Next the activity of 1 -5 against biofilms of C. albicans (SC5314) and polymicrobial biofilms of both species were established using the same XTT metabolic assay in line with previous work (Figure ). Against biofilms of C. albicans (SC5314), 1 and 3 were found to exhibit the greatest antibiofilm activity, competitive with 4 and 5 even at higher concentrations, as shown in Figure . Again, there is a distinctive decrease in antibiofilm activity with decreasing SSA concentration, as previously observed with P. aeruginosa (PAO1) biofilms (Figure ), supporting our previous hypothesis that enhanced adhesion of the SSA to the ECM may result in decreased antibiofilm activity at lower concentrations, causing 4 and 5 to exhibit a lower antibiofilm activity than the control compound TBACl at 0.32 and 0.16 mM. In general, the order of SSA activity against C. albicans (SC5314) biofilms follows the trend: (thio)urea sulfonate SSA (1, 3) > (thio)urea carboxylate SSA (2) > squaramide (4 and 5). This trend is the inverse of the SSA Kdim (Table ), the lower the Kdim the greater the antibiofilm activity. Co-formulations a, b and e which contain combinations of the most active single antibiofilm SSAs at lower concentrations (1, 2 and 3) were subsequently investigated for antibiofilm activity, Figure . Unlike the P. aeruginosa (PAO1) biofilms (Figure ), these co-formulations demonstrated enhanced activity against C. albicans (SC5314) biofilms (Figure ), at 0.08 mM these co-formulations still demonstrate almost complete biofilm inhibition. Again, these results show that the co-formulation of SSAs changes the antibiofilm properties of the individual SSAs, which we hypothesise to be a direct result of SSA co-formulation processes modifying the interactions of the SSA with biological membranes (Tables , Figure ). Finally, the activity of 1 -5 against polymicrobial C. albicans (SC5314) and P. aeruginosa (PAO1) biofilms was examined. Here, the noticeable difference in SSA activity against the heterogenous as opposed to the homogenous biofilms is the decreased activity of 3 at lower concentrations < 0.64 mM, as shown in Figure . We hypothesise that this may be due to the presence of the hydrophobic, planar benzothiazole functionality interacting negatively with the biofilm environment, preventing preferential antimicrobial interactions. However, the antibiofilm activity of 1 and 2 is maintained at lower concentrations (0.16 mM) between ~60-80 %. Again, coformulations a, b and e, containing combinations of the most active antibiofilm SSAs (1, 2 and 3) against this heterogenous biofilm were then investigated for their antibiofilm activity (Figure ). Here the co-formulations of 1 and 2 conserve the antibiofilm activity of the individual SSAs, however, in this instance the co-formulations of 3, which exhibited a lower antimicrobial activity at lower concentrations in comparison to 1 and 2, showed an enhanced antibiofilm activity when co-formulated with 1 and 2, providing evidence of a synergistic relationship between 1 and 3 (b), and 2 and 3 (e) towards increased antibiofilm activity. Interestingly, the minimum concentration of compound required to inhibit 100 % of growth, (minimum inhibitory concentration, MIC) determined for 1 -5 and a, b, e and j against a panel of Gram-positive and Gram-negative bacteria, showed these SSAs and their co-formulations to be more effective against microbes contained in biofilms (Figures and) compared to the planktonic cells (Section S18 ). However, it should be noted that an MIC is a different measure of antimicrobial activity, requiring complete inhibition of growth, while antibiofilm activity in this instance is measuring a percentage inhibition of biofilm formation.