Abstract: Purified polypeptides containing characteristic sequences common to the pyrrolidone carboxylyl peptidases (PYRases) of bacteria, for example of Streptococcus pyogenes, or containing fragments of these sequences; antibodies recognizing these polypeptides; polynucleotides coding for such polypeptides or fragments.Application, in particular, to the overproduction of PYRases by inserting a polynucleotide coding for a PYRase into a vector, and then culturing a host cell transformed using such a vector, or to the production of nucleic acid probes specific for a bacterium having a PYRase gene, expressed or otherwise. These nucleic acid probes may be used as capture or detection probes according to conventional hybridization techniques.