Biomedical subjects

Wilma C Hazeleger

Publications and source records attributed to Wilma C Hazeleger.

3 recordsLinked to original sources

PubMed2006

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

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 degrees 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.

Fluorescent Dyes↗

PubMed2006

Survival, elongation, and elevated tolerance of Salmonella enterica serovar Enteritidis at reduced water activity.

Growing microorganisms on dry surfaces, which results in exposure to low water activity (a(w)), may change their normal morphology and physiological activity. In this study, the morphological changes and cell viability of Salmonella enterica serovar Enteritidis challenged to low a(w) were analyzed. The results indicated that exposure to reduced a(w) induced filamentation of the cells. The amount of filamentous cells at a(w) 0.94 was up to 90% of the total number of cells. Surviving filamentous cells maintained their membrane integrity after exposure to low a(w) for 21 days. Furthermore, cells prechallenged to low a(w), obtained with an ionic humectant, demonstrated higher resistance to sodium hypochlorite than control cells. These resistant cells are able to survive disinfection more efficiently and can therefore cause contamination of foods coming in contact with surfaces. This points to the need for increased attention to cleaning of surfaces in household environments and disinfection procedures in processing plants.

Colony Count, Microbial↗

PubMed2003

Listeria monocytogenes: diagnostic problems.

The first isolation methods for the detection of Listeria spp. were generally based on the direct culture of samples on simple agar media, but isolation of the pathogenic Listeria monocytogenes was difficult. In time, new techniques were developed, based on a variety of selective and elective agents in isolation and enrichment media, which gained better and quicker results. Current reference methods allow the recovery of L. monocytogenes from a variety of foods with relative ease. However, more comparative studies are needed to select one horizontal method. It is suggested that the procedure of the International Organization for Standardization is a good base for such comparisons.

Animals↗