Cold and carbon dioxide used as multi-hurdle preservation do not induce appearance of viable but non-culturable Listeria monocytogenes.
OBJECTIVE
To study whether the exposure to cold (4 degrees C) and carbon dioxide which results in the elongation of Listeria cells, induces a viable but nonculturable (VBNC) state.


RESULTS
When cold and CO2 stressed L. monocytogenes were observed under a fluorescence microscope, using the LIVE/DEAD BacLight bacteria viability kit (Molecular Probes, Eugene, OR, USA), the healthy, mildly injured, and the putative VBNC cells accounted for 31.0% of the stressed cell population. By using the selective plate count, 31.4% of the same stressed cell population was found to be healthy and mildly injured (putative VBNC cells not included). If there were VBNC state cells present, we should have observed a significant difference between the above two numbers. In fact, there was no significant difference between the results obtained from those two methods.


CONCLUSIONS
There were no VBNC state cells observed in the stressed cell population. We conclude that cold and CO2 do not induce L. monocytogenes to enter a VBNC state.


CONCLUSIONS
Cold and modified atmospheres are widely used in fresh muscle food and fruit preservation. Whether they would induce L. monocytogenes into a VBNC state is of a great concern for microbial food safety.
Li
J
J
Department of Food Science, Cook College, Rutgers, The State University of New Jersey, 65 Dudley Road, New Brunswick, NJ 08901, USA.
Kolling
G L
GL
Matthews
K R
KR
Chikindas
M L
ML
D000255:Adenosine Triphosphate / Q000032:analysis; D002245:Carbon Dioxide; D003080:Cold Temperature; D015169:Colony Count, Microbial / Q000379:methods; D003470:Culture Media; D008089:Listeria monocytogenes / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D008856:Microscopy, Fluorescence
D003470:Culture Media; D002245:Carbon Dioxide; D000255:Adenosine Triphosphate