The use of reference materials (RM) is one of the principal tools used for assurance and quality control in food microbiology laboratories. In Brazil, Anvisa RDC nº 12/01 specifies the enumeration of coagulase-positive staphylococcus (CPS) as one of the parameters for evaluating cheese quality. The main challenge in the production of RM destined for microbiological assays is the natural instability of the microorganisms, which makes it difficult to develop and maintain them. This study aimed to produce a quantitative RM for use in enumeration assays of CPS in cheese matrixes. A sample of an ultra-filtered cheese with a CPS count of <10 CFU/g and a total nº of viable aerobes of 1.2 × 10³ CFU/g was used as the matrix to produce the RM. The matrix was distributed in flasks, contaminated with specific concentrations of the target bacteria and submitted to freeze-drying. Sucrose was used as the cryo-protector. The RM produced was considered homogeneous and stable at < -70ºC during the entire study period (10 months). The material was shown to be stable at 4, 25, 30 and 35 ºC for 4 days, although the results indicated a decrease in cell concentration at 35 ºC. At -20 ºC the RM was stable for 48 days. It was concluded that the material showed all the necessary requirements for a quality RM and could be transported to the laboratories taking part in a proficiency test at up to 35 ºC for up to 4 days, since the results indicated maintenance of the cell concentrations during this period. This is the first study to describe a methodology for producing MR containing CPS in a cheese matrix.
Reference material; Cheese; Staphylococcus
