When Starved, Dangerous Oral Bacteria Hang On

J. Craig Venter Institute (JCVI) postdoctoral fellow, Jonathon Baker, PhD and a team of researchers from JCVI, University of Washington, the University of California, Los Angeles, and The Forsyth Institute recently published their findings from the first study to examine the ecological dynamics of the oral microbiome during long-term starvation.

It is well-understood that many bacteria have evolved to survive adverse environmental events such as starvation, desiccation, and rapid changes in temperature and pH.  Mechanisms to accomplish this persistence include expression of stress-response genes, quiescence, necrotrophy, and rapid mutation to gain metabolic functions. However, Jon and his team were interested in understanding how individual species leverage these abilities to gain a competitive advantage in a complex ecological setting.

What they found when they starved bacteria from the human oral microbiome in saliva, was that during starvation, most species died off fairly quickly. However, three species, Klebsiella pneumoniae, Klebsiella oxytoca, and Providencia survived the longest, with Klebsiella pneumoniae and Providencia surviving long-term starvation for at least 100 days.

These findings are particularly interesting because although these species are usually found in very low numbers in the mouth, Klebsiella are significant human pathogens. They cause things like pneumonia, meningitis, and sepsis, typically in patients with an already weakened immune system. Klebsiella are particularly dangerous because they are very good at becoming resistant to antibiotics, and worse, they are also proficient at transferring this drug resistance to their neighbors. Several outbreaks of antibiotic resistant Klebsiella have been traced to back to hospital sinks and drains. Based on their findings, it is easy to imagine a scenario where Klebsiella survive for extended periods of time in mixtures of saliva and other fluids inside sinks and drains, and then subsequent use of the sink aerosolizes the bacteria and spreads the infection.

While they now know that these species are good at surviving long-term starvation, they still don’t understand how they do it. During the study, they found that the surviving species underwent several mutations that may have helped them survive, and also produced several compounds that may have been used to kill their bacterial neighbors. Their future work seeks to determine if these factors were indeed the key to their success. Research like this represents a big step forward in understanding the complex ecology of the oral microbiome and its impacts human health.