MALDI-TOF mass spectrometry speciation of staphylococci and their discrimination from micrococci isolated from indoor air of schoolrooms

The focus of our work is the identification of medically relevant staphylococci from the environment; these organisms are among the major opportunistic pathogens associated with human disease. Andersen sampling was performed in schoolrooms during the school year. Eleven of thirty six isolates (all Gram-positive tetrads) were identified as staphylococci and 23 were characterized as micrococci. MALDI-TOF MS profiling was used as the first stage in the classification followed by standard biochemical tests including API Staph profiling. The staphylococcal isolates were each speciated; coagulase positive (Staphylococcus aureus [3 strains]) and coagulase negative: Staphylococcus warneri (4 isolates), Staphylococcus hominis (2), Staphylococcus saprophyticus (1) and Staphylococcus cohnii (1). S. aureus is most commonly found in the human nares but is frequently isolated from skin. The other staphylococcal species are among those most commonly isolated from human skin. Micrococci were much more frequently isolated from indoor air than reported by others for clinical samples. It is suggested that, without discrimination from micrococci, misidentification of staphylococci would be common on air sampling.