Serotyping of Ureaplasma urealyticum by immunoperoxidase assay

The immunoperoxidase method was applied to the identification of Urea-plasma urealyticum serotypes. The assay used highly diluted antisera and could be run directly on primary plate isolates. It was ideal for detecting and identifying mixed serotypes because stained and unstained colonies could be visualized simultaneously by conventional light microscopy. Antisera run against eight serotypes revealed one-way cross-reactions between serotypes 3 and 5 and antiserum to 2, and between serotype 4 and antiserum to 8, at dilutions of less than 1:150. This cross-reactivity could be diluted out at the optimal antiserum dilution for the immunoperoxidase assay, but not for the growth inhibition assay or immunofluorescence test. The immunoperoxidase assay therefore proved ideal for serotyping U. urealyticum.