Category Archives: Yikes!

Plant virus can infect honeybees

TRSV particles from infected honeybees; figure 2 from Li et al

TRSV particles from infected honeybees; figure 2 from Li et al

I saw this news alert on Microbe World, which pointed to a primary research article in the American Society of Microbiology’s journal mBio. Honeybee colonies worldwide have undergone a phenomenon referred to as “colony collapse,” where the worker bees from a colony disappear. Pesticides, various viruses and bacteria, mites, and habitat loss have all been proposed as explanations however no clear front runner among these hypotheses has emerged. Honeybees are major pollinators of crops, with estimates that bees are responsible for pollinating up to $200 billion of crops each year. The number of beehives in the US has declined by 50% over the past 30 years, highlighting the seriousness of the problem.

The current study is a collaboration between researchers at the Chinese Institute of Agricultural Sciences, the US Dept. of Agriculture, the University of North Carolina, and Emory University in Atlanta, GA entitled “Systemic Spread and Propagation of a Plant-Pathogenic Virus in European Honeybees.” Viral infections do not easily jump between species. Indeed, although epidemiologists are extremely worried and closely track influenza viruses in mammal and avian populations, the so-called “bird flu” in itself does not readily infect humans. The concern about bird flu outbreaks is over a random mutation that allows a bird flu isolate to be easily spread between humans. Threats posed by viruses that infect a species extremely unrelated to humans are essentially non-existent, and so far there have only been rudimentary reports that this happens. This report from 2010 represents the first time that a plant virus had been implicated in human disease, however this study has not been followed up so far. The current study goes further, and clearly shows by a variety of methods that a plant virus can effectively replicate in insect cells, and infection of colonies with this virus is correlated with colony collapse disorder.

Most plant viruses are spread by herbivorous insect vectors that spread the virus from an infected plant to a healthy plant, and there is evidence that plant viruses can manipulate the behavior of insects that feed on infected plants. Tobacco Ringspot Virus (TRSV) infects a number of plants of economic importance, and causes malformation and stunted growth. A number of biting insect vectors have been implicated in the spread of TRSV, however additional spread via infected seeds is also critical in the long term spread of the virus. Honeybees have been found to play a role in this process by transferring infected pollen from plant to plant, however it had not been described previously that the bees could actually be infected with the virus by the pollen that they carried.

The researchers used bees from colonies kept at the USDA labs in Maryland, USA. Samples of workers from these colonies were analyzed for presence of the virus by several methods. Viruses were purified from whole bee homogenates, and visualized directly by electron microscopy–the picture above demonstrates the presence of virus particles that showed the same morphology as TRSV particles from plant sources. Several molecular analyses were also used, including polymerase chain reaction of isolated bee tissues using specific primer sets, and in situ hybridization of microscope slides of whole body sections of worker bees. Both of these approaches showed the presence of virus in a variety of tissues, indicating that the virus was actually replicating within the tissues of bees as opposed to being carried on the outside of the insect on pollen particles.

In situ hybridization detection of TRSV in honeybee tissue sections

In situ hybridization detection of TRSV in honeybee tissue sections

They further demonstrated the presence of TRSV in bees by analyzing the presence of virus in Varrao mites, which are obligate parasites of the honeybee and have been an important part of the problems facing the beekeeping industry. Indeed, it appears that the mites are able to transmit the virus between bees and are critical in the spread of the virus throughout a hive. The main block preventing easy infection of bees is the step of transfer and binding of virus to insect cells, and biting mites circumvent this process by introducing the virus directly into the body of the insect. The researchers found a strong correlation with the presence of TRSV in bee colonies plus other viral diseases of honeybees in colonies deemed “weak” or in danger of collapse. In contrast, “strong” colonies showed very low levels of TRSV and other seasonal viral infections of bees. They conclude by suggesting that the data argues that survival of honeybee colonies is dependent on infection with TRSV along with other specific viruses of bees.

Rapid drug resistance testing

Staphylococcus aureus - Antibiotics Test plate

Staphylococcus aureus – Antibiotics Test plate (Photo credit: Wikipedia)

I came across this news alert via Microbe World, which very briefly summarizes some research at St. George’s University of London investigating a hand held device to rapidly determine whether patient isolates of M. tuberculosis are antibiotic resistance. This new technology will use a cartridge based format to test sputum samples, and report in 15 minutes what antibiotics might be effective in patient treatment. Currently, the standard for antibiotic susceptibility are variations of disk diffusion or use dilution tests, both of which require incubation of an organism in the presence of control agents to assess susceptibility. Accurate determinations of susceptibility may require an extended incubation time, however good indications susceptibility can frequently be determined in a shorter amount of time, and better patient outcomes will be obtained by starting effective antibiotic treatment sooner rather than later. Susceptibility testing can also be accomplished using molecular genetic approaches, typically using a polymerase chain reaction based approach to directly detect genes that are involved in antibiotic resistance. Even still, this approach requires some time to complete, as DNA from a microbe of interest needs to be extracted prior to performing and analyzing the sample by PCR. So this new approach that suggests meaningful results in 15 minutes looks very interesting.

The original press release at the St. George’s website gives a little bit more information. This report indicates that the device uses a combination of DNA analysis (almost certainly PCR-based) and a TB identification system (probably a serological detection method) in a single unit. Polymerase chain reaction can be extremely rapid, and the procedure can actually be accomplished in a few minutes using conditions optimized for very specific conditions. Analysis would likely use a spectrophotometer based approach, which has been used to measure DNA concentration for years and can be scaled down into a remarkably small unit. The drawback of this type of approach would likely be one of specificity. If a patient has a M. tuberculosis infection, and if that isolate exhibits one of the standard forms of antibiotic resistance, the device would report back a meaningful result. However, if the patient has another infection, or if the patient isolate is resistant to another antibiotic, this machine might report back a “negative” result which in fact would not be a helpful diagnosis.

Although this is an intriguing approach in clinical diagnostics, and may have in specific clinical settings a very clear benefit, the headline of the report worries me a bit– “Unnecessary TB deaths to be thing of the past”–the overt implication being that we have solved the issue of antibiotic resistance with this very troubling pathogen. M. tuberculosis infection are becoming notoriously difficult to treat due to growing acquisition of antibiotic resistance. New patient isolates are arising that are resistant to many first and second line antibiotics. The article equates very early detection of infection with clear patient outcomes, and although this is true to some extent, it does not address those infection which are already resistant to antibiotic treatments. In these cases, the clearest benefit of detection is to the community at large, where the further spread of antibiotic resistance from undiagnosed cases can be prevented.

Who Knew I Could Relate to a Frog?

Courtney Golden (11 AM Micro) is worried about frogs, and found an article on Science Daily showing a link between an herbicide, a fungus, and how immunity of amphibians is affected by environmental levels of the herbicide. Courtney seems a bit surprised to find out about that amphibians have an immune system just as powerful as a human, however long time readers of BIO230 will recall my ode to the Nobel Prize winning work Jules Hoffman, who studied the ability of fruit flies to fight off fungal infections, and how the mechanisms are absolutely conserved by the human immune system.  Courtney’s title could also be rewritten as “Who knew I could relate to a Fruit Fly?” Here is what Courtney has to say about frogs:

Whenever I think of frogs, I think of little green creatures that hop around and “ribbit-ribbit” in the local ponds and streams. Frogs are much more than a green, hoppy, amphibian. Frogs are an important part of our ecosystem. According to Science Daily, frogs have immune systems just like ours, and while treating the land and our crops with herbicides; the herbicide atrazine has shown an increase in mortality rates in frogs. The herbicide atrazine can be deadly to frogs when exposed at an early age, but why is this herbicide so deadly? Atrazine works together with Chytridiomycota fungus. The Chytridiomycota fungus is a typical pathogen to frogs, but usually the infection is fought off by their immune system. The USF’s Department of Integrative Biology showed that when frogs were exposed early in development to atrazine, one of the most common herbicides used today, and were exposed to Chytridiomycota fungus, the fate of the frog was fatal. The herbicide atrazine can cause frogs to die within 46 days of exposure to the herbicide. A direct relationship is shown through the exposure of atrazine and the frog’s death. The death occurs because as the frog become exposed to atrazine, their immune systems cannot fight off the usually typical Chytridiomycota fungal infection, and their immunity deteriorates with time.

This certain case of atrazine herbicide and Chytridiomycota fungual infections show an instance of chance that one specific frog, could be exposed to a specific herbicide, and then exposed to a certain fungal infection, creating loss of immunity in the frog, just like how it could happen to a human. This mirrors the case in the Frontline episode we watched on Friday, October 25th, 2013. The little girl Addie, who was infected with a superbug, received some of the bug by coincidence. Addie picked at her scabs and contracted a Staph infection, which in turn opened the door for other infections. Just by this chain of coincidental events Addie and the frog both contracted diseases in which their bodies could not fight off, and her life depended on a lung transplant. Although one infection was fungal and the other was a Gram-negative bacteria, in both instances immunity was lost and death was a possibility.

In an additional article published by NPR, in a scientific study done by Jason Rohr, a biology professor at the University of South Florida in Tampa also showed that with increased amounts of atrazine, snail population flourished which is a kiss of death for frogs. The snails carry flatworm parasites, and due to the fact that atrazine damages and deteriorates the frog’s immune systems, the frogs cannot fight off the parasites.

It is crazy to think that frogs and humans have biological connections, including their immune systems. I have always just thought of a frog as a little green slimy creature that hops around on four legs and “ribbits” and croaks loudly to hear; but that is not the case, frogs have immune systems and diseases as well, just like humans.

Salmonella from breast milk!

Via the New York Times, a story to add to the list of things that have led to Salmonella outbreaks recently. A study published this week in the journal Pediatrics details a growing problem with breast milk sold or donated via websites that has been found to be contaminated with high levels of potentially pathogenic microorganisms. Researchers obtained 101 samples from a popular Internet milk-sharing website, as well as 20 samples of unpasteurized breast milk which had been donated to a more traditional local milk bank.  Most of the Internet samples (74%) were contaminated with Gram negative bacteria, whereas 35% of the banked milk were contaminated. Additionally, contaminated Internet samples had at least 10-fold higher levels of bacteria in comparison to the banked samples.  Internet samples were also contaminated with cytomegalovirus 20% of the time.

The authors conclude that the high level of contamination reflects the overall poor attention to “collection, storage, and shipping practices” with very fundamental lapses in aseptic technique. Although the websites typically prominently display collection criteria, because there is no oversight in the process, it is unclear what level of compliance is actually followed. Local milk bank resources on the other hand have strict guidelines, and the milk is pasteurized prior to distribution. Some advocates of the websites maintain that pasteurization itself diminishes the benefits of expressed breast milk relative to infant formula, however there doesn’t appear to be any concrete evidence that such benefits exist to use unpasteurized milk when pasteurization is easily accomplished. Comments in the Times article from Kim Updegrove, president of the milk-bank association, further underscore issues with these unregulated Internet sites, including the possibility that recipients might be getting cow’s milk or formula from an unknown Internet source.

Salmonella from the spice rack!

The Spice must flow!

Continuing with the running series on things that can make you sick when you eat them, published a post today detailing how many imported spices are contaminated with Salmonella. The article links back to a New York Times report, describing how FDA officials examined 20,000 shipments of imported spices, finding significant levels of Salmonella contamination in 7% of the samples. Over 10% of samples of coriander, oregano, and basil were contaminated, and high levels of bacteria were also found in curry powder and black pepper. The presence of in these foods should come as no surprise, given the large number of reservoirs that put people at risk for infection. The dried environment on spices will have a bacteriostatic effect on the growth of microorganisms, however drying will not typically kill microorganisms. Fortunately, most of these spices are traditionally used during cooking, and the high heat of cooking will kill introduced bacteria. It is only when seasoning is added after cooking that a significant risk exists.

The report is the result of a 3 year study by the FDA, and recently published in the primary research journal, Food Microbiology. Although the researchers found Salmonella isolates widely distributed geographically between 2007 and 2009, spice preparations from India and Mexico showed the greatest prevalence for being positive for Salmonella. Additionally, several samples were contaminated, even after being treated to reduce the presence of pathogens by a variety of processing methods. Researchers also found that around 7% of the samples positive for Salmonella were contaminated with isolates that were resistant to a variety of first line antimicrobials, including tetracycline, streptomycin, and nalidixic acid.

The report has resulted in some negative and positive responses. The chief of food safety inspections in Mexico maintains that the Mexican food supply remains safe and is checked daily. In contrast, Indian food officials have begun to institute measure to help prevent Salmonella introduction from bird droppings, and also to promote methods to eliminate bacterial contamination during the processing stages.

Outbreaks attributable to contamination of spices have been identified previously. As the NYT article states, outbreaks in 2009 and 2010 of Salmonella sickened hundreds in the majority of states in the country, and one spice processing facility in California was found to be extensively colonized with an infectious isolate of the organism. It is particularly difficult to track outbreaks attributable to contaminated spices, as the long shelf life of these products may mean that an infection may occur months to years after the microorganism entered the food supply. The best recommendations as is generally the case with food-borne illnesses is awareness of of their presence, and to ensure adequate food preparation (washing) and cooking to eliminate potentially pathogenic microorganisms.

Next up on BIO230: Why you shouldn’t wash the chicken prior to cooking!!

Red meat allergies and ticks

English: The tick Amblyomma americanum (Lone S...

English: The tick Amblyomma americanum (Lone Star tick) (Photo credit: Wikipedia)

Via Twitter, Heather’s friend Parva pointed out this story in the Wall Street Journal which describes a set of case studies of individuals who showed mild to severe allergies after eating various types of red meats such as beef, pork, or lamb. Epidemiological research at the University of Virginia Medical Center found that many of these patients had reported tick bites previously, and blood analysis indicated that the patients also had IgE antibodies (the kind associated with allergies) which were directed at antigens found in animal meats. In the WSJ summary, the basis of the syndrome appears to be either the direct transmission of animal antigens from a previous meal into a human via the tick intermediate, however the researchers could not exclude the possibility of either an infectious agent such as a bacterium that causes the syndrome after transmission by a bite, or a sensitivity to tick saliva creating the allergy condition.

In trying to find out more about the mechanism of this finding, I located this article from the primary medical literature from the researchers which reported their initial findings in 2009. In this article, it was found that IgE antibodies in the patients were directed at a carbohydrate antigen galactose-α-1,3-galactose (alpha-gal), which is commonly found on the surface of proteins from many non-primate mammals. Most non-immunocompromised adults already make significant numbers of antibodies to these antigens, but of the IgG subtype, and approximately 1% of the antibody present at any given time is directed against α-gal in the blood of a healthy adult. It is this IgG antibody against α-gal that is responsible for the extremely rapid response of pig-to-primate tissue rejection.

As can be seen from the figure, patients reporting the red meat allergies demonstrated strongly positive responses against a variety of meat antigens in a skin prick test, however it was noted that the responses were much more robust against freshly prepared antigen as opposed to commercially available antigen extracts that are generally available to allergists. The researchers could find no correlation between any of their patients and any potential foodborne insult or a genetic predisposition to developing the responsible IgE antibody.

Two intriguing questions were posed by the study. First, unlike many other allergy hypersensitivities, the reactions observed due to red meat ingestion developed over the course of hours instead of minutes. The authors suggest that possibly it is essential for the animal antigens must be partially digested before they can produce a more severe result. Second, the initial trigger that causes the immune system to produce the allergy-associated IgE antibodies instead of the usual IgG antibodies remains unknown. Further analysis was suggested as a result.

One possible explanation to the latter question was put forth in a publication from 2013. In this study, it was noted that there is a structural relationship between the α-gal antigen from animals, and the carbohydrate antigen found on human B-group red blood cells. Individuals who have type B blood do not make any antibodies against their own blood; if they did, they would experience cytolytic rejection of their own blood cells, which would have terrible effects. The researchers found that individuals of blood group B made significantly lower levels of antibody against the animal meat antigen. With this observation, one would then be able to predict that in a non type-B individual that they might show elevated levels of antibody against both the B blood antigen and the α-gal antigen. This was not the case, however, as in the allergy patients only antibodies against the animal antigen were found, with no measurable antibody against the human blood group antigen. They did find though that in patients with an elevated IgE (allergic) response that an elevated IgG (normal) response was also seen. They conclude from this analysis that all humans on a meat containing diet will produce normal antibodies against the meat antigens. In certain individuals–and blood group appears to offer some measure of protection–introduction of these antigens via an abnormal route by tick bite or other means causes an additional immune response to occur with the allergy associated symptoms.

%d bloggers like this: