LONDON _ An advisory committee to the U.K.government has called for a ban on some geneticallymodified foods containing antibiotic resistant marker genes.The Advisory Committee on Novel Foods and Processes(ACNFP) looked at a number of safety issues related togenetically manipulated organisms (GMO) and concludedthat only one, "the possibility of transfer and subsequentexpression of marker genes in gut micro-organisms," is ofsignificance. The ACNFP is an independent expertcommittee that advises U.K. ministers on the safety ofnovel foods and food processes.In its "Report on the use of antibiotic resistance markers ingenetically modified food organisms" the committee makesa number of recommendations to the government. All areintended to address the growing concern about the transferof antibiotic resistance to the human population throughnew foods.The ACNFP comes down heaviest on foods containing liveorganisms. "Genetically modified micro-organisms whichare intended to be ingested live in human foods, such aslactic acid bacteria, should not be permitted to containantibiotic _ resistance marker genes," the committeerecommends.The committee points out that there is "a widespread use ofmarker genes that code for resistance to antibiotic drugs."The concern, said the ACNFP, is that "if marker genes thatcode for resistance to antibiotics in clinical use were to betransferred from GMOs to pathogens, the therapeutic use ofthe such drugs could be jeopardised".Marker genes often accompany genes that code for adesired trait in an organism. The presence of the marker inthe GMO is used as a sign of the successful transfer of theactive trait gene. An organism's susceptibility to antibioticsis one way of eliminating variants that have not taken upthe marker, and the accompanying trait gene.The committee's guidelines on the information it needs toadvise on the acceptability of GMOs as novel foods, issuedin 1991, state that: "If the markers code for resistance todrugs in clinical use then evidence that they have beenjettisoned or suitably inactivated will normally benecessary."The report points out that "Gene transfer between micro-organisms and between micro-organisms and plants isknown to occur in nature." It also says that while thetransfer of marker genes has been shown "underexperimental conditions, their transfer under naturalconditions has not been identified."While the committee recommends a complete ban on theuse of live organisms containing antibiotic resistant genes,it calls for a case-by-case consideration where such genesoccur in "foods from genetically modified plants and fromnon-viable genetically modified micro-organisms." Anysafety evaluation of a new food would consider the clinicaluse of the antibiotic in question, "the likelihood of transferof the antibiotic resistance gene into, and expression in, gutmicro-organisms," and the "toxicity of the gene product."The report also said that the research community "shouldbe reminded of the extent of antibiotic resistance present inmicro-organisms and should be made aware of theimplications that this has for human health and safety, aswell as for veterinary medical practice." The committeeadvocates the development and use of "alternatives toantibiotic resistance markers and/or methods to jettisonthose used."Among the first food GMOs containing antibioticresistance markers are tomatoes containing thepolygalacturonase (PG) gene. The PG gene is intended toextend the shelf life of fresh fruit. The U.K.'s ZenecaSeeds, based at Fernhurst in Surrey, has the rights to marketmodified tomatoes for the processed food market. CalgeneInc., of Davis, Calif., plans to market fresh fruit under theFlavr Savr trademark.A spokesman for Zeneca said that the company believesthat the ACNFP's report will have no impact on thecompany's use of the PG gene. Processed tomatoes do notraise problems with their antibiotic resistant marker genesbecause the fruit will be cooked, destroying any geneticmaterial. However, the same argument does not apply tofresh tomatoes which will still contain the active markerwhen they reach the consumer.Zeneca has yet to submit details of its tomato to theACNFP. The spokesperson said that it is concentrating itsattention on the American market, where the FDA hasalready said that there are no problems with the company'splanned use of the PG gene in tomatoes intended forprocessing. The chairman of ACNFP has also said that thecommittee would probably take a similar line.The ACNFP has yet to rule on the acceptability of anyGMOs containing antibiotic resistant genes. It has receivedno applications. While it is not compulsory to consult thecommittee, a spokesman for the Ministry of Agriculture,Fisheries and Food (MAFF), the government departmentresponsible for regulating food safety, pointed out thatcompanies will find it difficult to market products withoutthe approval of the ACNFP.According to MAFF's spokesman, the committee hasreached no conclusion on how it would respond to anyparticular application. The committee issued its report sothat the industry could respond to its concerns. Thecommittee said that among other things, any safetyevaluation of a food GMO would consider three issues: theclinical use of the antibiotic involved, the likelihood of theantibiotic resistance gene into, and expression in, gutmicro-organisms and the toxicity of the gene product.The report said that in the committee's evaluation of foodsconsisting of GMOs from which antibiotic resistancemarkers have not been jettisoned or inactivated, it will"require evidence to demonstrate the safety of the antibioticresistance markers and the scientific need for theirretention." n
-- Michael Kenward Special To BioWorld Today
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