The science of salmonella
of Article: http://www.latimes.com/features/health/la-he-salmonella10-2009aug10,0,1339,full.story
The deadly bacterium, responsible for recent pistachio and peanut
recalls, can live in many wild animals and in almost any climate. And
it's thriving in our modern lifestyle.
By Karen Kaplan
August 10, 2009
This is salmonella's world. We're just living in it.
The bacterium appeared on the planet millions of years before humans, and
scientists are certain it will outlast us too. It's practically
guaranteed that salmonella will keep finding its way into the food supply
despite the best efforts of producers and regulators.
Since breaking off from its close cousin E. coli more than 100
million years ago, salmonella has evolved into more than 2,500 strains.
Some, such as Typhi, sicken humans but have no effect on other animals.
Others sicken animals but not humans, with certain strains unique to a
The bacterium is in so many wild animals that scientists have no hope of
"There won't be a world without salmonella, period," said
Eduardo Groisman, a molecular microbiologist at Washington University in
St. Louis. "I haven't kept track recently, but 15 years ago when I
last checked in detail, there were at least 100 different animal species
in which salmonella had been isolated, from camels to cockroaches."
Salmonella's goal in life is to find its way into an animal's gut, where
it can burrow in and multiply. Then, by triggering episodes of diarrhea
and vomiting, the bacterium makes sure it is spread far and wide in the
environment again, the better to find new hosts.
It can hitchhike its way into the gastrointestinal tract on cigarette
butts, pens or anything else that goes into the mouth.
Animals that live in close proximity to their feces can wind up with an
invisible coating of salmonella. The adorable baby chicks ubiquitous on
Easter are known to transmit salmonella to their handlers.
A Komodo dragon at the Denver Zoo sickened dozens of people -- and sent
eight to the hospital -- almost 15 years ago by licking handrails in its
exhibit area, which were then touched by visitors, who later ate without
washing their hands.
The baby turtle craze of the 1970s caused so many cases of salmonellosis
among children that the Food and Drug Administration banned the sale of
pet turtles with shells shorter than 4 inches.
The Centers for Disease Control and Prevention says there are 40,000
reported cases of salmonellosis in the U.S. each year. That's just the
tip of the iceberg. Epidemiologists estimate that for each case that is
reported, there are 38.6 additional patients who become ill but aren't
formally recognized by the medical system.
Salmonellosis kills 400 Americans annually, mostly children, the elderly
and people whose immune systems are already compromised by diseases such
Salmonella was discovered in the late 1880s by Dr. Theobald Smith while
he was developing vaccines for pigs at the U.S. Department of
Agriculture. The organism was named after his boss, Dr. Daniel Sal- mon,
first author of the report that introduced the bug to the scientific
The bacterium caused humans very little trouble until the 1940s. Then,
over the following 50 years, the incidence of salmonellosis jumped more
than tenfold, said Dr. Robert Tauxe, deputy director of the CDC's
division of food-borne diseases.
"It's a modern pathogen," he said. "It thrives in our modern
It resembles a tiny caterpillar, with long, flailing tails sticking out
in all directions to help it move. More than 100,000 of the organisms
would fit on the head of a pin -- but under the right circumstances, as
few as half a dozen could make a person sick.
Salmonella prefers warm, damp environments with little oxygen, which is
why it is so prevalent in manure and other forms of excrement. But it can
live in almost any climate. If conditions aren't suitable for growth, it
can lie dormant for a year or longer, waiting for the right opportunity.
"It's like the sea monkeys you had as a kid -- you add water and it
comes to life," said Bill Marler, a Seattle lawyer who specializes
in food-borne illness cases and updates his Salmonella Blog
several times a day.
The rise of salmonella as a problem is due, in large part, to the
industrialization of agriculture and food processing. One infected cow
can transmit salmonella to more animals when it is part of a larger herd.
Chickens can keep salmonella in check while they roam free, but after
they are packed into cages and loaded onto trucks, stress prompts them to
start shedding the bacterium.
Rodents, birds and other intruders can spread salmonella through a food
processing plant. FDA inspectors found dead mice, a bird nest and rodent
pellets "too numerous to count" earlier this year in a Texas
plant operated by Peanut Corp. of America, the company at the center of
one of the biggest outbreaks in history.
Eating trends are also favoring the bug. Time-strapped Americans are
consuming more preprocessed meals, which means the food on our plates has
had more opportunity to be contaminated by handlers, machinery and other
ingredients, Tauxe said.
Then there's the increasing popularity of raw and undercooked foods. A
burger patty containing salmonella will be safe to eat once grilled to at
least 145 degrees, and poultry is in the clear after reaching 165
degrees, according to the Department of Agriculture. But the bacterium
can survive in the pink center of a seared slice of ahi tuna.
Salmonella can be hard to remove from fresh fruit and vegetables.
"It's difficult to sterilize a tomato," said Dr. Ferric Fang, a
professor of laboratory medicine and microbiology at the University of
Washington in Seattle. "With cantaloupes, there's no way to wash
them off because their skin is a little bit porous."
Once swallowed, salmonella is usually wiped out by stomach acid. But
people who take antacids or heartburn medications give the pathogen a
hand by making the stomach's pH level more tolerable. Salmonella that
survive the stomach move on to the intestine, where they attach
themselves to the lining and do their dirty work.
Ironically, antibiotics can also make people more vulnerable by wiping
out some of the useful gut bacteria that protect against invading
Scarfing lots of ice cream or French fries may also do salmonella a good
turn, because the bug can cloak itself in a protective layer of fat, Fang
In the developed world, the most common disease-causing salmonella is the
Typhimurium strain of Salmonella enterica. Victims typically feel
symptoms of gastroenteritis within 12 to 72 hours of infection, which can
last up to a week.
In about 3% or 4% of cases, salmonella hitches a ride into the
bloodstream, requiring treatment with antibiotics. Nearly all patients
Typhi, a more deadly strain, produces typhoid fever in the developing
world. The bacterium travels through the bloodstream to the liver and
spleen, where it changes its surface proteins to protect itself from the
body's chemical defenses.
The CDC estimates that 21.5 million people are stricken by typhoid fever
each year. Patients suffer high fevers, headaches, stomach pains, vomiting
and diarrhea. If they aren't treated with antibiotics, about one in eight
will die, said Groisman of Washington University.
When he accidentally ingested the Typhi organism himself, "it was
like hell," he said. After initial symptoms passed, he felt incredibly
weak for two months. "It was the worst disease I've ever had in my
For those charged with tracking down the source of an outbreak,
salmonella cases are among the most difficult to solve. E. coli
O157:H7 lurks in a more limited range of foods -- usually beef, lamb and
produce -- but "salmonella can be on anything," said William E.
Keene, a senior epidemiologist with the Oregon Public Health Division in
"There was all the flap about the jalapeño outbreak and the peanut
butter outbreak," Keene said. In between, he said, "there were
two others with hundreds of cases in dozens of states, and we have no
idea what caused them."
In a sign of the times, the FDA’s website
contains a generic template that companies can use to announce
"XYZ Inc. of Anywhere, MS, is recalling its 5 ounce packages of
'Snackies' food treats because they have the potential to be contaminated
with Salmonella," the mock-up begins.