Detection of penicillin-binding proteins immunologically related to penicillin-binding protein 5 of Enterococcus hirae ATCC 9790 in Enterococcus faecium and Enterococcus faecalis

Penicillin-binding protein (PBP) 5 of Enterococcus hirae ATCC 9790 belongs to the class of the high-molecular mass, low-affinity PBPs which have been correlated with penicillin resistance in most Enterococcus species. Polyclonal antibodies were raised against PBP 5 and used to detect immunologically related membrane proteins in E. faecium and E. faecalis strains. Several strains of both species were found to have a membrane protein of similar molecular mass to E. hirae PBP 5 which reacted with the antibodies. Some E. faecium strains did not react with antibodies but their derivatives with increased penicillin minimal inhibitory concentrations did. In some E. faecalis strains the lack of a PBP 5-related protein was associated with failure to select stable penicillin-resistant derivatives.