Wednesday, April 7, 2010

Long-Term Consequences of Antibiotic Treatment

One week of antibiotic treatment can impact commensal bacteria populations and genetic resistance for years, according to a new study published in the Public Library of Science journal, PLoS ONE. A team of researchers led by Hedvig E. Jakobsson of the Swedish Institute for Infectious Disease Control observed the changes brought on by antibiotics prescribed for gastric and duodenal ulcers and found that the balance of commensal bacteria, particularly in the gut, was still disturbed four years following treatment.
The authors followed three patients with ulcers caused by the bacterium Helicobacter pylori and three controls. The case patients were treated twice a day for seven days with the standard course of antibiotics: metronidazole, clarithromycin, and omeprazole. In case patients, bacterial diversity in fecal samples decreased immediately following treatment, with a particular decline in Actinobacteria. In addition, the initially low abundance of erm(B) genes that code for antibiotic resistance increased by 3-5 orders of magnitude in case patients following treatment.
One year after treatment, erm(B) genes were still present at 1,000 times their pre-treatment level, and continued to be elevated four years post-treatment. According to the authors, this increase in resistance could be a result of horizontal gene transfer between bacteria or multiplication of existing drug-resistant bacteria following changes in commensal populations.
There were also changes in the throat microbiota of patients receiving antibiotic treatment, but this population showed more stability than gut bacteria.
Commensal intestinal bacteria are essential to the human immune system, and disruption of this population has potentially dangerous and long-lasting consequences. While calling for larger studies to back up their findings, the researchers emphasized the importance of limited and prudent antibiotic use to prevent the spread of potentially pathogenic antibiotic-resistant bacteria.

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