Table 1.

System used to grade biofilm formation

Biofilm coverage	Biofilm density	Biofilm thickness scale	Biofilm grade
Determined at 100× to 1000× mag	Determined at 10,000× to 30,000× mag	Determined at 10,000× to 50,000× mag	(coverage + density + thickness)
0 no biofilm 1 scarce (<  10% coverage) 2 clusters (10–70% coverage) 3 confluent (>  70% coverage)	0 no biofilm 1 low/very porous 2 intermediate 3 high/compact	0 no biofilm 1 thin (0.1–1.0 mm) 2 medium (1.1–7 mm) 3 thick (> 7 mm)	0 no biofilm 1–3 low grade 4–6 medium grade 7–9 high grade

The biofilm grade was calculated by adding together the scores for biofilm coverage, density, and thickness. Mag magnification