Fundamental Food Microbiology, Third Edition - Fuad Fathir

398 FUNDAMENTAL FOOD MICROBIOLOGY
H. Detection Method
Bac. cereus can be enumerated by surface plating on an agar medium containing
mannitol, egg yolk, and polymyxin B (as a selective agent). Colonies surrounded
by precipitation resulting from lecithinase of the cells are indicative of Bac. cereus.
A. Importance
IV. CHOLERA
Cholera, caused by Vib. cholerae 01, 1,2,8,9 is a noncontagious disease but can cause
large epidemics with high mortality. In the 19th century, both epidemic and
isolated cholera cases were recorded in the U.S. Since 1911, the disease was
thought to be eradicated. Most of the outbreaks in the 20th century were recorded
in Asian countries. However, in 1973, a cholera case was recorded in Texas.
Between 1973 and 1987, 6 outbreaks involving 916 cases with 12 deaths were
recorded, mostly in the coastal states of the U.S. Contaminated seafoods (cooked
crab, finfish, and raw oysters) were involved in these cases. In 1991 and 1992, a
large cholera epidemic that started in Peru spread to many South American
countries and affected ca. 640,000 people, with 5600 deaths. It was also introduced
into the U.S. by travelers from these countries who either ate contaminated
foods before entering the U.S. or brought contaminated concealed foods to the
U.S. In addition to the 01 strains, Vib. cholerae non-01 strains have also been
involved in cholera cases (also designated as non-01 gastroenteritis) in the U.S.
and other countries. Non-01 strains were previously thought to be incapable of
causing large epidemics, but in 1992, a non-01 serotype, non-0139, was involved
in large epidemics in Bangladesh and India.
B. Characteristics
Vib. cholerae, like other vibrios, is a Gram-negative motile, curved rod. The species
has many serogroups. Strains in 01 are associated with epidemic cholera. This
serotype is further characterized by biotype and serotype. The type currently associated
with cholera epidemics worldwide is of the El Tor biotype and either Inaba
or Ogawa serotype. Non-01 serotypes do not agglutinate with antibodies prepared
against 01 antigens. Also, non-01 serotypes, similar to 01 serotypes, are not sensitive
to trimethoprim-sulfamethoxazole with furazolidone. Both types are sensitive to heat
and are killed by the temperature used for cooking. Improper heating (at lower
temperature for a shorter time) may not be able to kill all the cells present in a food.
The optimum temperature of growth is between 30 and 35�C. The growth rate is
very rapid, even at room temperature. The cells do not multiply in contaminated
live crabs, oysters, or fish. However, in cooked seafoods, rapid growth can occur at
25 to 35�C. Alkaline foods facilitate rapid growth. Survival of cells is better in
cooked foods at 5 to 10�C. 9,10