TABLE 3.

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

Metal	Exposure timeb	FBC index with biocidec
		Polycide	Stabrom 909	70% (wt/vol) isopropanol	Virox
Ag+	5 min	ND	0.02	1.0	4.0
	30 min	0.36	0.04	ND	0.53
	24 h	1.0	ND	0.15	0.14
Cu2+	5 min	1.25	ND	2.0	2.0
	30 min	0.03	ND	0.72	0.51
	24 h	0.06	0.67	1.0	0.08
Al3+	5 min	0.5	ND	0.52	ND
	30 min	0.24	ND	0.52	0.52
	24 h	ND	1.7	2.0	0.08
SeO32−	5 min	2.0	ND	1.0	2.0
	30 min	0.13	0.05	0.53	0.53
	24 h	0.53	1.3	0.51	0.03
Zn2+	5 min	ND	1.1	1.1	1.0
	30 min	ND	0.52	2	0.52
	24 h	0.625	1.25	0.16	0.14

^aNote 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.

^bSusceptibility 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.

^cND, 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.