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Development of a presence / absence test for detection of salmonella in wastewater sludge

Hu, Catherine (1994) Development of a presence / absence test for detection of salmonella in wastewater sludge. Honours thesis, Murdoch University.

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Abstract

Issues of wastewater sludge disposal confront communities throughout the world. One of the most economically and environmentally feasible options for sludge disposal is re-use as an agricultural and horticultural soil amendment. However, re-use of sludge poses a potential risk to public health due to the possibilities for pathogen transmission. Several countries have developed regulations designed to limit potential health risks and Australia is in the process of formulating its own sludge management guidelines.

One pathogen of concern in wastewater sludge is Salmonella. Sludge management guidelines specify acceptable levels of Salmonella in sludge destined for re-use. However, no standard method exists for detection of Salmonella in wastewater sludge. This project aimed to determine appropriate methods for detecting the presence or absence of Salmonella in Australian sludges.

Four experiments were conducted. The first of these was designed to determine the most suitable culture media for analysis of raw, digested, dewatered and composted sludge and was based on a comparison of media recommended in the USA and in Australia. Rappaport-Vassiliadis broth (RV) and xylose lysine deoxycholate agar (XLD) were found to be the most efficient media for isolating Salmonella from raw and digested sludge. Dulcitol selenite enrichment (DSE) was the most efficient enrichment for composted sludge, and XLD was again determined to be the most efficient plating medium. Optimal media could not be determined for dewatered sludge.

The second experiment assessed the need for pre-enrichment of raw sludge samples. Pre-enrichment did not improve Salmonella detection. The third experiment determined the influence of the amount of sludge analysed on detection of Salmonella. A greater number of positive samples was detected when a 50 g sample was analysed as five 10 g subsamples than when it was not divided into subsamples, although the difference was not statistically significant. The final experiment evaluated the applicability of a commercial ELISA kit to use with sludge. The sensitivity of the assay was such that it was deemed unsuitable for monitoring the presence of Salmonella in sludge on a routine basis.

The final recommended protocol for detection of Salmonella in wastewater sludge was as follows:
1) pre-enrichment of samples,
2) enrichment for 48 h in RV and DSE for raw and digested sludge or tetrathionate broth, DSE and strontium chloride B broth for composted sludge,
3) subculture on XLD and bismuth sulphite agar after 24 and 48h enrichment.

This method was not completely satisfactory and this project highlighted the need for improvement of culture methods as well as development of alternative procedures.

Publication Type: Thesis (Honours)
Murdoch Affiliation: School of Biological and Environmental Sciences
Notes: A digital copy of this thesis is not available. Your library can request a copy from Murdoch University Library via Document Delivery. A fee applies to this service.
Supervisor: Ho, Goen and Gibbs, Robyn
URI: http://researchrepository.murdoch.edu.au/id/eprint/38370
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