Candida albicans, the most common human fungal pathogen, is particularly problematic for immunocompromised individuals. The reversible transition of this fungal pathogen to a filamentous form that invades host tissue is important for its virulence. Although different signaling pathways such as a mitogen-activated protein kinase and a protein kinase A cascade are critical for this morphological transition, the function of polarity establishment proteins in this process has not been determined. We examined the role of four different polarity establishment proteins in C. albicans invasive growth and virulence by using strains in which one copy of each gene was deleted and the other copy expressed behind the regulatable promoter MET3. Strikingly, mutants with ectopic expression of either the Rho G-protein Cdc42 or its exchange factor Cdc24 are unable to form invasive hyphal filaments and germ tubes in response to serum or elevated temperature and yet grow normally as a budding yeast. Furthermore, these mutants are avirulent in a mouse model for systemic infection. This function of the Cdc42 GTPase module is not simply a general feature of polarity establishment proteins. Mutants with ectopic expression of the SH3 domain containing protein Bem1 or the Ras-like G-protein Bud1 can grow in an invasive fashion and are virulent in mice, albeit with reduced efficiency. These results indicate that a specific regulation of Cdc24/Cdc42 activity is required for invasive hyphal growth and suggest that these proteins are required for pathogenicity of C. albicans.

This study investigated the potential application of allyl isothiocyanate (AITC) for the disinfection of water by examining the bactericidal effects of this compound against inoculated Escherichia coli in autoclaved, de-chlorinated tap water and against the natural microbiota (heterotrophic plate count bacteria, HPCs) in a surface water. Bacteriostatic trials for AITC demonstrated growth inhibition against E. coli in tryptone soy broth, with AITC concentrations of 47.5, 63.3 and 126.6 mg/l inhibiting growth over two hours of contact time and 505.5 mg/l achieving complete growth inhibition for seven days. These AITC concentrations were then used to assess the bactericidal effect of AITC in water matrices, through which at least a 1.22-log10 reduction of both E. coli and HPCs was achieved in all trials, and up to a maximum of 2.93-log10 reduction of E. coli with 126.6 mg/l of AITC and two hours of contact time. AITC was consistently less effective against the HPCs in the surface water compared to the inoculated E. coli in tap water. Under the conditions that were tested, AITC was unable to reduce the HPC values below 100 CFU/ml, the World Health Organization guideline for safe drinking water, suggesting that AITC should not be used as a potable water disinfectant on its own; however, there may be applications for AITC as a biocide for non-potable water storage or treatment.

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UV disinfection reactors are an effective and economic means to inactivate oocysts of the protozoan parasite Cryptosporidium in drinking water. Cryptosporidiosis outbreaks can occur as a result of filter breakthrough following increased oocyst loading of treatment processes (Bouchier, 1998). Oocysts are resistant to commonly used chlorine-based disinfectants and therefore filter failure can result in outbreaks of cryptosporidiosis (Korich et al., 1990). Low and medium pressure UV disinfection has been demonstrated to be effective at reducing oocyst infectivity at economic UV doses, and hence UV reactors have become increasingly common as drinking water treatments for inactivating oocysts and other waterborne pathogens