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The Effects of Water Matrix on Decay of Human Fecal Molecular Markers and Campylobacter spp.
Citation:
Green, H. C., O. C. SHANKS, M. SIVAGANESAN, R. A. HAUGLAND, AND K. G. Field. The Effects of Water Matrix on Decay of Human Fecal Molecular Markers and Campylobacter spp. Presented at American Society for Microbiology 110th General Meeting, San Diego, CA, May 23 - 27, 2010.
Impact/Purpose:
To inform the public.
Description:
Although molecular source tracking for human fecal contamination is used on a wide range of sample types, little is known about comparative decay of proposed molecular markers under different conditions, or correlation with pathogen decay. Our purpose was to measure correlations among markers and calculate decay rates in fresh and marine water in light or darkness. Methods: We spiked four microcosms containing natural fresh or marine water with human sewage and sampled them over 21 days. We extracted total nucleic acids and used QPCR to enumerate DNA markers and RNA transcripts from Bacteroides, enterococci, and Campylobacter spp. We measured fecal indicator bacteria by standard culture methods. Results: All molecular markers persisted longer in marine water compared to fresh water. While light drastically increased decay rates of culturable enterococci and E. coli, it had a slight or no effect on molecular marker decay. All Bacteroides markers showed similar decay profiles within treatments. For all but one assay, RNA decay closely followed that of DNA within each treatment. Campylobacter marker copy numbers increased in marine water treatments, suggesting periods of growth. Conclusions: The difference in molecular marker decay rates between fresh and marine waters suggests that water matrix characteristics such as salinity and bactivore concentration must be factored into risk assessment and source tracking models. Rapid decay of culturable enterococci vs. slow decay of DNA and RNA markers in light treatments suggests that viable but non-culturable cells may dominate the QPCR signal. The similar decay of all human-specific and general Bacteroides markers may permit ratios between them to be used to estimate human contamination. In fresh water, all Bacteroides markers correlated well with Campylobacter 16S markers, indicating that these markers may be good indicators for Campylobacter presence. In marine water, no molecular indicator correlated with Campylobacter markers, highlighting the need for development of other indicators that correlate with this pathogen in marine conditions.
