Growth of viruses and rickettsiae in the developing chick embryo

Plant hairy roots enable high throughput identification of antimicrobials against Candidatus Liberibacter spp

A major bottleneck in identifying therapies to control citrus greening and other devastating plant diseases caused by fastidious pathogens is our inability to culture the pathogens in defined media or axenic cultures. As such, conventional approaches for antimicrobial evaluation (genetic or chemical) rely on time-consuming, low-throughput and inherently variable whole-plant assays. Here, we report that plant hairy roots support the growth of fastidious pathogens like Candidatus Liberibacter spp., the presumptive causal agents of citrus greening, potato zebra chip and tomato vein greening diseases. Importantly, we leverage the microbial hairy roots for rapid, reproducible efficacy screening of multiple therapies. We identify six antimicrobial peptides, two plant immune regulators and eight chemicals which inhibit Candidatus Liberibacter spp. in plant tissues. The antimicrobials, either singly or in combination, can be used as near- and long-term therapies to control citrus greening, potato zebra chip and tomato vein greening diseases.

Non-specific resistance to experimental cholera in embryonated eggs

It has been confirmed that 11- and 13-day-old chick embryos are susceptible to lethal infection with minute inocula of V. cholerae, while 15-day-old embryos are relatively resistant. Twenty strains of E. coli were found to vary in their capacity to kill chick embryos, without relationship to their human enteropathogenicity. Prior infection of 13-day-old embryonated eggs with E. coli strains selected for low embryo virulence had a marked protective effect against superinfection with V. cholerae. This effect was duplicated by pretreatment of embryos with killed E. coli cells or endotoxin preparations but not with a suspension of killed cells of a Gram-positive species. Preparatory E. coli infection induces a phase of vibriostasis in the 13-day-old egg which may be sufficient to tide the embryo over into the phase of relative insusceptibility associated with age. Younger embryos exhibit only a lag in death under similar conditions. The chick embryo is presented as a potentially valuable tool for the study of combined infections and of the mechanisms of natural resistance.