A model of the transmission of micro-organisms in a public setting and its correlation to pathogen infection risks.

AIM: Gastro-intestinal infections are widespread in the community and have considerable economic consequences. In this study, we followed chains of infection from a public toilet scenario, looking at infection risks by correlating the transmission of bacteria, fungi and viruses to our current knowledge of infectious doses. METHODS AND RESULTS: Transmission of Escherichia coli, Bacillus atrophaeus spores, Candida albicans and bacteriophage MS2 from hands to surfaces was examined in a transmission model, that is toilet brush, door handle to water tap. The load of viable pathogens was significantly reduced during transfer from hands to objects. Nevertheless, it was shown that pathogens were successfully transferred to other people in contagious doses by contact with contaminated surfaces. CONCLUSIONS: Our results suggest that infection risks are mainly dependent on current infectious doses of pathogens. For enteritic viruses or bacteria, for example Norovirus or EHEC, only a few particles or cells are sufficient for infection in public lavatories, thus bearing a high risk of infection for other persons. However, there seems to be only a low probability of becoming infected with pathogens that have a high infectious dose whilst sharing the same bathroom. SIGNIFICANCE AND IMPACT OF THE STUDY: The transmission model for micro-organisms enables a risk assessment of gastro-intestinal infections on the basis of a practical approach.

The novel use of waste animal bone from New Zealand agricultural sources as a feedstock for forming plasma sprayed hydroxyapatite coatings on biomedical implant materials.

This study presents the feasibility of using animal bone-derived hydroxyapatite (HAP) as feedstock powders for plasma spraying. Bovine, cervine and ovine bone from abattoirs was boiled in a pressure cooker to remove blood, fat and adhering meat tissue. The bone was then placed in a muffler furnace, pyrolyzed at approximately 1000 degrees C to remove collagen and resid-ual organics, cooled and subsequently ground to a powder then digested in nitric acid. Sodium hydroxide was added to the digest to reprecipitate the HAP. Ageing of the precipitate followed by filtration, extensive washing and drying produced the white powder used as the feedstock. X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed the powder to be poorly crystalline HAP with low-level carbonate. Out of several batches of the sieved powders, one batch was plasma sprayed to produce adherent HAP coatings; therefore, demonstrating that animal bone-derived HAP powders can be seri-ously considered as a feedstock powder, subject to the powder being processed for the correct rheological characteristics for easy flowing within the plasma spray flow lines. The phase composition of the successful plasma sprayed HAP coatings on both stainless steel and titanium were found by XRD to be mainly HAP with minor contributions from á -tricalcium phosphate, tetra-calcium phosphate and CaO; therefore, demonstrating that feedstock decomposition on its passage through the plasma spray torch was insignificant under the conditions employed. Scanning electron microscopy (SEM) micrographs of the coatings indicated that their morphology featured the classical heterogeneous and splat-like appearance expected of plasma sprayed coatings. Young's modulus and Vicker's microhardness tests conducted on the coatings revealed values in the range, respectively, 22-87 GPa and 166-287 (HV200 ) indicating high strength plasma spray HAP coatings had been produced from the feedstock powder.

The processing and characterization of animal-derived bone to yield materials with biomedical applications. Part II: milled bone powders, reprecipitated hydroxyapatite and the potential uses of these materials.

Further studies on the processing and use of animal-bone-derived calcium phosphate materials in biomedical applications are presented. Bone powders sourced either from the direct crushing and milling of bovine, ovine and cervine bone or after being subjected to defatting and acid digestion/NaOH reprecipitation and sodium hypochlorite hydrogen peroxide treatment of animal bones were characterized using Fourier transform infra-red (FTIR) spectroscopy, 13C solid state magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, atomic absorption (AA) and inductively coupled plasma (ICP) spectrometric techniques. Bone powders were trialled for their potential use as a substrate for phosphine coupling and enzyme immobilization as well as a feedstock powder for plasma spraying on titanium metal substrates. Results indicated that enzyme immobilization by phosphine coupling could be successfully achieved on milled cervine bone with the immobilized enzyme retaining some activity. It was found that the presence of impurities normally carried down with the processing of the bone materials (viz., fat and collagen) played an important role in influencing the adsorbency and reactivity of the powders. Plasma spraying studies using reprecipitated bovine-derived powders produced highly adherent coatings on titanium metal, the composition of which was mostly hydroxyapatite (Ca10(PO4)6(OH)2) with low levels of alpha-tricalcium phosphate (alpha-Ca3(PO4)2) and tetracalcium phosphate (Ca4P2O9) also detected. In general, animal derived calcium phosphate materials constitute a potentially cheaper source of calcium phosphate materials for biomedical applications and make use of a largely under-utilized resource from abattoir wastes.