Antibiotics straightforward killing machines? Not so.
Most people have taken an antibiotic to treat a bacterial infection. Now researchers from the University of North Carolina at Chapel Hill and the University of San Diego, La Jolla, reveal that the way we often think about antibiotics -- as straightforward killing machines -- needs to be revised.
Biofilms are communities of bacteria that form on surfaces, a phenomenon dentists usually refer to as plaque. Biofilms are everywhere. In many cases, biofilms can be beneficial, such as when they protect plant roots from pathogens.
Antibiotics can independently and simultaneously induce potentially dangerous biofilm formation in other bacteria and that these activities may be acting through specific signalling pathways," according to a study be Bleich et al., (2015). "It has generated further discussion about the evolution of antibiotic activity, and the fact that some antibiotics being used therapeutically may induce biofilm formation in a strong and specific way, which has broad implications for human health."
Bacteria have evolved the ability to produce a wide range of structurally complex natural products historically called “secondary” metabolites. Although some of these compounds have been identified as bacterial communication cues, more frequently natural products are scrutinized for antibiotic activities that are relevant to human health. However, there has been little regard for how these compounds might otherwise impact the physiology of neighboring microbes present in complex communities.
Bacillus cereus secretes molecules that activate expression of biofilm genes in Bacillus subtilis. Here, Bleich et al., (2015) use imaging mass spectrometry to identify the thiocillins, a group of thiazolyl peptide antibiotics, as biofilm matrix-inducing compounds produced by B. cereus. They found that thiocillin increased the population of matrix-producing B. subtilis cells and that this activity could be abolished by multiple structural alterations. Importantly, a mutation that eliminated thiocillin’s antibiotic activity did not affect its ability to induce biofilm gene expression in B. subtilis. W
They go on to show that biofilm induction appears to be a general phenomenon of multiple structurally diverse thiazolyl peptides and use this activity to confirm the presence of thiazolyl peptide gene clusters in other bacterial species. Their results indicate that the roles of secondary metabolites initially identified as antibiotics may have more complex effects—acting not only as killing agents, but also as specific modulators of microbial cellular phenotypes.
Bleich R, Watrous JD, Dorrestein PC, et al. Thiopeptide antibiotics stimulate biofilm formation in Bacillus subtilis. PNAS, February 23, 2015 DOI: 10.1073/pnas.1414272112
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