Abstract
SUMMARY: The production of MSHA+(type-1 fimbriate) recombinants was observed in transductional crosses between different pairs of naturally occurring strains ofSalmonella paratyphi B. MSHA+recombinants were readily produced in transductions from MSHA+donor strains to MSHA(type-2 fimbriate or non-fimbriate) recipient strains, and less frequently between some pairs of MSHAstrains. The genetic evidence suggests that there are at least three different clones among MSHAstrains ofS. paratyphi B. Relationships between the different strains and their possible origins are discussed.