Comparison of filters for concentrating microbial indicators and pathogens in lake water samples

Abstract

Bacterial indicators are used to indicate increased health risk from pathogens and to make beach closure and advisory decisions; however, beaches are seldom monitored for the pathogens themselves. Studies of sources and types of pathogens at beaches are needed to improve estimates of swimming-associated health risks. It would be advantageous and cost-effective, especially for studies conducted on a regional scale, to use a method that can simultaneously filter and concentrate all classes of pathogens from the large volumes of water needed to detect pathogens. In seven recovery experiments, stock cultures of viruses and protozoa were seeded into 10-liter lake water samples, and concentrations of naturally occurring bacterial indicators were used to determine recoveries. For the five filtration methods tested, the highest median recoveries were as follows: glass wool for adenovirus (4.7%); NanoCeram for enterovirus (14.5%) and MS2 coliphage (84%); continuous-flow centrifugation (CFC) plus Virocap (CFC+ViroCap) for Escherichia coli (68.3%) and Cryptosporidium (54%); automatic ultrafiltration (UF) for norovirus GII (2.4%); and dead-end UF for Enterococcus faecalis (80.5%), avian influenza virus (0.02%), and Giardia (57%). In evaluating filter performance in terms of both recovery and variability, the automatic UF resulted in the highest recovery while maintaining low variability for all nine microorganisms. The automatic UF was used to demonstrate that filtration can be scaled up to field deployment and the collection of 200-liter lake water samples.

Fig 1

Sample sites for single and variability recovery experiments and field deployment.

Fig 2

General steps in filtration and processing of lake water samples by virus adsorption-elution (VIRADEL) and ultrafiltration (UF) methods showing removals for different microorganisms.

Fig 3

Percent recoveries of viruses in lake water, 2010 to 2011. (A) E. coli, (B) enterococci, (C) MS2 coliphage, (D) adenovirus, (E) norovirus GII, (F) enterovirus, (G) Cryptosporidium, and (H) Giardia. The numbers of samples for each filtration method are indicated in parentheses. Each box includes the median concentration (center line) and the 25th and 75th percentiles (lower and upper box limits, respectively). Error bars represent data values less than or equal to 1.5 times the interquartile range outside the quartile. Asterisks indicate outlier values greater than 1.5 times the interquartile range outside the quartile. Results of the Tukey-Kramer multiple-comparison tests are presented as letters, and recoveries with at least one letter in common do not differ significantly. Note the different scales for percent recoveries for different microorganisms.