered by the rougher regions and will be thereby cause a corresponding difference in the brightness value of the relevant pixels.

The apparatus may be used for the performance of the method described above. However it may also be used for a variety of microbiological tests wherein the regions of a nutrient or antibiotic are examined and a pixel map or series of pixel maps is used to derive information about growth or susceptibility or identification of a micro-organism.

Claims

CLAIMS 1. Apparatus for illuminating and examining microbiological tests, comprising an openable enclosure containing a platform for supporting a test dish, the enclosure including a support for at least one light source which has disposed to provide a respective collimated light beam towards a viewing region that includes the location or expected location of the test dish, whereby the region is evenly but not diffusely illuminated, and a mounting for a video camera such that the video camera is directed at the viewing region.
2. Apparatus according to claim 1 wherein there are at least four light sources each of which is arranged provided a collimated light beam illuminating a respective part of a region centred on the viewing axis of a camera disposed in the said mounting.
3. Apparatus according to claim 2 wherein the platform includes or is constituted by an optical filter which severely attenuates visible light.
4. Apparatus according to any foregoing claim wherein the or each light source is provided with an image-directing film.