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A study of isolation procedures for multiple infections of Salmonella and Arizona in a wild marsupial, the quokka (Setonix brachyurus)
Authors:R P Hart  J B Iveson    S D Bradshaw  T P Speed  
Institution:*Department of Zoology, University of Western Australia, Nedlands 6009, Australia.;?Public Health and Enteric Diseases Unit, State Health Laboratory Services, Queen Elizabeth II Medical Centre, Nedlands 6009, Australia.;?Department of Mathematics, University of Western Australia, Nedlands 6009, Australia
Abstract:Rectal swabs and faeces were used in the regular sampling for salmonellas and Arizonas from a heavily-infected population of a marsupial, the quokka ( Setonix brachyurus ). The media used were strontium selenite A and strontium chloride B enrichment broths, with subculture onto modified bismuth sulphite agar and deoxycholate citrate agar. A study of sampling, enrichment, sub-culture and colony selection procedures produced an optimal scheme giving high yields but consistent with reasonable economy of time and materials. A three-swab sample was taken and inoculated into the two enrichment media, and with each enrichment subjected to three subcultures. The absolute efficiency of this procedure was greater than 80% (and confirmed by a serological method), compared with only 67% for a single swab in a single enrichment. Recovery of some serotypes depended on the media used; e.g. Arizonas could not be recovered satisfactorily from strontium chloride B enrichment. Faeces samples were found to be greatly superior to rectal swabs for detecting salmonellas and arizonas but they were less convenient in field studies. In a comparison of rectal swabs and faeces samples where the actual concentration of salmonellas was known, it was found that the efficiency of rectal swabs approached 100% if there were more than 103 salmonellas/g faeces, but this declined to approximately 50% if there were 102-103 salmonellas/g faeces and only 25% if there were less than 102 salmonellas/g faeces. A new statistical procedure was introduced for comparing the number of isolations from two methods, and this should be of use in similar methodological studies.
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