Résumé:
The aim of this study is, firstly, to evaluate the method of MALDI-TOF MS for
bacteriological identification in the case of subclinical mastitis in dairy cattle and secondly, to test a
new antivirulent strategy against a bacterial species P. aeruginosa causing respiratory infections in
calves.
The first part consists in identifying 14 bacteria responsible for subclinical mastitis by
MALDI-TOF MS confronted with the 16S rDNA and the housekeeping gene rpoB sequencing
technique. Our results showed high reliability of identification by MALDI-TOF MS at the species
level covering 92.8% of cases (13 isolates) with a score greater than 2. MALDI-TOF MS and
bioinformatic analysis are tools that can substitute the identification by simple sequencing using the
16S and rpoB rDNA genes.
The second part consists of evaluating the efficacy of the enzyme SsoPox-W263I, to prevent
the establishment of virulence in three strains of Pseudomonas aeruginosa isolated from pneumonic
calves, the model strain P. aeruginosa PAO1 and three human strains. For this, we evaluated in
vitro the amount of pyocyanin, the proteolytic activity and the biofilm. In the presence of SsoPox
W263I, we observed a decrease in proteolytic activity and the production of pyocyanin in 100% of
the isolates. Biofilm synthesis decreased in 86% of isolates. The enzyme SsoPox W263I by
inhibition of quorum sensing attenuates the pathogenic power of P. aeruginosa. It can therefore be a
promising alternative to conventional treatments.
