TABLE 2.

Experimental design of study—dosing and treatment of poults

Day	Dosing and treatment for poults in pena:
	1	2	3	4
1	Dosing with antibiotic-susceptible serovar Newport	Dosing with antibiotic-susceptible serovar Newport	Dosing with antibiotic-susceptible serovar Newport and ESC-resistant E. coli	No treatment
2	Administration of CTF (0.17 mg in 0.2 ml of saline) subcutaneouslyb	Administration of saline (0.2 ml) subcutaneously	No treatment with antimicrobials	No treatment

^aThe pens were isolation units in an animal isolation building. Pens 1 and 4 contained 12 poults; pens 2 and 3 contained 13 poults. Poults given serovar Newport were dosed orally with 4.2 × 10⁶ (trial 1) or 3.8 × 10⁶ (trial 2) serovar Newport 02-6203 bacteria, an antimicrobial-susceptible strain that did not harbor any plasmids. The poults in pen 3 were also dosed with 2.5 × 10⁶ (trial 1) or 1.4 × 10⁶ (trial 2) bacteria of the ESC-resistant E. coli strain MPS57 that is resistant to AMP, AMC, CEF, CFT, CRO at 8 μg/ml; FOX; CHL, SPT, and SUL and that contains two plasmids of 66 and 72 MDa; the latter plasmid is self-transmissible, contains the cmy-2 gene, and encodes resistance to all the above-mentioned antimicrobials. Saline, phosphate-buffered saline.

^bAdministered subcutaneously at a dose and route indicated for the prevention of colibacillosis in 1-day-old poults (5).