Water quality is a concern for many in the Pensacola Bay area. Our bay has had many human induced stressors over the decades but “swimming alerts” or “health advisories” are of primary concern.
Health advisories are issued when indicator bacteria levels reach a high point. These bacteria are what care called fecal bacteria due to their association with feces. Most are found in the digestive tracts of birds and mammals and find their way into local waterways via defecation. Very high levels are thought to be more associated with human waste and are the reasons for labeling local waterways as impaired. Enterococcus sp. are one such indicator bacteria.
THE CREATURE – Enterococcus
- Spherical in shape – termed “coccus”
- Gram positive and produces lactic acid while decomposing organic matter
- The production of lactic acid decreases the pH within the gut which inhibits food spoilage
- Organoleptic = associated with the sight, smell, taste of food products
- Spherical diameter of 0.8 µm
- Ferments glucose with no gas production
- Grows in temperatures between 10-45 C (50 – 113 F); can live at 60 C (140 F) for 30 minutes
- Can live in pH of 9.6 and in very saline environments
- Enterococcus faecalis one of two species found in human gut (90-95%) and other mammals
- Enterococcus faecium (5-10% in humans)
WHY USE Enterococcus AS A FECAL INDICATOR IN SALT WATER
- There is a high concentration of Enterococcus in human feces: 10,000 – 1,000,000 / gm of feces
- Early monitoring for health advisories used total coliforms (1948)
- Once learned that other naturally occurring gram negative bacteria were present in the environment, they moved to “fecal” coliforms – which assumes that only a small fraction of coliforms are fecal.
- 1980’s it was discovered that Enterococcus occurrence in marine waters strongly correlated with gastrointestinal illness.
- 2000’s found strong correlation with recreational freshwater illness and Enterococcus
- 2004 World Health Organization (WHO) recommends Enterococcus as indicator for fecal waste in marine waters
HOW MONITORING WORKS; HOW MUCH IS TOO MUCH?
- Reported bacteria counts are the geometric mean over a period of time and/or statistical threshold values (single samples)
- EPA uses the threshold of 104 colony forming unites (CFU)/100ml for a single sample; 35 CFU/100ml for a geometric mean
- Microbial source tracking (MST) using animal host-specific gene markers in Bacteroidales are now being used. This will assist with determining whether the ENT is from humans or some other animal. There are trackers for humans.
SOURCES OF Enterococcus
- Agricultural run-off
- Direct input (animals)
- Plant debris
- Polluted groundwater
- Soils, sediments, and sands.
- Beach wrack.
- Most treatment plants are clean and discharge away from folks but: Sanitary Sewage Overflows (SSO), sewage pipe leaks, some urban and agricultural activities trigger levels (after rain) higher than raw sewage.
- There is a correlational with illness/ENT concentrations and urban runoff.
- 24% of US surface waters are listed as impaired due to bacteria – smaller fraction due to Enterococcus
FACTORS THAT CAN CAUSE Enterococcus numbers to change other than discharge of sewage
- Can be stressed by too much light or dark and by variable salinities
- Does not survive well in waters low in nutrients
- They have protozoan predators (single celled animals in the water)
- May attach to particles in the water column and settle to the bottom with them; thus not be detected – but still there
- Settling rate (when not attached to particles) 0.023 meters/day; with particles it depends on particle size and density; resuspension due to stirring up the bottom can happen
- Tides can impact Enterococcus concentrations
- Concentrations usually low at high noon due to photo suppressions (sunlight)
CURRENT FLORIDA STATE STANDARDS ON Enterococcus LEVELS
- In 2016 the Florida Department of Environmental Protection added Enterococci bacteria to Florida’s Surface Water Quality Standards, Florida Administrative Code Chapter 62-302.530, https://www.flrules.org/gateway/ChapterHome.asp?Chapter=62-302.
- This states that the amount of Enterococci bacteria in number per 100 milliliters shall not exceed a monthly geometric mean of 35 colonies nor exceed the Ten Percent Threshold Value (TPTV) of 130 colonies in 10% or more of the samples during any 30-day period.
- If a sample fails one of the above a second sample will be collected. If it also fails and health advisory will be issued.