Measurements of serum resistance (A) and tracheal ring binding (B) by parent, mutants and complemented strains. Strains are indicated below the solid lines as follows: parental, B. avium 197N; wlbA−, wlbA mutant PAS85; wlbL−, wlbL mutant PAS78. Abbreviations along the x-axis refer to the following: −, indicates strain containing no plasmid; v, indicates strain containing vector plasmid pLAFR5; av, indicates strain containing recombinant plasmid pLAF-av. Single asterisk indicates significant difference (P < 0.05) from parent B. avium 197N. Double asterisk indicates significant difference (P < 0.05) from mutant containing pLAFR5 as determined by Student’s t-test. Error bars indicate standard error. Refer to text for a description of the assays.