There is a need for the development of diagnostic and analytical models in experimental infection models. We performed in vivo cell-tracking of S. aureus functionalized in vitro with a hybrid antimicrobial peptide tracer 99mTc-UBI29−41-Cy5, containing both a fluorescent and radioactive moiety. To create an invasive infection in mice, viable 99mTc-UBI29−41-Cy5 functionalized bacteria were inoculated in a thigh muscle. Thereafter, the mice were imaged using SPECT and fluorescence imaging modalities at various intervals for a 28h time period. In addition, biodistribution studies were performed at all intervals for quantitative analysis of the colonization and dissemination of the bacteria.
SPECT and fluorescence imaging in mice revealed clear uptake of the tracer in the thigh muscle localization, decreasing over time from 52%ID/g at 4h to 44%ID/g (15% decrease) at 28h p.i. There was little uptake of the tracer in the urinary bladder only at 2-4h p.i.;. Since viable bacteria S. aureus were cultured in the urine samples obtained from the infected mice at all time-points it seems that this reduction is the result of bacterial dissemination. For the other tissues, no substantial accumulation of radioactivity or fluorescence was noticed.
This non-GMO approach of imaging bacteria allowed us to accurately map the distribution of the labeled bacteria in a non-invasive manner. Given the versatility of the approach we are confident that this will pave the way for the development of diagnostic and analytical options in fundamental and translational research on experimental infection models.