(2) Description of Related Art The related art in multiwell trays is described in U.S. Patent Nos. Des. 316,752 to Ricketts, 3,356,462 to Cooke et al., 3,649,464 to Freeman, 4,240,751 to Linnecke et al., 4,292,273 to Butz et al, 4,495,289 to Lvman et al., 4,545,958 to Dopatka, 4,560,535 to Bouchée, 4,735,778 to Maruvama et al., 4,741,619 to Humphries et al., 4,761,378 to Godsey, 5,462,860 to Mach, 5,508,005 to Mathus, 5,540,891 to Portmann et al., 5,587,321 to Smith, et al., 5,601,998 to Mach et al. Also WO 97/18455 to Croteau et al and WO 91/09970 to Nillingham et al describe culture trays.

None of these trays have a recess in a base for draining the culture medium while leaving culture medium in the wells or with a cover which can be positioned to open and then to close the recess. Such a construction would greatly facilitate the use of the tray for microorganism culturing.

OBJECTS It is therefore an object of the present invention to provide a tray with a recess and cover for opening and closing the recess. It is further an object of the present invention to provide a tray which is very economical to produce and which greatly facilitates culturing of the microorganisms. These and other objects will become increasingly apparent by reference

to the following description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view of a cover 11 and base 12 forming the tray 10 of the present invention.

Figure 2 is a plan view of the base 12 alone, as shown in Figure 1.

Figure 3 is a front view of the tray 10 including the cover 11 and the base 12 showing the recess 17 in the base 12 and the opening 18 in the cover 11.

Figure 4 is a side view of the tray 10 as shown in Figure 3.

Figure 5 is a rear view of the tray 10 shown in Figure 3.

Figure 6 is a cross-sectional view along line 6-6 of Figure 1 showing the cover 11, base 12, wells 13, recess 17 and opening 18.

Figure 7 is a partially enlarged cross- sectional view of Figure 6, particularly showing a lip 17A on the recess 17.

Figure 8 is a partial front view of the recess 17 and opening 18 showing the lip 17A.

Figure 9 is a partial cross-sectional view of the well 13 as shown in Figure 6.

Figure 10 is a partial enlarged cross- sectional view of the well 13 of Figure 9 which is tilted.

DESCRIPTION OF PREFERRED EMBODIMENTS The present invention relates to a microorganism culture tray which comprises: (a) an integral base with (i) a planar surface having multiple concentric circular rows of wells around a longitudinal axis for containing a liquid culture medium and the microorganisms, (ii) a first wall projecting from the planar surface above the wells around the axis with flat portions, (iii) a second regular polygonal wall with flat portions connected to the first wall to form an

inverted V intersection above the wells and planar surface and extending below the planar surface below the wells, and (iv) an outwardly extending flange from the second wall upon which the base rests; and (v) a recess in both of the walls at intersections of two of the flat portions of the walls which allows the liquid culture medium to be drained from the planar surface when the planar surface is tilted at an angle less than 900; and (b) a transparent integral transparent cover having flat portions defining a wall of the cover conforming to the second wall of the base wherein an intersection of two of the flat portions of the cover define an opening which exposes the recess when the cover is in one position and covers the recess when the cover is in another position on the base. Preferably the polygonal wall is hexagonal.

Figures 1 to 10 show various aspects of microorganism culture tray 10, including a transparent cover 11 and integral base 12. The base 12 includes wells 13 with a chamfered opening 13A at an angle from the planar surface P-P shown in Figures 9 and 10. The angle is preferably about 450. The liquid L is retained in the well 13 more readily when the base 10 is tilted as shown in Figure 10 to drain off excess liquid culture medium. As shown in Figures 1 and 2 the wells 13 form concentric circular rows on the planar surface P-P around longitudinal axis A-A (Figure 3). A first polygonal wall, preferably an octagonal wall 14, as shown in Figures 2 and 3 is provided around the axis A-A with flat portions 14A. A second polygonal wall 15 is provided around the axis A-A so that they join in an inverted "V" as shown in Figure 6 with corresponding flat portions 15A. A flange 16, which is preferably also polygonal at its extreme edge, extends from the second polygonal wall 15. A recess 17 is provided in both walls 15 and 16 at an intersection of two flat portions 14A and 15A (Figure 1) which allows the liquid

culture medium L to be drained from the wells 13 when the planar surface P-P is tilted at an angle of less than 900 as shown in Figure 6. The liquid culture medium L stays in the wells to be incubated with a microorganism.

The transparent cover 11 conforms to the second polygonal wall 15 of the base 12. In the preferred form, the cover 11 has eight (8) flat portions, conforming to the flat portions 14A and 15A.

The cover 11 is provided with an opening 18 which in a first portion allows fluid to be drained through the recess 17 (Figures 1, 3, 4, 6, 7 and 8), and in a second portion covers the recess. The flat portions 14A and 15A on the base 12 provide for these two positions without any potential for a mismatch. Thus, the polygonal shape of at least the second polygonal wall 15 is important. The first polygonal wall 14 is preferably the same shape as the second polygonal wall. The hexagonal shape of the outer edge of the flange 16 is preferred so that the trays 10 can be assembled in a closely packed relationship on a table top or the like.

The recess 17 has a protruding lip 17A which aids in preventing drips when culture medium is drained, as shown in Figure 6. This aids in preventing laboratory contamination. Typically the culture medium is provided in the tray 10 admixed with a sample suspected of being contaminated with a microorganism.

Culture medium such as described in U.S. Patent Application No. 08/753,715, filed November 27, 1996 can be used in the tray 10.

The base 12 and cover 11 can each be vacuum molded. The preferred material for the cover 11 is polyvinylchloride (PVC). The base 12 is coex polystyrene, which does not interfere with the culturing of the microorganisms.

EXAMPLE Each tray 10 preferably contains 84 fixed wells" which can hold approximately 0.06 mL of media, e.g., E. coli/T. coliform media. These fixed wells serve an analogous function to the 84 individual culture "tubes" used in traditional most probable number (MPN) methods, i.e., equivalent to the 84 tube MPN at a single level. The method is based on the same assumptions as for traditional MPN (tube) method: (1) the sample is prepared in such a manner that the bacteria are distributed randomly; (2) the bacteria are separate, not clustered together, and do not repel each other; and (3) the growth medium and conditions of incubation have been chosen so that every well that contains even one viable organism will produce detectable growth. The number of wells producing the desired reaction (.e.g, color change, fluorescence) represents an estimate of the original, undiluted concentration of bacteria in the sample in the same manner as the corresponding number of tube would in the MPN method. The mathematical relationship as derived from the MPN method is as follows: MPN = 2 (N Loge[N/(N-x)l) where N = number of tubes or wells, i.e., 84 for the tray 10 x = number of colored and/or fluorescent wells 2 = factor - as 1/2 sample poured off from the tray 10 In practice, 10 mL of media/sample mixture is added to the tray and the liquid distributed evenly over the fixed wells prior to pouring off the excess liquid (approximately 5 mL). The tray 10 is inverted and placed in an incubator at a specified temperature for a period of time. In the case of E. coli/T. coliforms, the tray 10 is incubated at 370C for 24 hours. Wells that contain members of the Enterobacteriaceae ("coliforms") appear red to purple and those that are red and fluoresce when exposed to U.V. light (365 nm) are E. coli Biotype I. The number of colored wells which also fluoresce are used to determine the number of E. coli in the sample using the aforementioned calculation.

It is intended that the foregoing description be only illustrative of the present invention and that the present invention be limited only by the hereinafter appended claims.