TABLE 1.

Quinolone susceptibilities of different S. maltophilia strains and their levels of Smqnr expression

Strain	Plasmid	Location of Smqnr^b	Mean amt of Smqnr ± SEM^c	MIC (mg/liter)^a
Strain	Plasmid	Location of Smqnr^b	Mean amt of Smqnr ± SEM^c	LVX	MOX	CIP	OFX	GAT
D457	None	C, none	1.0 ± 0.0	0.5	0.19	0.75	1	0.25
MBS108	pBS12	C, P	10.1 ± 2.5	1	0.75	2	3	0.75
MBS109	pVLT31	C, none	1.2 ± 0.3	0.5	0.19	0.75	1	0.25
MBS82	None	None, none	0.0 ± 0.0	0.25	0.064	0.5	0.5	0.125
MBS101	pBS12	None, P	9.57 ± 2.2	1	0.75	2	3	0.75
MBS100	pVLT31	None, none	0.0 ± 0.0	0.25	0.064	0.5	0.5	0.125

LVX, levofloxacin; MOX, moxifloxacin; CIP, ciprofloxacin; OFX, ofloxacin; GAT, gatifloxacin. MICs were determined by epsilon test (at least three determinations were made for each MIC).

C, the strain harbors a chromosomally encoded Smqnr gene; P, the strain harbors a plasmid-encoded Smqnr gene.

The amount of Smqnr was calculated by real-time reverse transcription-PCR using SYBR green PCR master mix (Applied Biosystems) and primers RTqnr1 (5′-TTCGAGGGAATCGACTGGAA-3′) and RTqnr 2 (5′-TCGCCCAGATCGGAATTG-3′). Results were normalized to those obtained for the sigma factor rpoD (primers rpoD1 [5′-GGTGCACATGATCGAAACGA-3′] and rpoD2 [5′-GCCGTACTGCTGGAGCATCT-3′]). Five different samples of each strain were analyzed. The relative amounts of mRNA for Smqnr in each case, normalized against an internal control (rpoD), were calculated by the 2⁻^ΔΔCt method (6). The values are expressed in arbitrary units referred to the expression level in wild-type strain D457.