Periodic Reporting for period 1 - ACtIVAtE (The virulence potential of human pathogens: how Acinetobacter baumannii survives Acanthamoeba castellanii predation)
Periodo di rendicontazione: 2018-01-01 al 2019-12-31
In this context, we wanted to first determine if the few classical reference strains of A. baumannii available represent good bacterial models to study the current and modern multidrug clinical isolates. Then, based on our phenotypic observations, we generate an experimental strategy to work on the capsule production. We could also study this phenomenon using a new host-pathogen interaction based on the phagocytic pressure exerted by the amoeba called Acanthamoeba castellanii. The aim being to develop a new infection model to study common resistance mechanism, shared by the majority of the current and modern clinical isolates. A better understanding of the resistance mechanisms is important for the development of further antimicrobial strategies.Beside this fundamental part of the project, we wanted to follow a more applied strategy, and also screened a compounds library to find new antibiotics against multidrug-resistant A. baumannii bacteria.
As we could show that A. baumannii strains are very heterogeneous, we generated a collection of A. baumannii isolates, including reference and current multidrug-resistant clinical isolates. We have now about 250 strains, and we obtain the whole genome sequencing of 48 of them.This allows us to know if the phenotype and new antimicrobial are specific of a few isolates or if they target the majority of the current clinical isolates.
We have developed a new method to assess the capsule production levels of each isolate, and did a proof-of-concept experiment using Transmission Electron Microscopy coupled with capsule labeling to validate our approach.
We showed a high heterogeneity amongst current clinical isolates in term of capsule production and virulence levels. Thus, former reference strains commonly used worldwide do not represent the whole heterogeneity observed for the current clinical isolates. This is the reason why we are working with dozens of isolates at the same time.
We implemented the amoeba Acanthamoeba castellannii as a new infection model as show that upon phagocytic pressure, the majority of the current clinical isolates become hyper-mucoid and resistant to phagocytic cells. This is a common trait shared by the majority of the isolates of our collection.
We also screened a small to medium library of compounds and found a new antimicrobial against multidrug-resistant A. baumannii bacteria. This compound is currently under characterization.
The fact that the reference strains do not reflect the whole diversity of modern clinical isolates is important and deserved to be taken into account to further study A. baumannii worldwide.
We can now use the amoeba Acanthamoeba castellanii as a new validated infection model to screen for anti-resistance factors, impairing the hyper-production of the bacterial capsule used to resist phagocytic cells