Isolation of Bacteroides fragilis Mutants with In Vivo Growth Defects by Using Tn4400′, a Modified Tn4400 Transposition System, and a New Screening Method

A modified version of the Bacteroides fragilis transposon Tn4400, designated Tn4400′, enabling rapid isolation and analysis of B. fragilis mutants has been constructed. To identify potential virulence factors, Tn4400′-generated mutants were screened by a new method; this resulted in the isolation of 21 mutant strains with impaired growth characteristics on tissue culture monolayers but normal growth in rich medium anaerobically.