Establishment And Evaluation Of Cultural Medium For Rapid Detection Of Coliform In Food Samples

Background and ObjectivesColiform level, one of the important indicators in food hygiene evaluation, has been widely used in the field of food hygiene monitoring. The detection of coliform bacteria has important significance because coliform bacteria can reflect not only the evidence of food contamination and the degree of contamination, but also the status of food sanitation during production, processing, transportation and storage process at some extent. The coliform bacteria detection is compulsive for food hygiene in national standard (GB4789) of China. Many methods are available for the determination of coliform bacteria in food, of which GB assay is the most widely used one. It is characterized in good accuracy, reliability, long checking time, and complicated procedure. The time consuming, and exhausting in manpower and resources limited its application on quick spot check for food sanitation. It is urgent to find out a faster and accurate detecting method to overcome the above disadvantages. The late of last century, the chromogenic media developed by French CHROMagar Company solved the problem of coliform detection to a certain extent. The preparation techniques for these medium were complex and not suitable for large scale sample detection. The goal of the study is to establish a rapid and accurate Chromogenic Medium for coliform detection in food samples and to evaluate the efficiency, sensitivity, and specificity of the Medium.MethodsTaking the ordinary agar medium as the basic component, the Coliform Chromogenic Medium was made by adding some substances that can promote coliform growth and inhibit other bacteria growth, such as agar, peptone, yeast extract, lactose, sodium chloride, sodium lauryl sulfate. The Medium contained enzymatic coloration substrates. The optimum formulation of the coliform Chromogenic Medium (hereinafter referred to as "CCM") was confirmed through two sets of optimization experiments and orthogonal experiment. By referring the GB method, comparing the detecting duration, efficiency, the coloration CCM, The capability of CCM was evaluated through the detection time, plate efficiency, specificity, sensitivity and accuracy100food samples contaminated with standard coliform strains and other bacterial strains of foodborne. The resultsColiform bacteria genus could be easily identified from the Chromogenic Medium under the cultural condition of37℃for18hour in the CCM. There was no significant difference (t=0.578, P>0.05) between the GB method (crystal violet neutral red bile salt agar) and the CCM method in the plating efficiency. The specificity and sensitivity of the CCM reached to100%and90%respectively. There was no significant difference (x2=0.125, P>0.05) between CCM method and the GB international standard method in the detection results.ConclusionThe developed CCM method is rapid, accurate, sensitive and specific.CCM is suitable for spot check on food hygiene regarding Coliform bacteria.