Enzyme release of antigen from Streptococcus faecalis and Listeria monocytogenes cross-reactive with Lancefield group G typing reagents

Enzyme extraction methods are commonly used to release antigen for Lancefield serogrouping of streptococci. Recently, up to 47% of enterococci have been found to possess antigens cross-reactive with both the group D and the group G grouping reagents. We investigated whether the organisms had recently emerged or whether changes in extraction methods (enzyme extraction) have resulted in our awareness of their existence. We found that approximately 20% of our enterococcal isolates released material cross-reactive with the group G reagents. These organisms have been present for at least 6 years, and probably for many more. In addition, we found that most strains of Listeria monocytogenes also released antigen cross-reactive with the group G reagent. The clinical significance of these findings is also discussed.