TABLE 5.

Percentage of E. coli isolates based on the MICs of nine antimicrobials that had either period, treatment, or period-treatment interactions in the proportional odds model

Antimicrobial	Treatmenta	Period	% of isolates by MIC (μg/ml):
			0.125	0.25	0.5	1	2	4	8	16	32	64	128	256	512	1,024
Amikacin	c-tyl	1			7.1	46.8	37.3	7.1	1.6
		2			0.7	37.3	45.3	14.7	2.0
	c-ctc	1			4.4	62.0	26.6	7.1	0
		2			0.8	50.0	34.1	13.5	1.6
	p-tyl	1			5.1	51.7	37.3	5.9	0
		2			3.3	36.0	47.3	11.3	2.0
	p-ctc	1			6.6	47.1	40.5	5.8	0
		2			3.4	44.5	34.9	15.8	1.4
	None	1			11.0	45.8	38.1	3.4	1.7
		2			0	28.9	46.9	20.3	3.9
Cefoxitin	c-tyl	1			0	9.5	46.8	34.9	7.9	0	0.8
		2			0	0	28	60.7	9.3	0.7	1.3
	c-ctc	1			0.9	6.2	48.7	32.7	8.0	0.9	2.6
		2			0	0	27.8	60.3	11.9	0	0
	p-tyl	1			0.8	5.1	46.6	40.7	6.8	0	0
		2			0	1.3	28.7	54.7	12.7	0.7	2.0
	p-ctc	1			0	5.0	48.8	35.5	10.7	0	0
		2			0	2.1	34.2	49.3	13.7	0.7	0
	None	1			0.8	2.5	44.9	44.1	7.6	0	0
		2			0	1.6	31.2	59.4	7.8	0	0
Ceftiofur	c-tyl	1	28.6	63.5	6.4	0.8	0	0	0.8	0
		2	7.3	77.3	14.0	0.7	0	0	0.7	0
	c-ctc	1	23.9	65.5	7.1	0	0.9	1.8	0.9	0
		2	3.2	75.4	20.6	0	0	0	0	0.8
	p-tyl	1	25.4	66.1	8.5	0	0	0	0	0
		2	10.7	70.0	16.0	2.7	0.7	0	0	0
	p-ctc	1	23.1	66.1	9.9	0.8	0	0	0	0
		2	14.4	63.7	20.6	1.4	0	0	0	0
	None	1	22.9	67.8	9.3	0	0	0	0	0
		2	4.7	73.4	19.5	1.6	0	0	0	0.8
Cephalothin	c-tyl	1					15.1	37.3	33.3	8.7	3.2	2.4
		2					1.3	18.7	53.3	20.7	3.3	2.7
	c-ctc	1					6.2	37.2	45.1	8.0	0	3.5
		2					1.6	19.0	57.9	15.1	3.2	3.2
	p-tyl	1					11.9	36.4	35.6	7.6	4.2	4.2
		2					1.3	17.3	35.3	35.3	6.0	4.7
	p-ctc	1					7.4	43.0	32.2	14.0	2.5	0.8
		2					4.1	23.3	37.7	24.0	10.3	0.7
	None	1					3.4	34.8	44.9	9.3	5.1	2.5
		2					0.8	14.8	60.9	19.5	3.9	0
Chloramphenicol	c-tyl	1					7.9	54.8	22.2	4.8	7.9	2.4
		2					1.3	58.0	26.7	8.0	2.7	3.3
	c-ctc	1					10.6	54.9	19.5	7.1	5.3	2.6
		2					10.3	57.9	22.2	0.8	1.6	7.1
	p-tyl	1					12.7	55.9	17.8	4.2	6.8	2.5
		2					6.7	56.7	24.0	0.7	6.0	6.0
	p-ctc	1					19.0	57.8	16.5	5.0	0.8	0.8
		2					4.8	58.9	29.4	1.4	2.7	2.7
	None	1					11.0	62.7	19.5	1.7	4.2	0.8
		2					3.9	56.2	28.1	1.6	2.3	7.8
Gentamicin	c-tyl	1		26.2	59.5	7.1	0.8	0	0	4.0	2.4
		2		15.3	63.3	16.0	3.3	0	0	2.0	0
	c-ctc	1		27.4	57.5	8.0	0.9	0.9	1.8	3.5	0
		2		18.2	55.6	11.9	1.6	0.8	2.4	7.1	2.4
	p-tyl	1		36.4	50.0	11.9	0	0	0	0.8	0.8
		2		19.3	63.3	6.7	2.0	0.7	2.0	2.7	3.3
	c-ctc	1		25.6	59.5	11.6	0.8	0	0	1.6	0.8
		2		17.8	61.6	16.4	1.4	0	0	1.4	1.4
	None	1		38.1	50.8	5.9	0.8	0.8	0.8	0.8	1.7
		2		4.7	62.5	22.7	3.9	0	0	0.8	5.5
Streptomycin	c-tyl	1									43.7	20.6	35.7
		2									74.7	10.7	14.7
	c-ctc	1									58.4	14.2	27.4
		2									65.1	7.9	27.0
	p-tyl	1									43.5	21.4	35.0
		2									65.3	18.0	16.7
	p-ctc	1									49.6	15.7	34.7
		2									73.3	6.2	20.6
	None	1									35.9	17.1	47.0
		2									82.8	3.9	13.3
Sulfamethoxazole	c-tyl	1								23.0	0	0	0	4.8	32.5	39.7
		2								56.7	0.7	0	0	4.7	11.3	26.7
	c-ctc	1								46.9	0	0	0	12.4	30.1	10.6
		2								69.8	0	0	0	1.6	11.9	16.7
	p-tyl	1								28.8	0	0	0	8.5	40.7	22.0
		2								58.0	0.7	0	0	1.3	18.0	22.0
	p-ctc	1								31.4	0.8	0	0	16.5	40.5	10.7
		2								74.0	0	0	0	2.1	12.3	11.6
	None	1								40.7	0	0	0.8	9.3	23.7	25.4
		2								81.2	0	0	0	0	3.1	15.6
Trimethoprim	c-tyl	1	40.5	40.5	15.9	1.6	0	0	1.6
		2	63.3	23.3	10.7	1.3	0	0	1.3
	c-ctc	1	57.5	25.7	13.3	0.9	0.9	0	1.8
		2	72.2	18.2	7.1	0.8	0	0	1.6
	p-tyl	1	55.1	33.9	8.5	0	0	0	2.5
		2	63.3	18.7	16.0	1.3	0	0	0.7
	p-ctc	1	54.6	28.1	10.7	4.1	0	0	2.5
		2	76.0	10.3	12.3	0	0	0	1.4
	None	1	71.2	19.5	7.6	0.8	0	0	0.8
		2	83.6	11.7	3.9	0	0	0	0.8

^aTreatment coding: c-tyl, continuous tylosin; c-ctc, continuous chlortetracycline; p-tyl, pulse tylosin; p-ctc, pulse chlortetracycline; none, no antimicrobials.