Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: February 22, 1999
Publication Date: N/A
B. bronchiseptica acquires iron through production of the siderophore alcaligen. A nonrevertable alcaligin mutant of the virulent swine strain 4609 (DBB25) was constructed by insertion of a kanamycin resistance cassette into alcA, one of the genes essential for alcaligen biosynthesis. In two experiments, the virulence of the alcA mutant in colostrum-deprived, ,Caesarean-derived piglets was compared with that of the parent strain. At one week of age piglets were inoculated with PBS, 4609, or DBB25 (1 x 10**6 CFU; N=6/group in each experiment). Two piglets in each group were euthanized on day 10 post-infection (PI); remaining piglets were euthanized 21 days PI. Respiratory tissues were harvested for quantitative culture and histologic examination. Nasal washes performed 7, 14, and 21 days PI demonstrated significantly reduced colonization of the nasal cavity by DBB25 as compared with 4609 (p</-0.03). Colonization of turbinate, trachea, and lung by DBB25, expressed as CFU/g of tissue, was also significantly reduced, both at day 10 PI (p</-0.05) and day 21 PI (p</- 0.03, except for lung in 1 experiment where p=0.09). Turbinate atrophy was more prevalent and more pronounced in piglets infected with the parent strain. Clinical signs, including fever, inappetence, cough, and nasal discharge, were present both in groups infected with 4609 and with DBB25 but were more pronounced in the former. We conclude from these results that the absence of siderophore production by B. bronchiseptica attenuates infection in swine and that the evaluation of siderophore mutants as as vaccine strains for swine respiratory disease is warranted.