2. Count and record colonies. If several types of colonies are observed which appear to be S. aureus on selected plates, count number of colonies of each type and record counts separately. When plates of the lowest dilution contain 200 colonies have colonies with the typical appearance of S. aureus and typical colonies do not appear at higher dilutions, use these plates for the enumeration of S. aureus, but do not count nontypical colonies. Select > 1 colony of each type counted and test for coagulase production. Add number of colonies on triplicate plates represented by colonies giving positive coagulase test and multiply by the sample dilution factor. Report this number as number of S. aureus/g of food tested.