Enterococcus growth on eelgrass (Zostera marina); implications for water quality.

Area of Science:

• Environmental microbiology
• Water quality monitoring
• Marine ecology

Background:

• Enterococci are key fecal indicator bacteria for assessing recreational water safety.
• Elevated enterococci levels typically signal fecal contamination, prompting public health advisories.
• The presence and growth of enterococci on aquatic plants may confound these assessments.

Purpose of the Study:

• To investigate the potential for enterococci to grow on eelgrass.
• To determine the species and clonality of enterococci found on eelgrass.
• To assess the implications of enterococcal growth on eelgrass for water quality monitoring.

Main Methods:

• Collected 69 eelgrass samples from six sites in Mission Bay, CA.
• Quantified enterococci by filtering eluant from shaken plant surfaces onto culture media.
• Identified enterococcal species using biochemical methods and assessed strain clonality via DNA typing (pulsed-field gel electrophoresis).

Main Results:

• Enterococci concentrations on eelgrass ranged from 8 to 14,000 CFU/g dry weight.
• Predominant species identified were Enterococcus casseliflavus, E. hirae, and E. faecalis.
• High clonality among isolates, with strains linked to specific eelgrass samples, indicated in-situ growth.

Conclusions:

• Enterococci demonstrate the capability to grow on eelgrass, evidenced by high densities and clonal strains.
• Plant-associated enterococci growth complicates the interpretation of water quality data.
• Regulatory agencies face challenges in attributing elevated enterococci levels solely to fecal pollution when plant growth occurs.