Probiotic Enterococcus mundtii Isolate Protects the Model Insect Tribolium castaneum against Bacillus thuringiensis

Thorben Grau,Andreas Vilcinskas,Gerrit Joop

doi:10.3389/fmicb.2017.01261

Abstract

Enterococcus mundtii strains isolated from the larval feces of the Mediterranean flour moth Ephestia kuehniella show antimicrobial activity against a broad spectrum of Gram-positive and Gram-negative bacteria. The in vitro probiotic characterization of one isolate revealed a high auto-aggregation score, a hydrophilic cell surface, tolerance for low pH, no hemolytic activity, and susceptibility to all tested antibiotics. We used the red flour beetle Tribolium castaneum, an established model organism, for the in vivo characterization of one probiotic E. mundtii isolate from E. kuehniella larvae. Tribolium castaneum larvae were fed orally with the probiotic isolate or the corresponding supernatant and then infected with either the entomopathogen Bacillus thuringiensis or Pseudomonas entomophila. Larvae exposed to the isolate or the supernatant showed increased survival following infection with B. thuringiensis but not P. entomophila. Heat treatment or treatment with proteinase K reduced the probiotic effect of the supernatant. However, the increased resistance attracts a fitness penalty manifested as a shorter lifespan and reduced fertility. T. castaneum has, pending on further research, the potential as an alternative model for the pre-screening of probiotics.

Highlights

All animals are associated with a diverse microbial community that promotes their health (McFallNgai et al, 2013; Sommer and Bäckhed, 2013)
For the further characterization of the antimicrobial compounds, we focused on the cell free supernatant (CFS) of E. mundtii isolate 1 using the agar well-diffusion assay (AWDA) (Table 2) because this isolate showed the best antimicrobial profile in the agar spot on lawn assay
colony-forming units (CFUs) start CFU pH 2 after 3 h CFU pH 3 after 3 h CFU pH 4 after 3 h Results are in log CFU ml-1 with SD

Summary

Introduction

All animals are associated with a diverse microbial community that promotes their health (McFallNgai et al, 2013; Sommer and Bäckhed, 2013). Probiotics are defined as “live microorganisms, that when administered in adequate amounts, confer a health benefit on the host” (Hill et al, 2014). Probiotics have many applications, including the optimization of growth and survival in animal species used for aquaculture and agriculture (Chaucheyras-Durand and Durand, 2009; Pandiyan et al, 2013), and the prevention or treatment of gastrointestinal tract infections in humans (Deshpande et al, 2010; Kotzampassi and Giamarellos-Bourboulis, 2012). Probiotics have several mechanisms of action, including the production of antimicrobial compounds, the inhibition of virulence genes, the enhancing of epithelial barrier functions or the stimulation of the host. The best-studied microorganisms with probiotic activity are the bifidobacteria, lactobacilli, enterococci and yeasts (Varankovich et al, 2015). Enterococci produce organic acids, hydrogen peroxide and up to four different classes of enterocins (Franz et al, 2007), supporting the call for a legislative framework for probiotics (Papadimitriou et al, 2015)

Methods

Results

Conclusion