It is well known that we have to be careful with what foods we eat, remembering to stay healthy and eat our fruits and vegetables. Diets high in fat can create serious health issues such as obesity, high cholesterol, and possibly Type 2 diabetes. Also on that list of related health problems is cardiovascular disease, which is characterized by blood clots, due to fat and plaque build-up in blood vessels, and can lead to a heart attack or stroke. Previous research has implied a connection between the microbiome and cardiovascular disease, due to the microbiome’s effect on production of a molecule called trimethylamine N-oxide (TMAO). As of yet, no research has been done to track the association between the microbiome and lipid (fat) build-up, so this is precisely what researchers published in Circulation Research set out to do.

The scientists located in The Netherlands, Poland, and Massachusetts, collected blood cholesterol measurements from 1500 LifeLines-DEEP subjects. LifeLines-DEEP is a collection of subjects used for assessing various health issues. Ethnic outliers and genetically related participants were removed from the study. Fecal samples were collected from 1180 participants, and sequenced. By the end of the data collection, 99 participants were excluded for reasons such as antibiotic use, or use of potentially microbiome-altering medications. In total there was a final number of 893 participants (380 men and 513 women) for which cholesterol samples, microbiome samples, and genotypic information was obtained. The participants included a wide range of age, BMI, and blood lipid levels.

The researchers found that gut microbiome species richness was significantly higher in women, and increased with age. Microbial richness was positively correlated with high density lipoproteins (HDL, the 'good cholesterol'), not correlated with low density lipoproteins (LDL, the bad cholesterol), and negatively correlated with body mass index (BMI). For example, the study confirmed that lower abundances of kingdom Archaea, families Christensenellaceae and Rikenellaceae, class Mollicutes, and genus Dehalobacterium are associated with high BMI. It was estimated that the microbiome could explain 4.57% to 65 of variation in BMI, triglyceride and HDL. No link was found between the gut microbiome and genetic predisposition to obesity of high blood lipid levels.

One hypothesis raised by the researchers is that bacteria potentially try to correct lipid imbalances, thereby helping to prevent cardiovascular disease. The strong associated between the gut microbiome and BMI and blood lipid levels – regardless of age, sex, and genetics – suggests that the microbiome does indeed play a role, if indirectly, in cardiovascular disease and other fat-related issues. 34 gut bacteria were found to be associated with BMI and blood lipids. There is a real potential for the utilization of this information in health therapies, such as blood clot and stroke prevention.

In general, a significant amount of attention is placed on microbiome communities in our gut and skin, and their respective relationships with other tissues in our bodies (the brain, for example). However, the cells and fluids that are essential to our survival, such as blood, may also play an important interactive role with our microbiome. This relationship is demonstrated in a recent study aimed at identifying bacteria found in standard blood-packs used for blood transfusions, and examining bacterial distribution and distinct strains present in blood-plasma and red blood cells.

Transfusion-transmitted infection remains the leading cause of post-blood transfusion mortality and morbidity even though these risks have declined significantly in recent years. As the name suggests, transfusion-transmitted infections result from the introduction of foreign pathogens to a patient’s blood stream via a blood transfusion. However, previous research has identified a significant discrepancy between post-transfusion infection rate and bacterial growth observed in the blood pack from which the transfusion was received. Specifically, a 16.9% rate of post-transfusion infection (11.8% under more reserved transfusion methods) is observed. However, data from standardized bacterial screening protocols indicate that less than 0.1% of blood packs actually contain bacterial growth.

Previous literature examining bacteria translocation into red blood cells concomitant to epidemiology data related to gum disease suggest that the oral cavity, or mouth, can serve as a viable access point for bacteria to enter into the blood stream. Furthermore, conventional methods used to screen for bacteria presence in blood packs does not account for bacterial adherence to red blood cells. To address this discrepant data and literature-supported suppositions, a twofold approach was taken. Researchers sought to determine if known oral cavity bacteria strains are found in donor blood packs and whether or not these bacteria adhere to red blood cells.

Blood was drawn from 60 healthy study participants and subjected to specific fractionation procedures to separate red blood cells from plasma. Red blood cell and blood plasma suspensions were subsequently plated on cell culture dishes and incubated for 7 days under specific conditions to allow researchers to isolate bacteria from red blood cells and identify the strains. General bacterial growth was evident in both red blood cell and blood-plasma dishes. Of the 60 plates corresponding to 60 patients, marked growth was observed in 35% of the red blood cell cohort and 53% of the blood-plasma cohort. DNA amplification of known bacteria found in the oral cavity was then used to determine the specific bacterial strains that were incubated on these plates. Various aerobic and anaerobic strains were identified and it was interestingly noted that these bacteria are undetectable using standardized bacterial screening techniques.

These findings certainly have major implications for clinical diagnosis of bacterial contaminants found in blood packs. In particular, detection capabilities of diagnostics must be improved, as it turns out that there may be significant amounts of bacteria in blood packs than previously realized. This study also illustrates that bacterial communities are mobile and are not limited to gut, skin, mouth, vagina, and other tissues we normally associate with the microbiome. The ability to adhere to red blood cells certainly gives microbiota populations a much more dynamic range of influence in our body’s respiratory, immunologic, and overall regulatory processes.

Associations between the microbiome and blood lipids

The blood microbiome and infection after transfusion