The effect of storage time on Vibrio spp. and fecal indicator bacteria in an ISCO autosampler
Creators: name: Ghazaleh, Maite
Publisher: name: The University of North Carolina at Chapel Hill University Libraries
Year: 2014

description: Monitoring concentrations of bacterial pathogens and indicators of fecal contamination in coastal and estuarine ecosystems is critical to avoid adverse effects to public health. During storm events, particularly hurricanes, floods, Nor’easters, and tropical cyclones, sampling of coastal and estuarine waters is not generally possible due to safety concerns. It is particularly important to monitor waters during these periods as at precisely these times pathogenic bacteria such as Vibrio spp. and fecal indicator bacteria concentrations increase, posing significant risks to public health. Automated samplers, such as the rosette based “ISCO” sampler, are commonly used to conduct sample collection in aquatic systems. In our case, we have designed an autonomous vertical profiler (AVP) that is deployed in the Neuse River Estuary, NC USA with an automated ISCO sampler attached. The AVP can be remotely enabled by cell phone or internet to collect water samples during severe storm periods. Water samples are then stored in a rosette of proprietary bottles until conditions are safe enough, typically in less than 21 h, to collect the samples. There is a paucity of data regarding the effects of containment on bacterial concentrations of water stored over these short durations. Concerns exists with regards to autosampler methodology and associated sample holding times that might impact bacterial concentrations invalidating the subsequent laboratory analyses due to water samples’ misrepresentation of original in situ conditions. Six experiments were conducted to address this concern, and data from the experiments were pooled into three sets for data analyses: short-term, long-term, and full-term. Estuarine water samples were collected in the fall of 2013, placed into an ISCO rosette and subsampled over relevant time frames and ambient temperature conditions. Vibrio spp. and fecal indicator bacteria were quantified over the course of the experiments using replicated culture-based methods, including EnterolertTM and membrane filtration. The experiments demonstrated no significant impact of storage time when comparing concentrations of total Vibrio spp., Vibrio vulnificus, Vibrio parahaemolyticus, Enterococcus spp., or E. coli after storage as compared to original concentrations. Small scale variations in concentrations of specific targets were observed, particularly during midday hours that appeared to follow a diel cycle. Only culture-based analyses were conducted as part of this set of experiments, and further examination of bacterial community dynamics is warranted. Based upon our experiments, holding times of up to 21 h appear to have a negligible effect on bacterial concentrations for estuarine waters. However, the findings also suggest that increased variability and growth can occur during the middle of the day. Therefore, if at all possible, analysis schedules should be modified to account for this variability, e.g. collection of samples after overnight storage should occur as early in the morning as practicable.