FILAMENT FORMATION IN LISTERIA-MONOCYTOGENES

Listeria monocytogenes strain SLCC 5764 cells were challenged with var ious NaCl concentrations and levels of pH. Cells were propagated in tr yptic soy broth containing 250 to 1,500 mM NaCl or TSB at pH values ra nging from 3.5 to 9.5. Microscopic analyses of the listerial cells fol lowing incubation revealed morphological changes under several adverse conditions. Filament formation occurred at NaCl concentrations above 1,000 mM with an increase in filament length as NaCl concentration inc reased. The same phenomenon was observed at pH values of 5.0 to 6.0 (a djusted with citric acid) and at pH> 9.0 (NaOH). The length of the fil aments increased as the growth environment became more challenging. Ce llular elongation of L. monocytogenes cells grown under these conditio ns suggests that an adaptation mechanism for survival may be involved Since long filament structures may form under certain stressful condit ions, these observations may be useful in preventing misidentification of L. monocytogenes.