Vulnificus is a Gram-negative
bacterium that is
not well recognized by
many microbiologists, and almost not at all by
the general public, even though it is
responsible for 95% of all seafood deaths in the
United States (Figure 1).
V. vulnificus belongs to the same
family as the bacterium
which is the causative agent of cholera.
V. vulnificus is
normally found in marine or estuarine
environments, including brackish ponds and
coastal areas. The bacteria can be isolated from
seawater and sediment, as well as plankton and
shellfish (oysters, clams, and crabs). Therefore,
usually occurs through the consumption of
infected seafood or from swimming in infected
waters with an open wound.
V. vulnificans most commonly infects those who are
immunocompromised, especially those that suffer
from chronic liver disease, leading to mild to
severe gastrointestinal illness, potentially
with a significant mortality rate among
This scanning electron micrograph
depicts a flagellated Vibrio vulnificus
bacterium [13184 X].
via a single flagellum and is
slightly curved in shape (Figure 2). It is considered a
moderate halophile, and thrives in warm
seawater. As a Gram-negative bacterium,
produces lipopolysaccharide (LPS) in its
outer membrane. The bacteria can also be
enclosed in a capsule, or have no capsule; this
characteristic relates to species virulence.
This colorized scanning
electron micrograph depicted a flagellated
Vibrio vulnificus bacterium [26367 X].
The primary indication that a particular
may be virulent is the presence of a
capsule. Strains that are capsulated are
pathogenic, while those without a capsule are
not. This can be determined by observation of
colonies, as noncapsulated
V. vulnificus colonies appear
translucent. This bacterium can be broken up
into two biotypes, namely, one that invades
humans, and a second that invades shellfish or
has type IV pili (fimbriae) which are required for virulence
These fimbriae are what allows the bacteria to
bind to human epithelial cells and is a key
factor in the virulence of the bacteria. The
receptor for the fimbrae has not yet been
elucidated. Yet another virulence1 factor
recently determined for
is the presence of an RTX toxin that
creates pores in red blood cells, depolymerizes
actin, and causes necrotic death of some cells (Gulig
et al., 2005).
with arrows pointing to several fimbriae.
Infections and Diagnosis: In
normal individuals, infection with
generally results in vomiting, diarrhea,
and abdominal pain. However, if a person is
immunocompromised (particularly suffering from
chronic liver disease) the bacteria can invade
the bloodstream and cause primary septicemia
(whole body inflammation in response to an
infection) which is characterized by fever,
chills, decreased blood pressure (septic shock),
and death. 70% of these cases are accompanied
with blistering skin lesions.
vulnificus can be diagnosed via the
individual's stool or blood. PNCC broth
(peptone, NaCl, cellobiose with colistin
1998) can be used to
increase low levels of
while selecting for
other types of bacteria. Generally, healthcare
providers should notice the combination of
gastrointestinal illness (vomiting, diarrhea,
abdominal pain) presenting after the ingestion
of oysters (or other seafood) should bring
to the top of the list as
possible pathogens. Additionally,
V. vulnificus will
affect males more than women, where 85% of cases
resulting in endotoxic shock are males. It has
been show experimentally that estrogen has a
protective effect against
(Merkel et al., 2001).
infection can be treated
if infection is caught early enough through the
use of the antibiotic tetracycline or
Chemical structure of tetracycline.
Bourdage, K., and Starks, A. (2005) Molecular
Microbiology, 43(S): 118-131.
Hsu, W., Wei, C., and
Tamplin, M. (1998) Enhanced Broth Media for
Selective Growth of
Merkel, S., Alexander S., Zufall, E., Oliver, J., and Huet-Hudson, Y. (2001).
Essential Role for Estrogen in Protection
Endotoxic Shock. Infection and Immunity,
69 (10): 6119–6122.