How to Define "Safe" Water? Southern California study highlights the limits of bacteria used as fecal indicators - http://goo.gl/C9LF
I recently made reference to this headline in a Twitter post, and how true it is. For both water in the environment and drinking water, the EPA relies on the occurrence of fecal indicators, which are usually bacteria that can be found in sewage. These are often referred to as Coliform bacteria, or total Coliform. The 14th Edition of Standard Methods for the Examination of Water and Wastewater defines total Coliform as a group of bacteria which is aerobic and facultative anaerobic, gram-negative, nonspore-forming, rod shaped bacteria which ferment lactose with gas formation within 48 hours at 35°C. This definition may define a particular type of bacteria, many of which may be found in mammalian intestinal tracts, and particularly in human intestinal tracts, but there are, unfortunately for us, many bacteria that fit this definition that can also exist quite nicely in the “outside world”, so to speak. When these bacteria are found in a water sample, it is looked upon by most of the regulatory community as an indication of possible fecal contamination of that water. But in fact, that may be very far from what is actually happening. It may just be indicative of a case where that bacterium is naturally prominent in the local area.
For example, I have seen test results from groundwater wells that are total Coliform positive, indicating a potential for fecal contamination. When the bacteria causing this sample of water to be total Coliform positive is analyzed further to see exactly what species of bacteria are present, it turned out to be Enterobacter cloacae. This bacterium does indeed occur in the intestinal tract of humans and other mammals. It also occurs in the guts of insects; in the soil; in surface and ground waters; on plants; and even inside of various fruits. The point here is that many of these bacteria that are used as indicators of potential fecal contamination can live almost anywhere. They are the epitome of an opportunistic life form: they don’t need oxygen, but can live in its presence; they can tolerate a wide range of temperatures, pH’s, moisture conditions, etc.; and they can use many sources of energy as a food source. Because of their flexibility, they can live almost anywhere, not just the mammalian gut, so their use as an indicator of fecal contamination of water is questionable. A better method would be to use a more specific group, such as fecal Coliform bacteria, or even a single organism, such as Escherichia coli, also known as E. coli. And, in fact, the regulatory community, with the EPA in the lead, is beginning to come around to this way of thinking as exhibited in new and pending regulations. The recently enacted Groundwater Rule uses E. coli or other very specific fecal organisms as the indicator; and the EPA is proposing changes to the Total Coliform Rule that also reflect the reality of the ubiquitous nature of Coliforms in the environment. That, in my opinion, is a trend worth furthering.
I recently made reference to this headline in a Twitter post, and how true it is. For both water in the environment and drinking water, the EPA relies on the occurrence of fecal indicators, which are usually bacteria that can be found in sewage. These are often referred to as Coliform bacteria, or total Coliform. The 14th Edition of Standard Methods for the Examination of Water and Wastewater defines total Coliform as a group of bacteria which is aerobic and facultative anaerobic, gram-negative, nonspore-forming, rod shaped bacteria which ferment lactose with gas formation within 48 hours at 35°C. This definition may define a particular type of bacteria, many of which may be found in mammalian intestinal tracts, and particularly in human intestinal tracts, but there are, unfortunately for us, many bacteria that fit this definition that can also exist quite nicely in the “outside world”, so to speak. When these bacteria are found in a water sample, it is looked upon by most of the regulatory community as an indication of possible fecal contamination of that water. But in fact, that may be very far from what is actually happening. It may just be indicative of a case where that bacterium is naturally prominent in the local area.
For example, I have seen test results from groundwater wells that are total Coliform positive, indicating a potential for fecal contamination. When the bacteria causing this sample of water to be total Coliform positive is analyzed further to see exactly what species of bacteria are present, it turned out to be Enterobacter cloacae. This bacterium does indeed occur in the intestinal tract of humans and other mammals. It also occurs in the guts of insects; in the soil; in surface and ground waters; on plants; and even inside of various fruits. The point here is that many of these bacteria that are used as indicators of potential fecal contamination can live almost anywhere. They are the epitome of an opportunistic life form: they don’t need oxygen, but can live in its presence; they can tolerate a wide range of temperatures, pH’s, moisture conditions, etc.; and they can use many sources of energy as a food source. Because of their flexibility, they can live almost anywhere, not just the mammalian gut, so their use as an indicator of fecal contamination of water is questionable. A better method would be to use a more specific group, such as fecal Coliform bacteria, or even a single organism, such as Escherichia coli, also known as E. coli. And, in fact, the regulatory community, with the EPA in the lead, is beginning to come around to this way of thinking as exhibited in new and pending regulations. The recently enacted Groundwater Rule uses E. coli or other very specific fecal organisms as the indicator; and the EPA is proposing changes to the Total Coliform Rule that also reflect the reality of the ubiquitous nature of Coliforms in the environment. That, in my opinion, is a trend worth furthering.
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