1.C.60 The Two-component Enterococcus faecalis Cytolysin (EFC) Family

The EFC family includes a single member, the cytolysin of E. faecalis which consists of two subunits, CylL (large; 68 aas) and CylL (small; 63 aas). They are post-transcriptionally modified by CylM and secreted by the ABC exporter, CylB (TC #3.A.1.111.1). Extracellularly, the two subunits are activated by a protease, CylA yielding the functional mature cytolysin subunits, CylL^"_L and CylL^"_S. CylI confers protection to the producer.

The cytolysin is a "pseudohaemolysin" which produces hemolysis on blood agar plates, but not in broth culture. This may be due to regulated synthesis of the cytolysin by an unusual two-component system that senses the extracellular concentration of an inducer via a quorum sensing autoinduction mechanism (Haas et al., 2002). In addition to its toxicity to animal cells, it is bacteriocidal for nearly all Gram-positive bacteria.