No stop­ping sal­mo­nella in its sickly mis­sion

Sci­ence can­not de­feat the in­vin­ci­ble gut bug, KAREN KA­PLAN finds

Weekend Argus (Saturday Edition) - - LIFE -

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

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