TABLE 1.

Comparison of the parental strain (197N) and a Ba1 lysogenic strain (AP21) with respect to turkey colonization, in vitro tracheal ring binding, and serum resistance

Strain	Mean ID50 (106)a ± SD	Mean CFU/ring (104)b ± SD	Mean % serum resistancec
197N	6.7 ± 7.0	3.7 ± 1.5	(100)
AP21	9.8 ± 9.3	2.8 ± 1.6	134 ± 25

^aID₅₀ determinations in 1-week-old turkey poults were performed as previously described (27). Isolates recovered from poults infected with strain AP21 were tested for lysogeny, and all were found to be lysogenic. There was no significant difference (P > 0.05) in the colonization rates between strains AP21 and 197N in an unpaired Student t test.

^bBacteria were incubated with tracheal rings for 1 h and treated as described by Temple et al. (27). There was no significant difference (P > 0.05) in the attachment levels between strains AP21 and 197N in an unpaired Student’s t test. A minimum of three independent assays, performed in duplicate, were averaged.

^cThe percentage of bacteria that survived in 50% naive turkey serum normalized to the percentage of 197N that survived (set at 100%) (25). Three separate measurements were averaged. There was no significant difference (P > 0.05) in serum resistance between the parent and lysogen in an unpaired, two-tailed Student t test.