Bacterial Recombination Helps Build Antibiotic Resistance
Bacteria may not reproduce sexually, but they do manage to diversify their genes by acquiring DNA molecules from their surroundings or from dead bacterial cells. This pseudo-asexual reproduction is known as recombination, and it is also the reason why so many bacteria are becoming resistant to antibiotic drugs. .
"During recombination, bacteria might incorporate new DNA, which makes them resistant to treatments, or they may take on genes which change their surface structure, enabling them to evade vaccines," said Dr. Rafal Mostowy, of Imperial College London's School of Public Health, in a statement. "Although we've known for almost a century that recombination takes place, it's only since DNA sequencing has become available that we have been able to determine how often this takes place and how significant the changes are."
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The studies were conducted on two "lineages" of the bacterium Streptococcus pneumonia, a major cause of mortality resulting from diseases like pneumonia, meningitis, and septicemia. The elderly and infants are most susceptible for these infections, with an estimated 1.1 million children dying each year due to pneumonia alone, according to the World Health Organization.
The scientists studied bacterial strains collected over 36 years and created an evolutionary chart for the two lineages by trying to understand when recombination took place, resulting in evolution of the bacteria. Earlier studies have shown recombination as a uniform process but the new models showed two distinct types of recombination, called micro and macro.
With "micro-recombination," the bacteria regularly incorporate small amounts of DNA, making only small differences in their genome. "Macro-recombination" occurs less frequently, but because it involves taking large amounts of DNA, significant changes occur, altering the genome - this is what happens during bacterial resistance.
According to the studies, recombination occurred more frequently in the evolution of the more resistant lineage they studied, and less frequently in the less resistant lineage. However, it was clear from the sequencing data that both strains had undergone micro- and macro-recombination.
"This is a major step forward in our understanding of how recombination can result in bacteria evading vaccines and acquiring resistance to antibiotics," Mostowy said in the release. "Currently we have effective means of preventing and treating pneumococcal disease, but it's not clear how bacteria will respond in the long term."
Nevertheless, the researchers were confident that current genome sequencing technology could help in monitoring the emergence of these mutations, which happen often. Their next goal is to see how recombination occurs in other types of bacteria.
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