Antibiotics, your gut, and you
We are always being told by marketers of yogurts that the human gut contains a bustling community of different bacteria, both good and bad, and that this balance is vital to keeping you healthy. But if you target the disease-causing bacteria with medicine, what might be the collateral damage to their health-associated cousins that call the human body home? A new study just published looks into the changes that happen in the human gut when it is exposed to the widely used antibiotic, ciprofloxacin.
Ciprofloxacin is prescribed for a number of conditions, including common afflictions such as urinary tract infections. It was previously believed to cause only modest harm to the abundant beneficial bacteria of the human body. The intestinal microbiota is essential to human health, with effects on nutrition, metabolism, pathogen resistance, and other processes. Antibiotics may disrupt these interactions and cause acute disease, as well as contribute to chronic health problems, although technical challenges have hampered research on this front. Several recent studies have characterized uncultured and complex microbial communities by applying a new, massively parallel technology to obtain hundreds of thousands of sequences of a specific variable region within the small subunit rRNA gene. These shorter sequences provide an indication of diversity.
To investigate ciprofloxacin’s effect on health-associated bacteria, researchers catalogued types of bacteria present in the faeces of volunteers who were undergoing a course of treatment of ciprofloxacin. The DNA-analysis technique massively-parallel pyrosequencing was central to their approach. With this technique, the researchers examined the diversity and abundance of bacteria present in human faeces, identifying over 5,600 different bacterial species and strains. The dramatically increased detection power of this approach allowed the team to track carefully the changes in the gut’s bacterial community both during and after the course of treatment. The study found that while the patients were undergoing treatment the overall abundance of approximately 30% of the species and strains was significantly affected. The effects varied greatly between individuals, with two of the subjects showing a strong reduction in diversity. The effects didn’t stop there. Once the course of treatment had been halted, it took up to four weeks for most strains of gut bacteria to return to their pre-treatment levels. Even six months later, some types of bacteria had not managed to return to pre-treatment abundance levels. During this time of population upheaval none of the patients in the study reported signs of gut-related problems.
The bacteria present in the human gut are responsible for various aspects of host nutrition, metabolism and immune responses. This study reveals aspects of resiliency in the indigenous microbiota when subjected to perturbation, but underlines the concern that antibiotic treatment, especially when prolonged or repeated, may have long-lasting effects on overall wellbeing that could go un-noticed.
The pervasive effects of an antibiotic on the human gut microbiota, as revealed by deep 16S rRNA sequencing. PLoS Biol 6(11): e280
The human intestinal microbiota is essential to the health of the host and plays a role in nutrition, development, metabolism, pathogen resistance, and regulation of immune responses. Antibiotics may disrupt these coevolved interactions, leading to acute or chronic disease in some individuals. Our understanding of antibiotic-associated disturbance of the microbiota has been limited by the poor sensitivity, inadequate resolution, and significant cost of current research methods. The use of pyrosequencing technology to generate large numbers of 16S rDNA sequence tags circumvents these limitations and has been shown to reveal previously unexplored aspects of the ‘‘rare biosphere.’’ We investigated the distal gut bacterial communities of three healthy humans before and after treatment with ciprofloxacin, obtaining more than 7,000 full-length rRNA sequences and over 900,000 pyrosequencing reads from two hypervariable regions of the rRNA gene. A companion paper in PLoS Genetics shows that the taxonomic information obtained with these methods is concordant. Pyrosequencing of the V6 and V3 variable regions identified 3,300–5,700 taxa that collectively accounted for over 99% of the variable region sequence tags that could be obtained from these samples. Ciprofloxacin treatment influenced the abundance of about a third of the bacterial taxa in the gut, decreasing the taxonomic richness, diversity, and evenness of the community. However, the magnitude of this effect varied among individuals, and some taxa showed interindividual variation in the response to ciprofloxacin. While differences of community composition between individuals were the largest source of variability between samples, we found that two unrelated individuals shared a surprising degree of community similarity. In all three individuals, the taxonomic composition of the community closely resembled its pretreatment state by 4 weeks after the end of treatment, but several taxa failed to recover within 6 months. These pervasive effects of ciprofloxacin on community composition contrast with the reports by participants of normal intestinal function and with prior assumptions of only modest effects of ciprofloxacin on the intestinal microbiota. These observations support the hypothesis of functional redundancy in the human gut microbiota. The rapid return to the pretreatment community composition is indicative of factors promoting community resilience, the nature of which deserves future investigation.
Related:
- Resistance to Widely-Used Antibiotics among Inhabitants of Remote South American Villages
- Probiotics – weapons in the war against gut pathogens
- Breast is Best?
- Probiotics – friendly bacteria?
Tags: Antibiotics, Bacteria, Biology, Health, Medicine, Microbiology, Science
