Antibiotic resistant bacteria in Irish waters: molecular epidemiology and hydrological control

Abstract

Antibiotic resistant bacteria can be detected in numerous environments. In recent years, agricultural practices have been demonstrated to contribute to the emergence and persistence of antibiotic resistance. Heavy rainfall events are capable of transferring microorganisms from land stores to receiving water sources. This thesis describes the increase in numbers of enterococci in a freshwater stream following heavy rainfall events in a catchment located in County Monaghan, republic of Ireland. During the summer event, an increase in the level of antibiotic resistance was observed preceding the peak of the storm. A survey of the farms surrounding the freshwater streams revealed that antibiotic resistant enterococci are prevalent in this area. Analysis of isolates from all farm and water samples using a combined approach of biochemical profiling and multilocus sequence typing (MLST) indicated that poultry farming is a major contributor to the presence of enterococci in the streams. Enterococci are a diverse genus, with some strains capable of causing nosocomial infections while some are harmless commensals or environmental strains. In addition to antibiotic resistance, detection of putative virulence factors was common among isolates of enterococci from both the farm and water environments in this catchment. The number of isolates carrying multiple virulence factors was higher than expected, indicating that some of these strains may be capable of causing infection. Mobile DNA accounts for a significant proportion of the enterococcal genome. Antibiotic resistance and virulence genes are commonly located on mobile DNA. This thesis describes the presence of pheromone-responsive plasmids among animal and environmental isolates of enterococci. The isolation of such a large number of isolates carrying these plasmids from environmental samples was a surprise, in particular from E. faecium isolates, as these plasmids are strongly associated with clinical isolates. Overall, this thesis indicates that this environment can provide a substantial reservoir and means of transfer for antibiotic resistant and potentially virulent isolates of enterococci.

Date of Award	Jun 2011
Original language	English
Sponsors	Environmental Protection Agency
Supervisor	James Dooley (Supervisor), Joerg Arnscheidt (Supervisor), Patrick Naughton (Supervisor) & Phil Jordan (Supervisor)