Streptococcus iniae has emerged as a leading pathogen of intensive finfish aquaculture operations worldwide, though an understanding of its virulence mechanisms and effective therapeutic strategies are lacking. The roles of four putative S. iniae virulence factors: Streptolysin S (SLS), capsular polysaccharide, M-like protein, and C5a peptidase, were investigated through targeted allelic exchange mutagenesis coupled with in vitro and in vivo models of bacterial pathogenesis. Highly attenuated mutants were then evaluated as live vaccine candidates. SLS is a potent, broad-spectrum, secreted cytolysin first characterized in group A Streptococcus. Allelic replacement of the sagA gene in the S. iniae SLS operon generated a mutant that was significantly less cytotoxic to a variety of fish cell types. Reduced cytotoxicity in vivo towards brain cells in particular may account for the mutant's high level of attenuation in a hybrid striped bass (HSB) challenge model. Capsular polysaccharide serves as a protective extracellular coating in many pathogenic streptococci. Targeted allelic replacement of the S. iniae cpsD capsule biosynthesis gene generated a mutant that was completely attenuated in HSB even at a dose 1,000X the lethal WT dose, likely due to its high susceptibility to phagocytic clearance, as demonstrated with a fish macrophage cell line. Through pyrosequencing of the S. iniae genome we identified gene homologues to classical surface-anchored streptococcal virulence factors: M-like protein (simA) and C5a peptidase (scpI). Analysis of the corresponding allelic mutants in HSB and zebrafish revealed that only simA contributes significantly to S. iniae pathogenesis. In vitro cell-based analyses indicated that SiMA, like other M family proteins, contributes to adherence and invasion and provides resistance to phagocytic killing. The immunoprotective capacity of the [Delta]sagA, [Delta]cpsD, and [Delta]simA attenuated mutant strains was compared with a killed bacterin vaccine in HSB through injection and immersion delivery. The [Delta]cpsD, [Delta]simA, and bacterin vaccines met vaccination safety criteria and were effective in generating high levels of immune protection through injection, however the [Delta]simA mutant was the only vaccine candidate to provide 100% protection through both injection and immersion delivery. Characterization of these four genes has contributed significantly to our understanding of S. iniae virulence mechanisms and demonstrates the application of pathogenesis research to vaccine development

Rezafungin is a long-acting, intravenously administered echinocandin for the treatment of candidemia and invasive candidiasis (IC). Non-inferiority of rezafungin vs caspofungin for the treatment of adults with candidemia and/or IC was demonstrated in the Phase 3 ReSTORE study based on the primary endpoints of day 14 global cure and 30-day all-cause mortality. Here, an analysis of ReSTORE data evaluating efficacy outcomes by baseline Candida species is described. Susceptibility testing was performed for Candida species using the Clinical and Laboratory Standards Institute reference broth microdilution method. There were 93 patients in the modified intent-to-treat population who received rezafungin; 94 received caspofungin. Baseline Candida species distribution was similar in the two treatment groups; C. albicans (occurring in 41.9% and 42.6% of patients in the rezafungin and caspofungin groups, respectively), C. glabrata (25.8% and 26.6%), and C. tropicalis (21.5% and 18.1%) were the most common pathogens. Rates of global cure and mycological eradication at day 14 and day 30 all-cause mortality by Candida species were comparable in the rezafungin and caspofungin treatment groups and did not appear to be impacted by minimal inhibitory concentration (MIC) values for either rezafungin or caspofungin. Two patients had baseline isolates with non-susceptible MIC values (both in the rezafungin group: one non-susceptible to rezafungin and one to caspofungin, classified as intermediate); both were candidemia-only patients in whom rezafungin treatment was successful based on the day 30 all-cause mortality endpoint. This analysis of ReSTORE demonstrated the efficacy of rezafungin for candidemia and IC in patients infected with a variety of Candida species.