Investigation of EPS matrix and antibiotic resistance in pneumococcal biofilms. 3A Scanning electron microscopy of pneumococcal biofilms on polystyrene by BS69 (a high BFI strain) and BS73 (a low BFI strain) showing cluster morphology and evidence of extracellular matrix. Extracellular material can be seen on higher magnification in both clinical isolates, however more matrix material is visible with BS69 compared with BS73. Areas of extracellular material can be seen tethering S. pneumoniae cells to the surface (arrows). Scale bar = 10 μm and 2 μm. Fig. 3B. Strain variability in EPS distribution of pneumococcal biofilms by different clinical isolates demonstrated by lectin binding. Lectin (green fluorescence) and Syto 59 (red fluorescence) indicate binding of probes to carbohydrate or nucleic acid, respectively. Yellow indicates co-localization of the two probes. Images are maximum projections or reconstructed confocal stacks consisting of a series of x-y sections. Scale bar = 10 μm. Fig. 3C. Pneumococcal biofilms treated with azithromycin. High ranked BFI strains (BS69 and BS72) show large cell clusters still viable with the BacLight LIVE/DEAD stain after 24 hours of antibiotic treatment. Low ranked BFI isolates (BS71 and BS73) on the other hand, show only a few viable attached cells (Scale bar = 8 μm.).