Disc Transfer Devices To Petri Dishes

Abstract

A disc transfer device for loading a Petri dish. The transfer device includes a plurality of storage tubes with stacks of discs of blotting paper which are, for example, impregnated with an antibiotic to be evaluated. A transfer plate displaces the discs at the bottom of their respective stacks to ejection locations in alignment with ejection passageways which have diameters slightly less than that of the discs thereby preventing the free fall of the discs onto the gelose medium. A control shaft is rotatable for displacing the transfer plate from its disc receiving position to its ejection position and slidably movable perpendicular to the receiving surface for descending plungers which drive the discs to the receiving surface. All the discs are brought into contact with the germ seeded gelose medium in the Petri dish with exactly the same contact pressure, reproductible from cycle to cycle, this pressure being determined by the mass of the plungers. The Petri box is provided with various indicia including intersecting perpendicular lines on its outer bottom wall for aiding the determination of the germ inhibiting zone measured by the discs in position at the intersections.

Description

The present invention relates to an improved device for the transfer of flat objects such as discs to a receiving surface. For the sake of clarity and simplicity the flat articles which are to be transferred to the receiving surface, as will be described below, are uniformly designated as discs; it is obvious, however, that this term is not intended as a limitation as to their configuration or shape.

This type of transfer device is employed for the simultaneous positioning of discs impregnated with different substances, antibiotics for example, for qualitative evaluation according to a particular characteristic; in the case of antibiotics, this is their activity with respect to a certain germ (micro-organism). The qualitative evaluation is produced in the form of an antibiogram which is a visual representation of antibiotic activity.

In order to construct such an antibiogram, the surface of a thin layer of a sterile gelose medium is seeded with the germ being studied; after suitable drying, the discs formed of blotting paper about 6 mm in diameter and about 0.8 mm in thickness, and previously impregnated with different antibiotics being evaluated, are regularly distributed over the surface of the seeded gelose medium. The combination is then maintained in an incubator for 18 hours at approximately 37.degree.C in order to enable the multiplication of the germ and the diffusion of the antibiotic through the medium. The reading of the antibiogram consists of measuring the diameter of the germ growth inhibiting zone centered on the disc. The discs, commonly less than 20 in number, are deposited individually by means of tweezers or simultaneously by means of an automatic transfer device.

The automatic transfer devices commonly used generally comprise several storage tubes each containing a stack of discs previously impregnated with a particular antibiotic. The maneuvering of ejection means enables the simultaneous discharge of a disc from each one of the storage tubes dropping them to the surface of the medium through a guide channel. These transfer devices are easy to operate but nevertheless have the disadvantage of not being able to assure a satisfactory contact of the discs on the medium which may cause the displacement of the disc in the course of subsequent handling, or an irregular or partial distribution of the antibiotic. In order to remedy the situation, the operator is obligated to carefully press each disc down so as to obtain intimate contact between the disc and the medium. It frequently occurs that the disc turns during its fall which complicates subsequent identification in the case of discs printed on only one face. It even happens that the disc rolls along the surface of the medium discharging part of its contents which invalidates the results of the antibiogram.

An aim of the invention consists in overcoming the drawbacks as well as the errors and loss of time in prior automatic transfer devices.

One aspect of the invention consists in a transfer device for depositing discs on the receiving surface of a Petri dish, comprising a casing with its bottom facing the receiving surface, a plurality of tubes mounted in the casing for storing stacks of discs, transfer means for transferring the disc at the bottom of each stack to an ejection position in alignment with a corresponding plurality of ejection passageways, a plurality of plungers arranged in alignment with said ejection passageways for sliding movement perpendicular to the bottom of the casing towards the receiving surface for driving the discs from their ejection position through said passageways onto the receiving surface.

Preferably, the plungers have a predetermined weight defining the pressure of application of the discs on the receiving surface.

Preferably, the cross section of the ejection passageways is slightly smaller than the cross section of the discs thereby preventing the free fall of the discs to the receiving surface without the force exerted by the plungers.

Preferably, the transfer device has a control shaft rotatably mounted for transferring the disc to the ejection position and slidably mounted for driving the discs to the receiving surface.

Advantageously, the bottom of the casing is adapted to cooperate with the side walls of the Petri dish, the said receiving surface being the bottom wall of the Petri dish.

The Petri dish is preferably of square shape and the bottom of the Petri dish has a network of spaced perpendicular lines parallel to the sides of the dish, the points of intersection of the lines defining points of application of the discs.

A principal advantage of the present transfer device is that drives the discs to the receiving surface with a precise, reproducible force assuring the desired contact between the disc and the receiving surface.

In the preferred field of application in combination with a Petri dish, the present transfer device drives the discs through the passageways onto the gelose medium depositing the discs thereon with a precise predetermined, reproducible force assuring the desired contact between the disc and the gelose medium.

Further features and advantages of the transfer device and Petri dish according to the present invention will be brought out in the description which follows with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of the base of the transfer device showing the mounting of the system of storage tubes and associated ejection passageways;

FIG. 2 is a sectional view taken along the line II--II in FIG. 1;

FIG. 3 is a sectional view taken along the line III--III in FIG. 1;

FIG. 4 is a sectional view similar to FIG. 2 with the control knob in its upper position after being turned through 90.degree. ;

FIG. 5 is a sectional view similar to FIG. 4 in which the control knob is brought into position by downward displacement after rotation;

FIGS. 6 and 7 are details in perspective on an enlarged scale, partly in section of a storage tube and an associated ejecting means which is shown in two different positions; and

FIGS. 8-11 show a preferred embodiment illustrating the Petri dish adapted to be associated with the transfer device shown in FIGS. 1-7 and its cover .

Reference will now be made to FIGS. 1-3 in which a transfer device designated generally by the reference numeral 1 is shown in position on a Petri dish 2, the bottom of the Petri dish being covered with a layer of gelose medium providing a receiving surface 3. The transfer device 1 essentially comprises a casing 4 receiving the disc storage tubes 5, a platen 6 carrying push members or plungers 7 as well as a control shaft 8 with a knob 9 at its outer end. The casing 4 comprises a body 10 with a base 11 and a cover 12. The outwardly projecting portions 13 on the base 11 rest against the sides of the Petri dish so that the lower face 14 of the base is at a predetermined distance from the gelose layer on the plate or receiving surface 3.

A series of cylindrical recesses 16 receive the lower ends of the storage tubes 5 and a series of bores 15 which form ejection passageways for depositing the discs on the receiving surface 3 are provided in the base 11.

In the illustrated embodiment the platen 6 comprises upper and lower plates 17 and 18 between which the flange 19 of the spindle 8 is held. The platen 6 is thereby secured to the spindle 8 for vertical displacement therewith. Heads of the plungers 7 are in rubbing contact and slidable along cylinders 21 formed in the platen 6, the cylinders 21 being slightly longer in axial dimensions than the heads 20.

The bottom of each of the storage tubes 5 keyed in an associated recess 16 is formed as a dimetral stirruplike member having transverse slots 23 (FIGS. 6 and 7) defining openings adapted to the dimensions of the discs being handled.

The upper end of each storage tube 5 is provided with resilient means (not illustrated) acting against the stack of discs for assuring the regular descent thereof according to the transfer cycle. The storage tubes 5 pass freely through the bores in the platen 6 and the cover 12 and are held in position by a horizontally displaceable locking plate 24 for the storage tubes responsive to a vertical force acting against the top portion of symmetrically oriented radial projections 25 arranged at a suitable position along the storage tubes 5. A pair of push buttons 26 and 27 each projecting from one side of the casing 4 permit the locking and unlocking of the storage tubes 5.

The transfer plate 28 is linearly slidably mounted on the base 11 of the casing and has a series of apertures 29 (FIGS. 6 and 7) each defining a transfer tongue 30 flanked by slots 31 providing passage to the bottom of the storage tube. The leading edge 32 of the tongue 30 shaped to conform to the shape of the disc, is illustrated in its rearaward position in FIG. 4, i.e., in horizontal and vertical alignment with the disc being transferred; and in its forward position in FIG. 7, the disc 33 having been displaced, as will be explained below, is in vertical alignment with the associated ejection passageway 15.

The displacement of the transfer plate 28 is controlled by the control spindle 8 in the following manner: a pivot 34 coaxial with the control spindle 8 and received in the base (FIGS. 1 and 2) has at its upper end pulley 35 with a lateral tab 36. A blind axial socket 37 of square cross section in the illustrated embodiment of FIG. 1 is arranged in the pulley 34. The lower end of a rod 38 also of a square cross section is received in the socket 37. Moreover, one end of a traction cord 40 is secured to the slide 39 coupled to the plate 28 at one side of the plate perpendicular to the direction of displacement. The other end of the cord is partly wound around the pulley 35 and connected to the tab 36. Clockwise rotation of the rod 38 therefore effects the displacement of the slide 39 and the transfer plate 28 in the direction of the arrow (FIG. 2).

The abutting of the slide 39 with the end of its housing precisely limits the path of movement of the transfer plate 28 which at the end of the cycle is returned to the starting position by return springs 41 schematically represented in FIG. 1.

Once the linear transfer movement of the transfer plate 28 has been inititated by the rotation of the pulley 35, retractable abutment means 42 shown in FIGS. 2, 4 and 5, comprising a leaf spring 43 inserted at one end in a swinging lever 44 while the other end of the leaf spring cooperates with a stop 45 on a slide 46 connected for movement with the plate 28, prevents the rearward movement of the plate 28 by the springs 41. At the end of the transfer cycle, the return of the slide 46 effects the resetting of the leaf spring 43.

The control spindle 8 has a tubular body 47 slidably and pivotally mounted in a sleeve 48, the lower end of the sleeve being secured to the cover 12. The body 47 ends with the flanged socket portion 49 which as described above is held in a cylindrical bore 50 in the platen 6. The mounting couples the platen 6 and the body 47 for up-and-down reciprocating movement but enables the free rotation of the socket 49 in the bore 50 and therefore the body 47. This socket 49 has a square interior cross section adapted to receive in rubbing contact for sliding movement the free end of the rod 38 coupled at its lower end to the pulley.

A guide plate 51 overlying the transfer plate 28 is provided for guiding the lower end of the plungers 7. The guide plate 51 has a plurality of bores 52 arranged along the axes of the ejection passageways 15 as well as for freely receiving the bases of the disc storage tubes 5.

The platen 6 is held in its upper position by springs 53 (FIGS. 1 and 3) guided in the tubular members 54 resting on the guide plate 51 and inserted at their upper ends in the cover 12. T-shaped keys 55 are held captive in the plate 6, the cross bars thereof extending into the apertures in the tubular members 54, said T-shaped keys providing a bearing surface for the upper ends of the springs 53.

As it will be described hereinafter, the operation of the transfer device comprises sequentially rotational then sliding linear displacement of the control spindle 8. For this purpose, the control knob 8 is provided with a vertically depending finger or key 56 (FIG. 4), the sleeve 47 having an opening 57 (FIG. 2) in which the finger or key 56 can be received.

Interlocking means, not illustrated in detail in the drawings, controls the control spindle 8 depending on the position of the locking plate 24 so that all rotational or sliding movement of the control spindle 8 is prevented when the locking plate 24 is not in its locked position.

The operation of the device as described above will now be described:

The storage tubes 5, once filled, are secured in position by the locking plate 24; the finger or key 56 rests on the sleeve 48 at a predetermined angular distance from the opening 57. The platen 6 is maintained in its upper position by the springs 54 whereas the transfer plate 28 is held in its rearward position by the springs 41. The head of each plunger rests on the bottom of its associated cylinder 21, the bottom of the push members or plungers being in engagement with the associated bore in the guide plate 51.

In the first phase of operation, the operator turns the control knob 9 in the clockwise direction (arrow G in FIG. 1); the cord 40 pulls the slide 39 in the direction of the arrow F and each of the tongues of the transfer plate 28 engage a disc at the bottom of a stack in a corresponding storage tube 5 to transfer the said disc to an associated ejection passageway 16 (FIGS. 6 and 7).

During the initial phase of operation, the retractable abutment means 42 protrudes to prevent the return of the transfer plate 28 until it has completed the movement of the discs to their ejection position and the discs arrive on the receiving surface.

When the discs come into forward abutment against the slide 39 (FIG. 4), they are in vertical alignment with the ejection passageways 16, the finger or key 56 on the control knob 8 being in alignment with the opening 57.

At a second phase of the operation, the operator exerts a force downwardly against the control knob 8 which brings about the descent of the platen 6 and the plungers 7. After passing through the guide plate 51, the plungers come into contact with the transferred discs and drive them down through the ejection passageways 16. The bores of these passageways are machined to a dimension slightly less than the disc diameter, for example 0.05 mm, so that only the positiive action of the plungers 7 is able to bring about the descent of the discs to the receiving surface. When the platen 6 arrives at its lowermost position (FIG. 5), the ejected discs emerge from the passageways 16 with the ends of the plunger 7. As it was noted above, the cylinders 21 with which the heads are in slight frictional sliding contact have an axial dimension slightly greater than that of the heads. From this fact it follows that the heads 20 which were in contact with the upper ends of the cylinders 21 continue there descending path of movement by gravity until they come to abut against the lower end of the cylinders. Consequently, the plungers 7 descend with the ejected discs and their free fall is calculated so that the discs are applied against the receiving surface 3 supporting the gelose medium by a force determined by the mass of the plunger which may therefore be precisely reproduced in another transfer device.

Once the downwardly directed force exerted by the operator is released, the springs 53 return the platen and the knob 6 upwardly; as soon as the key or finger 56 is out of engagement with the opening 57 the springs 41 act to return the transfer plate 28 to its rearward position while the control knob 8 undergoes a counterclockwise rotational movement returning it to the position shown in FIG. 2. The device 42 is reset during the return path of movement of the transfer plate; the transfer device is then ready for another transfer cycle.

Reference will now be made to FIGS. 8-11 showing an alternative embodiment of the Petri dish (FIGS. 8 and 9) whose receiving surface is adapted to receive the discs deposited thereon by the present transfer device. The cover therefor is shown in FIGS. 10 and 11.

The dish generally designated by the reference numeral 60 has a flat bottom wall 61 and upstanding side walls 62 connected by fillets 63. Supporting feet 64 are arranged at the corners of the dish 60.

A network of perpendicular straight lines equidistant from one another and parallel to the sides of the dish are provided on the exterior face of the bottom wall 61. The intersections of the perpendicular straight lines define points of application for the centers of the discs. The straight lines may be shaped as ribs formed during the molding of the dish or etched grooves.

Graduated scales are provided at 66 and 67 centered at points of intersection of the straight lines which may be millimetric or other suitable scales, such as concentrations expressed in micrograms per milliliter. These inidicia or scales may be etched into the bottom wall 61 or simply secured thereto by any suitable means, for example printed sheets readable through the transparent gelose medium and bottom wall.

The bottom wall could of course be provided with other indicia as a function of the measurements to be effectuated.

The cover 68 (FIGS. 9 and 10) is adapted to be received on the dish 60 and comprises a top wall 69 and a skirt which is fitted onto the side walls of the dish. Bosses 71 formed on the interior face of the top wall 69 prevent the top wall from resting directly on the edge of the side walls. In this way the interior of the dish 60 with its cover 68 is aerated thereby avoiding the formation of condensation along the interior face of the top wall of the cover which might interfere with readings.

The cover 68 has a rim 72 adapted to receive the support feet of the dish 60 for stacking the dishes with their covers on top of one another.

The problems solved relative to the particular application concerned by an aspect of the invention include:

a. the determination of the minimum inhibiting concentrations of the germs relative to various antimicrobic agents (by the technique of diffusion in a jellied medium with the aid of correlating curves); and

b. the clinical categorization of the results.

The advantages of the transfer device in combination with the Petri dish as described above include:

1. automatic operation of the device whereby it is no longer necessary to actually push each disc into the gelose medium;

2. the discs being put in contact with the gelose medium with the same reproducible pressure, the pressure exerted by each plunger being the same and constant from cycle to cycle (the intimate contact of the discs with the surface of the gelose medium assures excellent diffusion of the antibiotic therein);

3. the increase of the effective surface of the gelose medium owing to the particular arrangement of the discs;

4. reduction in the number of errors; and

5. the qualitative and quantitative reading of the results being more precise, rapid and easy since the 16 discs positioned at the intersection of the network of perpendicular lines associated with graduations marked on the outer face of the bottom of the box enable an immediate and precise reading of the "diameter" of inhibitor zone along each of two perpendicular axes.

It is preferable to deliver the dishes with the gelose medium therein (the thickness of the medium being about 4 mm), the variations of the diameter of the inhibitor zones due to the differences in the thickness of the gelose medium can be thereby avoided.

It is also possible to eliminate overlapping of the inhibitor zones (the overlapping creating qualitative reading errors) on the condition that the diameter of the zones does not exceed 30 mm which is generally not the case.

The present invention is of course not limited to the illustrated and described embodiment but, on the contrary, includes all alternatives and modifications within the scope of the appending claims.

Claims

I claim:

1. A transfer device for depositing discs on a receiving surface, comprising a casing having a bottom particularly adapted to face the receiving surface, a plurality of tubes mounted in the casing for storing stacks of discs, an ejection passageway in said casing laterally adjacent each stack, transfer means for transferring the disc at the bottom of each stack laterally to an ejection position in alignment with a corresponding one of said ejection passageways, a plurality of plungers arranged in alignment with said ejection passageways for sliding movement perpendicular to the bottom of the casing towards the receiving surface for driving the discs from their ejection position through said passageways onto the receiving surface and single control means for sequentially actuating said transfer means and said plunger.

2. A transfer device according to claim 1, together with a platen carrying said plungers for simultaneous movement, and means individually mounting each plunger on said platen for freedom of movement relative to said platen in a direction away from the bottom of the casing wherein the weight of each plunger defines the pressure with which each disc is applied against the receiving surface.

3. A transfer device according to claim 1, wherein the cross section of the ejection passageways is smaller than the cross section of the discs for which said tubes are intended to hold so as to prevent the free fall of the intended discs from their ejection position to the receiving surface.

4. A transfer device according to claim 3, wherein the largest lateral dimension of the intended discs exceeds the largest lateral dimension of the ejection passageways by 0.05 mm.

5. A transfer device according to claim 1, wherein the bottom of the casing is adapted to cooperate with the side wall of a Petri dish to accurately position said ejection passageways relative to the Petri dish, the bottom wall of the Petri dish constituting the said receiving surface.

6. A transfer device according to claim 5, further comprising a network of perpendicular lines parallel to the walls of the dish and equidistant from one another, the intersections of said perpendicular lines defining the centers of both said ejection passageways and the points of application of the discs on the receiving surface.

7. A transfer device according to claim 1, wherein said single control means includes a platen supporting all of said plungers for simultaneous movement and a control shaft, means mounting said control shaft for rotational movement relative to said platen and for conjoint axial movement with said platen.

8. A transfer device according to claim 7, wherein the rotational movement of the control shaft effects the displacement of the transfer means between its disc receiving position and the ejection position; and wherein the conjoint sliding movement of the control shaft effects in the downward direction the driving of the discs into contact with the receiving surface.

9. A transfer device according to claim 8, wherein means are provided to prevent the conjoint sliding movement of the platen with the control shaft until the control shaft has been rotated to bring the discs to their ejection position.

10. A transfer device according to claim 8, wherein the transfer means comprises a transfer plate, and further comprising retractable abutment means associated with the transfer plate for preventing its return to its disc receiving position until the discs brought to their ejection position are driven to the receiving surface.

11. A transfer device for depositing discs on a receiving surface, comprising a casing having a bottom particularly adapted to face the receiving surface, a plurality of tubes mounted in the casing for storing stacks of discs, an ejection passageway in said casing laterally adjacent each stack, transfer means for transferring the disc at the bottom of each stack laterally to an ejection position in alignment with a corresponding one of said ejection passageways, a plurality of plungers arranged in alignment with said ejection passageways for sliding movement perpendicular to the bottom of the casing towards the receiving surface for driving the discs from their ejection position through said passageways onto the receiving surface, each plunger including a rod for sliding movement in its associated ejection passageway and a head, a platen including a plurality of cylinders defined therein, and each plunger head being mounted for sliding movement in an associated cylinder which determines the path of movement of the plunger.

12. A transfer device according to claim 11, further comprising a control shaft, said control shaft being mounted for rotational movement relative to the platen and conjoint axial movement with said platen.

13. A transfer device according to claim 12, wherein the rotational movement of the control shaft effects the displacement of the transfer means between its disc receiving position and the ejection position; and wherein the conjoint sliding movement of the control shaft effects in the downward direction the driving of the discs into contact with the receiving surface.

14. A transfer device according to claim 13, wherein means are provided to prevent the conjoint sliding movement of the platen with the control shaft until the control shaft has been rotated to bring the discs to their ejection position.

15. A transfer device according to claim 13, wherein the transfer means comprises a transfer plate, and further comprising retractable abutment means associated with the transfer plate for preventing its return to its disc receiving position until the discs brought to their ejection position are driven to the receiving surface.