False positive results obtained with latex agglutination identification of Staphylococcus aureus caused by Macrococcus caseolyticus and Mammaliicoccus fleurettii

Abstract Reliable and rapid identification ofStaphylococcus aureusconstitutes a critical issue in food safety. A total of 180 meat samples were analysed, and 30 isolates that phenotypically matchedS. aureuswere obtained. All 30 isolates generated positive results in agglutination with the Slidex. Staph test. The results of agglutination were verified with the matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) method, S. aureus-specific PCR and sequencing of the 16S rRNA genes. Among 30 isolates positive in the SlidexStaph test, 17 were finally identified asS. aureus, eight asMacrococcus caseolyticus, four asMammaliicoccus fleurettii, and one single isolate asStaphylococcus pseudintermedius. In this study, we have demonstrated for the first time false-positive results of the rapid identification based onS. aureus-specific agglutination obtained forM. fleurettii.Antimicrobial resistance testing revealed a considerable prevalence of multidrug resistance amongM. caseolyticus(100%) andM. fleurettii(50%). This study highlights the possibility of obtaining false-positive results in agglutination tests withM. caseolyticusandM. fleurettii. Furthermore, the presence of multidrug-resistantM. caseolyticusandM. fleurettiiin meat samples raises food safety and public health concerns and requires further investigation.