Gut harbors antibiotic resistance

The millions of microbes that crowd the human intestinal tract are teeming with new antibiotic resistance genes that could jump to disease-causing pathogens, according to researchers from Harvard University.An artist's conception of microbialecology in the gut. Pathogenic bacteria(green coats) receiving Penicillinresistance genes from beneficialgut bacteria (blue rounded chains)Image courtesy of A. Canossa, M.Sommer and G. Dantas They found more than 90 undiscovered bacterial genes capable of c

By | August 27, 2009

The millions of microbes that crowd the human intestinal tract are teeming with new antibiotic resistance genes that could jump to disease-causing pathogens, according to researchers from Harvard University.
An artist's conception of microbial
ecology in the gut. Pathogenic bacteria
(green coats) receiving Penicillin
resistance genes from beneficial
gut bacteria (blue rounded chains)

Image courtesy of A. Canossa, M.
Sommer and G. Dantas
They found more than 90 undiscovered bacterial genes capable of conferring antibiotic resistance hiding in microbes harvested from two healthy adults. They report their linkurl:findings; in __Science__ today (August 27). "I thought this was an incredibly cool story," linkurl:Gerry Wright,; McMaster University chemical biologist, told __The Scientist__. "It tells you just how ignorant we are of microbial ecology." Wright, director of McMaster's Michael G. DeGroote Institute for Infectious Disease Research, said that the findings raise several key questions. "If there's so much resistance out there, how come [antibiotics] work at all?" asked Wright, who was not involved with the study. "It either means that we really don't understand how antibiotics work or we really don't understand how microbes work." This lack of understanding is underscored by the fact that humans have exposed their bodies to a potentially dangerous flood of antibiotics -- directly in medicines and indirectly through agriculture and cleaning products -- for decades. This exposure has likely selected for the newly discovered antibiotic resistance genes in our internal microbiome, according to lead author linkurl:Morten Sommer,; a postdoc in Harvard geneticist linkurl:George Church's; lab. "And that could be a problem when the microbiome interacts with disease-causing microbes," he told __The Scientist__. Sommer and his colleagues analyzed saliva and fecal samples from two healthy volunteers who had not been treated with antibiotics for at least one year, and the researchers isolated more than 500 bacterial strains. They cloned genes from those strains, inserted them into __E. coli__ hosts, and then exposed the __E. coli__ to 13 different antibiotics to determine which genes conferred resistance. linkurl:Stuart Levy,; Tufts University microbiologist and geneticist, agreed that the study highlights the dangers of irresponsible antibiotic use. He told __The Scientist__ that pathogenic bacteria could easily add antibiotic resistance genes to their genomes via horizontal gene transfer. "There's every chance that [antibiotic resistance genes] could come out of [the microbiome] genome and become a force for resistance in bacteria that we face," said Levy, who is also president of the Alliance for the Prudent Use of Antibiotics. "The majority of antibiotic resistance genes reside in bacteria that are harmless. These are reservoirs of antibiotic resistance." Indeed, Sommer and his colleagues are now searching for chemical signatures of horizontal gene transfer in known resistance genes. But just because a cache of antibiotic resistance genes exists in our own guts doesn't mean that bacteria are readily swapping them. "If there was horizontal gene transfer, you would expect that [antibiotics] would be useless by now," said Wright. While some multi-drug resistant strains of pathogenic bacteria have emerged recently, many antibiotics are still effective if administered properly. In addition to finding scores of new antibiotic resistance genes, Sommer and his colleagues showed that almost half of the already identified resistance genes they isolated from the gut were identical to antibiotic resistance genes now found in clinically pathogenic microbes, such as pathogenic strains of __E. coli__ and __Salmonella enterica__. While this does not conclusively prove that horizontal gene transfer has occurred between beneficial bacteria in the human gut and disease-causing bacteria, said Sommer, "It does say that there's a close evolutionary history between strains in the human microbiome and pathogens."
**__Related stories:__***linkurl:The Microbial Health Factor;
[August 2009]*linkurl:The number two-ome;
[July 2009]*linkurl:Mysterious resistance;
[September 2008]


Avatar of: Doug Czor

Doug Czor

Posts: 1

August 27, 2009

Tried everything to print or forward article about microbes in the gut that acquire immunity, or lack of proper treatment, but to no avail. You think you could mount a bigger defense for your articles?\nI would be glad to help.\n Best, Doug
Avatar of: anonymous poster

anonymous poster

Posts: 107

August 28, 2009

This is a powerful protocol for detecting antibiotic resistence genes. It would be interesting to repeat it on subjects from pre-industrial parts of the world, before jumping to conclusions about the role of medical or agricultural pollution.\n\nDoug, I had no trouble pasting the entire article into a Word document and saving it in that form.
Avatar of: Alison McCook

Alison McCook

Posts: 68

August 28, 2009

Sorry to hear you're having trouble printing and forwarding articles. Did you see the box that appears in the upper right-hand corner that gives you the option of printing and emailing the articles to a friend?\n\nAlison McCook\nDeputy Editor
Avatar of: anonymous poster

anonymous poster

Posts: 8

August 28, 2009

This worked well: from page tools at top right select "printer friendly version," save to "my documents" & email from there.
Avatar of: Lon Jones

Lon Jones

Posts: 17

September 4, 2009

The benefits of blocking transmission of MRSA organisms by enhanced use of gown, gloves, etc. was recently borne out by the CDC report of less resistance in the S. aureus that remained. This is in accord with Paul Ewald's concept that bacteria adapt to changes in their context; if that context contains antibiotics they will adapt toward resistance, if not, and they can't get around as easily they will adapt toward symbiosis.\n\nA different way to do the same thing is discussed in our book, THE BOIDS AND THE BEES. Using the ideas of Nathan Sharon, interfering with bacterial adherence applies the same pressure to adapt toward symbiosis as does blocking their transmission. Sharon uses mannose to block the adherence of the urinary pathogen E. coli. Dietary mannose fills the Type 1 lectins on these bacteria and they are subsequently replace by non-infection causing strains. Cranberry juice likely works in this way. Xylitol has been found similarly to block the adherence of nasal pathogens and spraying it into the nose regularly reduces respiratory pathogens.\n\nUnfortunately neither mannose nor xylitol are easy to classify and market as drugs so this understanding is hampered by the rule of the market: no drug, no money; no money, no research; no research, no claims; and no one knows.

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