Background: Staphylococcus argenteus and Staphylococcus schweitzeri have been recently described as new species within the Staphylococcus aureus complex. The need to distinguish species within the complex for routine purpose is currently questionable as no difference in morbidity, mortality or transmission between S. aureus and S. argenteus have been described and no human infections with S. schweitzeri have been reported so far. However, the distinction is valuable to further clarify the epidemiology and clinical impact of these two novel species. In this study, we tried to establish if their differentiation is possible using the MALDI -TOF technology.
Materials/methods: A total of 234 spectra were acquired on 49 strains (29 S. aureus, 18 S. argenteus and 2 S. schweitzeri strains) obtained from different sources, including the French National Reference Center for Staphylococci. Spectra were acquired following direct deposit on a VITEK® MS slide, in the 3000 to 17000 Da mass range and integrated into the next release of the VITEK® MS knowledge base. Data were analyzed using Multidimensional Scaling (MDS). Performance was evaluated using a cross-validation approach.
Results: The cross-validation study performed on the updated database, containing 41922 spectra covering 1257 bacterial species, showed that the correct identification rates at species level reached 97.3% for S. aureus and 100% for S. argenteus. Conversely, only 8.3% of the spectra from S. schweitzeri were identified at species level, 66.7% were identified in low discrimination with the two other members of the complex, 8.3% were not identified while 16.7% were misidentified either as S. aureus or S. argenteus. The MDS confirmed that a clear differentiation is possible between S. aureus and S. argenteus but not between S. schweitzeri and the two other members of the complex.
Conclusions: This study demonstrates that MALDI -TOF using VITEK® MS platform is able to differentiate S. argenteus from S. aureus but not S. schweitzeri from S. argenteus and S. aureus. The identification of S. argenteus at species level could help to clarify its involvement in clinical infection and, if warranted, to implement future surveillance or infection control measures.