TABLE 2.

Incidence of single and multiple resistance to tested antibiotics in fecal E. coli from sows and pigs of various ages exposed to high and low antibiotic usage

Drug and resistance pattern	% of isolates with indicated resistance pattern from animals and farm type (n)a
	Sows		Pigs, 7 days		Pigs, 35 days		Pigs, 63 days
	HU (322)	LU (140)	HU (1,731)	LU (747)	HU (1,683)	LU (729)	HU (999)	LU (407)
Apramycin
Single	0	0	0	0	0	0	0	0
Multiple	0.3	0.7	8.2	9.2	60.9	7.1	29.5	5.8
No resistance	99.7	99.3	91.8	90.8	39.1	92.9	70.5	94.2
Carbadox
Single	0	0.7	0.1	0.9	1.7	0	0	0.2
Multiple	17.7	37.8	35	17.8	55.3	17.1	47.3	20.6
No resistance	82.3	61.5	64.9	81.3	43.0	82.9	52.7	79.2
Gentamicin
Single	0	3.6	0.5	5.9	0.1	6.4	0	0
Multiple	74.8	82.8	73.3	75.8	91.9	71.0	85.9	72.5
No resistance	25.2	13.6	26.2	18.3	8.0	22.6	14.1	27.5
Neomycin
Single	0	0	0.2	0	0	0	0	0
Multiple	56.2	53.6	55.2	44.6	54.8	41.7	64.6	34.3
No resistance	43.8	46.4	44.6	55.4	45.2	58.3	35.4	65.7
Tetracycline
Single	17.4	5.0	16.7	10.8	2.9	11.0	5.2	22.6
Multiple	81.7	79.3	79.5	71.8	91.4	78.9	93.6	76.9
No resistance	0.9	15.7	3.8	17.4	5.7	10.1	1.2	0.5

^aThe approximate least significant difference between percentages ranges from 3 to 8.