Factors determining distribution and abundance of pathogenic bacteria,
with a focus on Vibrio spp.
Sophie Anna Allen
Waterborne diseases caused by bacteria are global health hazards. Two projects are
presented in this thesis, which examines the presence and proliferation of selected
pathogenic bacteria in the cool Swedish climate. The first project, which was a general
screening survey, tested different aquatic species and substrates using polymerase chain
reaction (PCR) for the detection of associated pathogenic bacteria. Some species of
Vibrio bacteria were identified from the Baltic Sea, a river, and two lakes in central
Sweden. These species were tentatively identified as Vibrio diazotrophicus, V. cholerae
and an unknown Vibrio species. Campylobacter species and Helicobacter pylori were not
detected at these sampling locations. The second project was a controlled-factor
experiment designed to assess the individual and combined impacts of temperature and
dissolved organic matter (DOM) on the abundance and growth of four pathogenic Vibrio
species in Baltic seawater. The Vibrio species studied were V. cholerae, V. vulnificus, V.
parahaemolyticus and V. alginolyticus. The DOM was obtained from a Nodularia
spumigena algal bloom in the Baltic Sea. Addition of algal DOM was found to cause
Vibrio bacteria to grow several orders of magnitude faster- particularly V. cholerae.
Increased temperature was found to have a synergistic effect, also additionally
increasing the growth of Vibrio bacteria. In this study, at 18 °C or over with addition of
algal DOM, V. cholerae reached levels that are hazardous to humans. Therefore algal
blooms in the Baltic Sea potentially promote the risk of V. cholerae outbreaks.
Degree project in Biology
Examensarbete i biologi, 20 p, 2005
Biology Education Centre and Microbial Ecology Group, Department of Limnology,
Uppsala University
Supervisors: Dr. Stefan Bertilsson and Dr.Willem Goedkoop