No stopping salmonella in its sickly mission
Science cannot defeat the invincible gut bug, KAREN KAPLAN finds
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 to fight it.
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 single species.
The bacterium is in so many wild animals that scientists have no hope of controlling it.
“There won’t be a world without salmonella, period,” said Eduardo Groisman, a molecular microbiologist at Washington University, St. Louis. “I haven’t kept track recently, but 15 years ago when I last checked in detail, there were at least 100 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 diarrhoea and vomiting, the bacterium makes sure it is spread far and wide in the environment again, 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 close to their faeces can wind up with an invisible coating of salmonella. The adorable Easter chicks are known to transmit salmonella to their handlers.
A Komodo dragon at the Denver Zoo sickened dozens of people almost 15 years ago by licking handrails in its enclosure, 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 small pet turtles.
The Centres for Disease Control and Prevention says there are 40 000 reported cases of salmonellosis in the US each year. Epidemiologists estimate that for each case that is reported, there are 38.6 extra victims.
Salmonellosis kills 400 Americans annually, mostly people whose immune systems are compromised by diseases such as HIV/Aids.
Over the past 60 years, the incidence of salmonellosis has jumped more than tenfold, said Dr Robert Tauxe, deputy director of the CDC’s division of food-borne diseases.
“It thrives in our modern lifestyle,” he said. More than 100 000 of the organisms would fit on the head of a pin – but 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.
The rise of salmonella as a problem is due, in large part, to the industrialisation of agriculture and food processing. One infected cow can transmit salmonella to more animals in a large herd. When chickens 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 centre of one of the biggest outbreaks in history.
Eating trends also favour the bug. Time-strapped Americans are eating 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°C, and poultry is in the clear after reaching 165°C, according to the Department of Agriculture. But the bacterium can survive in the pink centre of a seared slice of ahi tuna.
Salmonella can be hard to remove from fresh fruit and vegetables. “It’s difficult to sterilise a tomato,” said Dr Ferric Fang, a professor at the University of Washington, Seattle.
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 do their dirty work.
Ironically, antibiotics can also make people more vulnerable by wiping out some of the useful gut bacteria.
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 said. – LA Times