Table 1.

Characteristics of tester and driver strains

	MLSTA
Strain	STB	ST complex	Phylogenetic groupC	% Embryo deathsD	Pathogenicity groupE
APEC O1	95	95	B2	60	High
APEC 113	79	95	B2	15	Intermediate
UPEC 88	73	73	B2	45	NA
UPEC CFT073	73	73	B2	40	NA

^AMLST, multilocus sequence typing.

^B ST, sequence type.

^C E. coli isolates in phylogenetic groups B2 and D are more likely to be associated with disease than phylogenetic groups A and B1.

^D20 eggs were inoculated for each isolate. There were no deaths in the control groups (PBS-inoculated and uninoculated eggs).

^EPathogenicity group of the 2 APEC strains were determined according to a previously described scheme [32]. Highly pathogenic (high) isolates caused mortality or severe lesions (pericarditis, perihepatitis, and/or liver necrosis) in >50% of the chickens inoculated. Intermediate pathogens did not cause death and produced lesions in <50% of chickens inoculated. Weak pathogens (low) produced no mortality and occasional airsacculitis NA – not applicable, because pathogenicity of UPEC isolates for day-old chickens was not determined.