Microbial Population Dynamics in the Hemolymph of Manduca sexta Infected with Xenorhabdus nematophila and the Entomopathogenic Nematode Steinernema carpocapsae

Abstract

cXenorhabdus nematophila engages in a mutualistic association with the nematode Steinernema carpocapsae. The nematode invades and traverses the gut of susceptible insects. X. nematophila is released in the insect blood (hemolymph), where it suppresses host immune responses and functions as a pathogen. X. nematophila produces diverse antimicrobials in laboratory cultures. The natural competitors that X. nematophila encounters in the hemolymph and the role of antimicrobials in interspecies competition in the host are poorly understood. We show that gut microbes translocate into the hemolymph when the nematode penetrates the insect intestine. During natural infection, Staphylococcus saprophyticus was initially present and subsequently disappeared from the hemolymph, while Enterococcus faecalis proliferated. S. saprophyticus was sensitive to X. nematophila antibiotics and was eliminated from the hemolymph when coinjected with X. nematophila. In contrast, E. faecalis was relatively resistant to X. nematophila antibiotics. When injected by itself, E. faecalis persisted (ϳ10 3 CFU/ml), but when coinjected with X. nematophila, it proliferated to ϳ10 9 CFU/ml. Injection of E. faecalis into the insect caused the upregulation of an insect antimicrobial peptide, while the transcript levels were suppressed when E. faecalis was coinjected with X. nematophila. Its relative antibiotic resistance together with suppression of the host immune system by X. nematophila may account for the growth of E. faecalis. At higher injected levels (10 6 CFU/insect), E. faecalis could kill insects, suggesting that it may contribute to virulence in an X. nematophila infection. These findings provide new insights into the competitive events that occur early in infection after S. carpocapsae invades the host hemocoel.

Death Becomes Them: Bacterial Community Dynamics and Stilbene Antibiotic Production in Cadavers of Galleria mellonella Killed by Heterorhabditis and Photorhabdus spp

“…Many early studies noted the presence of non-Photorhabdus or non-Xenorhabdus bacteria within cadavers, at least at low levels (16)(17)(18)(19), and even attributed the occasional lack of nematode development to such toxic contaminants (20)(21)(22)(23)(24)(25). More recently, culture-dependent studies have isolated various non-Photorhabdus or non-Xenorhabdus bacteria from cadavers infected with different EPN species (26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37). In at least some instances, the identified bacteria suggest more than stochastic cadaver contamination: Jackson et al (27) isolated Providencia spp.…”

Histological Observation and Expression Patterns of antimicrobial peptides during Fungal Infection in Musca domestica (Diptera: Muscidae) Larvae

“…Knowledge on how the insect innate immune response fights infection may aid the understanding of the first step in the human host-pathogen interaction (Wang et al 2013;Singh et al 2014;Wu et al 2014;Khalil et al 2015). Many models and techniques of insect infection have been successfully established, including injury, rolling and ingestion methods.…”

“…These methods model the natural infectious process of pathogenic invasion into the epidermis and intestinal tract, which can then cause local infection that may gradually develop into systemic infection (Onfelt et al 2001;Nayduch et al 2013;Wu et al 2014). The injury method mainly used needles to deliver pathogens by piercing the somatic layer or directly injects pathogens into the insect coelom to cause acute infection and rapidly activate the immune response (Matsumoto et al 2012;Singh et al 2014). However, the inevitable mechanical injury caused by this method may affect the experimental results.…”

Role of Secondary Metabolites in Establishment of the Mutualistic Partnership between Xenorhabdus nematophila and the Entomopathogenic Nematode Steinernema carpocapsae

“…The IJs invade soil-dwelling insects through natural openings, such as the mouth or anus, migrate to the midgut, and penetrate the intestine to enter the body cavity (hemocoel) of the insect, where X. nematophila is released, transitioning to its pathogenic phase (4). During the invasion process, insect gut microbiota translocate to the hemocoel, where they may proliferate and compete for resources (7). During early infection of the tobacco horn worm, Manduca sexta, some transient competitors, such as Staphylococcus saprophyticus, are eliminated, while other more persistent microorganisms, such as Enterococcus faecalis, grow in the hemolymph as X. nematophila proliferates to high cell densities (7).…”

“…During the invasion process, insect gut microbiota translocate to the hemocoel, where they may proliferate and compete for resources (7). During early infection of the tobacco horn worm, Manduca sexta, some transient competitors, such as Staphylococcus saprophyticus, are eliminated, while other more persistent microorganisms, such as Enterococcus faecalis, grow in the hemolymph as X. nematophila proliferates to high cell densities (7). S. saprophyticus was shown to be more sensitive to X. nematophila antimicrobials, while E. faecalis was relatively resistant.…”