I’m Dr. Tony Kingston, a research scientist living in the suburbs of Boston. I recently left academia to work in in industry, but I miss teaching so I decided to start writing articles on interesting discoveries in the world of microbiology. My goal is to uncover subjects that are unusual, unique, and might one day have a major impact on our daily lives.

Probiotics: Living medicine.

Today I’ll be covering probiotics, live microbes that confer a health benefit when administered (1). Think of them as good bacteria that can help humans (or other hosts) out in a number of ways. They can attack pathogens, synthesize nutrients, or consume toxins and they have a clear advantage over traditional medicine in that they can live for an extended period within our bodies to continuously have an effect.

Probiotics might seem dangerous at first glance since it involves filling humans with living organisms, but keep in mind that humans are already full of bacteria. Our microbiome (the bacteria living within our bodies) contains more bacterial cells than there are human cells in our body and plays an active role in keeping us healthy. We are ingesting and breathing new bacteria every day, but the health implications of these environmental bacteria are rarely noticed or considered. Most probiotics have either been shown to be safe from years of normal human consumption (ie. the bacteria in yogurt), and any marketed as drugs are heavily tested for side effects (2). Probiotics labeled as “dietary supplements” aren’t subject to as much scrutiny, but overall the health concerns of probiotics are fairly minimal.

Bacteria play a role in many of the foods we eat. They are sometimes considered probiotics, but experts debate whether the health benefits are directly from living microbes.
The field of probiotic research has already made significant progress and some probiotic treatments are available. For example, several studies have reported successful treatment of Clostridium difficile infections with probiotics (3). Unfortunately, most probiotics on the market today are “dietary supplements” offered by vitamin companies that haven’t really proven the health benefits of their products.

^{Rule of thumb:
The nicer the label, the less effective it is.}

These pseudobiotics will hopefully be replaced by science-validated probiotics in the near future. Biotech companies have begun to invest in probiotics to combat specific diseases or promote the immune system. During a job interview I had a year or so ago, I talked with a company that engineers bacteria to treat genetic metabolic deficiencies in humans and the results they had were quite impressive. These kinds of medical applications are still mostly in the testing stages, but hopefully they reach patients in the next few years.

Rather than review the topic as a whole, I thought I’d do a deep dive into a recent paper on the subject. To that end, I’ll be covering the “Effect of Probiotic Bacteria on Oral Candida in Frail Elderly” published in the Journal of Dental Research by the Twetman lab at the University of Copenhagen in Sweden (4). I like this paper because it’s a very clear example of a “good” bacteria helping humans get rid of a “bad” microbe.

Exploiting the elderly…for Science!

In this paper, the authors tested the effect of probiotics on dental health in ~200 elderly patients in a nursing home. My favorite part of this paper is that it finally finds a use for old people, but there are two other major players in this story:

The good guys: The probiotic used in this study was Lactobacillus reuteri, a common gut bacterium. It was chosen because previous studies had shown this strain to have antimicrobial activity.

The bad guys: The authors monitored the effect of the probiotic on yeast of the Candida genus. These microbes are present in most humans in small quantities, but can often cause infections in elderly or otherwise immunocompromised patients.

The authors split the elderly into two groups, a probiotic group and a placebo group. They administered Lactobacillus reuteri to the probiotic group as a Lozenge, a tablet designed to dissolve in the mouth (similar to a cough drop), twice daily for 12 weeks. The placebo group also had to take a lozenge, but it didn’t have any bacteria (though it tasted just as terrible according to the patients).

The main goal of the study was to determine if probiotic treatment influenced the levels of Candida in the patients. To get this information, the authors took saliva and plaque samples from patients before and after the experiment. They then analyzed these samples for Candida levels by spreading them on growth media and counting how many Candida colonies grew. To simplify the analysis, the samples were classified as either having low or high levels of Candida. The major results of this experiment are presented in one big table shown below.

This table compares the number of participants showing either high or low Candida levels (CA counts) in their saliva and plaque before and after the experiment. The key result to notice is that probiotic treatment reduced the number of patients with high Candida levels while the placebo treatment had no significant effect. Since the only difference between the two groups is the presence of Lactobacillus reutei, the authors conclude that the reduction in Candida levels is due to this probiotic.

Conclusion: Probiotics remove pathogens

The main takeaway from this paper is that probiotic lozenge treatments actually did reduce the amount of a potentially harmful microbe in the elderly. This isn’t the first time such a study has been done, but its use of human subjects and clear results present a very strong case for the health benefits of Lactobacillus reutei. However, keep in mind the limitations of this work. It doesn’t explain how the probiotic gets rid of Candida species and it doesn’t show whether this effect is maintained over a period longer than 12 weeks. Ultimately, more work needs to be done, but it’s great to see a simple and promising result in a study like this.

Miscellaneous Musings

According to the paper, 11 patients died during the course of the 12 week study. About half died from the placebo group so death doesn’t seem to be caused the bacteria, but I hope none of them choked on the lozenge.

I am not advocating anyone start drinking bacterial cultures. However, some extra yogurt or cheese now and then can’t hurt.

The author’s data table really should have been presented as a chart. We’re looking at numerical differences here and it’s much easier to do that with a bar graph. This is an amateur mistake and a rather frustrating one seeing as this data isn’t particularly complicated.

References:

(1) http://ajcn.nutrition.org/content/73/2/361s.full
(2) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3294522/
(3) https://www.ncbi.nlm.nih.gov/pubmed/28760934
(4) https://www.ncbi.nlm.nih.gov/pubmed/26202995

Images:

All images used have been labelled for re-use on Google Images or are taken directly from the publication. If any image owner has an issue with this article, please contact me and I will address the issue.