Serotyping of Serratia marcescens: current status of seven recently described flagellar (H) antigens

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Abstract
The slightly revised current scheme of 20 H antigens [Ag] of S. marcescens was examined. The 7 new H Ag were antigenically distinct as determined with Le Minor''s H-immobilization test. The H-immobilization antibodies [Ab] of rabbit anti-H immune sera proved resistant to treatment with 2-mercaptoethanol and dithiothreitol, respectively. Dual absorptions of rabbit anti-H immune sera with killed cells of Staphylococcus aureus strain Cowan I, i.e., protein A, failed to reduce significantly H-immobilization titers of rabbit sera, although human immunoglobulins [Ig]G and IgM were bound by protein A. The 2-mercaptoethanol- and dithiothreitol-refractory H-immobilizing rabbit Ab belonged to the IgM class. H-Ag (phase) variation was not demonstrable in several extramural, clinical isolates of S. marcescens for which this phenomenon was claimed. Of these 6 isolates, 4 consist of cell populations of 2 distinct serotypes, as shown by bacteriocin typing; the flagellar H-Ag of the remaining 2 isolates were stable, with minor, heterologous H-Ag cross-reactivity.