Fig. 4. Biofilms formed from four different sputum samples (I–IV) with enlarged images showing the different bacterial shapes found.

Biofilms were stained with a LIVE/DEAD BacLight Bacterial Viability Kit (a and b) and with a Gram Stain Kit (c and d), which stains Gram-negative bacteria blue and Gram-positive bacteria green. Scale bar represents 20 μm. The images shown are representative of one biofilm formed per each sputa, that was repeated at least two times, yielding the same results.