CA2136424A1 - Culture device for sampling and/or counting micro-organism - Google Patents

Abstract

The invention provides a culture device comprising a body of culture medium (20) and supporting means for maintaining the integrity of the body of culture medium, the culture medium providing a surface (6) having a defined endless boundary or perimeter, the body of culture medium protruding from and the culturing surface being spaced from any aforesaid means disposed externally of the body of culture medium. The supporting means may include an anchor internal of the culture medium and a base external to the culture medium. Apparatus for use in preparing the culture device and methods of preparing the culture device are disclosed.

Description

WO 93/24608 pcr/Gs93/olo63 ~13~24 CULTURE DEVICE FOR SAMPLING AND/OR COUNTING MISRO-ORGANISM

The present inveDtion relates to a culture device for sampling micro-organisms and/or counting micro-orga~isms. The presen~ invention also relates to apparatus by means o~ which such a culnlre device c~ be prepared.

~Iicrobial count tests have become a useful sa~ita~r control tool for :
mor~itoring sanitation and qualitv levels of food plants to ensure that productsare safe and wholesome. The tests involve transfer of n~icro-organisms ~om cleaned and sal~itised test surfac~s onto a culture agar medium (CAM) which allows growth of a wide range of micro-organisms. After a period of cubation, each m~crobial cell~ develops into a visible colo~y of ccl~s. The number: of coloI~ies provides a measure of tbe number of micro-organisms on the test surface. ~ ;

larious methods are avai1able for assessment of microbiologic~l status of ~ood c ~tac~ suraces in equipme~t such ~s piping, contai~ers~ tables and conveyors which ~are in co~tac~with~ food ;products. Of these metElods, the ril~sing, swabbing aIld: agar contact methods have been consider d as satisfactory and have gained general acceptance.

I D the agar contact method~a replicate organism dir~ct agar contact (RODAC~
plate is used. The RODAC plate prov~des a simple agar contac~ tool for :. , sampling surfaces. It is useful for monitoring ~he sani~a~y quality of sur~aces ::: used in foad industries and hospitals. ~he RODAC plate is best suited for flat smooth imperYious sur~aces such as ceiling, wall and ~oor surfaces an~
: ~ surfaces of tablrs, containers and conveyors.

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The RODAC plate has a rim and is filled with CAM which has a slightly convex surface with the centre of its meniscus risillg aboYe the rim. The surface of the CAM is pressed against the test surface to be sampled. It LS
necessa~v to make good contact of the agar wi~h the test surface. Accordingly when sampling~ care has to be taken to ensure that the entire agar mer~iscus conta~s the test surface: a rolling uniform pressure o~ the back of the plate to effect contact aids in achieving this.

A disadvantage inherent in the nnsing, swabbing and agar contact methods is that uniforrI~tv and consistencv in sampling depend primarily on the skill of persons taking the samples. Technicians need to be trained in sampli~g technique in order tO ~obtain uni~orm and meaningful results.

panicular: m the agar contact method the filling of the RODAC plate with CAM to achieYe a slightly cohvex surface is a slow, careful and exacting p~ocess. A~ditionally it is not sufficient simply to press the CAM of the fil~edplate agaLnst the~test sur~ace since only that part of ~he suF~ce of the ~M
within the ~ved edge portion of the meniscus woul~ contact the test surface.
'rhis par~ of :$he sur~ace Is~ of ~mdefinite area. Thus the area of the test surface contaaed would be indehnîte and~ consequently aIl accurate accouIlt of micro-org~isms per unit a~e:a~o~the test surface wo~d not be obtainable.

~he present invention: enables the above-mentioned disadva~lage to be overeome and provides, at least in preferTed embodimerlts, additional advantages.

In~ accordance with a first aspect of the inventio~, there is provided a culturedevice comprising a body~ of culture medium and supporting me~n~ for maintaming the integri~v of: the body of culture medium, the culture medium ~ wo 93/24608 pcr/Gs93/olo63 ``; 21~12'~

providin a surface (referred to bel~w as the "the culturing surface") havi~g a defined endless ~oundary or perimeter, the body of culture medium pro~ruding ~rom and the culturing surface being spaced from any aforesaid ~: mea~s disposed externally of the body of culture medium.

:~; The endless boundarv or:perimeter is defined by a side surface on COIltigUOUS
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side surfaces of ~he clllture medium, which side sufface or surfaces meet the cultunng sur~ace, preferably abruptly, along an endless line or endless series of lines at an angle substantially differing from 180~, preferably at an angle of 90. so that the boundarv or periuneter is preciselv defined.

The defined boundarv or penmeter of the culturing surface enables its surface area to be clearlv ascertained. This enables the number of micro~organisms ::per unit area on a test su~face and which ha~e been transferred to the :culturing surface to be accurately evaluated.

:The suppo~ing: means may be at least paI-tly external to ~he body of culture ~nedium ~nd/or may be at least partly internal to the body:of cul~e medi~

:Thus the :suppornng means mav be wholly external to the body of culture medium, wholly internaI: :of the body: of culnlre medium or may be in pa~t external to and in part internal of the body of culnlre medium.
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e supporting means may comprise an open cell sponge or ~am or matelial having a three-dimensional retlculaied structure, such as a skeletal foam~ or : oth~r pervious or permeable material irnpregnated with the culture medium.
A suitable material is like that used in household sco~ g spon~es. O~her suitable materials include pervious or permeable fle~ble and preferably soft sheet materials such as woven and non-woven fa~ric and wet-strength paper.

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WO 93/24608 pcrJGs93/olo63 ~36Q~

l~iIaterials as described in the preceding paragraph allow liquid cul~ure medium to infiltrate and impregnate their voids and interstices and they provide good support a~d anchorage ~or the culture medium whe~ it has solidified :

l~e supporting means may comprise a base external to the body of culture medium.

When the supporting means is in part external and in part internal to the body of culture medium, the part internal to the bodv of culture medium constitules an anchor ~o hold the culture medium on the part of the suppor~ng means ex~ernal tO the cult~e medlu~L which latter part m~y constitute a ba~e.
~, Prèferably the ~ chor is held: fast or otherwise attached to the base.

Preferably the culnlring sur~ace is spaced from a peripheral por~ion of the base by ~.g. 1 ~ 5 m~.: ~

~he cul~ing~ surface ~mav be circular, recta~gular or square.

he ~ulture medium may~compnse ag~.

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The cul~uring surface may be flat. This enables the ~lture dev}ce to be applied directly tO a fla~ test area to achieve full contact with the test area wiehout manipulation~of the culture device.

~Iternatively the cultunng surface may be conYex or concave for application to par~ic~lar shapes of test surface.
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The anchor may be a disc or plate preferably perforate or in the form of agrid. It may alternatively consist of a flexib1e porous or perrious absorbe~t material such as descnbed above in respect of the suppon~g means.

The base may be in the form of a container, the peripheral portion of ~he base being a rim of the container.

The term "rim" in relation to the container is intended to encompass a~y endless free edge or extrem~y of the container, which free edge or ex~remity can su~ouDd :and d~fine the extem of the body of the culture medium.

When the base is in the form of a container, the anchor may be a snap fit on ~. ~
a pro~ection UpStaIldi~lg from centre~ of ;the corltainer or may ~e connected toor inte~ with a~ member which is fric~ion fit in the co~ainer. Such an anchor i preerably level with the ~im of the bas~e.

It maY be particularb advantageous for the base to comprise a soft 1exible or : pliable: sheet and for the aDchor, if present,~ o to be ~exible or pliable. This enables the body of clilture medium to be deformed so tha~ the culrure :surface call coxiform Io the ~hape of a test surface to whick it is app~ied.

In accordance with the inYeMion there is further provided an apparanls for preparing a~culture device,::comprising a base for h~lding a body of culture i ~ medium, and a cover whlch can cooperate with the base to define, together with the base, a cavity~for shaping a body of culture medium, the cavity having a sur~ace provided by the cover for fonning the culturing surface of the :: culnlre medium~ said suffaee of the cav~r being spaced from a peripheral por~ion of the bas~e when ~the: eoYer cooperates with the bas~e and haYi~g a defined endless boundary or penmeter so that the body of culture medium : , WO 93/24608 PCI`/GB93/01063 - ~ ~

~,~3 ;shaped in the canry has a correspondiDg defined endless boundary or perimeter spaced from the peripheral portion of the base.
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The surface of Ehe canty may comprise an mternal surface of the cover.

lhe base may be in the fonn~ of a container, the peripheral ponion of the base being a nm of ~the :ontainer.

e cover mav include means to space said surface of the can~ from the rim of the ~base bv a desired distance when the cover is fitted onto the base.

Said~ means ma~ comprise~ ~a~shonlder or abutment of the cover, which shoulder or abutment is engagable with the rim of the base.

The base may be~ as described above -~nth ~re~erence to the~ suppor~ing means.

The `apparatus may ~include~ an~ anchor such as described above, to be em~edded~in the cnlttlre medi~

ac ord~ce~ th a~ c nd, ~pr ~ red ~e~o f the i~e on there is pr~vided~a ~ulture~ dénce~ ~comprising~ a strip of fabric ~or other fle~a~le perlrious or permeàble~material), a central po~io~ of which~is irnpregllated by d ~supports a bodv of ~culture ;medium providing a cult~g surface spaced from the strip ~and having~ a de~ined endless~ bolmdary or perimeter, end portions of ~ the stnp, for~ use i~ manipuIa~ing the device, being ~ee of the ulture ~ medium. ~

In ac~ordance with the ~ vention there is funher provided apparanls for ;prepariDg~ ~a culhlre~device, compnsing a container and a flexible sheet ~, : ~

.~ ` WO 93/24608 pc~/Gss3/olo63 `` 2136~2~L

element having at least a central portion which is porous" permeable or pervious, first means providing a cany in a container for receiving the ce~tral portion of the sheet element and for shaping a bodv of culture medium form~d by solidificauon or setti~lg of li~uid culture medium, the culture mediurn when liquid impregnating the central portion of the sheet element whereby the body af the cuiture medium and the sheet element form a culture device. ths central portion supporting the culture medium and maintaining the inlegri~v thereof when the culture medium is solidified, the body of culture medium ha~ng a culturing surface and the cavity defining side surfaces of said :: :
bodv, which;side surfaces meet the cultunng surface to provide a defined endless bo~daIv or perimeter of the culturing surface~ a~d second means tO
maintain the centra~ portion of the sheet element taut in the cavity and for :allowing end portions of the sheet element to be kept ~ree of the culture medium when the culn~re: medium is solidifying or setting.

Pre~rably~ the container has a base which constinltes the base of the cavi~.

Preferably side walls of the comainer form side walls of the ca~ity.

;Preferably~ the second means not only holds the cemral por~ion of ~he shee~
elemeM taut but: also forms side walls of the cav~

There is further proYided a method of preparing a culture device comprising providing a container ~and ~a flexible sheet elemen~ havi~g a~ leas~ a central por~on:which is permeable or:pervious, locaung the celltral por~ion of the sheet element in a cavity defined in ~he con~ainer with end porlions of the sheet element external:to the cavi~, introducing li~uid culture medium into the cavity to Impregnate the central porrion of the sheet elemen~ and, while maintaining end portions of the sheet element free of the culture medium and WO 93/24608 pcr/GB93/olo63 ~ }

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maintaiI~inP the central portion of ~he sheet element taut, allowing or causing the c~llture medium tO solidifv to form a body of c~lture medium having a free upper culturing surface or a culturing surface defined by a base of the savitv and Ihe cavi~y defining side surfaces of said body which side sur~aces meet the culnlring surface to provide a defined endless boundary or perimeter of the ~l~g surface.

: ~ ; Preferably the sheet element is of woven or non-woven fabric.

Prefera~ly the cavitY is de~ned by side walls and a base of the container and by means which hold the central portion of the sheet element ~au~.

Another culture ~device according to the inven~ion comprises a sheet member de~I~ing a plurality of ca~ities and a sheet of ~abric or other pervious material e~endi~g over the sheet a~d into the cavi~ies, the ~ody ~f culture medium filling at lea~t the bottom portion of each cavity and impregna~g the pennous materi:al,: whereby the peIvioùs: matenal L~ each cavity forms an aIlchor for the bodv o~ culture mediurn,:~lbe~base of each cavi~y:de~ning a culnlring surface :of the culture mediuIIL the culnlring surface ha~ring a defined endless bounda~y or~penmeler. ~

:~e::invention is funher :descnbed below by way of example with refere~ce to the accompan~nng drawingsi, wherein:

igure 1 is a perspec~ive view of a culture device according to the i~Ye~tion;
Figure 2 is a perspective:new of apparatus according tO the i~ven~io~ for preparing the culture device of Figure 1;
Figure 3 is a vertical sectional view of part of the side walls of the apparan~sof Figure 2;

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~1 WO 93/24608 PCr/GB93/01 063 ` 21~6~2~

Figure 4 is a vertical sectional view of part of the apparatus of Figure showing an anchor; and Figure SA is similar to Figure 4 but shows an alternative anchor;
Figure ~B is similar tO Figures 4 and SA but shows a~other altemative anchor;
Figure 6 is a perspeclive view of a container and a lid of a ~ther apparatus according to the invention;
Figure 7 is a plan view of a fabnc s~rip of the apparatlls of Figure 6;
Figure 8 is a secnonal view along a vertical plane of the apparatus of Figllre 6, culture medium hav~ng been added to the apparatus to prepare a culnlre device accordirlg to the invention;
Figure 9 is a vertical plan v~ew of the culture device of Figure 8 or Figure 10,Figure 10 is similar to Figure 8 but shows a modi~cat~on of the apparatus, Figure 11 shows another ombodiment of the inven~on; and , Figure 12 shows a modification of the embodiment of Figure 11.

Refening to the drawings~ there is shown a circu~ar culture dev~ce 1 omprlsing a b~e or container ~ which holds a bodv of culture medium 20.
The base 2 :has a bottom wal1 3 and a side wall 4. The side wall 4 has a rim So The culture medium 20 protrudes from Ihe base 2 ~ d has a smooth~ flat sur~ace 6 ("the culturing surface") raised above the rim 5 by a distance o 2 ~: :
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A side surface 7 of the ~ulture medium 20 extends upwardly from the nm 5 of the base 2 to the ~ulturirIg surface 6. The culturing surface 6 and the side surface 7 meet at a~ angle of 90 to provide a precisely defined endless ~- ~ bolmdary or perimeter 6a of the culturing sufface. This defined perimeter enables the surface area of the culturing su~ace 6 to be precisely determined.

WO 93J24608 pcr/GB93/olo63 ?,~36 ~ o The internal diameter of the base 2 is selected to provide a predeterrnined surface area of the culnlri~g surface 6.
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The base 2 may be provided, as shown in Figure 4, with an anchor comprisL~g a thin disc 8 which is on the same horizontal plane as the rim 5 of tbe base 2. The disc 8 is a snap fit on a post 9. The post` 9 is integrally forrned with he base 2 and pro)ects upwardly &om ~he bottom wall 3 of ~he base. The diameter of the disc 8 is less than the inter~al diameter of the base 2. The disc 8 is preferably pefforale. The ~disc 8 serves to hold and support the culturing medium.

Figure 5A shows an alternative:anchor. The anchor comprises a perforate disc 8 integrally formed with a dependi~g peripheral side wall or skirt 8A
which c~ fit within the ~base 2 and frictionaJly engage the side wall 4 of the base. (Figure S shows a ~space between the side walls 4 and 8A merely for c lari~ of ill~stra~io~

The cnltnre device ~ I fnrther~in~ludes a lid ~or cover 10 which is a close fit onto the base part 2 to define,~ together with the base part 2, a cavity 11. The cover lQ although close:fit~ihg~on the base 2. is not tight~fittiIIg and accordingly can be~readily sllpped:onto the base 2 and easily; removed.

Thc ~cover~ lO ~ has ~a top: wall~ 12~ and~ a side wall 13. These walls provide respecuve~y an internal flat smooth top surface 14 and a cvlindrical internal side surface 15. ~These surfaces meet at an angle of 90.

The side wall 13 of the cover 10 is ~provided w~th an abutment or shoulder 16.

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.!''"'' '' ~, WO 93~24608 pcr/GB93/olo63 . .. .

The side wall 13 o~ the cover 10 has an internal lip 17 below the abutment or shoulder 16. The lip 17 can cooperate with a corresponding external lip 18 on the side wall 4 of the base 2.

The cover 10 can be ~tted into the base 2 wi~h ~he shoulder 16 resting on the rim S so that the base is fully closed and the surface 14 of the cover is separated from the nm ~ of the base 2 bv a desired dista~ce (preferably about ~ mm). Alternatively the cover 10 can be fitted onto the base 2 with the lip 17 resting on the lip 18 so that sboulder 16 is held above tbe rim 5.

In order to prepare the ~lture device 1, a culture medium in liquid form e.g.
melted agar, is introduced into the cover 10. This can be carned out by :
invertirlg the cover 10 and pouring the culture medilLm d~ectly ~to the co~er ~d then fis~ing ~he base 2 onto the c~ver or by pouring the culnlle medium o the base 2 ~d then fitting ~he cover onto the base and inver~iDg the base 2 and ~he ~coveF 10 togeth~r to trans~er the culnlre medium i~to the cover.
The~ culn~re medium is then allowed to cool thereby to set or s~lidify to form the bodv 20 of culhlre medium. The amOllIlt of ~ ure medium must be sueh as to more than f~ll the ~ca~ 11 from the surface 14 of the cover 10 to the rim 5 of the ~base 2. If the base 2 is provided with the anchor 8, then the arlchor becomes embedded in the solidiISed culture medium aIld holds ~he culture medium ~firmly :in~place. The s~ace 14 of ~he cover shapes the ing surface 6 of the culture mediurn as ~he cul~ure medium solidihes.
Similarly the surface 15 of the cover shapes the side sllrface 7 of the culture medium.

The cover 10 ca~ be removed for irlspection of the solidi~ed ~turs medillm or for use of the ~ulture device. Preferably the cover 10 is kept on the base 2 until the culture device 1 is to be used in order to protect the culnlre WO 93/~4608 pcr/Gs93/olo63 ~ .}

36~ 12 med~ from cont~ation. If desired the cover 10 can be replaced on tbe base 2 without touching the surface of the culnlre medium by resting the lip 17 on the lip 18.

In use of the culture dence 1, the cover 10 is removed and the culturing surface 6 is pressed direc~y against a test su*ace to transfer II~icro-organismsto the culturing surface 6 from Ihe test surface. The sur~ace 6 is then removed from the ~est surface and the micro-orgaDisms transferred to the surface 6 are ~owed to multiply i~to visible colonies. The number of colonies corresponds to the number of micro-organisms transferred ~om the test surface to the surface 6. Since the area of the surface 6 is precisely determinablet the number of miero-orgar~sms transferred f rom the test surface t o the surface 6 per unit area of the test surface can be precisely determined.
The culnlre device 1 may be round (as shown) or square in plan. It is pr:eferred that the~ base 2:~and the cover 10 are round for co~enience, vers~lity~ and~ ease of matupulation. The base par~ 2 and ~he cover 10 may be~ made of clear transparent materiaL such as polys~erle, which le~ds itself to fabncadon:and can withstand sterilizing tempera~ures or gamma radiation.

e~perforated disc or plate 8~ formlng the anchor in Figu~e SA may be replaced, as~shown in~Flgure SB, by porQus or pervious material such as ope~
cell sponge or fo~n :or~a: reticulated stru~ure, such as that used in household scouring sponges. The anchor 8 mav be covered by fabric, towelling, or wet strength paper se~red to:the arlchor. Alterrla~ively the a~chor i~self could be made of fabric or wet stren~h paper, towelling, sponge or other materials as discussed above.

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~, WO 93/24608 pcr/GB93/olo63 2 ~ 3 ~ . 2 '~

Reference is now made to Figures 6 to 10.

Apparatus for prepariIlg a cul~ure device comprises a re~angular parallel-pipedal open-topper container 200, a lid or cover 202 for the container a~d a stnp 204 of woven or non-woven fabric.

The width of the s~rip malches the internal width of the container 200. The leng~h of the strip is somewhat greater than the total of the intemal lengLh of the coIltainer plus twice the internal heigh~ of the container. Spring clips 206, as shown in Figure 8, may be provid~d to hold the strip 2~4 in the co~tainer 2û0 with a central portion 204' of the strip held taut between the ends of the container and in contact with the base of tbe container ~d with end poruons 204" of the s~rip extending oYer end walls of the conta~ner.
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The clips 206 have iimbs 206'~whieh are sufficiently loIlg to press the central por~ion 204' of the strip 204 i~to close:contact with the base of the container 200. ~ ~

In use of tbe appar~tus~:the strip 204 is arranged as shown in F;gllre 8, the si~ip beillg held taut between the clips 206 a~d pressed against the base of thecontainer 200. Then iiquld culture medium is poured i~to the container. The culture medium is spread ou~ over the fabric s~np in a layer 212 and solidifies ;~ to form a body of culture m~dium 212 supported by and impregna~iIlg the fabric.

The hpper horizontal surface of the solidifiied body 212 of culnlre medium constitu2es a culturing surface. The side walls of the container 200 and the li~bs 2~61 of the clips 206 de~me side surfaces of ~he bodv of culture mediurn d the side w211s of the container 200 also define side suffaces of ~he body : ~:

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WO 93i24608 Pcr/Gss3/olo63 ~ ~
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?~3~ 14 ~12 of cul~ure medium. These side surfaces meet the culture surface at 90 and thus the culturing sur~ace has a defined endless boundary or perimeter.

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A lid 202 may be placed on the conta~er 200 to protect the body 212 of culture medium from contamination.

The fabric strip with the solidified bodv 212 of culture medium constitutes a culture device. In use of the culture device the device is removed from the : ~ . : container and manipulated by means of the end porrions 204" of the fabric stnp.

The culn~re device mav be used in like maImer to the cul~e device described abo~e. After~ application of the CllltU~g surface to a test surface the cul~re device may be replaced in the container 200 to allow incuba~ion of mioorganisms on Ihe cul~ring surface. The lid 202 may be used to pr~vent contamination of: the cultuling surface during incubation of the microorganism~

I t :will be appreciated that ~because the fabric strip 204 is flexible the device caD be used in conjun~ian ~with test surfaces which ~may be flat, curved or ::un~ven, the body ~of culture medium and the ~a~nc strip accommoda~ing hemselves to the shapes of such test surfaces.

i ~ ~ The strip 204 may be of wet strength paper instead of woven or non-wove fabnc. ~ ~

The stnp 204 may be temporarily stuck to the end walls and b~se of the con~ainer 200 by adhesive thereby obv~a~ing ~he use of the clips 206.
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WO 93/24608 PCI`/GB93/01063 2~3~Jl~

Figure 10 shows a modificauon of the apparatus shown in Figure 8.

Refe~Ting tO Figure 10, the ~limbs ~06' of the clips 206 are shorter so that thecentral po~ion 204' of the strip 204 when held taut between the ends of the container 200 is spaced from the ~ase of the container. The culture medium when set impregnates the central portion 204' of the strip 204 but has a layer between ~he :slrip and the base of the container. l~e lower surface of the set culture medium consti~utes a culturing surface, which is smoother tha~ the g surface pro~ded; by use of the apparatus shown in Figure 8.

Figure 11 shows a further embodiment of the invention.

KefeF~i~g to Figure 11,~ a sheet 300 of~ clear transpareIlt pla~ic (e.g.
pc~tvr~ne~ is formed to provide a plurality of blisters or cavities 302, each havi~g~a~:qli~drical~side~wall which meets the:base:of the cavilv at 90. A
piece;of:fabric 3~4 is~laid~over the plastic ~o as to hang int~ each ca~n~,v. The fabnc 304 ha~ g~into~ th~: cavi~r may have a piece of spo~ge attached to it.
A~piece: of sponge 310:~is:~shown in cavitv 302 in Figu~e 11. The culture medium is~:$hen poured over~the: fa~ric and penetrates; through the fab~c to fill~each~caviy. ~e cillnire~medium is allowed ~o set. The resul~ing solidi~ed bod,v 306;of cult~re~medium in:each cavi~, forms a cul~re de~rice, the culturç
medi~lm~impregrlating ~the ~fabnc/sponge which fo~ anchor for the 'medium.~ A~:sheet:of ~a~u~inium foil 308 may be laid over the ~abnc tO shield the culture devices f,rom~ contamination. A suitable plastic sheet 312 may be added to protect the ~aluminium foil. ~

It will be appreciated that the~ base o~ each caviq defines a CUltUIiIlg surfaceof the body of culture mediu~ he ~Iture surface having a defined endless boundary or perimeter.~

WO 93/24608 PClr/GB93/01t)63 t~ ~
~3~ 41 Figure 12 shows a modi~ca~ion of the embodiment of Figure 11. As show~
in Figure 12, the piece of fabnc 304 extends down the sides of each cavity and across each cavitv adjacent/alorlg its base. The upper horizontal surface of the solidified body of culture medium cons~itutes the cul~ing surface.

Each culture dev~ce may be individually removed ~om its caviLy for use whe~
required.

It will be ~further appreciated that the alum~nium foil may be firmly adhered ~ .
t~ ~he fab~ic and solid~ed culture:medium to provide an assembly in which the culture devices are hermeticalb sealed. The assembly may be provided ~th~ pe~forations between~ the cul~ure devices so that the por~ivns of the asse~ly, each containing :one culture dev~ce, can be readily separated ~om the~ remainder of the~ assembly. When the alum~ium foil is removed from such ~a separated~ por~ion of~ the assembly, the ~ foil ca~ then be removed from that:~por~ion and;the culture device lifted out of the cavi~y.
After~complelion of sa2npling the culture device ca~ be placed with the culture s~rface upward~on:~he separa~ed:pomon of the~plas~ic sheet. The separated por~ion of the~ c~ is~use~ t~: coYer the culture device ~d the ~wo p~ ~re stapled together for: incu~ation.

The ca~n,r 302 may be round,: as shovm. or square or recta~gular.

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Claims

171. A culture device comprising a solid body of culture medium and supporting means for maintaining the integrity of the body of culture medium, the culture medium providing a surface (referred to in claims below as the "culturing surface") having an endless boundary or perimeter, the body of culture medium protruding from and the culturing surface being spaced from any aforesaid means disposed externally of the body of culture medium, the endless boundary or perimeter being defined by a side surface or contiguous side surfaces of the culture medium, which side surface or surfaces meet the culturing surface abruptly along an endless line or endless series of lines at an angle substantially differing from 180° so that the boundary or perimeter is sharply defined, the supporting means being at least partly internal of the body of culture medium.
2. A culture device according to claim 1, wherein the side surface or surfaces meet the culturing surface along endless line or series of lines at an angle of 90°.
3. A culture device according to either of claims 1 and 2, wherein the supporting means is partly external to the body of culture medium.
4. A culture device according to any preceding claim, wherein the supporting means at least in part is flexible or pliable to allow the culture medium to deform to accommodate to the shape of a test area to which the culture medium is applied.

5. A culture device according to any preceding claims wherein the supporting means comprises porous, pervious or permeable material impregnated with the culture medium.

6. A culture device according to claim 5, wherein the porous, pervious or permeable material comprises open cell sponge or foam or material having a three-dimensional reticulated structure.

7. A culture device according to claim 6, wherein the pervious or permeable material comprises woven or non-woven fabric or wet strength paper.

8. A culture device according to any preceding claim, wherein the culturing surface is spaced from a peripheral portion of the supporting means external to the culture medium by 1 to 5 mm.

9. A culture device according to any preceding claim, wherein the culturing surface is flat.

10. A culture device according to any of claims 1 to 8, wherein the culturing surface is convex or concave.

11. A culture device according to any preceding claim, wherein the supporting means comprises a disc or plate internal of the body of culture medium.

12. A culture device according to claim 11, wherein the disc or plate is perforate or in the form of a grid.

13. A culture device according to any preceding claim, wherein the supporting means comprises a base external to the body of culture medium and an anchor internal of the body of culture medium and the anchor is held fast or otherwise attached to the base.
14. A culture device according to claim 13, wherein the base comprises a container, the peripheral portion of the base being a rim of the container.
15. A culture device according to claim 14, wherein the anchor is a snap fit on a projection upstanding from the centre of the container or is connected to or integral with a member which is a friction fit in the container.
16. A culture device according to claim 15, wherein the anchor is level withthe rim of the base.
17. A culture device according to claim 1 or 2, wherein the supporting means comprises a strip of fabric or other flexible porous, pervious or permeable material, a central portion of which is impregnated by and supports the body of culture medium providing the culturing surface spaced from the strip and having the defined endless boundary or perimeter, end portions of the strip, for use in manipulating the device, being free of the culture medium.18. Apparatus for preparing a culture device, comprising a container and a flexible sheet element having at least a central portion which is porous, permeable or pervious, a cavity being provided in the container for receiving the central portion of the sheet element and for shaping a body of culture medium formed by solidification or setting of liquid culture medium in the cavity, the culture medium when liquid impregnating the central portion of the sheet element whereby the body of the culture medium and sheet element form a culture device, the central portion supporting the culture medium and maintaining the integrity thereof when the culture medium is solidified, the body of culture medium having a culturing surface and the cavity defining side surfaces of the body which meet the culturing surface abruptly to define a sharply defined endless boundary or perimeter of the culturing surface and removable means for defining side walls of the cavity and for maintaining the central portion of the sheet element taut in the cavity and for allowing end portions of the sheet element to be kept free of the culture medium when the culture medium is solidifying or setting, said means forming walls of the cavity.
19. Apparatus according to claim 18, wherein side walls of the container form side walls of the cavity (in addition to the side walls formed by the second means).
20. Apparatus according to claim 19, wherein the container has a base which constitutes the base of the cavity and serves to shape the culturing surface, the base meeting the side walls of the cavity abruptly to provide the sharply defined endless boundary or perimeter of the culturing surface.
21. A method of preparing a culture device comprising providing a container and a flexible sheet element having at least a central portion which is porous, permeable or pervious, locating the central portion of the sheet element in a cavity defined in the container with end portions of the sheet element external to the cavity, introducing liquid culture medium into the cavity to impregnate the central portion of the sheet element, and, while maintaining end portions of the sheet element free of the culture medium and maintaining the central portion of the sheet element taut, allowing or causing the culture medium to solidify to form a body of culture medium having a free upper culturing surface or a culturing surface defined by a base of the cavity and the cavity defining side surfaces of said body which side surfaces meet the culturing surface to provide a defined endless boundary or perimeter of the culturing surface.
22. A method according to claim 21, wherein the sheet element is of woven or non-woven fabric.

23. A method according to claim 21 or 22, wherein the cavity is defined by side walls and a base of the container and by means which hold the central portion of the sheet element taut.
24. A culture device comprising a sheet member defining a plurality of cavities and a sheet of fabric or other pervious material extending over the sheet and into the cavities, the body of culture medium filling at least the bottom portion of each cavity and impregnating the pervious material, whereby the pervious material in each cavity forms an anchor for the body of culture medium, the base of each cavity defining a culturing surface of the culture medium, the culturing surface having a defined endless boundary or perimeter.
25. Apparatus for preparing a culture device, comprising a base for holding a body of culture medium and a cover which can cooperate with the base to define, together with the base, a cavity for shaping a body of culture medium, and supporting means at least partly within the cavity and for maintaining the integrity of the body of culture medium, the cavity having a surface provided by the cover for forming a culturing surface of the body of culture medium, said surface of the cavity being spaced from a peripheral portion of the base when the cover cooperates with the base and having an endless boundary or perimeter, the endless boundary or perimeter being defined by a side surface or contiguous side surfaces of the cavity, which latter surface or surfaces meetthe first-mentioned surface of the cavity abruptly along an endless line or series of lines at an angle substantially differing from 180° so that theboundary or perimeter is sharply defined, whereby the body of culture medium shaped in the cavity has a corresponding sharply defined endless boundary or perimeter spaced from the peripheral portion of the base.
26. Apparatus according to claim 25, wherein the supporting means at least in part is flexible or pliable to allow the culture medium to deform to accommodate to the shape of a test area to which the culture medium is applied.

27. Apparatus according to claim 26, wherein the supporting means comprises porous, pervious or permeable material impregnated with the culture medium.

28. Apparatus according to claim 27, wherein the porous, pervious or permeable material comprises open cell sponge or foam or material having a three-dimensional reticulated structure.

29. Apparatus according to claim 28, wherein the pervious or permeable material comprises woven or non-woven fabric or wet strength paper.

30. Apparatus according to any of claims 25 to 29, wherein the supporting means comprises a disc or plate internal of the body of culture medium.

31. Apparatus according to claim 30, wherein the disc or plate is perforate or in the form of a grid.

32. Apparatus according to any of claims 25 to 31, wherein the supporting means comprises an anchor to be internal of the body of culture medium and held fast or otherwise attached to the base.

33. Apparatus according to any of claims 25 to 32, wherein the first-mentioned surface of the cavity is flat.

34. Apparatus according to any of claims 25 to 32 wherein the first-mentioned surface of the cavity is convex or concave.

35. Apparatus according to any of claims 25 to 34 wherein the base is in the form of a container, the peripheral portion of the base being a rim of the container.

36. Apparatus according to any of clams 25 to 35, wherein the cover is provided with a shoulder or abutment with the rim of the base to space the first-mentioned surface of the cavity from the peripheral portion of the base.

37. A method of preparing a culture device comprising inverting the cover of the apparatus according to any of claims 25 to 36, introducing liquid culturemedium into the inverted cover to fill the cover at least up to the level of theperipheral portion of the base when the cover cooperates with the base and then effecting setting or solidification of the culture medium with the base inverted and fitted to the inverted cover.

38. A method of sampling micro-organisms and/or counting micro-organisms on a test surface, comprising applying to the test surface the culturing surface of a culture device according to any of claims 1 to 17 or claim 24 or prepared by a method according to any of claims 21 to 23 and 37 to transfer micro-organisms from the test surface to the culturing surface, removing the culturing surface from the test surface and thereafter allowing the micro-organisms transferred to the culturing surface to multiply into visible colonies.