50 PRINCIPLES OFFOODSANITATION
healthy individuals, including family mem-
bers of patients. Sewage-contaminated
water is a source of transmission of this
microorganism (Wesley, 1997).
Legionellosis
Legionella pneumophilais a vibrant bac-
terium that causes Legionnaires’ disease.
This facultative gram-negative microbe is
found in contaminated waters in most of the
environment and is becoming a widespread
concern. This bacterium is able to multiply
intracellularly within a variety of cells. The
dominant extracellular enzyme produced by
L. pneumophilais a zinc metalloprotease,
also called a tissue-destructive protease,
cytolysin, or major secretoryprotein. This
protease is toxic to different types of cells
and causes tissue destruction and pul-
monary damage, which suggests its involve-
ment in the pathogenesis of Legionnaires’
disease.
This microorganism causes 1 to 5% of
community-acquired pneumonia in adults,
with most cases occurring sporadically. The
Center for Disease Control and Prevention
receives 1,000 to 3,000 reports of cases of
Legionnaires’ disease each year. Most of the
outbreaks have been shown to be caused by
aerosol-producing devices, such as cooling
towers, evaporating condensers, whirlpool
spas, humidifiers, decorative fountains,
shower heads, and tap water faucets.
Water is the major reservoir for Legionella
organisms; however, this microorganism is
found in other sources, such as potting soil.
Amoebae and biofilms, which are ubiquitous
within plumbing systems, have a critical role
in the amplification process of supporting
the bacterial growth.
Legionellosis is usually transmitted
through the inhalation ofLegionellaorgan-
isms as liquid that has been aerosolized to
respirable size (1 to 5 μm). Occasional trans-
mission occurs through other routes, such as
inoculation of surgical wounds with contam-
inated water during the placement of surgi-
cal dressings.Vibriospp.
Several species ofVibrio, such as Vibrio
parahaemolyticus,Vibrio cholerae, and Vib-
rio vulnificans, are known pathogens. This
microbe is a gram-negative, non-spore-
forming, straight to curved facultatively
anaerobic rod.V. parahaemolyticusgrows at
13 to 45ºC with an optimum range of 22
to 43ºC. This microbe grows at pH 4.8 to
11.0 with an optimum range of 7.8 to 8.6,
while the range and optimum for V. cholerae
is 5.0 to 9.6 and 7.6 and for V. vulnificusis
5.0 to 10.0 and 7.8. The minimal Awis 0.94,
0.96, and 0.97 for V. parahaemolyticus,
V. vulnificus, and V. cholerae, respectively.
The optimal amount of salt is 0.5, 2.5, and
3.0 for V. cholerae,V. parahaemolyticus, and
V. vulnificus, respectively. The primary habi-
tat for Vibriois seawater.
The onset time for V. parahaemolyticus
gastroenteritis is 8 to 72 hours with an aver-
age of 18 hours. Symptoms include diarrhea
and abdominal cramps accompanied by
nausea, vomiting, and mild fever. Illness
duration is 48 to 72 hours with a low mortal-
ity rate. The number of cells required to
cause illness is 5 to 7 logs.Why Psychrotrophic and Other Pathogens
Have Emerged
In addition to improved detection meth-
ods for emerging pathogens, other reasons
exist for the emergence of these microbes.
Examples are:1.Changes in eating habits. Some “organ-
ically grown” products perceived to be
healthy are unsafe. An outbreak of lis-
teriosis was linked to coleslaw that was
made from cabbage fertilized with
sheep manure.