The National Academy of Sciences published a new study that uses three-dimensional microscopy on almost clear zebrafish to reveal how antibiotics, even in minimal dosages, can change gut bacteria community structures in such a way that leads to drastic reductions in bacterial population.
The study was released in a publication this week. Raghuveer Parthasarathy, who works as a physics professor at UO’s Institute of Molecular Biology, attributed his comments on ‘environmental contaminants’ to the study.
“The weak and almost non-existent doses of antibiotics found in the environment due to their rampant use in livestock farming is an example,” he stated. He further went on to say, “It is widely accepted that minute doses of antibiotics can change the human gut microbiome, but the reason behind it has never been explained.” PhD student and postdoc Travis J. Wiles worked on the project under the supervision of Brandon H. Schlomann.
“The larvae of zebrafish is an excellent test subject,” Perthasarathy stated, “as they have a lot of anatomical features in common with other vertebrate and humans, along with having their gut microbes being visible.” Under environmental circumstances, they were studied with the antibiotic ciprofloxacin, which is almost always microscopically exposed in 3D.
The scientists studied zebrafish individually infected with one the two distinct species of bacteria commonly residing within the zebrafish intestines. Bacteria in one of the species are motile and swim swiftly. Bacteria of the second motile species are mostly found clustered in dense colonies.
When these species were administered an antibiotic, both strains exhibited some profound behavioral alteration. The species that usually travels actively swam slower and formed clusters. The normally cluster-forming species underwent structural changes to massive, less fragmented, clusters.
In both instances, the increased sensitivity to the mechanical contractions of the intestines due to the enhanced aggregation led to more expulsion from the gut and a greater than hundred-fold drop in the intestinal populations.
“Antibiotics meddled with the microbiomes to a degree much stronger than what was predicted,” said Parthasarathy. “This is what we discovered. The intestines in a way enhance the impacts of feeble antibiotics.”
In connection to their findings, the researchers proposed a bacterial growth model for the gut that has ‘some’ correlation with colony sizes based on experimental data. The model draws parallels between the growth of polymers and the model of microparticles and, as the co-authors state, shows that concepts originated from physics can indeed be successfully utilized in the investigation of the gut microbiome.
Expectedly, Parthasarathy claims that the scope of relevance of the research outcomes goes beyond the scope of zebrafish.
“A large number of bacteria exhibit shape and aggregation behavior modification in response to weak antibiotics,” he said. “The intestines of all vertebrates, including humans, have the function of transporting food along with microbes, and the dynamics of the intestine drives the motion of bacterial consortia. Therefore, we can assume that many of the things we have found are rather universal across species — humans and other animals included.”
Parthasarathy and fellow colleagues construct the model with the intention of aiding the assessment of the effects of antibiotic disruption in humans and other animals. This five member team proposes that the process of aggregation which leads to the expulsion of live antibiotic treated bacteria from the intestinal tract of animals serves as a means through which antibiotic resistance is disseminated.
Source: UNIVERSITY OF OREGON