The effect of OMVs on colistin and melittin was evaluated by incubating these molecules with OMVs and recording their mass spectra using MALDI TOF. The OMVs were re-suspended in 10 Mm phosphate buffer to a final concentration of 10 g/mL. In separate experiments, colistin and melittin were added to this suspension to final concentrations of 10 g/mL each. The mass spectrum was recorded at different time intervals after incubating the vials at 37 ◦C. The spectra were recorded by using one L of the reaction mixture and 0.5% -cyano-4-hydroxycinnamic acid (CHCA) in 1:1 acetonitrile and 0.1% trifluoroacetic acid was used as a matrix. The mass spectrometer ab4800 (Applied Biosystems, Foster City, CA,
USA) is equipped with Nd: YAG laser (355 nm), was set at positive ion reflector mode for recording the spectra. The MS/MS spectra of
the peptides and the digested fragments were recorded in collision
induced dissociation (CID) mode using air as collision gas.
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