The invention relates to novel interfering peptides having peptide sequence S with between 7 and 12 amino acids, originating from the peptide sequence of an antigenic protein of a micro-organism M, the sequence S being aligned with a peptide sequence S′ with between 7 and 12 amino acids originating from the peptide sequence of a target protein of a micro-organism M′ that is different from the micro-organism M, provided that: sequences S and S′ have at least 50% identity over their length of 7 to 12 amino acids and at least 4 identical or analogous contiguous amino acids and their length is identical or they have 1 or 2 different amino acids distributed at one and/or the other end of the sequences. The invention also relates to a method for the in vitro immunoassay-based detection of the presence of a micro-organism M′ or M in a biological sample.
