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Genetic Characterization of Enterococcus in California Coastal Environments

  • Author(s): Ferguson, Donna Marie;
  • Advisor(s): Ambrose, Richard F;
  • Jay, Jennifer A
  • et al.

Enterococcus are used as fecal indicator bacteria used to assess the possible presence of fecal contamination of recreational waters. Current enterococci laboratory methods do not distinguish between enterococci from fecal and non-fecal sources, confounding assessments of water quality assessment and efforts to identify and remediate fecal sources. Moreover, the ability of enterococci to grow marine environments indicate that contributions from natural sources may further limit their use as fecal indicators. Genetic characterization of enterococci from varied sources may reveal gene signatures that may distinguish fecal and nonfecal sources and also demonstrate enterococcal growth in marine habitats.

In this study, the distribution of enterococcal virulence genes and antibiotic resistant determinants was examined among E. faecalis and E. faecium from varied coastal environments and potential sources including humans, sewage, septage, animals, birds, seawrack, eelgrass and urban runoff. DNA typing by pulsed-field gel electrophoresis was used to compare the genetic relatedness of E. faecalis strains and possible correspondence with virulence genes. Other genomic typing methods including multi-locus sequence typing (MLST) and single nucleotide polymorphism typing (SNP) were used to infer strain relatedness and source origin and to identify clinically relevant enterococcal MLST sequence types (STs) of E. faecalis from coastal environments.

The combined findings demonstrated that E. faecalis harbor higher frequencies of virulence genes as compared to E. faecium and that E. faecalis from the beach environment had a lower prevalence of virulence and antibiotic resistance genes relative to that of humans, animals and birds. PFGE showed that high diversity of E. faecalis and some correspondence between clusters and the asa1 virulence gene. MLST and SNP typing of beach strains identified STs shared with humans and animal strains that were not part of pathogenic clonal complexes. The asa1 and cylA, genes associated with the E. faecalis pathogenicity island were found among beach, dog and bird strains suggesting that further studies are warranted to determine source origin, transmission and health implications to beach goers. PFGE revealed the presence of clonal E. casseliflavus, E. hirae and E. faecalis isolates, suggesting that these species may be capable of growing on eelgrass washed up on beach sand.

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