Aims: To identify proteins regulating antimicrobial peptide (AMP) resistance in Vibrio parahaemolyticus using membrane subproteome analysis. Methods and Results: Three synthetic AMPs (Q4, Q6 and H1) and a natural one from fish (pleurocidin) were used for selection of AMP‐resistant strains. Differential expression patterns of the outer and inner membrane proteins (OMPs and IMPs) among wild‐type and the resistant strains were obtained using two‐dimensional gel electrophoresis. Two OMPs (TolC and flagellin) and five IMPs [transcription termination factor (NusA), long‐chain fatty acid transport protein (FadL), elongation factor Tu (EF‐Tu), ATP synthase F1, alpha subunit (F1‐ATPa) and dihydrolipoamide dehydrogenase (DLD)] were identified using LC‐ESI‐Q‐TOF MS/MS and Mascot program. Real‐time quantitative polymerase chain reaction was also performed to determine the mRNA expression level of the target genes. All seven membrane proteins except FadL were upregulated in the AMP‐resistant clones, both in the translational and transcriptional levels. Conclusions: Our results suggested that V. parahaemolyticus may obtain their resistance against AMPs through upregulation of the multidrug efflux transporter, effective repair of damaged membranes and prevention of cellular penetration of AMPs. Significance and Impact of the Study: To the best of our knowledge, this is the first report describing bacterial AMP resistance mechanism using proteomic methodologies. Elucidating the mechanism could help in the development of more sustainable antimicrobial agents.
Vibrio parahaemolyticus is a common foodborne pathogen frequently causing outbreaks in summer. Maintenance of virulence by the viable but nonculturable (VBNC) state of this pathogen would allow its threat to human health to persist. This study reports on the change in virulence and concomitant changes in activity of two enzymes and fatty acid profiles when V. parahaemolyticus ST550 entered the VBNC state in the modified Morita mineral salt-0.5% NaCl medium incubated at 4 degrees C. The major change in fatty acid composition occurred in the first week, with a rapid increase in C15:0 fatty acid and saturated/unsaturated ratio while a rapid decrease in C16:1 was observed. The activity level of the inducible protective enzyme superoxide dismutase became undetectable in the VBNC state, whereas that of constitutive glucose-6-phosphate dehydrogenase did not change in either the exponential phase or the VBNC state. Cytotoxicity against HEp-2 cells and a suckling mouse assay showed that virulence was lowered in the VBNC state compared with exponential-phase cells. Longer incubation times were required by the VBNC cells to achieve the same level of virulence as seen in exponential-phase cells. Culturable cells were recovered on selective agar medium from the VBNC cultures injected into suckling mice, probably as the result of in vivo resuscitation. Results of this study add to our understanding of the biochemical and physiological changes that have not been reported when V. parahaemolyticus enters into the VBNC state.
Vibrio parahaemolyticus, an important seafood-associated enteropathogen, usually encounters different adverse conditions in its native or food-processing environment, and the stresses resulting from these conditions may affect the survival of this pathogen and thus change its risk with regard to food hygiene. In this study, we investigated the thermotolerance of V. parahaemolyticus under sublethal heat shock and characterized this response by examining the changes in protein profiles and toxin production. Logarithmically grown cells heat shocked at 42 degrees C for 30 min were more resistant to thermal inactivation at 47 degrees C than were unshocked cells. After the 25 degrees C culture was heat shocked, 24 species of proteins were induced, while 13 species were inhibited, as indicated by polyacrylamide gel electrophoresis. DnaJ-, GroEL-, and GroES-like proteins with molecular sizes of 47, 62, and 12 kDa, respectively, were detected by immunoblotting with antibodies raised against the Escherichia coli proteins. During 1 to 8 h of heat shock, GroEL-like protein was produced in substantial amounts and was present in the periplasmic and extracellular fractions, while DnaJ- and GroES-like proteins were present mainly in the total cellular fraction. DnaK-like protein was not detected; nevertheless, the presence of the dnaK-like genetic element was revealed by Southern blotting. Production of thermostable direct hemolysin, the major virulence factor in V. parahaemolyticus, was enhanced in the cells heat shocked at 42 degrees C but not in those heat shocked at 37 degrees C.
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