Table 1.

Analysis of tet(M) expression as assayed by determination of MICs, qRT-PCR analysis, and β-galactosidase activity assay

S. pneumoniae isolate	MIC (μg/ml)	qRT-PCR resulta		E. faecalis transformant datab
				MIC (μg/ml)	β-Gal activity (Miller units)c
		Noninduced cells	Induced cells		Noninduced cells	Induced cells
140	2	18	114	2	15	168
140-M1	64	650	551	64	669	1,188
10	64	308	470	64	627	1,197
59	2	7	41	1.5	14	76
108	16	302	379	24	288	420
52	1	776	880	1	252	213
52-M1	32	890	904	12	—	—

^aRelative levels of tet(M) transcripts were measured by qRT-PCR analysis of RNAs extracted from exponentially growing S. pneumoniae cells cultivated without or with a subinhibitory concentration of Tc (0.2 μg/ml). Expression levels were normalized by using gyrA as an internal standard and are indicated as threshold cycle ratios. Values are means for four technical replicates and are representative of two independent experiments showing less than 10% variation.

^bE. faecalis BM4110 was transformed with the reporter plasmid pTCV-tet(M) or with pTCV-lac containing the tet(M) promoter regions of the corresponding pneumococcal strains. —, not tested.

^cβ-Galactosidase was assayed on exponentially growing E. faecalis cells cultivated without or with a subinhibitory concentration of Tc (0.2 μg/ml). Values are representative of two independent experiments showing less than 10% variation.