Jeq50224 1018..1025

Due to the difficulties in testing for specific pathogens, water samples are tested for the presence of nonpathogenic indicator organisms to determine whether a water supply has been contaminated by fecal material. An implicit assumption in this approach is that where pathogenic microorganisms are present fecal indicator organisms are present as well; yet surprisingly few studies have been conducted that directly compare the transport of indicator organisms with pathogenic organisms in ground water environments. In this study we compared the cell properties and transport of Escherichia coli, a commonly used indicator organism, and Campylobacter jejuni, an important enteropathogen commonly found in agricultural wastes, through saturated porous media. Differences in cell properties were determined by measuring cell geometry, hydrophobicity, and electrophoretic mobility. Transport differences were determined by conducting miscible displacement experiments in laboratory columns. Under the experimental conditions tested, C. jejuni was much more negatively charged and more hydrophobic than E. coli. In addition, C. jejuni cells were slightly longer, narrower, and less spherical thanE. coli. The variations in cell properties, primarily surface charge, resulted in significant differences in transport between these two microorganisms, with the transport of C. jejuni exceeding that of E. coli when conditions favored low attachment rates, thus calling into question the usefulness of using E. coli as an indicator organism for this important pathogen. INFILTRATION of fecal material into the subsurface can result in contamination of soils and ground water by enteropathogenic microorganisms such as bacteria, viruses, and protozoa. Recent studies have shown that fecal contamination has been detected in nearly half of all the drinking water wells tested in the United States (Macler and Merkle, 2002). Some of the most cited sources of fecal contamination of ground water supplies are agricultural activities (USEPA, 1994) including use of manure for crop fertilization (Gagliardi and Karns, 2002), pasturing of livestock, animal feeding operations (Gerba and Smith, 2005), wash water from animal housing (Mawdsley et al., 1995), and leaky manure storage lagoons (USEPA, 1993). Several recent studies have found a strong link between human illness and land application of agricultural waste (Clark et al., 2003; Stanley and Jones, 2003; Valcour et al., 2002). Although the presence of pathogenic microorganisms in drinking water supplies is a threat to public health, rarely are concentrations of these particular organisms measured. Rather, water samples are tested for the presence of nonpathogenic microorganisms commonly found in fecal material, referred to as indicator organisms. The presence of these indicator organisms does not mean necessarily that the water is unsafe for consumption; rather it indicates that the water has likely been contaminated by fecal material and thus potentially contains pathogens (Leclerc and Mosel, 2001). Commonly used indicator organisms include total coliforms, fecal coliforms, E. coli, and enterococci. To be effective, an indicator organism must occur in a sample when fecal pathogens are present, but in far greater numbers than the pathogen(s) of interest. Additionally, the indicator should respond to natural environmental conditions and water treatment processes in a manner similar to the pathogen(s) of concern. In ground water environments this requires that the indicator organism have similar or greater transport and survival characteristics than the pathogenic microorganisms of concern to ensure detectable quantities of the indicator organism in fecally contaminated waters. Given the diversity of potentially pathogenic microorganisms found in animal manures, it is reasonable to expect diversity in the cell surface properties of these microorganisms. For instance, Lytle et al. (2002) have shown that several important microorganisms to public health such asE. coliO157:H7,Cryptosporidiumparvum oocysts, and Vibrio cholorae all have significantly different charges (zeta potential) on their outer surface. Given that the movement of bacteria through the subsurface is governed, in part, by cell properties such as surface charge (Busscher et al., 1984; van Loosdrecht et al., 1987a), cell geometry (Fontes et al., 1991; Gannon et al., 1991; Weiss et al., 1995), and hydrophobicity (Stenstrom, 1989; van Loosdrecht et al., 1987a, 1990), it is likely that there exists a range of transport characteristics for the variety of microorganisms commonly found in fecal material. Therefore, it seems unlikely that a single organism, for example E. coli, can adequately serve as a surrogate for the subsurface transport of all pathogenic microorganisms. Indeed, the effectiveness of E. coli as an indicator of enteric virus transport in ground water has already been questioned (Borchardt et al., 2003; Meschke and Sobsey, 2003). The objective of our study was to compare key cell properties and transport characteristics of C. jejuni, an important pathogen commonly found in agricultural wastes (Wesley et al., 2000) and a leading cause of gastroenteritis in theUnited States (Allos, 2001), andE. coli, a commonly used indicator of fecal contamination. Although Campylobacter spp. has been detected in ground C.H. Bolster and K.L. Cook, USDA-ARS, 230 Bennett Lane, Bowling Green, KY 42104. S.L. Walker, Department of Chemical and Environmental Engineering, University of California, Riverside, B355 Bourns Hall, Riverside, CA 92521. Mention of trade names or commercial products is solely for the description of experimental procedures and does not imply recommendation or endorsement by the U.S. Department of Agriculture. Received 4 June 2005. *Corresponding author ([email protected]). Published in J. Environ. Qual. 35:1018–1025 (2006). Technical Reports: Ground Water Quality doi:10.2134/jeq2005.0224 a ASA, CSSA, SSSA 677 S. Segoe Rd., Madison, WI 53711 USA R e p ro d u c e d fr o m J o u rn a l o f E n v ir o n m e n ta l Q u a lit y . P u b lis h e d b y A S A , C S S A , a n d S S S A . A ll c o p y ri g h ts re s e rv e d . 1018 Published online May 31, 2006