Use of monoclonal antibodies to identify phospholipase C as the enterotoxic factor of the bifunctional hemolysin-phospholipase C molecule of Vibrio cholerae O139

Exogenous Polyunsaturated Fatty Acids Impact Membrane Remodeling and Affect Virulence Phenotypes among Pathogenic Vibrio Species

The pathogenic Vibrio species (V. cholerae, V. parahaemolyticus, and V. vulnificus) represent a constant threat to human health, causing foodborne and skin wound infections as a result of ingestion of or exposure to contaminated water and seafood. Recent studies have highlighted Vibrio's ability to acquire fatty acids from environmental sources and assimilate them into cell membranes. The possession and conservation of such machinery provokes consideration of fatty acids as important factors in the pathogenic lifestyle of Vibrio species. The findings here link exogenous fatty acid exposure to changes in bacterial membrane phospholipid structure, permeability, phenotypes associated with virulence, and consequent stress responses that may impact survival and persistence of pathogenic Vibrio species. Polyunsaturated fatty acids (PUFAs) (ranging in carbon length and unsaturation) supplied in growth medium were assimilated into bacterial phospholipids, as determined by thin-layer chromatography and liquid chromatography-mass spectrometry. The incorporation of fatty acids variably affected membrane permeability, as judged by uptake of the hydrophobic compound crystal violet. For each species, certain fatty acids were identified as affecting resistance to antimicrobial peptide treatment. Significant fluctuations were observed with regard to both motility and biofilm formation following growth in the presence of individual PUFAs. Our results illustrate the important and complex roles of exogenous fatty acids in the membrane physiology and virulence of a bacterial genus that inhabits aquatic and host environments containing an abundance of diverse fatty acids.IMPORTANCE Bacterial responses to fatty acids include, but are not limited to, degradation for metabolic gain, modification of membrane lipids, alteration of protein function, and regulation of gene expression. Vibrio species exhibit significant diversity with regard to the machinery known to participate in the uptake and incorporation of fatty acids into their membranes. Both aquatic and host niches occupied by Vibrio are rife with various free fatty acids and fatty acid-containing lipids. The roles of fatty acids in the environmental survival and pathogenesis of bacteria have begun to emerge and are expected to expand significantly. The current study demonstrates the responsiveness of V. cholerae, V. parahaemolyticus, and V. vulnificus to exogenous PUFAs. In addition to phospholipid remodeling, PUFA assimilation impacts membrane permeability, motility, biofilm formation, and resistance to polymyxin B.

Vibrio harveyi hemolysin induces ultrastructural changes and apoptosis in flounder (Paralichthys olivaceus) cells

Vibrio harveyi hemolysin (VHH) is considered a major pathogenic virulence factor to fish. However, the VHH active-site mutant has lost all hemolytic and phospholipase activities as well as pathogenicity. In this study, the effect of VHH on erythrocytes and a gill cell line from flounder was elucidated. Erythrocyte membranes formed thin tubular protrusions immediately after exposure to VHH, and membrane corrugations were evident after extended incubation. In contrast, the mutant VHH did not induce any gross morphological changes. With VHH-treated FG-9307 cells, a cell line derived from flounder gill, destruction of organelles and formation of features resembling apoptotic bodies were observed. Immunogold staining showed that a large amount of VHH was deposited on the membranes and membrane debris of erythrocytes and FG-9307 cells after treatment with VHH. Apoptotic features, such as chromatin condensation and apoptotic bodies, were observed in VHH-treated FG-9307 cells using DAPI staining. Moreover, cell cycle analysis showed that VHH increased the proportion of cells in G1 phase. In addition, VHH significantly increased the percentage of apoptosis, the number of TUNEL positive apoptotic cells, and caspase-3 activity in FG-9307 cells when compared with the untreated controls. These data suggested that VHH killed the cells through apoptosis via the caspase activation pathway.

A single residue change in Vibrio harveyi hemolysin results in the loss of phospholipase and hemolytic activities and pathogenicity for turbot (Scophthalmus maximus)

Vibrio harveyi hemolysin, an important virulence determinant in fish pathogenesis, was further characterized, and the enzyme was identified as a phospholipase B by gas chromatography. Site-directed mutagenesis revealed that a specific residue, Ser153, was critical for its enzymatic activity and for its virulence in fish.

Enterotoxins in Aeromonas-associated gastroenteritis

Aeromonas species produce an array of virulence factors, and the pathogenesis of Aeromonas infections is therefore complex and multifactorial. Aeromonas-associated gastroenteritis is especially a problem in young children. The potential involvement of enterotoxins in the pathogenesis of Aeromonas infections is discussed.

Comparative analysis of cytotoxin, hemolysin, hemagglutinin and exocellular enzymes among clinical and environmental isolates of vibrio cholerae O139 and non-O1, non-O139

The presence of three major virulence genes toxR, tcpA and ctxA as well as expression of several putative virulence factors were compared in 12 Vibrio cholerae O139 and non-O1,non-O139 strains of clinical and environmental origin. All the strains possessed the gene encoding the regulatory protein TOXR. None of the non-O1, non-O139 strains as well as one of the O139 environmental strains carried the genes for ctxA and tcpA. Statistically significant differences in hemagglutinin and hemolysin production were observed amongst the strains depending on the source of their isolation. Expression of extracellular enzymes such as protease, elastase, neuraminidase, phospholipase A and phospholipase C, however, did not vary significantly from the groups of strains isolated from different sources.