Abstract: The present invention relates to a method for determining the methicillin-resistance properties of a Staphylococcus aureus strain present in a biological sample, the method comprising the following steps: •a) incubating the biological sample containing the Staphylococcus aureus strain for at least 15 minutes in the presence of an antibiotic from the class of beta-lactams selected from the following group: cefoxitin and 6-APA (6-aminopenicillanic acid); •b) isolating the bacteria present in the biological sample; •c) lysing the bacteria and hydrolysing the bacterial proteins in order to obtain a mixture of peptides; and •d) analysing this mixture of peptides by targeted mass spectrometry, the detection of at least one peptide originating from the protein PBP2a (SEQ ID NO. 1) or PBP2c (SEQ ID NO. 2) during this analysis step being indicative of the methicillin resistance of the Staphylococcus aureus strain present in the biological sample.