Tenebrio molitor as a model system to study Staphylococcus spp virulence and horizontal gene transfer.

Invertebrates can provide a valuable alternative to traditional vertebrate animal models for studying bacterial and fungal infections. This study aimed to establish the larvae of the coleoptera Tenebrio molitor (mealworm) as an in vivo model for evaluating virulence and horizontal gene transfer between Staphylococcus spp. After identifying the best conditions for rearing T. molitor, larvae were infected with different Staphylococcus species, resulting in dose-dependent killing curves. All species tested killed the insects at higher doses, with S. nepalensis and S. aureus being the most and least virulent, respectively. However, only S. nepalensis was able to kill more than 50% of larvae 72 h post-infection at a low amount of 105 CFU. Staphylococcus infection also stimulated an increase in the concentration of hemocytes present in the hemolymph, which was proportional to the virulence. To investigate T. molitor's suitability as an in vivo model for plasmid transfer studies, we used S. aureus strains as donor and recipient of a plasmid containing the gentamicin resistance gene aac(6')-aph(2″). By inoculating larvae with non-lethal doses of each, we observed conjugation, and obtained transconjugant colonies with a frequency of 1.6 × 10-5 per donor cell. This study demonstrates the potential of T. molitor larvae as a reliable and cost-effective model for analyzing the virulence of Staphylococcus and, for the first time, an optimal environment for the plasmid transfer between S. aureus carrying antimicrobial resistance genes.

Fire Ant Venom Alkaloids Inhibit Biofilm Formation.

Biofilm formation on exposed surfaces is a serious issue for the food industry and medical health facilities. There are many proposed strategies to delay, reduce, or even eliminate biofilm formation on surfaces. The present study focuses on the applicability of fire ant venom alkaloids (aka 'solenopsins', from Solenopsis invicta) tested on polystyrene and stainless steel surfaces relative to the adhesion and biofilm-formation by the bacterium Pseudomonas fluorescens. Conditioning with solenopsins demonstrates significant reduction of bacterial adhesion. Inhibition rates were 62.7% on polystyrene and 59.0% on stainless steel surfaces. In addition, solenopsins drastically reduced cell populations already growing on conditioned surfaces. Contrary to assumptions by previous authors, solenopsins tested negative for amphipathic properties, thus understanding the mechanisms behind the observed effects still relies on further investigation.

The complete mitochondrial genome of the subsocial cockroach Nauphoeta cinerea and phylogenomic analyses of Blattodea mitogenomes suggest reclassification of superfamilies.

The genome of the subsocial cockroach Nauphoeta cinerea was partially sequenced in one-twelfth of an Illumina HiSeq lane. The mitochondrial genome was assembled using MIRA software, yielding a circular molecule of 15,923 bp in length and deposited in GenBank under the accession number KY212743. As expected, the mitogenome contained 13 protein-coding genes, 22 transfer tRNAs and 2 ribosomal RNAs. The molecule was assembled using 35,163 sequencing reads of 120 bp each, resulting in ∼286.9× coverage of uniformly distributed reads along the genome. All the 6 complete mitochondrial genomes available for the roaches from the superfamily Blaberoidea were downloaded and compared with the mitogenome of N. cinerea. We also downloaded complete mitochondrial genomes from the superfamily Blattoidea, including 6 mitochondrial genomes of Termitoidae, 2 mitogenomes of Cryptocercoidae and 3 from Blattoidae. A supermatrix dataset presenting the concatenated alignment of all mitochondrial genes was used as input for a maximum likelihood phylogeny. The phylogenomic tree obtained was consistent for most clades, with a relevant exception in the position of the Corydioidea species E. sinensis. Mitochondrial gene information suggests that superfamily Corydioidea should be classified as a clade inside Blattoidea. Nuclear markers and other Corydioidea mitogenomes should be studied to confirm the evolutionary relationships of Blattodea superfamilies.