TABLE 2.

Effect of a ΔtolC deletion and the efflux pump inhibitor, PAβN, on the minimal inhibitor concentration of amotosalen and other psoralens in E. coli K-12^a

Antimicrobial	wt	ΔtolC	wt + PAβN	ΔtolC PAβN
Amotosalen	128	2	32	4
8-MOP	>256	`32	128	32
AMT	64	8	16	8
CLIP	64	2	4	2
MINP	16	2	N.D.	N.D.
EtBrP	512	16	N.D.	N.D.
FAP	>128	2	>128	0.5
CHLP	8	2	4	2
APRN	4	4	8	4
GENN	0.5	0.25	0.5	0.5
MERN	0.125	0.25	N.D.	N.D.
RIFN	4	4	1	1

Escherichia coli Keio wild type (wt) strain and isogenic ΔtolC mutant, that cannot produce functional RND (resistance-nodulation-division) efflux transporters due to the absence of the required TolC outer membrane component, were used for analysis. Modal MIC (MIC) was determined from three technical replicates and are representative of at least two separate experiments, listed in μM for amotosalen and μg/mL for other antibiotics. PAβN = phenylalanine-arginine β-naphthylamide at 18 μM (6.75 μg/mL).

^a8-MOP, 8-methoxypsoralen; AMT, 4’-aminomethyltrioxsalen hydrochloride; CLI, clindamycin; MIN, minocycline; EtBr, ethidium bromide; FA, fusidic acid; CHL, chloramphenicol; APR, apramycin; GEN, gentamicin; MER, meropenem; RIF, rifampin; Superscripts following drug names; Superscript P, positive control; Superscript N, negative control; N.D., not done.