Table 3.

Criteria of interpretation of biofilm production

Biofilm production	average optical density (OD)
no biofilm producer	≤ ODc
weak biofilm producer	ODc < ~ ≤ 2 × ODc
moderate biofilm producer	2 × ODc < ~ ≤ 4 × ODc
strong biofilm producer	> 4 × ODc

Note: optical density cut-off value (ODc) = average OD of negative control + 3 × SD of negative control.