The river Barrow has been of importance to the inhabitants of Ireland for over five thousand years and has recently been targeted as a priority resource for tourism. One essential factor in the successful tourist development of the river is high water quality.

At the Institute of Technology, Carlow, two microbial aspects of water quality are being investigated: the presence of microorganisms that indicate recent faecal contamination, and the prevalence of microorganisms that are resistant to antibiotics used in animal and human medicine. The significance of the antibiotic resistant microorganisms is that they may constitute a pool of drug resistances that could potentially transfer into human and animal pathogens, undermining success-ful antibiotic therapy.

Our investigations of selected sites from the Barrow have indicated recent ongoing faecal pollution resulting in introduced populations of microorganisms originating from the mammalian gut. This investigation is ongoing and a more complete picture of the faecal contamination and the resulting river microflora will be available.

When levels of river microorganisms resistant to antibiotics were analysed, between 20% and 59% were resistant to three or more antibiotics used in human and veterinary medicine. In addition, it was found that a sample of the multi-resistant bacteria identified could be stably maintained in the absence of selective pressure, suggesting a stable pool of antibiotic resistance genes in the bacterial population of the river.

The possibility of these antibiotic resistances being plasmid borne and therefore transmissible to other microorganisms was investigated, and we have detected transfer of resistances both in in vitro experiments and in non sterile microcosms into the enteric bacteria Escherichia coli. The significance of these results is the demonstration of the presence of a stable pool of transferable antibiotic resistance genes both in the indigenous and in the introduced microbial population in the river Barrow that could potentially enter the mammalian food chain.

The role of prescribed veterinary antibiotics entering the river in the establishment and maintenance of such populations is not known. In the US it has been suggested that antibiotics used in farming and aquaculture have become widely disseminated in waterways and sewage systems, resulting in multidrug-resistant organisms.

Our investigations are continuing with the aims of determining the levels of antibiotic resistant introduced and indigenous microorganisms in the Barrow, and of identifying possible hotspots for plasmid transfer in the water system.