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In vitro Characterization of Infection Strategies of the Bacterial Pathogen Photorhabdus Open Access

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Bacterial pathogens have evolved fascinating ways of communicating amongst themselves in order to reach their overall goal, which is to eventually use their host’s resources for their own means. They do this through Quorum Sensing, a response system that depends on the population density of bacteria in order to activate chemical signal molecules called auto-inducers that promote bacterial virulence, bioluminescence, antibiotic production and other factors. Our investigation on bacterial cooperation involves the gram-negative pathogenic bacteria Photorhabdus asymbiotica and Photorhabdus luminescens. Through the use of two distinct insect cell lines from Drosophila melanogaster and Spodoptera frugiperda, it was found that these two Photorhabdus bacteria influence the metabolism and survival of these insect cell lines differently. This is due to the toxins and virulence factors that these bacteria produce and inject into the host. In addition, the metabolic rates of both Photorhabdus species are unique in the presence and absence of these distinct insect cells. Bacterial behavior due to quorum sensing for these bacterial species was identified. P. asymbiotica come together to form needle-like structures while P. luminescens link together to form chains at just 3 hours into infection. This behavior is constant until the bacterial population becomes too dense to observe. The decrease of insect cell viability is due to the increased metabolic activity of Photorhabdus asymbiotica and Photorhabdus luminescens. Moreover, quorum sensing is essential for bacteria to regulate the gene expression of certain genes for virulence, metabolism and behavior. This communication becomes an important factor that happens at the beginning of infection, which could contribute to cytotoxicity.

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