Emergence of a unique O3:K6 clone of Vibrio parahaemolyticus in Calcutta, India, and isolation of strains from the same clonal group from Southeast Asian travelers arriving in Japan

Abstract

Active surveillance of Vibrio parahaemolyticus infection among hospitalized patients in Calcutta, India, was initiated in January 1994. The incidence of cases of V. parahaemolyticus infection suddenly increased in February 1996 and has remained high since then. One hundred thirty-four strains of V. parahaemolyticus isolated from January 1994 to August 1996 were examined for serovar, the presence of the thermostable direct hemolysin gene (tdh) and tdh-related hemolysin genes (trh1 and trh2), production of urease, and antibiogram. Strains of the O3:K6 serovar appeared for the first time in February 1996. The O3:K6 serovar strains accounted for 50 to 80% of the strains isolated during the high-incidence period (February to August 1996). All of the serovar O3:K6 strains carried the tdh gene but not the trh genes and did not produce urease. All of the isolates except two were sensitive to all of the antibiotics tested. These and the results of analysis by an arbitrarily primed PCR method indicated that the O3:K6 serovar strains belong to a unique clone. When the O3:K6 serovar strains, isolated from travelers arriving in Japan from Southeast Asian countries, were compared by the arbitrarily primed PCR method, the strains isolated between 1982 and 1993 were distinct from Calcutta O3:K6 while the strains isolated in 1995 and 1996 were indistinguishable from the Calcutta O3:K6 strains. The results suggest that this unique O3:K6 clone may have become prevalent not only in Calcutta but also in Southeast Asian countries very recently. Not only the O3:K6 strains but also the non-O3:K6, tdh-bearing strains isolated in 1996 produced thermostable direct hemolysin at high levels, and thus the level of hemolysin produced does not appear to have influenced the high incidence of serovar O3:K6 strains.

A unique and common restriction fragment pattern of the nucleotide sequences homologous to the genome of Vf33, a filamentous bacteriophage, in pandemic strains of Vibrio parahaemolyticus O3:K6 O4:K68, and O1:K untypeable

“…2A, lanes 232 7). This result provides another line of evidence to support the hypothesis that the pandemic strains belonging to O3:K6, O4:K68, and O1:KUT serovars are clonal [6,7].…”

“…A possible explanation for the outbreak of the pandemic strains is that these strains may be more virulent than other strains, or may survive better in environments, or both. Between the pandemic strains and the others, there is no signi¢cant di¡erence in the level of the TDH product and antibiotic susceptibility [7]. Other characteristics possibly associated with virulence and survival in the environments need to be searched.…”

Resuscitation of viable but non-culturable Vibrio parahaemolyticus in a minimum salt medium

“…The O3:K6 strains considered are the first pandemic strains of this pathogen that spread rapidly throughout many Asian countries since 1996. These O3:K6 strains have a very close clonality, as determined by pulsed-field gel electrophoresis or other molecular methods [12,21]. However, the induction time of the VBNC state was also strain-dependent (Table 1).…”

Molecular characterization of thermostable direct haemolysin‐related haemolysin (TRH)‐positive Vibrio parahaemolyticus from oysters in Mangalore, India

“…The pathogenic V. parahaemolyticus bearing tdh and/or trh genes belong to diverse serotypes. However, since 1996, a pandemic clone of O3:K6 which was first detected in Calcutta, India (Okuda et al ., 1997) has been responsible for many outbreaks in Asia and the USA (WHO, 1999;Daniels et al ., 2000;Chowdhury et al ., 2004). These strains were tdh positive, trh and urease negative.…”