Evaluation of bacterial intracellular internalization and persistence
We previously demonstrated the power of Imaging Flow Cytometry (IFC) to precisely estimate the percentage of osteoblasts infected with S. aureus strains in a sample of 10,000 MG-63 cells. Here we report the internalization rate, expressed as percentage of internalization after 3h of infection and the persistence rate after 24h of infection (figures 1 and 2).
At 3h p.i., ATCC12598 internalized in 70 ±17.04% of MG-63 cells, a slightly lower ability to internalize was found for clone ST239-III (50.24±2.26%), while ST228-I showed the lowest internalization rate, accounting for 29.8±2.31% (p=0.015). The lower ability to internalize of the ST228 strain was also evident comparing it to ST239 (p=0.0004) (Figure 1). Persistence inside cells was measured after 24h of incubation: 49±1.96% of ATCC12598 bacterial cells persisted inside MG-63 cells; the same ability to persist was found in clone ST239-III (45.2±6.2%), while ST228-I showed a decreased rate of persistence, 20.7±1.80% (p<0.0001). The lower ability to persist of ST228 was also evident comparing it to ST239 (p=0.0028) (Figure 2).