Salt-induced filamentous growth of a Salmonella strain isolated from blood.

A strain of Salmonella choleraesuis subsp. choleraesuis serovar paratyphi-A isolated from the blood of a febrile patient grew into filaments on a nutrient agar containing various salts, such as NaCl, KCl, MgCl2, NH4Cl, (NH4)2SO4, or (NH4)2HPO4, at concentrations of 50 to 400 mM. The filamentous cells were nonseptate and multinucleate, and they had colony-forming ability. This mutant strain, however, did not show filamentous growth in liquid media which contained the same salts. On nutrient agar containing 20% sucrose but no salts, some of the cells formed large spheroplasts. Both ampicillin treatment and in vivo environment may in part be responsible for the induction of the mutant strain.