488 Chapter 28
indicator of fecal contamination in recre-
ational water. Fung et al. (2007) developed
the Fung Double Tube (FDT) system, which
can detect live C. perfringens in the tubes
about 5 hour after sampling the seawater. The
generation time (time for doubling of a popu-
lation of cells) of C. perfringens in ideal con-
ditions, such as in the FDT, is as short as
7.1 min at 42 ° C. This is the fastest method
known to obtain visible colony - forming units
of any bacteria in an agar system. More
recently, in 2009, by adding the phosphatase
test to the agar system, the black presumptive
C. perfringens colonies can be confi rmed as
C. perfringens in the FDT, due to the fl uo-
resces surrounding the black colony. With
more confi rmation, this test will help authori-
ties determine when to close beaches to
protect the public from contamination by
fecal microbes in recreational waters.Salmonella
Salmonella is the classic example of food -
borne infection. Salmonella enteritidis was
isolated in 1884 and still is an important
food - borne organism. In 2002, there were
357 outbreaks, with 32,610 cases and 13
deaths due to Salmonella reported in the
United States. The organism is a Gram -
negative, facultative anaerobic, non - spore -
forming rod, motile by peritrichous fl agella.
It does not ferment lactose and sucrose but
ferments dulcitol, mannitol, and glucose.
There are exceptions to the general charac-
teristics. For example, lactose - positive cul-
tures have been found, and nonmotile species
exist, such as S. pullorum and S. gallinarum.
The organism is heat sensitive but can toler-
ate a variety of chemicals, such as brilliant
green, sodium lauryl sulfi te, selenite, and
tetrathionate. These compounds have been
used for the selective isolation of this organ-
ism from food and water. To confi rm the
isolate as Salmonella , one must perform
serologic tests using polyvalent anti - O anti-
serum (against cell surface antigens) orannual cost of $123 million to the U.S.
economy. C. perfringens is a Gram - positive
anaerobic spore - forming rod and produces at
least 13 different toxins, which can cause
diseases such as gas gangrene. One of the
toxins is named Clostridium perfringens
enterotoxin (CPE), which is released in the
intestinal tract and causes infection/intoxica-
tion by this organism. Spores of this organ-
ism naturally distribute widely and can easily
contaminate foods.
Most of the incidents of C. perfringens
food poisoning involve meats prepared in
large quantities one day and consumed the
next day, after the food has been kept at luke-
warm temperatures. In such conditions, most
vegetative cells of competitors die off, while
the spores of C. perfringens have a chance
to survive, germinate, and grow into large
numbers (about 10,000 to 1 million per
gram). When ingested by a susceptible
person, these will start to sporulate in the
small intestine due to the favorable anaerobic
environment there. The gene coded for spor-
ulation also controls the release of an entero-
toxin that is responsible for the diarrhea
characteristics of C. perfringens food poison-
ing. It is noteworthy that C. perfringens does
not sporulate in foods, and therefore, the CPE
is not preformed in food to cause food - poi-
soning cases.
Symptoms occur between 8 and 20 hours
after ingestion of a large number of viable C.
perfringens and include acute abdominal
pain, diarrhea, and nausea, with rare vomit-
ing. The symptoms are milder than those
caused by Salmonella. Detection of this
organism is by anaerobic cultivation of food
using differential anaerobic agar, such as
tryptose sulfi te cycloserine agar. C. perfrin-
gens forms black colonies in this agar
medium. Immunologic methods such as
reverse - passive agglutination assay and
ELISA test have been developed to detect the
CPE in food, culture fl uid, and feces.
Recently, in the State of Hawaii, there has
been interest in using C. perfringens as the