Biology Reference
In-Depth Information
30 min at 50°C or 1 h at 56°C. After washing, alkaline phosphatase activity
was then assayed with nitroblue tetrazolium plus 5-bromo-4-chloro-3-
indolyl-phosphate. Color development of
V. vulnifi cus
colony blots was
complete within 60 min. The method has the advantage of not requiring
purifi cation of colonies or metabolic characterization of isolates.
VIBRIO PARAHAEMOLYTICUS
Overview
Vibrio parahaemolyticus
is a Gam-negative polarly fl agellated facultatively
anaerobic enteropathogenic rod indigenous to coastal marine environments
and shellfi sh, that is capable of causing mild gastroenteritis to severe
debilitating dysentery
.
Infections of the gasro-intestinal (GI) tract are
usually due to consumption of raw shellfi sh. In addition, extra-intestinal
infections have also been reported to be due to the organism such as eye
and ear infections, and wound infections of the extremities. The fi rst
recorded outbreak of seafood infection due to
V. parahaemolyticus
occurred
in Japan in 1950 (Miwatani and Takeda, 1976; Fujino, 1951). Among
272 patients with acute gastroenteritis, 20 succumbed. The incubation
period with most cases was 2 to 6 h. The symptoms included acute
abdominal pain, vomiting, and diarrhea which was watery and in some
cases bloody diarrhea. A more severe and debilitating dysenteric form
of gastrointestinal infection with bloody stools and marked leucocytosis
requiring hospitalization has been observed in South East Asia, India, and
Bangladesh, with several outbreaks in the U.S., due particularly to strains
of the serotype O3 : K6 (Bolen et al., 1974; Hughes et al., 1978; Daniels et
al., 2000).
The organism is considered to be halophilic with an optimum NaCl
concentration of about 3.0% (Takikawa, 1958). The characteristics of the
organism were fi rst described in detail by Fujino et al. (1953). A major
distinction between
V. parahaemolyticus
and members of the genera
Aeromonas
and
Pseudomonas
is the formation of spheroplasts (Fujino et
al
.,
1965). All strains of
V. parahaemolyticus
have been found to possess
a thermolabile hemolysin encoded by the
lht
gene which is not directly
related to virulence. PCR primer pairs have therefore been developed
utilizing the resulting amplicons from the
lht
gene for identifi cation of all
isolates of
V. parahaemolyticus
. Virulence has been found to be associated
with two principle genes that code for (1) a thermally stable direct acting
hemolysin (
tdh
) and (2) a thermally stable direct acting—related hemolysin
(
trh
). However, not all clinical strains have been found to possess the
trh
gene. Primer pairs targeting sequences of the
tdh
gene are therefore used to
distinguish virulent from nonvirulent strains. Virulent strains are usually
characterized as Kanagawa Phenomenon (KP) positive which refers to
