Ds ir1 camera

Overall, 1.5 × 10⁵ Vero E6 cells were seeded in a eight-well chamber (LabTek™, Nunc) and infected with WT-VSV, SARS-CoV-2, or rVSV-ΔG-spike for 24 h. Cells were then fixed with 3% paraformaldehyde (PFA) in PBS for 20 min and permeabilized with 0.5% Triton X-100 for 2 min. The fixed cells were blocked with PBS containing 2% FBS and stained with either hyperimmune rabbit serum from intravenous SARS-CoV-2 infected rabbits diluted 1:200 (in-house preparation), naive or vaccinated hamster sera diluted 1:200, or COVID-19 convalescent human sera diluted 1:200 for 1 h. After washing with PBS, cells were incubated with either Alexa Fluor 488 conjugated goat anti-rabbit at a dilution of 1:200 (Sigma, Israel, Cat# F6005), Alexa Fluor 488 conjugated goat anti-hamster at a dilution of 1:100 (Jackson, Cat# 107-545-142), or Alexa Fluor 488 conjugated goat anti-human at a dilution of 1:200 (Sigma, Cat# F0132, lot SLBR4951V). Nuclei were visualized by 4′,6-diamidino-2-phenylindole (DAPI). Images were acquired by an Axioskop (Zeiss) equipped with a DS-iR1 camera and NIS-elements software (Nikon).

The IFA assay allowed the visualization of the bacteria in different matrixes. A total of 2 µL of inoculated BC with or without supplements was applied onto slides, air dried and fixed in 10% formalin for 30 min. An Alexa 488-conjugated anti-Y. pestis polyclonal antibody (5 µL) [45 (link)] was applied on the spots and incubated at 37 °C for 30 min. After washing with tap water, the spots were visualized by a fluorescent microscope equipped with a green filter (excitation: 475 nm/emission: 530 nm). The bacteria were visualized in × 400 magnification using an Axioskop (Zeiss Thornwood, Thornwood, NY, USA) and a DS-iR1 camera (Nikon, Melville, NY, USA). The images were taken using NIS-elements software (Nikon, Melville, NY, USA).