Molecular Evidence of Clonal Vibrio parahaemolyticus
Molecular Evidence of Clonal Vibrio parahaemolyticus
The upsurge in worldwide incidence of Vibrio parahaemolyticus infection in the last 5 years has been attributed to the recent appearance of three serotypes with pandemic potential: O3:K6, O4:K68, and O1:K untypeable (KUT). Thirty-five strains of these serotypes, isolated from different countries over 4 years, were characterized by ribotyping and pulsed-field gel electrophoresis to determine their origin. The ribotypes of the strains of these serotypes were indistinguishable, except for a Japanese tdh- negative O3:K6 strain and a U.S. clinical O3:K6 isolate, which had slightly different profiles. The migration patterns of the NotI-digest of the total DNA of the strains were similar, and only slight variations were observed between the serotypes. By contrast, the O3:K6 and O1:KUT strains isolated before 1995 and strains of other serotypes had markedly different profiles. The O4:K68 and O1:KUT strains most likely originated from the pandemic O3:K6 clone.
Infections caused by Vibrio parahaemolyticus, a halophilic member of the genus Vibrio, have increased globally in the last 5 years. V. parahaemolyticus diarrhea results from consuming raw or undercooked seafoods, although other routes of transmission have been documented. Studies implicate the thermostable direct hemolysin (TDH) and the TDH-related hemolysin (TRH), encoded by the tdh and trh gene, respectively, as the major virulence factors of this organism. Therefore, the presence of the tdh gene marked by a beta-type hemolysis on Wagatsuma agar, the trh gene correlated to a positive urease test, or both serve as markers for pathogenic strains. Recently, three major serotypes--O3:K6, O4:K68, and O1:K untypeable (KUT), listed in chronological order of appearance-- have caused a pandemic of V. parahaemolyticus infection. Strains of these serotypes have been responsible for gastroenteritis in India, other Southeast Asian countries, and the United States. In Calcutta, strains of the O3:K6 serotype have been responsible for the high incidence of V. parahaemolyticus-mediated gastroenteritis since February 1996. Likewise, this serotype was isolated in other Asian countries (including Laos, Taiwan, and Japan) and the United States.
This alarming rise of a serotype previously associated with only sporadic cases of gastroenteritis was monitored closely. The O3:K6 strains isolated before 1995 (henceforth referred to as old O3:K6) and those isolated since 1995 (referred to as new O3:K6) were analyzed for variation in nucleotide sequence of the toxRS region and differed invariably in seven bases within the 1,364-bp toxRS region. Two out of the seven unique bases were exploited to develop the group-specific polymerase chain reaction (GS-PCR) that distinguished between the new and the old O3:K6 isolates. Examination of the non-O3:K6 isolates by GS-PCR showed that the toxRS sequences of the recent isolates of O4:K68 and O1:KUT serotypes were identical to those of the new O3:K6 isolates. All the strains of the new clone (regardless of serotype or place of isolation) carried the tdh gene but not the trh gene. These strains also exhibited a unique arbitrarily primed PCR profile distinct from the strains of other serotypes, supporting the hypothesis that the O4:K68 and O1:KUT strains evolved from the newly emerged O3:K6 clone. Using ribotyping and pulsed-field gel electrophoresis (PFGE), we examined whether a single clone expressed as three different serotypes of V. parahaemolyticus is causing the pandemic.
The upsurge in worldwide incidence of Vibrio parahaemolyticus infection in the last 5 years has been attributed to the recent appearance of three serotypes with pandemic potential: O3:K6, O4:K68, and O1:K untypeable (KUT). Thirty-five strains of these serotypes, isolated from different countries over 4 years, were characterized by ribotyping and pulsed-field gel electrophoresis to determine their origin. The ribotypes of the strains of these serotypes were indistinguishable, except for a Japanese tdh- negative O3:K6 strain and a U.S. clinical O3:K6 isolate, which had slightly different profiles. The migration patterns of the NotI-digest of the total DNA of the strains were similar, and only slight variations were observed between the serotypes. By contrast, the O3:K6 and O1:KUT strains isolated before 1995 and strains of other serotypes had markedly different profiles. The O4:K68 and O1:KUT strains most likely originated from the pandemic O3:K6 clone.
Infections caused by Vibrio parahaemolyticus, a halophilic member of the genus Vibrio, have increased globally in the last 5 years. V. parahaemolyticus diarrhea results from consuming raw or undercooked seafoods, although other routes of transmission have been documented. Studies implicate the thermostable direct hemolysin (TDH) and the TDH-related hemolysin (TRH), encoded by the tdh and trh gene, respectively, as the major virulence factors of this organism. Therefore, the presence of the tdh gene marked by a beta-type hemolysis on Wagatsuma agar, the trh gene correlated to a positive urease test, or both serve as markers for pathogenic strains. Recently, three major serotypes--O3:K6, O4:K68, and O1:K untypeable (KUT), listed in chronological order of appearance-- have caused a pandemic of V. parahaemolyticus infection. Strains of these serotypes have been responsible for gastroenteritis in India, other Southeast Asian countries, and the United States. In Calcutta, strains of the O3:K6 serotype have been responsible for the high incidence of V. parahaemolyticus-mediated gastroenteritis since February 1996. Likewise, this serotype was isolated in other Asian countries (including Laos, Taiwan, and Japan) and the United States.
This alarming rise of a serotype previously associated with only sporadic cases of gastroenteritis was monitored closely. The O3:K6 strains isolated before 1995 (henceforth referred to as old O3:K6) and those isolated since 1995 (referred to as new O3:K6) were analyzed for variation in nucleotide sequence of the toxRS region and differed invariably in seven bases within the 1,364-bp toxRS region. Two out of the seven unique bases were exploited to develop the group-specific polymerase chain reaction (GS-PCR) that distinguished between the new and the old O3:K6 isolates. Examination of the non-O3:K6 isolates by GS-PCR showed that the toxRS sequences of the recent isolates of O4:K68 and O1:KUT serotypes were identical to those of the new O3:K6 isolates. All the strains of the new clone (regardless of serotype or place of isolation) carried the tdh gene but not the trh gene. These strains also exhibited a unique arbitrarily primed PCR profile distinct from the strains of other serotypes, supporting the hypothesis that the O4:K68 and O1:KUT strains evolved from the newly emerged O3:K6 clone. Using ribotyping and pulsed-field gel electrophoresis (PFGE), we examined whether a single clone expressed as three different serotypes of V. parahaemolyticus is causing the pandemic.
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