Method and device for bacterial testing

Claim 1

A culture test process for culturing a number of samples possibly containing bacteria and identifying any samples among said number which do contain bacteria, by indicating the production of gas during growth of cultures corresponding to said bacteria-containing samples, said process comprising: (a) introducing each of said samples possibly containing bacteria into a respective sterile liquid growth medium in a first container of a respective culture test device, the medium being such that it generates gas if bacterial growth occurs; (b) providing in each said first container a gaseous head space above said liquid medium and a closure for said first container above said head space which is gas tight except for an exit path for liquid via a narrow tube, said tube having a first opening below the surface of said liquid medium in said first container and leading upwards to a respective second, upper liquid container, each said upper liquid container being located above said first container and having a transparent wall for indicating visually the presence of liquid in said upper container, said second, upper liquid container being provided with at least one of a flexible wall for increasing a volume of the interior thereof and means for venting gas from the interior thereof in response to a pressure change in the interior said first container having a gaseous head space above said liquid medium and a closure for said first container which is gas tight except for an exit path via a narrow tube; said narrow tube opening below the surface of said liquid medium and leading upwards to a second and upper liquid container; said upper liquid container having a transparent wall for indicating visually the presence of said liquid in said upper liquid container; said upper liquid container being provided with at least one of a flexible wall for increasing a volume of the interior thereof and means for venting gas from the interior thereof in response to a pressure change in the interior thereof so that liquid can enter said upper liquid container via said narrow tube in response to gas production in said first container with minimal change in interior pressure of said second container; whereby in use of the device in the event of growth of a bacterial culture in said liquid medium and gas production by said culture, pressure develops in said gaseous head space and drives part of said culture upwards into said upper liquid thereof so that fluid can enter said upper liquid container through said tube in response to gas production in said first container with minimal change in interior pressure of said second container; (c) incubating said culture test devices together to culture said respective sample in each said device, whereby in the event of bacterial growth and consequent gas production in any of said devices, pressure develops in a corresponding one of said gaseous head spaces and drives part of said respective liquid culture upwards into said respective upper liquid container, thereby to provide visual indication of said gas production in said respective device, thereby to identify the corresponding sample as positive for bacteria.