Enteric glia protect against Shigella flexneri invasion in intestinal epithelial cells: a role for S-nitrosoglutathione.

BACKGROUND: Enteric glial cells (EGCs) are important regulators of intestinal epithelial barrier (IEB) functions. EGC-derived S-nitrosoglutathione (GSNO) has been shown to regulate IEB permeability. Whether EGCs and GSNO protect the IEB during infectious insult by pathogens such as Shigella flexneri is not known. METHODS: S flexneri effects were characterised using in vitro coculture models of Caco-2 cells and EGCs (or GSNO), ex vivo human colonic mucosa, and in vivo ligated rabbit intestinal loops. The effect of EGCs on S flexneri-induced changes in the invasion area and the inflammatory response were analysed by combining immunohistochemical, ELISA and PCR methods. Expression of small G-proteins was analysed by western blot. Expression of ZO-1 and localisation of bacteria were analysed by fluorescence microscopy. RESULTS: EGCs significantly reduced barrier lesions and inflammatory response induced by S flexneri in Caco-2 monolayers. The EGC-mediated effects were reproduced by GSNO, but not by reduced glutathione, and pharmacological inhibition of pathways involved in GSNO synthesis reduced EGC protecting effects. Furthermore, expression of Cdc42 and phospho-PAK in Caco-2 monolayers was significantly reduced in the presence of EGCs or GSNO. In addition, changes in ZO-1 expression and distribution induced by S flexneri were prevented by EGCs and GSNO. Finally, GSNO reduced S flexneri-induced lesions of the IEB in human mucosal colonic explants and in a rabbit model of shigellosis. CONCLUSION: These results highlight a major protective function of EGCs and GSNO in the IEB against S flexneri attack. Consequently, this study lays the scientific basis for using GSNO to reduce barrier susceptibility to infectious or inflammatory challenge.

Cellular lipid fatty acid pattern heterogeneity between reference and recent food isolates of Listeria monocytogenes as a response to cold stress.

Cells of four reference strains (Scott A, LO 28, CNL 895807 and ATCC 19115) and of five recent food isolates (A00M011, A00M018, A00M087, A00M092 and A00M123) of Listeria monocytogenes were grown until late exponential phase in Brain Heart Broth at two different temperatures (37 degrees C and 4 degrees C). Our results show that significant differences exist between the cellular lipid fatty acid profile of reference and recent food isolates. Like the reference strains, and in keeping with previous reports on the cellular lipid fatty acid profile of L. monocytogenes, the recent food isolates were characterised by the presence of ai15:0, i15:0 and ai17:0. In addition, the fatty acid ai13:0 was observed in all of the recent food isolates grown at 4 degrees C, whereas only two reference strains, Scott A and LO 28, showed ai13:0 in their cellular lipid fatty acid profile at 4 degrees C. When grown at 4 degrees C, the recent food isolates showed a mean aiC15/aiC17 ratio of 66, while reference strains were characterised by significantly lower ratios, ranging between 4.3 (ATCC 19115) and 28.9 (Scott A). These results showed that all of the recent food isolates, Scott A and LO28 strains use chain length and anteiso-branching (ai15:0) as their major response to cold temperature adaptation. However, the cold adaptation response of reference strains CNL 895807 and ATCC 19115 appears to be different.

Effect of salting and cold-smoking process on the culturability, viability, and virulence of Listeria monocytogenes strain Scott A.

The aim of the present study was to determine the effect of the different steps of the cold-smoking process and vacuum storage on the culturability and viability of Listeria monocytogenes strain Scott A inoculated in sterile salmon samples. Additionally, the virulence of L. monocytogenes cells was assessed by intravenous inoculation of immunocompetent mice. Salmon (Salmo salar) portions were inoculated with L. monocytogenes at a level of 6 log CFU/g and were then dry salted (5.9%), smoked (0.74 mg phenol per 100 g), partially frozen (-7 degrees C), vacuum packed, and stored for 10 days at 4 degrees C followed by 18 days at 8 degrees C. Salting represented the only step of the process with a weak but significant listericidal effect (0.6 log reduction). Although the other processing steps had no immediate reduction effect on L. monocytogenes, the combination of steps significantly lowered by 1.6 log CFU/g the number of L. monocytogenes. The culturable count remained less than 7 log CFU/g until the end of the storage period, whereas in unprocessed samples (control) the culturable counts reached values up to 9 log CFU/g. To mimic a postprocess contamination, salmon portions were also inoculated with L. monocytogenes after being cold-smoke processed. A reduction of the culturable count during the 2 first weeks of storage was observed, but then growth occurred and identical values observed for preprocess contamination were reached at the end of the storage. A viable but nonculturable state transition of strain Scott A was not observed, and the cold-smoking process did not affect the virulence of bacteria isolated at the beginning and end of the storage.