Wadhawan, A. | bioRxiv Science

bioRxiv2022

E. faecalis acquires resistance to antimicrobials and insect immunity via common mechanisms

Enterococcus faecalis is a normal member of the gut microbiota and an opportunistic pathogen of many animals, including mammals, birds, and insects. It is a common cause of nosocomial infections, and is particularly troublesome due to extensive intrinsic and acquired antimicrobial resistance. Using experimental evolution, we generated Drosophila-adapted E. faecalis strains, which exhibited immune resistance, resulting in increased in vivo growth and virulence. Resistance was characterised by mutations in bacterial pathways responsive to cell envelope stress. Drosophila-adapted strains exhibited changes in sensitivity to relevant antimicrobials, including daptomycin and vancomycin. Evolved daptomycin-resistant strains harboured mutations in the same signalling systems, with some strains showing increased virulence similar to Drosophila-adapted strains. Our results show that common mechanisms provide a route to resistance to both antimicrobials and host immunity in E. faecalis and demonstrate that the selection and emergence of antibiotic resistance in vivo does not require antibiotic exposure. One sentence summaryHost interaction can promote antimicrobial resistance and antimicrobial treatment can promote virulence in E. faecalis.

microbiology↗

bioRxiv2020

EslB is required for cell wall Integrity and cell division in Listeria monocytogenes

Lysozyme is an important component of the innate immune system. It functions by hydrolysing the peptidoglycan (PG) layer of bacteria. The human pathogen Listeria monocytogenes is intrinsically lysozyme resistant. The peptidoglycan N-deacetylase PgdA and O-acetyltransferase OatA are two known factors contributing to its lysozyme resistance. Furthermore, it was shown that the absence of components of an ABC transporter, here referred to as EslABC, leads to reduced lysozyme resistance. How its activity is linked to lysozyme resistance is still unknown. To investigate this further, a strain with a deletion in eslB, coding for a membrane component of the ABC transporter, was constructed in L. monocytogenes strain 10403S. The eslB mutant showed a 40-fold reduction in the minimal inhibitory concentration to lysozyme. Analysis of the PG structure revealed that the eslB mutant produced PG with reduced levels of O-acetylation. Using growth and autolysis assays, we show that the absence of EslB manifests in a growth defect in media containing high concentrations of sugars and increased endogenous cell lysis. A thinner PG layer produced by the eslB mutant under these growth conditions might explain these phenotypes. Furthermore, the eslB mutant had a noticeable cell division defect and formed elongated cells. Microscopy analysis revealed that an early cell division protein still localized in the eslB mutant indicating that a downstream process is perturbed. Based on our results, we hypothesize that EslB affects the biosynthesis and modification of the cell wall in L. monocytogenes and is thus important for the maintenance of cell wall integrity. IMPORTANCEThe ABC transporter EslABC is associated with the intrinsic lysozyme resistance of Listeria monocytogenes. However, the exact role of the transporter in this process and in the physiology of L. monocytogenes is unknown. Using different assays to characterize an eslB deletion strain, we found that the absence of EslB not only affects lysozyme resistance, but also endogenous cell lysis, cell wall biosynthesis, cell division and the ability of the bacterium to grow in media containing high concentrations of sugars. Our results indicate that EslB is by a yet unknown mechanism an important determinant for cell wall integrity in L. monocytogenes.

microbiology↗