Microbial Communities Can Compromise the Effectiveness of Antibiotics

Researchers have discovered that the local microbial community can affect the vulnerability of bacteria to antibiotics. Bacteria that would normally die after exposure to antibiotics can survive and multiply if other resistant microbes are in the area. The findings may change our understanding of antibiotic resistance. The details are in a paper that was just published in the journal PLOS Biology.

Antibiotic resistance is a serious problem in modern medicine. Bacteria can mutate to develop resistances and then pass along the genes to other bacteria. This is only one method of developing resistance, however. Researchers are beginning to investigate other factors that contribute to antibiotic resistance, including the environment and the presence of other microbes.

A team of researchers had found that Streptococcus pneumoniae bacteria could grow in the presence of chloramphenicol, an antibiotic, as long as they were mixed with resistant bacteria. No genes were transferred yet the vulnerable bacteria could survive and multiply as long as they were near bacteria that had already developed a resistance. This mystery was the focus of a new study, in which the team tracked the activity of Streptococcus bacteria using microscopy.

Resistant bacteria and non-resistant Streptococcus were exposed to chloramphenicol. Bacteria with the resistance gene were labeled with a green fluorescent dye so that the researchers could track them separately. If non-resistant bacteria gained the resistance gene, they would begin to glow green. Interestingly, the non-resistant Streptococcus survived and then began to multiply—quickly out-competing the resistant bacteria. This happened without any form of gene transfer. Instead, the bacteria were taking advantage of the resistant bacteria’s ability to break down the antibiotics. Once the antibiotic concentration was low, the non-resistant bacteria could bounce back and eventually reproduce. This explains why antibiotic resistance can pop up even when samples show that the bacteria in question should be vulnerable to drugs.

The team’s findings emphasize the need for looking at the full picture when studying antibiotic resistance in bacteria. Vulnerable bacteria can take advantage of resistant microbes in the area. As resistant microbes break down antibiotics, other bacteria can grow in places that would normally be inhospitable. The team also points out that many antibiotics don’t outright kill bacteria but instead prevent them from reproducing. While this tactic can be effective, it also means that bacteria can potentially survive short-term exposure and then begin growing again later. Understanding these mechanisms may help scientists come up with a better solution for dealing with antibiotic resistance.


Sorg et al. Collective Resistance in Microbial Communities by Intracellular Antibiotic Deactivation. PLOS Biology (2016).

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