Petri dishes used for plating food samples generally state the sample number, the decimal dilution plated together with the date of analysis, the medium used or other relevant information. Such a manual coding practice is time-consuming and tedious; therefore we decided to use a label-marker allowing of a clearer and quicker marking.
From label-markers used in supermarkets we chose one with six marking positions. The first three can indicate any number between 1 and 999 and once a label has been coded, the next label automatically gets the next number. With the other three positions, the numbers 1 to 9 can be selected or a minus sign to code e.g. the medium and the decimal dilution plated. For Petri dish-coding the first three numbers can indicate the sample number, the fourth the medium code (e.g. 1 = Plate Count Agar, 2 "=-Violet Red-Bile Glucose Agar) and positions 4 and 5 can indicate the decimal dilution plated (e.g. --3 = 10 3, or the 1 in 1000 dilution). The code 1332-2 represents therefore the Violet Red-Bile-Glucose Agar plate of the l0 -2 dilution of sample 133. The six positions used in combination with a range of coloured labels provide a versatile, convenient and labour-saving method for the coding of Petri dishes and also of sample pots, Stomacher bags, dilution tubes, M.P.N. tubes and the like.