By Carol A. Kemper, MD, FACP
Dr. Kemper reports no financial relationships relevant to this field of study.
Wee Bacterium Parasitizes Other Oral Bacteria
Scientists estimate that 99% of the bacteria on the planet have not been discovered, including a large portion of the human microbiome. All previous efforts at isolation of bacteria have been limited by what is willing and able to grow on a Petri dish. But new tools for growing bacteria and molecular techniques are affecting our knowledge of the microbial world around us.
McLean and colleagues, at the University of Washington School of Dentistry (in American Society for Microbiology abstract, June 2016), presented evidence supporting the presence of a wee bacterium, as yet unnamed, that essentially parasitizes Actinomyces odontolyticus, a bacterium found in the mouth.1 By electron microscopy, they could observe the larger bacteria covered by the smaller bacteria, latched onto its surface. RNA from this organism had been observed previously, but it wasn’t clear from where it came. It’s so teeny, it’s only 700 genes large. Cultivation and isolation of the organism proved impossible, until researchers discovered that it has no biosynthetic pathways of its own, and is entirely dependent on the molecular machinery of its host to produce amino acids. Its relationship with A. odontolyticus appears symbiotic, and may facilitate its ability to evade opsonization or intracellular killing by macrophages in the oral cavity.
McLean and colleagues have been instrumental in piecing together the tale of another similar bacterium, Candidate Phylum TM7, which also appears to parasitize A. odontolyticus in the oral cavity. This organism represents an entirely new phylum (TM7), and was originally found in a peat bog in northern Germany in the 1990s. Both organisms are so teeny (0.2 micrometers in diameter), they can slip through filters. And both organisms appear to be associated with increased inflammatory conditions in humans — increased amounts of their bacterial RNA have been found in patients with gum disease, inflammatory bowel disease, and cystic fibrosis. Interestingly, unlike the newer organism above, TM7 appears to be able to kill its host. There is also some suggestion that the co-existence of either bacteria somehow rend A. odontolyticus resistant to streptomycin.
Scientists hope the discovery of these kinds of organisms, referred to as “microbial dark matter,” will lead to the discovery of new antimicrobials.
- Coghlan A. New life form found in saliva. New Scientist July 2, 2016.
How Safe Is Your Honey?
SOURCE: ProMED-mail post, Sept. 15, 2016. Contaminated honey — USA: Glyphosate. Available at: www.promedmail.org. Accessed Nov. 12, 2016.
Weeds. Weeds. Anyone with a garden understands. Even my neighbor, with his “organic” pinot vineyard, has given up, and uses Roundup, which contains the active weed killer glyphosate. Of course, his vineyard worker only sprays it “between” the vines (while he is wearing a Hazmat suit). Commercial agriculture depends on Roundup, and crop seeds have been genetically modified to withstand its use. While there is not much research on the effects of Roundup on bees, the chemical may remain in the ground for some time, and the spray creates an aerosol, which can be carried by the wind. I tried keeping bees for years on the property, but they kept vanishing.
Now, the U. S. Food and Drug Administration (FDA) reports finding small amounts of the weed killer glyphosate in samples of U.S. honey. The amount of glyphosate found was as much as 107 parts per billion in some samples, which is small but nonetheless more than that permitted by the European Union (< 50 parts per billion). The FDA has not stipulated a limit for glyphosate in food substances, such as honey. And, up until this year, no testing for this chemical was performed on food substances in the United States. Independent agencies, which have identified Roundup in cereal, oatmeal, and flour samples, may have focused the FDA’s attention on this concern. Obviously, the bees are collecting it with their nectar, and bringing it back to the hive. How much is a risk to humans is not clear.
Benefits of TB Screening Confirmed
SOURCE: Screening for latent tuberculosis infection in adults. U.S. Preventive Services Task Force Recommendation Statement. JAMA 2016;316:962-969.
If corporate America wishes to embrace globalization, they should heed the global disease burden, at least to the degree that it puts their own work-force at risk from tuberculosis exposure. Too often in Silicon Valley, we see another case of active tuberculosis (TB) in a visiting student, or a young high-tech worker on an H-1B visa, or in an elderly immigrant, none of whom have been screened and treated for latent TB (LTBI).
This updated statement from the United States Preventive Services Task Force (USPSTF) advocates, with “moderate certainty,” for a “moderate net benefit” for the screening and treatment of persons at increased risk for TB. Based on a current assessment of the benefits and harms, screening and treatment of individuals with latent TB is of overall benefit, regardless of age, even if they are currently asymptomatic or considered lower risk.
Based on 2011-2012 National Health and Nutrition Examination Survey data, the prevalence of LTBI in the United States is estimated to be between 4.7% to 5.0%. Approximately 5-10% of these will progress to active TB or reactivation disease. Rates of progression to active disease are higher in the elderly, and in those with diabetes, kidney disease, and immunosuppression. Not only does the risk of reactivation increase to 20-25% by the time you are in your 80s, but the risk of mortality also is considerably increased. Although active TB is considered a treatable disease, it is important to recognize the overall mortality for active TB is approximately 4%, even with treatment.
In 2015, 66% of cases of active TB occurred in foreign-born persons, and the case rate of active TB was approximately 13 times higher in foreign-born persons compared with those born in the United States. More than half of those who develop active TB are from five countries: the Philippines, Vietnam, India, China, and Mexico. The prevalence of LTBI also is greater in the homeless, persons in long-term care facilities, and those in correctional facilities.
The USPSTF concluded that the two types of screening tests (skin test and IGRA tests) are fairly sensitive and specific, and the evidence for harm in being screened is nil. The risk for harm in the treatment of LTBI has been well characterized, and is comparatively less than the risk of harm from developing active or reactivation TB. In concrete numbers, if 100,000 persons at increased risk for TB were screened and treated for LTBI, 52 to 146 cases of active TB would be prevented, seven to 67 cases of hepatotoxicity would occur, and 111 persons would discontinue treatment for adverse effects. To prevent one case of active TB, approximately 111 to 314 persons (depending on risk factors) would need to be treated for LTBI. In contrast, the number of persons needed to cause one case of hepatotoxicity from LTBI treatment would range from 279 to 2,531 (depending on the treatment).
Make it your job — and the job of your primary care colleagues — to screen persons at risk for LTBI, especially anyone born in a foreign country endemic for TB, regardless of age, and make an effort to target those individuals who are allowed to enter this country without screening for LTBI.