A research article published Nov. 3, 2010 in the journal Microbiology, came to the startling conclusion that even a short course of antibiotics can leave normal gut bacteria harboring antibiotic resistance genes for up to two years after treatment.

What many people forget is that the body is filled with both "good" bacteria -- such as the normal microbial flora of the human gut -- as well as "bad" or pathogenic bacteria. Antibiotics can alter the composition of microbial populations and allow micro-organisms that are naturally resistant to the antibiotic to flourish. This reduces the ability of the body to react to the pathogenic entities, potentially leading to other illnesses.

The impact of antibiotics on the normal gut flora has previously been thought to be short-term, with any disturbances being restored several weeks after treatment. However, the review of the long-term impacts of antibiotic therapy reveals that this is not always the case. Studies have shown that high levels of resistance genes can be detected in gut microbes after just seven days of antibiotic treatment and that these genes remain present for up to two years -- even if the individual has taken no further antibiotics.

The consequences of this could be potentially life-threatening, explained Dr. Cecilia Jernberg, of the Swedish Institute for Infectious Disease Control, who conducted the review. "The long-term presence of resistance genes in human gut bacteria dramatically increases the probability of them being transferred to and exploited by harmful bacteria that pass through the gut. This could reduce the success of future antibiotic treatments and potentially lead to new strains of antibiotic-resistant bacteria."

The review highlights the necessity of using antibiotics prudently. "Antibiotic resistance is not a new problem and there is a growing battle with multi-drug resistant strains of pathogenic bacteria. The development of new antibiotics is slow and so we must use the effective drugs we have left with care," stated Dr. Jernberg. "This new information about the long-term impacts of antibiotics is of great importance to allow rational antibiotic administration guidelines to be put in place," she said.

SOURCE: Microbiology 156 (2010), 3216-3223; DOI 10.1099;