Reduced virulence of a Bordetella bronchiseptica siderophore mutant in neonatal swine

One means by which Bordetella bronchiseptica scavenges iron is through prod uction of the siderophore alcaligin, A nonrevertible alcaligin mutant deriv ed from the virulent strain 4609, designated DBB25, was constructed by inse rtion of a kanamycin resistance gene into alcA, one of the genes essential for alcaligin biosynthesis, The virulence of the alcA mutant in colostrum-d eprived, caesarean-delivered piglets was compared with that of the parent s train in two experiments. At 1 week of age, piglets were inoculated with ph osphate-buffered saline, 4609, or DBB25, Two piglets in each group were eut hanatized on day 10 postinfection, The remainder were euthanatized at 21 da ys postinfection. Clinical signs, including fever, coughing, and sneezing, were present in both groups. Nasal washes performed 7, 14, and 21 days post inoculation demonstrated that strain DBB25 colonized the nasal cavity but d id so at levels that were significantly less than those achieved by strain 4609, Analysis of colonization based on the number of CFU per gram of tissu e recovered from the turbinate, trachea, and lung also demonstrated signifi cant differences between DBB25 and 4609, at both day 10 and day 21 postinfe ction, Mild to moderate turbinate atrophy was apparent in pigs inoculated,v ith strain 4609, while turbinates of those infected with strain DBB25 devel oped no or mild atrophy. We conclude from these results that siderophore pr oduction by B. bronchiseptica is not essential for colonization of swine bu t is required for maximal virulence, B. bronchiseptica mutants with nonreve rtible defects in genes required for alcaligin synthesis may be candidates for evaluation as attenuated, live vaccine strains in conventionally reared pigs.