Chaining in enterococci revisited: correlation between chain length and gelatinase phenotype, and gelE and fsrB genes among clinical isolates of Enterococcus faecalis

Enterococci, like streptococci, are typically described as showing chaining in Gramstains of clinical samples. The degree of chaining seems to vary amongst enterococcal clinical isolates; however, there are no recent studies validating chaining by enterococci since they were classified out of the genus Streptococcus nor any studies of the mechanism of cellular chain length. A marked increase in chaining seen in an Enterococcus faecalis OG1RF mutant (TX5128) has been explained by the lack of the GelE protease (gelatinase) suggesting the possibility that chaining among clinical isolates (one-third of which are gelatinase non-producers) might be associated with the absence of GelE (Singh et al., 2005; Waters et al., 2003). GelE is an enterococcal zinc-metalloprotease (Bleiweis & Zimmerman, 1964) that is capable of degrading a broad spectrum of substrates, including insoluble collagen fragments (Makinen & Makinen, 1994) and polymerized fibrin (Waters et al., 2003). Synthesis of GelE in E. faecalis is regulated by the fsr locus (Qin et al., 2001), a quorum-sensing system that positively regulates expression of gelE. The fsr locus and gelatinase production have been shown to contribute to the virulence of E. faecalis OG1RF in several models, including mouse peritonitis, Caenorhabditis elegans and biofilm formation (Mohamed et al., 2004; Qin et al., 1998, 2000; Sifri et al., 2002; Waters et al., 2003).