Fig. 1

The effect of priming agents on M. marinum loads in adult zebrafish. (A) Outline of the study. Adult wild-type zebrafish were primed with 0.5×10⁷-1×10⁷ colony-forming units (cfu) per fish of heat-killed bacteria or with other priming agents (13.5 µg per fish, except MDP 4.5 µg) 1 or 7 days prior to M. marinum infection (−1/7 day) with an i.p. injection. Sterile 1× PBS was used as an injection control. The following day (0 day), a low dose of M. marinum was injected i.p. into the zebrafish. Internal organs were collected either 2, 4 or 7 weeks post infection (wpi), DNA was extracted and the bacterial counts were measured with M. marinum-specific qPCR. (B) Priming with heat-killed L. monocytogenes (HKLm) reduces mycobacterial loads at 7 wpi. Zebrafish were primed with either PBS (n=8), heat-killed M. marinum (HKMm; n=9), HKLm (n=10), heat-killed S. iniae (HKSi; n=8), heat-killed E. coli (KHEc; n=9), lipopolysaccharide (LPS; n=8), paclitaxel (n=5), muramyl dipeptide (MDP; n=9) or zymosan (n=10) 1 day prior to M. marinum infection (16±4 cfu). Organs were collected at 7 wpi. Priming with HKLm led to a bigger decrease in the mycobacterial loads in adult zebrafish compared to other tested priming agents. Paclitaxel increased the mycobacterial loads in adult zebrafish. Medians are shown in the figure. (C) Priming with HKLm 1 day prior to M. marinum infection increases the frequency of clearance. The fold change in the percentage of fish that were able to clear the M. marinum infection was higher in the group that was primed with HKLm 1 day prior (3.7-fold; PBS: n=12, HKLm: n=13) to infection compared to group that was primed 7 days (2.3-fold; PBS: n=12, HKLm: n=12) before the infection.