Category Archives: You are what you eat
Laura Conway (3PM Micro) loves eating on the couch with her dog and cat. She is interested whether it’s a good idea to have a spoonful of Ben and Jerry’s after Zeus and Minnie have theirs. An article from the Journal of Clinical Microbiology sheds some light on the normal oral microbiology of dogs, and whether those organisms pose a risk to humans if we eat after them. Here is Laura’s summary (additional kudos for working with a primary research article!):
As a pet lover and enthusiast I cannot resist sharing with my Yorkie-Chihuahua, Zeus, or my Lilac-point Siamese, Minnie, when they sit quietly and patiently while I eat. I’ve had them both since they were a couple weeks old, so they have grown to understand I will share my food with them, so begging has never been necessary. The sharing is not limited to letting them clean dinner plates though, they will lick my ice cream cones, I will let them take food off of my fork, and so on. Accepting your pet as a family member is not an uncommon trend in the US, but how far is too far? Well, the Journal of Clinical Microbiology must have been wondering the same thing, because they performed a study on the cultivable oral microbiota of a domestic dog. The study focuses on how to improve canine oral health, so scientists collected dental plaque and saliva of fourteen dogs to get a better understand of what was growing inside of our lovable pets mouths. The dogs tested had not received antibiotics within the three months prior to the study, and were housed in environmentally enriched facilities. Saliva samples were collected in two ways: playing with a ball causing the dog to salivate, or by using salivates – then utilizing a syringe to collect saliva. Plaque samples were collected by using a curette or dental probe, from the gingival margin, but when a periodontal pocket was present, the sample was taken from the base of the pocket.
So the results? A total of 339 bacterial isolates were recovered from the cultures. Based on literature research, 28% of the bacterial isolates are considered indigenous oral microbiota of humans. 11.6% of the plaque microbiota collected, and 25.5% of the saliva microbiota belonged to the speciesActinomyces, a gram positive, rod-shaped, facultatively anaerobic or strictly anaerobic. Actinomyces lives harmlessly in the mouth, throat, and GI of humans. If tissue in any of these areas becomes damaged the bacteria may become pathogenic, causing inflammation and pus-filled abscesses. Granulicatella and Streptococcus species were found abundantly in the saliva, and Porphyromonas and Neisseria species were found in the plaque samples.
In four of the cases, the closest human origin match for bacteria were Micrococcus luteus (normal flora of mammalian skin), Dialister invisus (found commonly in the oral cavity of humans), Propionibacterium acnes (another microbiota normal to our bodies, but in opportunistic conditions causes acne, or infections), and Wolinella succinogenes (which is normal flora found in cows, but is also known to cause GI infections in humans). In conclusion, the collected data shows that the cultivable oral microbiota of dogs differs significantly from the oral microbiota of humans. While some of the bacteria that was collected may be normal inhabitants of human bodies, placement is key. Bacteria can be residents in one area of the body where they do no harm, but when introduced to new territory, the bacteria often become pathogenic. So for now… I’ll take my chances, but I would definitely not suggest immunocompromised patients to share their fork with Fido.
An article entitled The intestinal microbiota and host immune interactions in the critically ill, by TJ Schuitj and co-workers, and published recently in Trends in Microbiology, nicely reviews the complex set of issues caregivers need to be aware of with this set of patients (note: this article may be downloaded without cost while logged into the York College network.) All BIO230 students should find the article relatively easy to follow, particularly as we work through Chapter 15 on Innate Immunity. The article begins by summarizing the diversity of microorganisms in the healthy human gut. Surprisingly, across all human cultures, the composition of the intestinal microbiota can be organized into three broad clusters or enterotypes, and these clusters are independent of continental or national location. Recent research suggests that people with the different enterotypes might potentially respond differently to different drugs and diets, and so further study of the specific composition between healthy individuals and the role that these enterotypes play in normal health is important.
It is easy to think of the microorganisms of the mammalian gut as being free loaders with little contribution to the host, however the presence of the normal microbiota is actually very important for proper health. The principle of competitive exclusion or microbial antagonism has been brought up previously in class; the presence of relatively benign microorganisms can prevent the overgrowth of more pathogenic microorganism. This principle has been further used to postulate that microorganisms now missing from frequent human contact (parasitic worms for instance) have led to increased levels of autoimmune and allergic diseases in modern human societies, in a hypothesis called the “hygiene hypothesis.” However, the benefit of these normal organisms goes significantly further than that, as illustrated by Figure 1c from this article. The presence of the normal microbial flora is also critical to break down dietary components into a form that the human intestine can adsorb, and these organisms also produce a number of compounds such as vitamins that our bodies are unable to make on their own. In the absence of these microorganisms, the majority of foodstuff passes through the small intestine essentially undigested and moves out of the body.
In my journal search over the weekend, I came across an article with the intriguing title “Lactobacillus plantarum passage through an oro-gastro-intestinal tract simulator,” which was very recently published in the journal Microbiological Research. Given our recent bonus submission from Sandra, I thought this article might help to address whether or not orally ingested organisms actually survive passage through the stomach in any significant numbers. The digestive tract has a number of very potent defenses against growth of microbes, including the very low pH of the stomach, the action of bile salts secreted into the small intestine, plus the action of digestive enzymes mainly by the exocrine pancreas. Any microorganisms that survive the action of these defenses must be significantly resistant to them. Some of these defenses include bacterial proteins which repair proteins that become damaged, enzymes such as catalase that help to detoxify reactive oxygen compounds used to destroy bacteria, and membrane protein pumps that counteract decreases in pH. Additionally, ingested compounds known as prebiotics can also protect probiotic microorganism during their transit through the gastrointestinal tract to the colon.
This current study reports the viability of one probiotic bacterium, Lactobacillus plantarum, after being exposed to conditions that mimic the oral cavity, the stomach, and the small intestine. L. plantarum is a commonly found inhabitant of the mammalian colon, and is also frequently found in many fermented foods. A number of lactic acid bacteria also are found in a variety of foods marketed as probiotics. Bacteria in this study were grown to mid-exponential phase, and resuspended into a carrier matrix. Various carrier matrices included: 10% reconstituted skim milk, saline solution, ordinary pasta and barley glucan-enriched pasta. Simulation of the various oro-gastro-intestinal environments was by mixing matrix embedded bacteria as follows:
- oral cavity–5 minutes in the presence of lysozyme, pH 6.5
- gastric environment–25 minutes in the presence of lysozyme plus pepsin, pH 5.0, followed by duodenal stress with 85 minutes in the presence of pancreatin plus bile salts, pH 6.5
- gastric compartment–65 minutes in the presence of lysozyme plus pepsin, pH 3.0, followed by duodenal stress with 125 minutes in the presence of pancreatin plus bile salts, pH 6.5
Following each of the treatments, bacteria were recovered, and gene expression levels were measured by polymerase chain reaction amplification of messenger RNA. The researchers found that many of the genes involved in stress responses were rapidly turned on by exposure to the simulated gastric environment, further supporting their role in protecting cells from a harmful environment. The most potent stimulator of the stress response genes was the low pH of the gastric compartment. Furthermore, increased survival of L. plantarum was observed when organisms were exposed to this environment in the presence of complex or nutrient-rich matrices, also supporting their role in facilitating the successful transit of the bacteria to the colon.
The take home message from this study is that L. plantarum possesses important defenses that enable it to the environmentally hostile areas of the mammalian digestive tract, which can enable it to reach the more amenable region of the lower colon. Poorly digestible food additives (complex plant carbohydrates) can aid in the ability of the organism to more effectively colonize the colon. The study also opens up the potential for using the gene sequences identified here as markers for the screening of other bacterial species that might have potential suitability in probiotics.
Our first guest posting from Spring 2013: Sandra Malinowski (11 AM Micro, and niece of Randi-11 AM Micro, Spring 2009) is interested in probiotics. The premise behind probiotics is that the introduction of living, non-pathogenic microorganisms in the diet can help to eliminate harmful microorganisms from the body and alleviate disease. One student from last fall felt that the data regarding probiotics was not very conclusive so far. Here is Sandra’s take on this topic, via an article in the New York Times:
In today’s world we think of bacteria as a bad thing when it comes to what we are ingesting, but what we don’t account for is the good bacteria that are in most of the foods we eat on a daily basis. In fact processes like fermentation is what gives some of our favorite foods the flavor that we know and love. Fermented food is that whose taste and texture have been altered by the addition of beneficial bacteria or fungi. Some of the most popular foods that contain these good bacteria include cheese, soy sauce, sauerkraut, salad dressings, bread, beer, wine and several other foods we come into contact with on a day to day basis. In an article posted by the New York Times, Mr. Katz, an individual that is a fermentation guru, explores the benefits of what good bacteria does for our bodies and how it has personally helped him in his struggle with HIV aids.
Our ancestors even used fermentation to make drinks out of liquefied berries, which shows how bacteria has been influencing societies and evolution even before our time. Mr. Katz spends a majority of his time experimenting with these good bacteria to come up with different concoctions and flavors that can add to his diet consisting of bacteria infused foods. He actually has his own fermentation laboratory where he carries out his trials. One of the major ingredients used in these experiments is mold, which many of us would turn up our noses to. Katz fuses mold with rice or barley and then adds it to the base of soybeans. This complex is then mixed with pine nuts, pistachios, and lentils to make flavorful miso. A renown chef came and sampled a lot of Katz’s creations and found them to be delightful, and giving him new ideas for his own dishes and exploration into new microbial pathways.
When we are dining we are actually sharing our experience with a vast army of microbial companions that most of us are unaware of and if we are try not to think too much into it because its isn’t very appetizing to think about. Although this is true, foods containing these beneficial bacteria and fungi have several internal health benefits. Mr. Katz describes how although these foods have not cured his HIV aids, they have alleviated a large majority of the adverse side effects that the medications cause. There are several bacteria that are harmful to our bodies but these beneficial bacteria that our diets contain keep us healthy and our bodies functioning optimally. Some of these bacteria include Bifidobacterium, Lactobacillus, and certain Streptococci. These bacteria can help to stabilize the intestinal tract and ensure that you have regulatory bowel movements. These bacteria can also help in the production vitamins, especially B complex, and improve nutrient. Who would have suspected that bacteria and mold are in the foods we eat every day and hold such positive health benefits daily without us even realizing it?
Angela (3 PM Micro) told me she would be late for class on Wednesday, due to a dental appointment, and I told her about this news alert from io9.com describing research from Nature Genetics. (Sorry, paywall!) Scientists at Australia’s University of Adelaide isolated preserved dental plaque from excavated human remains covering a range of 7500 years, buried in Northern Europe. DNA was isolated from the preserved remains that gave a snapshot of the microorganisms living in the human oral cavity during different historical eras, and that DNA was analyzed to determine the diversity of those organisms.
The interactions of organisms in the mouth, and their relative ability to cause disease is nothing new. Longtime BIO230 fans may recall this posting from March 2011, which proposed a novel way to inhibit tooth decay by introducing a new bacterium into the mouth. This current report indicates that dental caries may be a very new problem in human health, and that it may coincide with the development of agriculture and the concurrent shift in human diet to one richer in carbohydrates. The researchers found that the diversity of microorganisms associated with the mouth have significantly decreased in phylogenetic diversity over the past 7500 years, and today’s mouths are much more heavily colonized by Streptococcus mutans, a species that is the primary agent in dental caries.
The researchers characterized two shifts in microbial diversity in the oral cavity, the first several thousand years ago coinciding with the introduction of agriculture and the shift in human diet, and another one 150 years ago during the Industrial Revolution. It was at this time that processed sugars and flour became widely available throughout society. The most significant decrease in microbial diversity occurred at this time, as the figure shows. The authors of the study argue that the human mouth exists in a constant diseased state in modern times, in large part attributable to the loss of bacterial diversity and the dominance by caries causing strains.
The comment thread on i09 then degenerated into an argument detailing the virtues and drawbacks of the paleo diet, as a possible way to “regress” the oral microbiome to a state resembling those that ancestral humans might have had. There are very few peer-reviewed articles looking at the positive and negative effects of altering the diet to make one rich in protein/lacking processed grains. One review article from 2009 summarized controlled human studies, and found that there were “promising” results, but no clear cut benefits from such a diet, and furthermore that the limited diet could actually be detrimental due to lack of vitamins and calcium. Additionally, a broad metagenomic analysis of the human gut microbiome indicated that there is actually not a large diversity of organisms between distant geographical locations. Humans show shifts in the microbial flora during different times in our lives (or perhaps age-related changes are due to the organisms influencing us), however there was no real correlation with different groups of microorganisms with any particular cultural group. That latter study strongly argues that there is very little we can do to broadly influence our microbial flora with any degree of success.
I skipped the report on kidney damage from synthetic cannabinoid use, and went straight to the CDC notice about an outbreak of a rare strain of Salmonella during summer/fall 2012 in the United States, as published in the current issue of Morbidity Mortality Weekly Report. In late August 2012, PulseNet-the national outbreak surveillance group of the CDC-reported 14 cases of infection due to Salmonella serovar Bredeney, a very rare form of the organism with only 1 documented outbreak in the US before 2012. A quick search of titles of articles through Pubmed suggests that Salmonella Bredeney infections occur throughout the world, and seem to be associated with infections that are becoming resistant to antibiotics. One epidemiological report from Morocco indicated that about 10% of Salmonella isolates were of this serovar, and that multiple drug resistance was prevalent. That study pointed out the critical need to be aware of Salmonella isolates in the food chain, and to actively work to prevent acquisition of antibiotic resistance.
The current outbreak reported in MMWR encompassed 41 patients in 20 states. Ages of patients covered a wide range (1 year old to 79 years old), with the majority of the patients under the age of 10. Ten patients were reported to have been hospitalized, with no deaths reported. For the 32 patients for whom information was available, 78% of them reported eating Valencia peanut butter purchased from Trader Joes. Testing conducted by state clinical laboratories identified Salmonella Bredeney in unopened jars of the peanut butter, which led the CDC to conduct an inspection of the Sunland, Inc manufacturing facility in New Mexico. The manufacturer initiated a voluntary recall of jarred nut butter products, and extended it as well to in shell raw and roasted nuts.
Immediately following the notice of the outbreak, the CDC recommended that consumers comply with the recall and dispose of opened or unopened containers listed in the recall notice. Consumers under the age of 5 are particularly at risk for Salmonella infections, as well as older adults, and other individuals with compromised immune systems. Although the current outbreak appears to be over, the CDC warns that many of these food sources have long shelf lives, and still may be in people’s homes. Awareness of foodborne avenues of infection continues to be our best defense against infection.