My research goal is to investigate the ecology of pathogenic water- and food-bornebacteria, specifically bacteria in the genus Vibrio. These bacteria arethe causative agent of intense gastrointestinal infections if ingested. Additionally, one member of this genus, V. vulnificus, is the leading cause ofseafood-borne deaths in the United States. People consuming raw or undercooked shellfish are at increased risk forinfection by this organism, and contaminated shellfish are the source of over90% of these cases. Once consumed, thebacteria will disseminate throughout the body, and can cause necrotizing fasciitis,commonly known as flesh-eating disease. Furthermore,swimmers or seafood handlers with wounds or even small cuts in the skin canbecome infected by these deadly bacteria when they are exposed toseawater. These grievous woundinfections often require amputation and have a case fatality rate of nearly 50%even with aggressive medical treatment. To reduce the number of infections we need to understand thefollowing: 1) biological features thatenable the bacteria to cause human infections; 2) how this organism interactswith its shellfish host to cause food-borne disease; and 3) the environmentalfactors that can increase water-based wound infection risk by promotingincreases in pathogenic bacterial loads.
I have been involved in many projects addressing the needs stated above. My earliest work was primarily laboratorybased and focused on understanding objective 1. Through that research I was able to publish evidence that there aresubtypes of V. vulnificus bacteria,some of which appear to be deadlier than others, and that these subtypes can bequickly and easily identified by examination of their DNA (Froelich and Oliver 2011). With this new knowledge it may be easier toidentify which specific V. vulnificus bacteriaare the disease causers and determine which oysters are harboring them. Additionally, the bacteria can produce a capsule,the sticky coating on the cell surface that is required for infection, and myresearch was able to demonstrate that the bacteria phase this ability on andoff and detailed specific conditions encouraging this change (Hilton, Rosche et al. 2006). With greater understanding of this process,we could conceivably subject the bacteria, or oysters containing the bacteria,to the specific conditions that would phase off their capsule production andrender them unable to cause infection.
The next phase of my research integrated bench work and field work and specificallyaddressed objective 2. I was able todetermine that the more harmful and less harmful types of V. vulnificus bacterial cells are taken up by water-filteringshellfish at different rates (Froelich, Ringwood et al. 2010). The rate difference, however, was notsufficient to explain the disparity between the two bacterial populations foundin shellfish. While discussingaquaculture and shellfish aquarium maintenance with the man who literarilywrote the book on oyster biology, Dr. Evan Ward, I hypothesized the techniquesI used to measure bacterial uptake in oysters, which have been used nationwidefor decades, were not sufficient and proposed an alternative technique thatfirst allows V. vulnificus bacteriato attach to larger particles before feeding these to oysters. This technique allows filter-feeding oystersto better capture laboratory grown bacteria and allows us to better mimicenvironmental conditions in our in vitro experiments. Publication of this work is currently underreview (Froelich and Oliver 2012).
Having become accustomed to environmental field work and remote sample processing, Icompleted a joint project between UNC-Charlotte and UNC-Chapel Hill. This study examined the effects of long-termdrought on the population dynamics of V.vulnificus bacteria in both water and oysters (Froelich, Williams et al. 2012). It was found that an unprecedented droughtcaused the bacteria to become rare in North Carolina. The most interestingfindings came after the drought eased and conditions returned to theirpre-drought levels. The bacteriareturned to the coastal waters but did not repopulate the oysters inhabitingthe very same water. It was found thatdrought caused an increase of the proportion of salt in the coastal ecosystemsand more salt-tolerant bacteria were able to colonize the oysters. These salt-tolerant bacteria were preventing V. vulnificus from returning to theirprimary environmental host, the oysters. This environmental study sheds light on the effects of extreme conditionson V. vulnificus and confirms thatextreme salinity can reduce harmful bacterial loads in oysters. As the work on this project was beingconducted, results were presented at national and international conferences andeach time won first place awards. Thecommercial impacts of this work were presented to the North Carolina GeneralLegislative Assembly in Raleigh, NC.
A project that combined research goals 2 and 3 involved examining the effects ofpollution and oxygen depletion on Vibrio bacteriapopulation in oysters. We found thatheavy metal pollution significantly increased the levels of these harmfulbacteria indicating that human activity could be a culprit in the increase ofinfections (Ivanina, Froelich et al. 2011).
My current work involves sampling of the Neuse River estuary, part of the NorthCarolina coastal region where the Neuse River meets the ocean, for these deadlyVibrio bacteria. This work is being conducted at the UNCInstitute of Marine sciences. Bycombining the information on bacteria with environmental data, such as salinityor temperature, we are hoping to gain some insight on what conditions trigger a“bloom” of the most infectious strains of Vibrios, directly addressing researchgoal 3. Early data analysis on thisproject shows that virulent strains of the bacteria react to the environmentdifferently than the species as a whole. This promising data, presented at a conference on the ecology andevolution of infectious diseases, could allow us to predict infection riskbased on easily measured parameters and provide warnings to swimmers, boaters,and seafood handlers.
Future projects with UNC include a proposed study of how the Vibrio bacteria are transported along of the Neuse River estuaryvia wind events and storms. Bymonitoring and collecting data before, during, and after periods of highvelocity wind, we hope to undercover infection risk that is typicallyunaccounted for. We plan to use a novelsampling platform, termed the “Autonomous Vertical Profiler” or AVP, which iscapable of sampling from the surface to the bottom of the water column, and canobtain samples mechanically even when wind or rain would traditionally preventmanual sampling, by boat.
By combining the results from projects covering all three research goals, thegeneral understanding of how this pathogen interacts with its human host,natural animal hosts, and aquatic environment will be advanced. The ultimate goal is with enough of theseadvances in knowledge, to significantly reduce or even eliminate the diseasescaused by these bacteria.