Not All E. Coli Are Created Equal
Brett Smith for redOrbit.com – Your Universe Online
New research from Mercyhurst University and the University at Buffalo recently suggested that current testing methods for E. coli in lakes and rivers are insufficient. According to the scientists report in the journal“¯Applied and Environmental Microbiology, E. coli that produce a particular toxin are able to fend off predators and survive longer in lake water than their more benign counterparts.
“The take-home lesson is that“¯E. coli that produce Shiga toxin persisted longer in recreational water than“¯E. coli that don´t produce this toxin,” said study leader Gerald Koudelka, a biology professor at UB. “This is because the toxin appears to help“¯E. coli resist predation by bacterial grazers.”
Previous studies have shown that overall“¯E. coli concentrations aren´t always linked to the levels of the more dangerous Shiga toxin-producing“¯E. coli present in lake or river water, Koudelka said. He added that the new study can help to explain that discrepancy.
E. coli that produce Shiga toxin can cause severe intestinal illness and even lead to death in some cases.
In their new study, Koudelka and his colleagues obtained water samples from northern Pennsylvania containing tiny, single-celled protozoa that feed on“¯E. coli. Several different strains of“¯E. coli were placed into the water samples: three strains of Shiga-producing“¯E. coli (STEC) that were known to cause illness in humans and three strains of more benign“¯E. coli.
The researchers found that the toxic E. coli fared much better against their predators than their less dangerous counterparts. Over a 24-hour period, STEC populations fell by a 1.4-fold, compared to a 2.5-fold drop for the toxin-free bacteria.
After testing each“¯E. coli strain in its own separate experiment, the researchers found that the most potent STEC strain was also the longest lasting, surviving against its predators for about 48 hours before declining in population.
According to Koudelka, the findings indicate that current water quality tests may be inadequate when it comes to assessing“¯E. coli danger in lakes and rivers.
“If you´re only testing generally for fecal indicator bacteria, you could miss the danger because it´s possible to have low levels of“¯E. coli overall, but have most of that“¯E. coli be of the STEC variety,” he said. “This would be worse than having a large“¯E. coli population but no STEC.”
Koudelka added that the reverse situation would also be undesirable.
“You could have high“¯E. coli populations in a lake, but absolutely no STEC,” he said. “This is the economic part of it: It´s a problem because you might have a beach that´s closed for days even though it´s safe.”
Koudelka is still conducting investigations into the relationships among aquatic microbes, particularly how one species may influence the level of others. He has suggested that Shiga and other dangerous toxins are probably the result of a sort of “microbiological arms race,” and not intended to kill or harm humans.
The findings of the study have a particular resonance for the area surrounding the University at Buffalo, where heavy rains can result in sewage overflows and diluted, but untreated, sewage water being discharged into local waterways — thus allowing the E. coli living there to flourish on fresh fecal matter.