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The technology used for the detection of micro-organisms on the RIDA^®COUNT test cards is generally based on a cultivation method using standard nutrients combined with a specific chromogenic detection system. During the growth phase micro-organisms will form typical colonies whilst specific enzymes will turn the original colourless substances to characteristic detection colours. All of the different products of the RIDA^® COUNT line are suitable for the detection of micro-organisms deriving from food or feed, contact samples, membrane filtration as well as air samplings.

Unprocessed food and feed are known to possess enzymes similar to specific bacterial enzymes. These enzymes originate from the plant or meat cells, which are found in food or feed and have been found to cause problems within the sample analyses with RIDA^®COUNT Staph. aureus. The influence of these food enzymes might lead to background effects shown by an overall colouration of the test cards which could interfere with the evaluation of the test results. The detection of the typical blue-green coloured colonies of Staphylococcus aureus became all the more difficult as the background effects increased.
This problem has now been solved as changes have been made to the chromogenic system of RIDA^®COUNT Staph aureus, which also crucially improved the detection of S. aureus colonies. On the new RIDA^®COUNT Staph aureus (R1005) test card, positive colonies are clearly set apart from the background more so than with the performance of the old product version. This is due to the formation of black colonies surrounded by a blue halo which are developing within an incubation time of 24 to 48 hours at 35 °C. As a result of the reduction of blue colouring chromogen the occurrence of background effects has been reduced to a point that the new improved test card can be used without restrictions for analysis of any kinds of food and feed now.

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