Canine faeces: the microbiology of an environmental health problem

The overall aim of the research work reported in this Thesis was to study a variety of aspects of dog faeces in relation to public health, their fertilizer potential and possibility that such faeces might be remediated using larvae, ultimately to provide a source of biodiesel. The results can be summarized as follows:
1) Dog faeces were shown to be source of pathogenic bacteria, notably Escherichia. coli and Salmonella. These bacteria were shown to be transferred to the soil of a local playing field by direct, in situ, transfer from dog faeces undergoing weathering. E. coli and Salmonella enterica were isolated from all four sites while no such isolates were obtained from the fifth location which was uncontaminated with dog faeces
2) It was shown here that “common or garden” slugs can transfer potentially pathogenic bacteria from dog faeces to lettuce.
3) The feeding of Black Soldier Fly Larvae on faeces led to a statistically significant increase in the number of bacteria inside the BSFL gut and the same trend was seen in relation to dog faeces fed Fruit Beetle Larvae. This trend of increasing bacterial numbers in larvae fed on dog faeces is particularly worrying in relation to the potential feeding of these larvae to animals- post exposure to faeces.
4) Dog faeces were shown to have potential inherent fertilizer content; the nutrients present being released over a time period mimicking the natural weathering of dog faeces in the environment.
5) As a generalization, the addition of both types of larvae to dog faeces significantly reduced the concentration of indigenous plant nutrients over the entire four week incubation period; exceptions to this were nitrate and phosphate concentrations in BSFL treated faeces, where significant increases were seen at week 4 and 3 respectively and in faeces treated with FBL, where ammonium concentrations were significantly increased at weeks 2-4, and phosphate at week 4. While the addition of both larvae therefore
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initially decreased levels of indigenous plant nutrients there was a trend in some of the nutrients to increase the longer the incubation went on. This suggests that perhaps a longer term exposure of dog faeces to the two larvae might have lead to increase in ammonium, nitrate, sulphate and phosphate concentrations. The addition of ammonium, elemental sulphur an insoluble phosphate to dog faeces which had been modified by the two larvae led to significant increases in nitrate, sulphate and plant-available phosphate, results which shows that that dog faeces contains the indigenous microflora required for the transformation of these amendments (which simulate fertilizer addition). The results suggest the possibility that larval modified dog faeces could be used as compost additive fertilizer, or perhaps even be used as an agricultural soil fertilizer.
6) The potential for using fly larvae for the bioremediation of dog faeces was investigated. Black Soldier Fly (BSFL) and Fruit Beetle (FBL) Fly larvae were shown to dramatically improve the physical nature of canine faeces, even after only a short exposure period, giving a bioremediated product which is markedly improved in terms of texture, reduced odour and overall reduced offensiveness. The bioremediated dog faeces product was also found to be suitable as potting compost when “diluted” with proprietary potting compost.
7) The haemolymph and total body extracts of BSFL and FBL were shown to be antibacterial.
8) The potential for using dog faeces and dog faeces which had been treated with BSFL and FB as a source of biodiesel was determined. It was shown that potential biodiesel precursors) (mainly fatty acids) were present both in the raw dog faeces and in faeces which were treated with the two different larvae.
9) The number of bacteria present in dog faeces disposed of in plastic bags dramatically increased over exposure to the UK summer, when temperatures were recorded between 10-270C.