Lowest FBC indices for combinations of biocides and metals tested against P. aeruginosa ATCC 15442 biofilms during high-throughput screening to determine synergy (using CBDs)a

MetalExposure timebFBC index with biocidec
PolycideStabrom 90970% (wt/vol) isopropanolVirox
Ag+5 minND0.021.04.0
30 min0.360.04ND0.53
24 h1.0ND0.150.14
Cu2+5 min1.25ND2.02.0
30 min0.03ND0.720.51
24 h0.060.671.00.08
Al3+5 min0.5ND0.52ND
30 min0.24ND0.520.52
24 hND1.72.00.08
SeO32−5 min2.0ND1.02.0
30 min0.130.050.530.53
24 h0.531.30.510.03
Zn2+5 minND1.11.11.0
30 minND0.5220.52
24 h0.6251.250.160.14
  • a Note that these assays were performed using a high-throughput screening method that judges killing qualitatively. Incomplete killing of microbial populations may still occur synergistically with short exposure times, but this is not detected by the high-throughput method employed here.

  • b Susceptibility testing was performed in ddH2O for exposure times of 5 and 30 min, whereas 10% TSB-0.9% NaCl was used for 24-h exposures.

  • c ND, results could not be determined from the concentration ranges examined experimentally, i.e., the agents did not effectively kill the biofilms. Data shown in bold denote a synergistic interaction, as defined by the criteria outlined in Materials and Methods.