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Lu (2003) found that the incorporation of sphingomyelinase (10 units/l)
to blood agar base containing 5.0% defi brinated sheep blood resulted in
most shellfi sh isolates of V. parahaemolyticus exhibiting readily discernible
but weak β-hemolysis. Sakazaki et al. (1968) reported that 2,655/2,720
(96.6%) of human clinical isolates were KP + and that only 7/650 (1%)
of environmental isolates were KP + . Thompson et al. (1976) found only
4/2,218 environmental isolates to be KP + .
Chun et al. (1974) found that the addition 0.01 M CaCl 2 to Wagatsuma
blood agar resulted in KP - strains becoming strongly hemolytic after 24 h
incubation and the hemolysis of KP + strains was greatly intensifi ed.
Nishibushi et al. (1985) developed a 406-bp gene probe specifi c for the
Vp-TDH gene. All 66 KP + strains examined were detected with the probe,
in addition to 12/14 weakly KP + strains and 10/61 KPO-strains. Among
121 other Vibrio isolates exclusive of V. parahaemolyticus , only V. hollisae
strains reacted with the probe under stringent conditions.
Molecular epidemiological studies have revealed that not only strains
carrying the tdh gene but strains carrying a trh gene or both genes are
strongly associated with gastroenteritis (Okuda et al ., 1997a; Shirai et al.,
Shirai et al. (1990) used tdh and trh gene probes to detect the TDH and
TRH producing genes in strains of V. parahaemolyticus . Among a total of
214 clinical strains, 112 (52.3%) had the tdh gene only, 52 strains (24.3%)
had the trh gene, and 24 strains (11.2%) carried both the tdh and trh genes.
Among 71 environmental strains, 5 (7.0%) exhibited weak hybridization
with the trh gene probe and none hybridized with the tdh gene probe.
These results suggest that the TRH as well as the TDH is an important
virulence factor for V. parahaemolyticus .
DePaola et al. (2003b) examined oysters for the presence and density
of V. parahaemolyticus harvested from March, 1999 through September,
2000 in Mobile Bay, Alabama, U.S.A., a coastal area known to endemically
harbor the organism and to be involved in outbreaks at that time. DNA
probes targeting the tlh and tdh genes were used for confi rmation of total
and pathogenic ( tdh + ) strains. V. parahaemoltyicus was detected in all 156
samples with densities ranging from <10 to 12,000/g.
Urease (Uh) Production
The majority of clinical and environmental isolates in early studies were
usually found to be urease negative (Uh - ). Sakazaki et al. (1963) reported
only 4% of strains tested to be urease positive. Abbott et al. (1989) were the
fi rst to report the isolation of Uh + clinical strains from the West Coast of
California and Mexico and indicated that by 1983, Uh + V. parahaemolyticus
had become the predominant biotype in California outbreaks. A correlation
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