Rapid dead-end ultrafiltration concentration and biosensor detection of enterococci from beach waters of Southern California Stephaney D. Leskinen, Valerie J. Harwood and Daniel V. Lim ABSTRACT Stephaney D. Leskinen (corresponding author) Daniel V. Lim Division of Cell Biology, Microbiology and Molecular Biology, Department of Biology, University of South Florida, 4202 E. Fowler Ave., SCA 110, Tampa FL 33620-5200, USA Tel.: +1 813-974-1316 Fax: +1 813-974-5175 E-mail: sleskine@cas.usf.edu Valerie J. Harwood Division of Integrative Biology, Department of Biology, University of South Florida, 4202 E. Fowler Ave., SCA 110, Tampa FL 33620-5200, USA Same-day microbial water quality assessments are not possible with standard methods, which increases the possibility of public exposure to fecal pathogens. This study examined the efficacy of high-volume hollow fibre ultrafiltration coupled to biosensor detection for enterococci in marine waters to allow same-day public notification of poor water quality. Fifty-six 100 l ultrafiltered samples and 100 ml grab samples were collected weekly from May to July 2007. Post-ultrafiltration processing included sonication and micron sieve passage to remove interfering particulates, followed by centrifugation for secondary concentration. Levels of enterococci in grab and ultrafiltration samples were determined by a standard method (EPA method 1600) for calculation of recovery efficiencies and concentration factors. Each final retentate was analysed with the RAPTOR evanescent wave biosensor. Enterococci levels increased over 26,000-fold in final retentates. Enterococci were detected when ambient concentrations exceeded the regulatory standard for a single sample ($105 CFU/100 ml), and detection was highly correlated with breaches of the single-sample regulatory limit. The combined procedure required 2.5 h for detection compared with 24 h for EPA method 1600. This field study achieved rapid detection of enterococci by ultrafiltration, secondary concentration and biosensor analysis, and demonstrates its potential usefulness for water quality monitoring. Key words | beach water, biosensor detection, dead-end ultrafiltration, enterococci, recreational water quality INTRODUCTION The indicator paradigm states that certain microorganisms, including enterococci, act as sentinels for the possible presence of human pathogens of fecal origin. Standard monitoring techniques for fecal contamination involve culturing indicator organisms, which requires an incubation period of 24 hours or more (US Environmental Protection Agency 2000, 2002). Recreational water users may be exposed to fecal contamination of those waters prior to the posting of beach advisories during the sample proces- sing period. Rapid approaches for assessing microbial water quality are needed to identify fecal pollution events to prevent this exposure. Several technologies have recently been developed for rapid detection of microbial targets in complex matrices, including nucleic acid-based and antibody-based pro- cedures (Lim et al. 2005). In general, nucleic acid-based detection systems are more sensitive; PCR assays detect as few as 30 cells in a short period (Fode-Vaughan et al. 2003; Ibekwe & Grieve 2003; Haugland et al. 2005). However, PCR requires samples to be relatively free of inhibitors commonly found in complex matrices, such as environ- mental waters. Another possible weakness of PCR is its high sensitivity and the chance of amplifying the DNA of other organisms present in the sample, which can result in doi: 10.2166/wh.2009.086 674 Q IWA Publishing 2009 Journal of Water and Health | 07.4 | 2009