Frequency of Aggregation Substance and Cytolysin Genes among Enterococcal Endocarditis Isolates

Abstract

Enterococcus faecalisblood isolates were probed for the serine protease activator of cytolysin (cylA) and aggregation substance (asa1), traits that generally reside on pheromone-responsive plasmids, to determine how commonly these genotypes were associated with disease. In dot blot assays, no significant difference was found in the frequency ofasa1for blood isolates [55 of 103 (54%)] and isolates recovered from stool [9 of 14 (60%);P> 0.1, χ2test]. In contrast,cylAoccurred more frequently among bacteremia isolates [34 of 68 (50%)] than endocarditis [4 of 35 (11%)] or stool isolates (0 of 14;P< 0.001; χ2test). However, when the clonality of isolates was accounted for, the frequency ofasa1andcylAamong unrelated strains was not significantly different among the three sets of strains (P> 0.2, χ2test). The lack of enrichment forasa1orcylAamong clonally unrelatedE. faecalisbloodstream isolates fails to support a role for plasmid-encoded aggregation substance or cytolysin in the transition from bacteremia to endocarditis. Clonally related, cytolytic strains, however, demonstrated an increased propensity to cause bloodstream infection.