Abstract
BackgroundHemolysis of bacteria is an important phenotype used for typing and characterizing strains with specific biomarkers and even a virulence factor in bacterial pathogenesis. In Vibrio cholerae, hemolysin HlyA is responsible for hemolysis of sheep red blood cells, and this hemolytic phenotype is used as a biotyping indicator and considered one of the virulence factors. At the beginning of the seventh cholera pandemic, the El Tor biotype strains of serogroup O1 were distinguished by hemolysis from the sixth pandemic O1 classical biotype strains, whereas during the following epidemics, nonhemolytic El Tor strains appeared, suggesting phenotypic and genetic variations in these strains. This study aimed to investigate the possible mechanisms involved in nonhemolysis of El Tor strains.ResultsFive sequence types of hlyA genes were found in the studied O1 El Tor strains isolated during the seventh pandemic. A 4-base deletion in hlyA caused the HlyA protein mutation and non-hemolytic phenotype. Some strains carry wildtype hlyA genes but are still non-hemolytic, and greatly reduced hlyA transcription and blocked secretion of hemolysin were observed in hemolysis tests of the subcellular components and transcription/expression analysis of hlyA.ConclusionsMechanisms responsible for nonhemolysis of the epidemic O1 El Tor strains are complex and not only confined to gene mutation but also deficiencies of transcription and extracellular transport of HlyA. Mutations in gene regulation and protein secretion systems of HlyA in the nonhemolytic V. cholerae strains should be areas of concern in future studies.
Highlights
Hemolysis of bacteria is an important phenotype used for typing and characterizing strains with specific biomarkers and even a virulence factor in bacterial pathogenesis
We focused on the hemolysis phenotype of the El Tor strains isolated in the seventh pandemic, with the goal of analyzing the hemolysin gene variance and the activities of the hemolysin in these hemolytic and nonhemolytic El Tor strains of V. cholerae
Variance of hlyA genes among the hemolytic/ nonhemolytic strains C6706 is a strain of V. cholerae El Tor biotype in the seventh pandemic with a typical hemolytic positive phenomenon and intact hlyA gene
Summary
Hemolysis of bacteria is an important phenotype used for typing and characterizing strains with specific biomarkers and even a virulence factor in bacterial pathogenesis. The causal strains of the seventh pandemic belong to serogroup O1, El Tor biotype, which can generate multiple toxins (mainly cholera toxin, CT) and toxin-related factors, and it can trigger severe watery diarrhea, dehydration and Hemolysin is an important virulence factor in many pathogenic bacteria, such as Streptococcus suis [5], Listeria monocytogenes [6], V. parahaemolyticus [7] and others. These hemolysins damage cells by forming pores in the cell membrane. Hemolysin acts on the target cell membrane, inserting into the lipid bilayer and forming a pentamer channel [12], which causes a large number of intracellular components to leak out and leads to cell death
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