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A novel Escherichia coli outer membrane protein A (OmpA) was discovered through a proteomic investigation of cell surface proteins. DNA polymorphisms were localized to regions encoding the protein's surface-exposed loops which are known phage receptor sites. Bacteriophage sensitivity testing indicated an association between bacteriophage resistance and isolates having the novel ompA allele.

The occurrence of Cryptosporidium oocysts in feces from a population of wild eastern grey kangaroos inhabiting a protected watershed in Sydney, Australia, was investigated. Over a 2-year period, Cryptosporidium oocysts were detected in 239 of the 3,557 (6.7%) eastern grey kangaroo fecal samples tested by using a combined immunomagnetic separation and flow cytometric technique. The prevalence of Cryptosporidium in this host population was estimated to range from 0.32% to 28.5%, with peaks occurring during the autumn months. Oocyst shedding intensity ranged from below 20 oocysts/g feces to 2.0 x 10(6) oocysts/g feces, and shedding did not appear to be associated with diarrhea. Although morphologically similar to the human-infective Cryptosporidium hominis and the Cryptosporidium parvum "bovine" genotype oocysts, the oocysts isolated from kangaroo feces were identified as the Cryptosporidium "marsupial" genotype I or "marsupial" genotype II. Kangaroos are the predominant large mammal inhabiting Australian watersheds and are potentially a significant source of Cryptosporidium contamination of drinking water reservoirs. However, this host population was predominantly shedding the marsupial-derived genotypes, which to date have been identified only in marsupial host species.

A combined immunomagnetic separation (IMS) and flow cytometry (FC) technique was developed for the sensitive detection of Cryptosporidium in faecal samples. The IMS/FC technique was found to be approximately 50-fold more sensitive than formol-ether concentration, which is commonly used for Cryptosporidium epidemiological investigations. Of 31 faecal samples from captive animals 16 were found to contain Cryptosporidium oocysts when analysed using the IMS/FC compared to four when using formol-ether concentration (FEC). In a wild population of eastern grey kangaroos Macropus giganteus 66.3% of infected animals were shedding <500oocysts/gfaeces when analysed using IMS/FC. This is below the detection limit for the FEC method. The dispersal of Cryptosporidium in host populations is aggregated, with many individuals shedding low numbers of oocysts and few individuals shedding numbers of oocysts sufficiently high to be detected by FEC. This research demonstrates that the prevalence and oocyst shedding intensity of Cryptosporidium in animal populations will be significantly underestimated using standard detection methods.