Automated dead-end ultrafiltration of large volume water samples to enable detection of low-level targets and reduce sample variability

Abstract

Aims: A Portable Multi-use Automated Concentration System (PMACS) concentrates micro-organisms from large volumes of water through automated dead-end ultrafiltration and backflushing. The ability to detect microbial targets from ground, surface and cooling tower waters collected using standard methods was compared with samples from the PMACS in this study. Methods and Results: PMACS (100 l) and standard grab samples (100-500 ml) were collected from sites in Florida and South Carolina, USA. Samples were analysed for the presence of faecal indicator bacteria (FIB; ground and surface water) or Legionella pneumophila (Lp; cooling tower water). FIB were enumerated by growth on selective media following membrane filtration or in IDEXX defined substrate media. Lp cells were detected by direct fluorescence immunoassay using FITC-labelled monoclonal antibodies targeting serogroups 1, 2, 4 and 6. FIB were found in PMACS samples from ground and surface waters when their concentrations were below detection limits in grab samples. The concentrations of Lp in cooling tower samples collected over 5 months were more consistent in PMACS samples than grab samples.Conclusions: These data demonstrate that PMACS concentration is advantageous for water monitoring. FIB were detected in PMACS samples when their concentrations were below the detection limits of the standard methods used. PMACS processing provided more representative samples of cooling tower waters reducing sample variability during long-term monitoring. Significance and Impact of the Study: This study highlights the utility of PMACS processing for enhanced monitoring of water for low-level microbial targets and for reducing sample variability in long-term monitoring programmes.

Comparison of Filters for Concentrating Microbial Indicators and Pathogens in Lake Water Samples

“…A dead-end concentrator was designed for sampling recreational waters (40) and is commercially available (IntelliSense Design, Inc., Tampa, FL). A manual UF system (41) that operates on the same principle as the automatic UF but without a computer-controlled system worked well in recovering pathogens from 100-liter samples during field studies at Great Lakes and inland lake beaches (data not shown).…”

Laboratory and Pilot-Scale Dead-End Ultrafiltration Concentration of Sanitizer-Free and Chlorinated Lettuce Wash Water for Improved Detection of Escherichia coli O157:H7

“…Flow rate and pre-and postfilter pressures were monitored during filtration. The PMACS automated recovery cycle was then initiated to recover the material collected on the filter: 0.01% sodium polyphosphate in 0.1 M sodium phosphate buffer (PB-NaPP) (23,27,29) was pumped into the filter in the direction opposite to the forward flow (back flushed) to generate approximately 400 ml of retentate. The retentate was collected in a sterile polystyrene bottle and measured using a sterile 500-ml graduated cylinder.…”

“…The PMACS was cleaned after each inoculated wash trial by installing a dedicated cleaning filter and initiating the automated cleaning cycle: 2 to 4 liters of acidified (pH 6.0) solution with 540 ppm of sodium hypochlorite were pumped in the forwardflow direction through the inlet path and sample collection lines (27,29). The cleaning solution was then recirculated through the system for 20 to 30 min, followed by recirculation of a 0.1% sodium thiosulfate solution to neutralize residual sodium hypochlorite.…”

“…Several studies have used HFUF to concentrate microorganisms from 20-to 100-liter volumes of tap water, groundwater, reclaimed water, and various types of surface water, followed by standard cultural and/or rapid detection methods (18,21,25,27,28). Jimenez and Chaidez (21) reported a 32% higher incidence of Salmonella in river water samples using tangential HFUF in combination with a standard isolation method compared with the results for a most-probable-number method.…”

“…Hence, the goal of this study was to evaluate an automated system based on dead-end ultrafil tration, the Portable Multi-use Automated Concentration System (PMACS) (27), for concentrating E. coli 0157:H7 from large-volume samples of inoculated simulated com mercial lettuce wash water containing a 5% organic load (wt/vol; blended iceberg lettuce). The work included establishing the PMACS performance parameters and evaluating its concentration efficacy using standard micro biological procedures and an electrochemiluminescence (ECL) immunoassay (23,29).…”