Development of a standard protocol for detecting or enumerating a specific microorganism or group of microorganisms on or in produce should include experiments to validate the efficiency of recovery based on a known number of cells applied. This can be done using a known volume of inoculum containing a known number of test cells. Although some cells may die during the drying period following application of inoculum, efficiency of retrieval can be more accurately measured using spot inoculation than dip or spray inoculation, which do not enable measurement of the number of cells adhering to the produce.
The efficiency of retrieval of microbial cells naturally occurring on produce is not easily determined, simply because the actual number of retrievable cells is not known . The presence of a surfactant in peptone water used to remove pathogens from produce, e.g., cantaloupes, may enhance the number detected . A comparison of various combinations of sample weights, wash fluids, diluents, homogenization or washing treatments, and neutralizers (in the case of chemical sanitizer tests) should be made before choosing test parameters that give the highest percentage of viable microorganisms recovered. Some protocols have been demonstrated to be more efficient than others, and a single basic protocol should be selected for analysis of specific fruits, vegetables, or groups of produce in all laboratories.
Was this article helpful?