Fluorescence microscopy of NaCl-stressed, elongated Salmonella and Listeria cells reveals the presence of septa in filaments

• Published in: International journal of food microbiology Vol. 112; no. 3; pp. 288 - 290
• Main Authors: Hazeleger, Wilma C., Dalvoorde, Marinka, Beumer, Rijkelt R.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.12.2006; Elsevier
• Subjects: bacterial contamination; Biological and medical sciences; culture media; enteritidis pt4; environments; escherichia-coli; Filaments; fluorescence; Fluorescence microscopy; Fluorescent Dyes - metabolism; food contamination; Food Contamination - analysis; Food Contamination - prevention & control; Food industries; Food Microbiology; food pathogens; food preservatives; Fundamental and applied biological sciences. Psychology; growth; Hydrogen-Ion Concentration; Indoles - metabolism; Listeria monocytogenes; Listeria monocytogenes - drug effects; Listeria monocytogenes - ultrastructure; microscopy; Microscopy, Fluorescence - methods; monocytogenes scott-a; morphology; replication; Salmonella enteritidis; Salmonella enteritidis - drug effects; Salmonella enteritidis - ultrastructure; salt concentration; Salt stress; Septation; septic shock; sodium chloride; Sodium Chloride - pharmacology; Temperature; temperatures; Time Factors; vegetative cells; Salmonella enteritidis; Listeria monocytogenes; Salt stress; Filaments; Fluorescence microscopy; Septation; Salt; Bacteria; Stress; Enterobacteriaceae
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2006.04.026

The cell morphology of Salmonella enteritidis and Listeria monocytogenes after the application of stress was examined. Cells were stressed by plating the bacteria on Tryptone Soya Agar (TSA) plates, with 5–10% NaCl. The plates were subsequently incubated for 6 days at 25 °C. Finally, the cells were harvested and subjected to different fluorescent probes in order to visualize the possible presence of septa in elongated cells. Use of the stain 4′,6-Diamidino-2-phenylindole (DAPI), which is a blue fluorescent nucleic acid stain that preferentially stains double-stranded DNA, showed clearly the presence of dark spots, probably cellular partitions where no nucleic acids were present, in both Salmonella and Listeria cells. Another stain, FM 4-64, a lipophilic styryl dye for red staining of the inner membrane, showed the presence of highly fluorescent spots in Listeria cells, probably indicating the presence of membranes. For Salmonella, however, FM 4-64 was not successful in revealing septa in filaments. Double staining applied to elongated Listeria cells showed areas with high fluorescence in DAPI-staining (DNA-rich spots) which contained low fluorescence in FM 4-64-staining (membrane spots) and vice versa, which is a confirmation that the elongated cells are indeed composed of several normal size cells.