A study published in 2023 in Scientific Reports has shed light on how the antibiotic metronidazole affects the gut microbiome of dogs and its subsequent recovery. The research, conducted by a team from the Waltham Petcare Science Institute, provides valuable insights into the short- and long-term effects of antibiotic treatment on canine gastrointestinal health.
Led by Zoe V. Marshall-Jones and colleagues, the study examined 22 dogs prescribed a seven-day course of metronidazole for suspected giardiasis. Faecal samples were collected before, during, and up to six months after treatment to analyse changes in the dogs’ gut microbiota using 16S rRNA sequencing.
The researchers found that metronidazole administration significantly reduced microbial diversity in the dogs’ guts. Shannon diversity, a measure of both abundance and evenness of bacterial species, decreased markedly during treatment and remained lower for up to three days after the antibiotic course ended. However, diversity began to recover within a week of treatment cessation.
Interestingly, the study revealed that while diversity started to rebound relatively quickly, the overall community composition of gut bacteria took longer to stabilise. The authors noted that an altered bacterial community persisted for four to six weeks post-treatment before returning to a composition similar to pre-treatment levels.
One of the most striking findings was the dramatic shift in the relative abundance of certain bacterial genera immediately following metronidazole treatment. The researchers observed increases in Lactobacillus, Bifidobacterium, and Enterococcus species. Marshall-Jones and her team suggest this may be due to the natural antibiotic resistance often exhibited by these organisms.
As the gut microbiome began to recover in the weeks following treatment, other genera that had initially been sensitive to metronidazole started to rebound. Notably, bacteria belonging to the Erysipelotrichaceae family played a significant role in driving compositional changes during this recovery period.
The study also highlighted that many of the bacteria initially reduced by metronidazole treatment were associated with carbohydrate fermentation. This observation led the authors to suggest that there may be potential for interventions to support gastrointestinal health and aid in the re-establishment of a healthy microbiome following antibiotic treatment.
In addition to microbial analysis, the researchers assessed faecal consistency throughout the study using the Waltham Faeces Scoring System. They found that faecal scores peaked at the end of the seven-day treatment period but then stabilised, correlating with the return of bacterial diversity to pre-antibiotic levels.
The research team acknowledges some limitations of their study, including the lack of baseline microbiome data prior to the development of suspected giardiasis. As dogs were only recruited after veterinary prescription of antibiotics, it’s unclear whether the observed “recovery” represents a return to the pre-disease state or simply a new stable equilibrium.
Despite these limitations, this study provides valuable insights into the dynamics of the canine gut microbiome following antibiotic treatment. The findings have important implications for veterinary practice and canine health management.
Marshall-Jones and her colleagues emphasise the need for responsible antibiotic use in veterinary medicine. They suggest that their results could inform strategies to mitigate the side effects of antibiotic treatment, such as antibiotic-associated diarrhoea, and support the restoration of a healthy gut microbiome in dogs.
The study also raises interesting questions about the potential use of probiotics alongside antibiotic treatment. While the researchers note that certain probiotic species naturally increase in abundance following metronidazole exposure, they caution against the indiscriminate use of probiotic supplements, particularly those containing Enterococcus species, due to concerns about antibiotic resistance.
As antibiotic resistance continues to be a major concern in both human and veterinary medicine, studies like this one are crucial for understanding the complex interactions between antibiotics, the gut microbiome, and overall health. The research by Marshall-Jones et al. not only advances our knowledge of canine gastrointestinal health but also opens up new avenues for developing targeted interventions to support microbiome recovery following necessary antibiotic treatment.