The gram-positive bacterium Listeria monocytogenes is a food-borne pathogen of both public health and food safety significance. It possesses three small, highly homologous protein members of the cold shock protein (Csp) family. We used gene expression analysis and a set of mutants with single, double, and triple deletions of the csp genes to evaluate the roles of CspA, CspB, and CspD in the cold and osmotic (NaCl) stress adaptation responses of L. monocytogenes. All three Csps are dispensable for growth at optimal temperature (37°C). These proteins are, however, required for efficient cold and osmotic stress tolerance of this bacterium. The hierarchies of their functional importance differ, depending on the environmental stress conditions: CspA>CspD>CspB in response to cold stress versus CspD>CspA/CspB in response to NaCl salt osmotic stress. The fact that Csps are promoting L. monocytogenes adaptation against both cold and NaCl stress has significant implications in view of practical food microbial control measures. The combined or sequential exposure of L. monocytogenes cells to these two stresses in food environments might inadvertently induce cross-protection responses.

Listeria monocytogenes are important foodborne pathogens that can cause outbreaks of serious human disease. These organisms frequently colonize and proliferate on preserved food products despite exposure to stress conditions induced by low storage temperatures, inclusion of organic acid-based preservatives, and high osmolarity. To assess alternative sigma factor sigma(L) contributions to such stress resistance of L. monocytogenes, quantitative RT-PCR assays and sigL gene deletion mutagenesis were applied in L. monocytogenes EGDe. Transcription of sigL was significantly induced by growth of EGDe under cold, organic acid, and elevated NaCl salt concentration stress conditions. The growth of a DeltasigL strain exposed to these stress conditions was also found to be significantly impaired in comparison to that of its isogenic wild-type strain. The contribution of sigma(L) to transcription control of cold and NaCl stress adaptation genes, oppA, cspD, and clpP, was also comparatively assessed in DeltasigL and wild-type EGDe cells. Transcription of the oppA gene, which encodes the OppA protein that also promotes L. monocytogenes cold growth, was significantly reduced in cold stress-grown DeltasigL cells compared to levels of the wild-type EGDe strain. These findings therefore suggest important roles of sigma(L) regulatory pathways in facilitating resistance of L. monocytogenes organisms against stress conditions associated with low storage temperatures, exposure to organic acid, and elevated NaCl salt concentrations.

BackgroundThe aim of this case report was to describe the clinical findings, treatment and outcome of lumbosacral discospondylitis in a calf.Case PresentationA 5.5-month-old calf was presented with difficulty in rising, a stiff and slightly ataxic gait in the hind limbs and a shortened stride. The lumbosacral region was severely painful on palpation.Radiographic examination confirmed lumbosacral discospondylitis. Medical treatment with stall rest was instituted over six weeks. Radiographic and ultrasonographic follow-up examinations showed lysis of the endplates initially, then collapse of the intervertebral space at the lumbosacral junction and progressive sclerosis in the periphery of the lytic zones. Four weeks after institution of treatment, the calf could rise normally and the general condition gradually had returned to normal. The calf was discharged after 6 weeks and was sound at 3.5 months clinical and radiographic follow up examination. Thereafter, it was kept on alpine pastures without problems and was pregnant 1 year after the last examination.ConclusionsThis report shows that recovery from lumbosacral discospondylitis is possible in heifers, provided that treatment is started before major neurologic deficits have developed and is continued for an extended period of time.

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