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Biological Sciences


Enumeration of enterococci (EN) bacteria in water is an USEPA approved indicator of fecal pollution and the possible presence of enteric pathogens. Along the northern Gulf of Mexico, the water is shallow with a high organic and particulate load because of the Mississippi River discharge. Disturbance of coastal sediments during wind/wave action caused either by the weather or human activities may increase bacterial counts as a result of increased EN persistence in the water column and/or resuspension of EN in the sediment. The goals of this project are to determine the relationship between organic content and EN counts in the water and whether bacterial resuspension from the sediment contributes to elevated EN counts. We found that EN counts in the water were correlated with wave conditions at seven sites along the Mississippi Gulf Coast. During calm wave conditions, low bacterial levels (1.0 – 227 CFU/100mL) were observed in the water with higher counts in the sediment; the reverse was observed (10 – 351 CFU/100mL) during rough wave conditions. EN counts were positively correlated with organic content of the sediment. Wave activity to keep EN in suspension was apparently critical for high counts. EN counts decreased by 50% in 4 hr from 38 to 17 CFU/100mL in the absence of resuspension and decreased to 1 CFU/100mL after 48 hr. EN in the sediment are not stationary as genetic fingerprinting using REP-PCR showed low persistence of specific isolates over time. Jackknife analysis revealed low similarity among EN isolates from the water and sediment collected on the same day and site during calm wave conditions. This shows that EN are not persisting for long periods in the same area but instead are resuspended and redistributed along the coast. Results from this study provide evidence that high organic content and resuspension of isolates from the sediment during periods of strong wave action contribute to high EN counts. Current research on the survival of EN in estuarine habitats will provide insight on the balance between environmental persistence and fecal pollution in causing high EN counts along beaches in the northern Gulf of Mexico.