Table 3. Segregant frequencies in evolved CTX-M-15-Kp populations and fitness estimates of plasmid-free segregant isolates.

Subject	Ancestor isolate		Segregant frequency a		Relative fitness of segregant isolates b w (95% CI)	P value c	Relative growth rates of segregant isolates d (95% CI)	P value e
	Sample	ID	Pop 1%	Pop 2%
Child 1	First	Kp2158	0.83	4.17	1.02 (0.93–1.12)	0.615	1.027 (1.007–1.047)	0.01*
	Last	Kp734	1.67	2.50	0.97 (0.92–1.02)	0.203	0.950 (0.926–0.975)	<0.001*
Child 2	First	Kp2180	12.50	5.00	0.96 (0.92–0.99)	0.02*	1.017 (0.992–1.045)	0.189
	Last	Kp723	0.83	6.67	0.97 (0.91–1.02)	0.208	1.004 (0.978–1.031)	0.751
Child 3	First	Kp2223	3.33	1.67	0.98 (0.95–1.02)	0.309	1.023 (0.997–1.050)	0.078
	Last	Kp798	17.50	6.67	0.97 (0.93–1.02)	0.201	1.003 (0.964–1.039)	0.863
Child 4	First	Kp2166	4.17	13.85	0.99 (0.93–1.05)	0.613	1.013 (0.997–1.031)	0.138
	Last	Kp848	4.17	5.38	1.01 (0.96–1.06)	0.721	1.030 (0.999–1.056)	0.039*

^aEndpoint segregant frequency after serial transfer for ~ 430 generations (two evolved populations, Pop1 and Pop 2, per ancestor isolate).

^bThe ratio of the Malthusian parameters of the plasmid-free segregant to that of its plasmid-carrying evolved ancestor isolate. A relative fitness of 1.0 denotes no difference in relative fitness (i.e. no cost of plasmid carriage). A relative fitness >1.0 is indicative for plasmid-carriage associated fitness costs, whereas values <1.0 are indicative for a benefit of plasmid-carriage to the host strain. Number of parallels: n = 9

^cStandard one-sample t-test, two tailed.

^dThe ratio of the growth rate of the plasmid-free segregant to that of its plasmid-carrying evolved ancestor isolate. Relative growth rates >1.0 are indicative for plasmid-carriage associated fitness costs, whereas values <1.0 are indicative for a benefit of plasmid-carriage to the host strain. Number of parallels: n = 9, except Kp2158 n = 7.

^eStandard two-sample t-test, two tailed.

*Significant values (P<0.05).