Table 2. Mobilization frequency (italics) of pEC156-derivative pIB8 (EcoVIII R⁺M⁺).

		Donor R+M+
		E. coli DH5α Rif [F’, pIB8]	E. cloacae [F’, pIB8]	K. oxytoca [F’, pIB8]	C. freundii [F’, pIB8]	S. enteritidis [F’, pIB8]
Recipient	E. coli HB101 [pBR322]	8.4 ± 4 ×10−4	1.8 ± 0.2 ×10−5 *	<1.8 ×10−9	< 1.8 ×10−9 *	< 1.8 ×10−9 *
		2.2± 1.5 ×10−3	4.6 ± 0.4 ×10−5	< 1.8 ×10−9	1.8 ± 0.3 ×10−7 *	2.6 ± 2.6 ×10−9 *
	E. coli MG1655Δlac [pBR322]	2.5 ± 0.2 ×10−4	5.6 ± 3.2 ×10−6 *	< 1.1 ×10−9	< 1.1 ×10−9 *	< 1.1 ×10−9 *
		2.3 ± 0.2 ×10−4	1.3 ± 0.4 ×10−6 *	< 1.1 ×10−9	3.0 ± 0.3 ×10−8 *	1.8 ± 1.8 ×10−8 *
	E. cloacae [pBR322]	2.5 ± 0.7 ×10−7	3.2 ± 0.4 ×10−7 *	5.6 ± 1.6 ×10−8 *	9.2 ± 3.9 ×10−9*	3.0 ± 1.5 ×10−8 *
		3.7 ± 0.7 ×10−7	6.2 ± 0.5 ×10−7 *	1.3 ± 0.4 ×10−9 *	1.0 ± 0.03 ×10−7	< 1.0 ×10−9 *
	K. oxytoca [pBR322]	1.8 ± 0.9 ×10−6 *	2.0 ± 1.9 ×10−7 *	8.7± 2.3 ×10−8 *	2.2 ± 0.3 ×10−8 *	6.7 ± 1.3 ×10−8 *
		1.63 ± 0.5 ×10−8 *	3.0 ± 2.6 ×10−8*	1.3 ± 1.3 ×10−9 *	2.6 ± 0.1 ×10−8 *	< 1.1 ×10−9 *
	C. freundii [pBR322]	1.64 ± 0.9 ×10−7 *	1.0 ± 0.2 ×10−7 *	4.6 ± 2 ×10−8	1.9 ± 0.6 ×10−7 *	8.0 ± 3.8 ×10−8 *
		< 1.8 ×10−9	< 1.8 ×10−9	< 1.8 ×10−9 *	1.0 ± 0.2 ×10−6	< 1.8 ×10−9 *
	S. enteritidis [pBR322]	3.0 ± 1.1 ×10−9	2.2 ± 1.2 ×10−7 *	1.0 ± 1 ×10−8	< 1.6 ×10−9 *	< 1.6 ×10−9 *
		< 1.6 ×10−9	1.4 ± 1.1 ×10−8	< 1.6 ×10−9 *	< 1.6 ×10−9 *	1.3 ± 1.2 ×10−6

The frequency of F-plasmid conjugal transfer is given in boldface. Mobilization frequency/conjugal transfer frequency is the number of transconjugants per recipient. Shown are mean values from 3 independent experiments, and standard deviations are indicated. Asterisks next to the specific values in Table 2 indicate statistically significant differences between mobilization of pIB8 and pIB9 (P<0.03; Student t test).