TABLE 2.

Antimicrobial susceptibility clusters of fecal E. coli from pre-weaned calves^a

Cluster	No. of isolates	Mean inhibition zone size (mm)
		Beta-lactams				Aminoglycosides			Sulfonamides		TET	CHL	NAL
		AMC	AMP	CEF	XNL	AMK	GEN	STR	SULF	SXT
A	357	22	20	18	27	22	21	16	24	28	21	23	23
B	55	21	19	18	27	22	20	15	22	27	7	21	22
C	3	9	6	6	21	23	21	17	26	28	21	21	19
D	7	18	10	15	25	22	21	11	6	20	20	24	24
E	67	21	19	18	26	22	21	9	6	20	6	23	23
F	16	19	6	17	25	21	19	11	20	27	6	21	22
G	13	24	23	22	28	22	19	6	6	6	6	24	24
H	4	10	6	6	19	23	21	11	25	27	6	24	22
I	35	19	6	17	27	22	21	7	6	19	6	23	23
J	8	22	20	19	25	21	16	6	6	16	6	6	22
K	6	19	6	19	27	23	21	7	6	6	6	23	23
L	26	10	6	6	20	22	21	8	6	20	6	22	23
M	35	19	6	17	27	22	7	7	6	6	6	24	23
N	8	19	6	18	26	22	20	6	6	6	6	6	25
O	14	10	6	6	17	22	21	6	6	6	6	23	22
P	12	18	6	13	26	22	6	7	6	6	6	6	25
Q	16	10	6	6	16	21	19	6	6	19	6	6	22
R	7	19	10	17	26	22	10	6	6	6	6	6	6
S	35	9	6	6	18	21	7	8	6	6	6	23	24
T	25	10	6	6	18	22	21	7	6	6	6	6	25
U	10	9	6	6	18	22	7	6	6	21	7	6	23
V	42	9	6	6	17	22	9	6	6	6	6	6	23
W	105	10	6	6	15	6	6	6	6	6	6	6	21
X	3	9	6	6	17	16	9	6	6	6	6	6	6
Sum	909

^aThis clinical trial evaluated the influence of antimicrobials in the milk replacer and as therapy on antimicrobial susceptibility in fecal commensal E. coli. The clusters are described by their mean zone sizes (in mm) in the disk diffusion assay to the 12 antimicrobials and ordered according to decreasing sum of mean zone sizes to the 12 antimicrobials. Boldface numbers indicate clusters where the mean antibiotic zone size was described as resistant.