Modernist-Cuisine-Vol.-1-Small

2
THE ORIGIN OF
Scientific Names
In 1735, the great Swedish botanist Carl von Linné (better
known as Carolus Linnaeus) invented a naming system that
is still the preferred method for the scientific classification
of living things. Under Linnaeus’s system, every organism
receives a two-part scientific name. The first part, the
genus, is akin to a family’s surname, whereas the second,
the species, refers to a specific representative of that clan.
A typical scientific name of a bacterium, for example, is
Escherichia coli. In this case, Escherichia denotes the genus,
and coli refers to the species. By convention, researchers
italicize the full name, capitalize the first letter of the genus,
and leave the species in lowercase letters. An abbreviated
scientific name consists of only the first letter of the genus,
followed by the full species name: E. coli.
The same naming convention applies to nearly all organisms,
extant or extinct, which makes the king of the dinosaurs
Tyrannosaurus rex, or T. rex, and we humans Homo sapiens, or
H. sapiens. To refer to an entire genus, the abbreviation “spp.”
is sometimes used: Salmonella spp. means the species within
the genus Salmonella.
Species in the same genus are close relatives: E. coli and
E. albertii, for example. But they can remain quite different,
even though they may still interbreed. H. sapiens, for example,
differs rather markedly from the now-extinct Neanderthal, or
H. neanderthalensis.
The person who first describes an organism generally
names it as well. Sometimes the scientist’s name becomes
part of the organism’s: E. coli, for instance, was named in
honor of the German pediatrician Theodor Escherich, who
observed the bacterium in 1885.
Scientists have argued for years over how to name viruses.
Most researchers now accept a genus–species classification
system for viruses while often pairing scientific and informal
monikers: Desert Shield virus and Norwalk virus, for example,
are two species within the genus Norovirus.
Note that viral species names are often not italicized.
Informally, their names still can be a single word—norovirus,
for example—or multiple words such as human immunodeficiency
virus, otherwise known as HIV.
Naming prions has proved even more problematic, but the
largest international database of viral names gives prions their
own genus. Labels for other nonliving biological entities such
as plasmids do not follow species-naming conventions at all
and can be rather complicated.
Foodborne diseases from viruses proved far less
severe in general, resulting in only 129 deaths
(7.1%), despite the huge number of viral cases.
And the few cases that the study ascribes to
parasitic worms did not cause any fatalities at all.
The CDC study indicates, for instance, an estimated
mortality rate of three deaths per 1,000 cases of
trichinellosis, compared with 200 deaths per
1,000 cases of listeriosis.
Foodborne diseases can be exceedingly common.
The CDC study, for example, estimates that
every year, some 76 million cases occur in the
United States alonerepresenting a case in
roughly one in four U.S. residents. Nevertheless,
the vast majority of cases produce few symptoms,
and most cases that result in serious illness,
hospital admission, or death tend to occur among
people who are vulnerable for various reasons:
infants, the elderly, or people with compromised
immune systems, such as chemotherapy patients
or those with acquired immune deficiency syndrome
(AIDS) or AIDS-related complex.
But while many people experience a mild bout
of foodborne illness, very few die from it in the
richer countries of the world. Based on the estimated
U.S. population of 273 million in 1999, the
odds of someone dying from a foodborne illness
that year in the United States would have been
about one in 52,500. Given that Americans
consumed about 300 billion meals that year, the
odds of any particular meal proving lethal were
about one in 58 million.
Compare that with the risks of driving to
dinner or the supermarket. In the same year that
the CDC did its study, about 42,000 Americans
were killed in motor vehicle accidents, yielding
odds of one in 6,500 of dying from a car crash that
year, a factor of eight higher than the odds of
dying from foodborne illness. This comparison in
no way minimizes the importance of taking
adequate precautions to avoid foodborne illness,
of course, but provides perspective. It is worth
remembering that life carries risks and that the
risk of fatalities resulting from foodborne diseases
is considerably lower than those related to other
routine activities.
Contamination Sources
Food is not a natural habitat for pathogenic microorganisms.
Instead, it must be contaminated from
external sources with live organisms, their spores,
Domain: Eukarya (Plantae, Fungi, Animalia, and Protista)
Sea star Snake Rabbit Cat Fox Coyote Wolf
Kingdom: Animalia
Phylum: Chordata
Domain: Bacteria
Kingdom: Eubacteria
Phylum: Proteobacteria
Viruses Sicken, but Bacteria Kill
The vast majority of illnesses and deaths from foodborne microorganisms in the United
States are caused by three kinds of microbes: viruses, bacteria, and protists, according to
estimates made in 1999 by researchers at the U.S. Centers for Disease Control and
Prevention (CDC). Viruses, led by norovirus infections, are the biggest culprits in
foodborne morbidity. They are implicated in about two-thirds of illnesses from contaminated
food (left).
But most viral illnesses are mild, so the picture for mortality (right) is quite different.
Protists, which cause fewer than 3% of cases, result in more than 20% of deaths, due in
large part to the lethality of Toxoplasma gondii. And although bacteria may cause fewer
than half of foodborne illnesses, they are blamed for almost 75% of fatalities; salmonellas
and listerias are the worst offenders. The only parasitic worm included in the CDC study is
Trichinella spiralis, which is so rare a pathogen as to barely show up in the statistics.
Class: Mammalia
Class: Gamma-proteobacteria
Illnesses by organism
Deaths by organism
All life on Earth fits into the naming scheme
invented by Carl von Linné (know as Linnaeus).
The hierarchy includes kingdom, phylum, class,
order, family, and finally the two grouping levels
that are most often mentioned: genus and species.
Here we show two examples. The bottom left bar
represents dogs, which form the subspecies Canus
lupus familiaris. They fit into a specific part of the
hierarchy. To the right is E. coli O157:H7, a
foodborne pathogen that fits into a different part
of the same hierarchy.
Order: Carnivora
Family: Canidae
Genus: Canis
Species: Canis lupus
Subspecies: Canus lupus familiaris
Order: Enterobacteriales
Family: Enterobacteriaceae
Genus: Escherichia
Species: Escherichia coli
Strain: Escherichia coli O157:H7
Viruses
67.2%
Worms
0.0004%
Bacteria
30.2%
Protists
2.6%
Viruses
7.1%
Protists
21.2%
Bacteria
71.7%
112 VOLUME 1 · HISTORY AND FUNDAMENTALS
MICROBIOLOGY FOR COOKS 113