Assessment of the Effects of Holding Time and Temperature on Escherichia coli Densities in Surface Water Samples

Abstract

Escherichia coli is a routinely used microbiological indicator of water quality. To determine whether holding time and storage conditions had an effect on E. coli densities in surface water, studies were conducted in three phases, encompassing 24 sites across the United States and four commonly used monitoring methods. During all three phases of the study, E. coli samples were analyzed at time 0 and at 8, 24, 30, and 48 h after sample collection. During phase 1, when 4°C samples were evaluated by Colilert or by placing a membrane onto mFC medium followed by transfer to nutrient agar containing 4-methylumbelliferyl-␤-D-glucuronide (mFC/NA-MUG), three of four sites showed no significant differences throughout the 48-h study. During phase 2, five of seven sites showed no significant difference between time 0 and 24 h by membrane filtration (mFC/NA-MUG). When evaluated by the Colilert method, five of seven sites showed no significant difference in E. coli density between time 0 and 48 h. During phase 3, 8 of 13 sites showed no significant differences in E. coli densities between time 0 and the 48-h holding time, regardless of method. Based on the results of these studies, it appears that if samples are held below 10°C and are not allowed to freeze, most surface water E. coli samples analyzed by commonly used methods beyond 8 h after sample collection can generate E. coli data comparable to those generated within 8 h of sample collection. Notwithstanding this conclusion, E. coli samples collected from surface waters should always be analyzed as soon as possible.Escherichia coli testing is an important tool used by public health experts for the prevention of waterborne disease. The detection of E. coli in a water sample from an environmental source provides direct evidence of fecal contamination. Regulatory agencies are increasingly requiring more emphasis on E. coli testing as part of programs aimed at curtailing waterborne disease. Holding time and temperature can have a significant impact on the density of microbiological indicators at the time of sample analysis (4, 5, 7). Recommendations for E. coli holding times range from 8 h (2, 3, 9) to 24 h (8), and holding temperatures below 10°C are generally considered acceptable (2,3,8,9). It is also recommended that when transport conditions result in delays longer than 6 h, the use of field laboratory facilities located at the site of collection or delayed incubation procedures be considered (2). The Surface Water Treatment Rule requirements of the U.S. Environmental Protection Agency (USEPA) for total coliform and fecal coliform monitoring of surface water used as drinking water sources (3) specify that the time from sample collection to initiation of analysis is not to exceed 8 h; the regulations also encourage (but do not require) drinking water system personnel to hold samples at below 10°C during transit.Unfortunately, data from evaluations of microbiological indicator density that support current holding time recommendations are limited, particularly for E. coli....

Effects of Stock Use and Backpackers on Water Quality in Wilderness in Sequoia and Kings Canyon National Parks, USA

“…Equipment was maintained in sterile condition by flame sterilization (Myers et al 2007). Holding time tests confirmed previous studies that indicated minimal changes in E. coli and total coliform concentrations within 24 h of collection if samples are held unfrozen below 10°C (Myers et al 2007;Bordner and Winter 1978;Pope et al 2003).…”

Modelling storm-eventE.colipulses from the Motueka and Sherry Rivers in the South Island, New Zealand

“…For the current study, we had to relax these requirements to permit use of auto-samplers (without carousel chilling), which were triggered automatically by events. Pope et al (2003) found that E. coli concentrations in samples held at less than 108C were generally consistent with those measured within 8 h. Similarly, Stadler et al (2008) reported only minor sample deterioration for holding temperatures of around 58C. So the main issue is the holding time within the instrument shack, after collection, but before auto-samples were retrieved and stored on ice.…”

“…Pope et al 2003;Stadler et al 2008) and cross-contamination through carry-over from residues in the sampler pipework and mechanisms (e.g. Anderson & Rounds 2010;Solo-Gabriele et al 2000).…”

Evaluating appropriate maximum holding times for private well water samples

“…Furthermore, there is limited and inconsistent scientific evidence supporting these policies, none of which is specific to groundwater samples. Previous studies have investigated surface water (lakes and rivers, often those receiving municipal or agricultural waste) (Standridge and Lesar 1977;Dutka and El-Shaarawi 1980;Pope et al 2003;Aulenbach 2010), municipal and industrial effluent (Standridge and Lesar 1977;Dutka and El-Shaarawi 1980;Selvakumar et al 2004), stormwater (Selvakumar et al 2004), and water from within municipal distribution systems (McDaniels et al 1985). Survival rates were variable for different fecal indicator bacteria (FIB), with total coliforms often decreasing shortly after collection (Mendez Novelo et al 2010), whereas fecal coliforms generally survived longer, possibly up to 62 h (Aulenbach 2010).…”

“…Survival rates were variable for different fecal indicator bacteria (FIB), with total coliforms often decreasing shortly after collection (Mendez Novelo et al 2010), whereas fecal coliforms generally survived longer, possibly up to 62 h (Aulenbach 2010). Some studies observed significant decreases in Escherichia coli (E. coli) density by 18Á24 h (Selvakumar et al 2004, Aulenbach 2010, while other studies suggested that up to 48 h was acceptable (Pope et al 2003). Notably, across all of these studies, there was very little power to analyze holding times greater than 48 h.…”