Avirulent Viable But Non Culturable cells ofListeria monocytogenesneed the presence of an embryo to be recovered in egg yolk and regain virulence after recovery

Abstract

-The aim of this study was to assess the efficiency of the embryonated egg model to recover Viable But Non Culturable (VBNC) cells of Listeria monocytogenes. L. monocytogenes cells were incubated in filtered sterilised distilled water. The VBNC state was obtained after a 25 to 47 days incubation period (concentration of culturable cells less than 1 cfu/mL). Fifteen days after the VBNC state was reached, non culturability was checked in various media. One milliliter of each VBNC suspension that contained 10 4 metabolically active cells (i.e. Direct Viable Count + cells) was inoculated into the vitellus fluid of embryonated and non-embryonated eggs. Culturable cells were detected in a large proportion of the embryonated eggs (18/32), but not in the non-embryonated eggs (1/32). The recovery rate was higher after culture of the vitellus fluid plus embryo (18/32) than after culture of the vitellus fluid alone (6/32). The results indicate that the embryo likely plays a prominent part in the recovery process. The virulence of recovered cells was assessed by the ability to form plaques in HT-29 cell monolayers and by the ability to colonise mouse spleens. Although the cells were classified as avirulent when in the VBNC state, the virulence was recovered after resuscitation.VBNC / virulence / embryonated eggs / Listeria monocytogenes

Stress- and Growth Rate-Related Differences between Plate Count and Real-Time PCR Data during Growth of Listeria monocytogenes

“…In addition, extracellular DNA might be lost during DNA isolation, but VBNC and dead cells will be recovered. There might be a benefit for risk assessment from detection of VBNC L. monocytogenes in real-time PCR but whether VBNC L. monocytogenes poses a threat to human health is controversial (11). These cells might represent injured cells needing time and optimal conditions for repair and recovery (14).…”

“…Recent efforts focused on skipping the enrichment step, thus enabling faster and direct detection as well as quantification of L. monocytogenes in a wide variety of sample types such as food, blood, or sewage sludge (7,20,35,38). However, this approach bears the possibility of falsepositive results and overestimation of the bacterial cell count due to the detection of viable but nonculturable (VBNC) cells (which might or might not be a benefit for risk assessment), dead target cells, or extracellular DNA from these cells by PCR, which would otherwise be diluted in the enrichment (18,11,24).…”

Critical Issues in Detecting Viable Listeria monocytogenes Cells by Real-Time Reverse Transcriptase PCR

“…Various culture-independent methods, particularly nucleic acid amplification methods such as PCR and real-time (quantitative) PCR, offer rapid and sensitive options for Listeria detection (9). In addition to improved detection efficiency and sensitivity, the culture-independent methods may be able to identify injured or viable but nonculturable cells, which are unable to grow in selective media, particularly after processing treatments, but have the potential to recover and cause further damage in hosts (2,3,8,18). However, because of false-positive results due to the DNA molecules in dead cells, DNA-based amplification methods are unsuitable for viability assessments (13,17).…”

Can sludge dewatering reactivate microorganisms in mesophilically digested anaerobic sludge? Case of belt filter versus centrifuge

“…However, a critical point about the VBNC concept is that, even though the cells enter the VBNC state, they are still considered viable and carry their infectious properties in vivo (Cappelier et al, 2007). In addition, those bacteria do not persist in the VBNC state indefinitely.…”