Discrimination of S. aureus strains using MALDI-TOF-mass spectrometry

Staphylococcus aureus is an important human pathogen frequently resistant to a wide range of antibiotics. Methicillin-resistant Staphylococcus aureus (MRSA) strains are common nosocomial pathogens that pose a world-wide problem. Rapid and accurate discrimination between methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus is essential for appropriate therapeutic management and timely intervention for infection control. We report here the application of MALDI-TOF-MS for monitoring the bacterial fingerprints expressed by two well characterized S. aureus strains ATCC 29213 (MSSA) and ATCC 43330 (MRSA). Consistent strain-specific data were obtained from subcultures analyzed over a period of three months as well as after changing the growth media from Mueller-Hinton to blood agar indicating the reliability of the method. The bacterial fingerprints of these two strains were compared to independent clinical isolates of S. aureus. A uniform signature profile for MRSA could not be identified. However, the bacterial fingerprints obtained proved to be specific for any given strain. This study demonstrates that MALDI-TOF-MS is a powerful method for rapid identification of clonal strains of S. aureus, which might be useful for tracking nosocomial outbreaks of MRSA and for epidemiologic studies of infections diseases in general.