TABLE 1.

FQ efflux systems of gram-positive bacteria^e

Organism(s)	Efflux componenta					Regulatory gene(s)	Expressionb	Substrates	Reference(s)c
	MFP	RND	OEP	MFS	MATE
B. subtilis				Bmr	PmrA	bmrR, mta	wt +, bmr ++d	antibiotics, dyes, lipophilic cations	46
				Blt		bltR, mta	wt −, mutant ++	antibiotics, dyes, lipophilic cations	4
Enterococcus spp.	?	?	?	?	?	?	?	?	34
S. aureus				NorA		norR?, arlRS?	wt +, mutant ++	Antibiotics, dyes, lipophilic cations	20, 26, 29, 30, 42, 48, 60, 64
S. pneumoniae				PmrA		?	wt?, mutant +	Antibiotics, dyes, lipophilic cations	10, 12, 22, 65
Viridans group streptococci	?	?	?	?	?	?	?	?	19

^aIn organisms whose FQ efflux systems have been identified, components are identified as members of the single-component MATE or MFS group of efflux pumps or as members of the three-component RND-MFP-outer membrane efflux protein (OEP) group. 

^bwt +, mutant ++ or wt +, bmr ++, efflux system is expressed in wild-type cells (under laboratory growth conditions) but expression is enhanced in resistant or bmr strains, respectively; wt −, mutant +, efflux system is not expressed in wild-type cells but is expressed in resistant strains. 

^cWhere the identity of an FQ efflux system has yet to be made, references supporting the existence of FQ efflux mechanisms are shown in italics. Where FQ efflux systems have been identified, the more general references in support of efflux are indicated in boldface type, and references pertaining to specific FQ efflux systems are indicated in lightface type. Only the initial description of the latter references are cited here. Details of the regulation and substrate specificity are cited in the text. 

^dEnhanced resistance attributable to bmr in mutant strains is actually due to gene amplification and not enhanced bmr gene expression. 

^e?, unknown.