chiarimento:antibiotici

["Alessandro Gimona" <agimona@hotmail.com>]

Perche' i cibi transgenici possono favorire la comparsa di resistenze ad 
antibiotici?

Brevemente,
dipende dal processo di produzione.

Molti cibi modificati hanno un gene marcatore per la resistenza ad 
antibiotici, associato ai geni che si vogliono inserire. Siccome il processo 
di incorporazione spesso non funziona, questo aiuta la selezione degli 
organismi che hanno incorporato i geni estranei (cioe' quelli resistenti - e 
quindi modificati- possono venir selezionati con l'antibiotico).

Nell' intestino, frammenti di DNA e quindi anche geni per la resistenza, 
possono venire in contatto con normali batteri intestinali e venire da loro 
incorporati. Questi possono poi passare la resistenza a eventuali batteri 
patogeni con cui in un secondo tempo, siano venuti a contatto. Si puo' 
creare cosi un ceppo di patogeni resistenti a quell' antibiotico.

Quanto e' probabile che questo accada?
difficile dirlo.
Per esempio, sotto riporto una notizia, pubblicata da New Scientist, e 
ripresa da Reuters riguardo a  uno studio olandese che conferma che la 
probabilita' non e' affatto remota:

Spero serva

Ciao
Alessandro Gimona
Peacelink

PS
dovremmo essere ancora piu' preoccupati del trattamento di animali con 
antibiotici, perche' la comparsa di batteri resistenti e il passaggio della 
resistenza a batteri patogeni e' molto probabile.

Per una visione d'insieme del grave problema della comparsa di resistenze 
potresti esaminare il rapporto OMS che tratta di questo tema.

Lo trovi al seguente indirizzo:

http://www.who.int/infectious-disease-report/index.html


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Antibiotics: Dutch Study casts doubts on genetically modified food

LONDON, Jan 27 1999 (Reuters) - An artificial gut designed by Dutch
researchers has cast doubts on the safety of genetically modified food, New 
Scientist
magazine reported on Wednesday.

The computer-controlled model of the stomach and intestines, designed to
mimic human food digestion, showed that antibiotic-**resistance** genes
introduced into food could jump to bacteria in the gut.

"The results show that DNA lingers in the intestine, and confirms that
genetically modified bacteria can transfer their antibiotic-**resistance**
genes to bacteria in the gut," according to the magazine.

One of the concerns about genetically engineered crops is that
antibiotic-**resistant** genes could transfer to animals and humans and 
create superbugs
that cannot be killed by even the strongest **antibiotics**.

Some scientists claimed it could never happen because the modified DNA
breaks down so quickly. But the Dutch research showed DNA from the bacteria
had a half-life of six minutes in the large intestine.

"This makes it available to transform cells," said Robert Havenaar, the
designer of the artificial gut.

Hub Noteborn of the State Institute for Quality Control of Agricultural
Products in the Netherlands said the results of the study contradict the
safety assurances.

"It was a surprise to see that DNA persisted so long in the colon," he
told the magazine.

Not all bacteria transferred the **resistance** genes to normal gut
bacteria. A tomato engineered to resist rot caused no problems.

Havenaar and his colleagues plan further studies and are planning to ask
the European Union for funding.

Last week, a committee from Britain's House of Lords (upper house)
announced that the benefits of genetically modified food outweighed the
risks. They also concluded it was "extremely unlikely" that genes from food 
could
jump into gut bacteria.

Environmental groups have urged the government to ban all genetically
modified food. Top British chefs on Tuesday put their weight behind
opposition to what some have nicknamed "Frankenstein's food".

{Reuters:International-0127.00411} 01/27/99
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