Lockable contact plate

1. A contact plate comprising

(a) a circular dish supported on a circular base, said dish having a bottom plate and a bottom cylindrical side wall, and

(b) a circular lid having a top plate and a top cylindrical side wall, said lid sized so as to fit over the bottom cylindrical side wall of said dish

wherein said base and said lid are provided with locking means for securing said base and said lid in locking engagement, said locking means comprising at least two pairs of locking members, each of said pairs of locking members comprising (i) a radial sheath having an entry, and (ii) an elongate radial tab sized and shaped so as to be slidably engagable with said radial sheath wherein said radial tab has at least one protrusion and said radial sheath has at least one indent, with said protrusion and said indent being sized and located so as matingly engage each other;

and wherein said at least one protrusion is proximal to the entry of said sheath and said at least one indent is distal to the entry of said sheath;

and wherein said sheath has a closed end distal to said entry.

2. The contact plate of claim 1 wherein said tab has two protrusions.

3. The contact plate of claim 2 wherein said sheath is integral with said base and said tab is integral with said top cylindrical side wall.

4. The contact plate of claim 3 wherein said sheath and said tab are slidably engagable with each other by rotating said lid relative to said base.

5. The contact plate of claim 4 wherein said sheath and said tab are slidably disengagable from each other by rotating said lid relative to said base.

6. The contact plate of claim 5 wherein said lid is transparent.

7. The contact plate of claim 6 wherein said base has a multiplicity of spacers around its periphery to prevent said lid from sealingly engaging said base.

8. The contact plate of claim 7 wherein said dish contains microorganism growth medium.

9. The contact plate of claim 8 packaged in sterile packaging.