TABLE 4.

Antimicrobial susceptibility cluster distribution of fecal E. coli isolates from calves treated with ceftiofur within 5 days of sampling compared to calves not treated^a

Cluster	No. (%) of isolates in cluster
	Group 3b		Group 4c
	No treatment	Treatment	No treatment	Treatment
A	18 (17.5)	7 (13.0)	0	0
B	21 (20.4)	12 (22.2)	0	0
C	0	0	0	0
D	1 (1.0)	0	0	0
E	9 (8.7)	1 (1.9)	2 (1.3)	0
F	7 (6.8)	0	0	0
G	0	0	0	0
H	0	0	0	0
I	7 (6.8)	0	3 (1.9)	0
J	1 (1.0)	0	1 (0.6)	0
K	0	0	1 (0.6)	0
Ld	4 (3.9)	1 (1.9)	0	0
M	5 (4.9)	0	0	0
N	0	0	0	0
O	0	3 (5.6)	7 (4.5)	0
P	2 (1.9)	0	5 (3.2)	1 (6.7)
Q	7 (6.8)	4 (7.4)	3 (1.9)	2 (13.3)
R	1 (1.0)	0	5 (3.2)	0
S	9 (8.7)	7 (13.0)	4 (2.6)	0
T	4 (3.9)	4 (7.4)	11 (7.1)	0
U	0	4 (7.4)	0	0
V	4 (3.9)	7 (13.0)	17 (10.9)	8 (53.3)
W	3 (2.9)	4 (7.4)	94 (60.3)	4 (26.7)
X	0	0	3 (1.9)	0
Sum	103	54	156	15

^aComparison includes 14- and 28-day samples from calves not supplemented with antimicrobials in their milk replacer (group 3) and calves supplemented with antimicrobials in the milk replacer (group 4) on a commercial calf ranch.

^bCalves fed no antimicrobials in milk replacer.

^cCalves fed neomycin sulfate and tetracycline HCl in milk replacer.

^dBoldface indicates clusters with ceftiofur resistance.