TABLE 2.

Hill PD parameters describing the concentration-response profiles of colistin (0–16 mg/L) in the presence of fixed tigecycline concentrations (0–0.5 mg/L) at low and high inoculums^a.

TGC (mg/L) in combination	106 cfu/mL			108 cfu/mL
	Emax	EC50	N	Emax	EC50	N
PD parameters for E. coli ATCC 25922
0	−9.61	1.58	2.24	−6.46	6.19	1.94
0.03	−9.85	1.01	1.53	−8.95	4.95	1.12
0.06	−8.74	0.83	1.30	−9.09	3.47	1.40
0.13	−7.22	0.55	1.73	−9.13	2.01	1.43
PD parameters for E. coli carrying blaNDM–5 (i.e., isolate 2630)
0	−9.43	0.82	8.13	−9.11	6.75	4.68
0.13	−9.68	0.49	10.7	−9.14	5.45	3.71
0.25	−9.56	0.27	10.1	−9.17	4.98	1.18
0.50	−9.57	0.26	12.9	−9.41	2.36	1.22
PD parameters for E. coli carrying mcr-1 only (i.e., isolate 3112)
0	−5.60	5.98	2.07	−2.28	8.68	1.04
0.13	−9.48	3.96	2.55	−4.33	6.01	1.71
0.25	−9.42	2.34	2.37	−7.05	3.55	1.49
0.50	−9.30	1.05	1.84	−7.52	3.48	1.59
Mean PD parameters for E. coli carrying blaNDM–5 and mcr-1 (i.e., 1320, 2610, and 2121)
0	−6.53	7.37	5.66	−2.31	10.6	4.34
0.13	−8.23	5.50	3.97	−5.25	9.91	3.69
0.25	−9.42	2.09	2.56	−7.49	7.02	2.83
0.50	−9.36	0.80	4.17	−8.60	3.98	2.13

^aE_max, maximum effect compared to the no drug control for a log₁₀ change of bacterial density after the 48 h study period; EC₅₀, colistin concentration required to achieve 50% E_max; N, slope of the concentration-effect curve.