The Dance of Virulence

The Dance of Virulence

Double Agent: The fungus Candida albicans lives a double life. It co-exists as a harmless “commensal” inside our mouth, gut and urino-genital tract. Occasionally, it flares up as thrush, treatable with over the counter medication. But given the opportunity to breach our defenses, Candida can cross into the bloodstream and switch from peaceful coexistence to attack mode, producing long filaments that dig into tissues and destroy them. You can see the yeast-like buds germinating into hyphae on the left image. On the right, hyphae labeled with green fluorescent protein insert between intestinal cells (marked in red, with blue nuclei) in a macabre dance of virulence. This is particularly dangerous to people with weak immune systems (HIV/AIDS, cancer) who have less than 50% survival rates with systemic candidiasis. 

More than a Junk Yard: In a study just published, we showed that the pH of the fungal vacuole (seen as dark holes inside the fungi on left) was crucial for the switch from yeast to hyphae. This was a surprising finding, because the vacuole is best known as the cell’s recycling center – a junk yard. But our previous study showed that an popular antifungal drug, fluconazole, blocked the vacuole from becoming acid, leading us to suspect that this may be important for fungal virulence. We focused on the V-ATPase, a cellular pump that has wide-reaching functions and acidifies many parts of the fungal cell. One component or subunit of this pump exists in duplicate forms, coded by two separate genes. Inactivating either one has no effect because the other one serves as a back-up, compensating every function – except one. We found that the vacuole exclusively depends on one version of the duplicated genes to become acidic. Without this one crucial function, Candida could no longer morph from yeast to hyphae. It also lost all ability to kill infected mice. In contrast, mice injected with the healthy Candida strain succumbed to infection.

A Chink in the Armor: The study revealed a vulnerability that could be exploited by targeting the vacuole’s pH, rendering Candida harmless while potentially posing little risk to infected patients. For example, FDA-approved drugs known to alter cellular pH could be repurposed to treat fungal infections. This is important because there are relatively few classes of antifungals known, and it is particularly dangerous when fungi become drug resistant. That is why we are always looking for new chinks in the fungal armor. This may be one. 

News Report: Science Daily “Possible way to turn fungus from foe to friend” http://goo.gl/mtXLGM

REF: C. Patenaude, Y. Zhang, B. Cormack, J. Kohler, R. Rao. Essential Role for Vacuolar Acidification in Candida albicans Virulence. Journal of Biological Chemistry, 2013; 288 (36): 26256 DOI: 10.1074/jbc.M113.494815

#ScienceEveryday    #ScienceSunday  

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45 Responses to The Dance of Virulence


  1. Congratulations on the paper Rajini Rao this is awesome!

  2. Rajini Rao says:


    Thanks, Buddhini Samarasinghe . For a change, I’m writing about our work here on G+. We have another press release that I’m particularly excited about coming out on Monday 🙂


  3. Looking forward to it! Really liked the Science Daily writeup too!

  4. Sunil Bajpai says:


    Thanks for sharing your work. This is special Rajini Rao. 

  5. Kawthar A says:


    Great read as always Rajini Rao congrats and good luck 🙂

  6. Rajini Rao says:


    Thanks, Kawthar AL ABDALLA  and Sunil Bajpai 🙂

  7. Jim Carver says:


    There’s a pretty good consensus among health care practitioners that if not caused by an immune system disease, this condition is probably related to food allergies. Until those allergies are identified in otherwise healthy persons, it is likely that the condition will return after drug treatment until the cause is identified.


    Diet is important, and one should avoid things that were or could be fermented for a while and add them back gradually. Capricin and garlic are often used as they have mild anti-fungal properties and immunity is not an issue, Taheebo tea (Pau D’Arco) and/or clove tea may help. Greek yougurt and Filmjolk is always a good idea for the colon and try to crowd the fungus out with beneficial bacteria.

  8. Rajini Rao says:


    Candida infections flare up with sugar in the diet, Jim. Fungi love fermenting sugars. 

  9. Jim Carver says:


    Yep, and I forgot to mention avoid broad spectrum antibiotics if at all possible and steroids, including birth control pills.

  10. Rajini Rao says:


    It’s important to make the distinction, though, from surface infections of Candida, like thrush, that can be controlled with staying off antibiotics and sugar, eating yogurt, cranberry juice and such, versus acute, blood stream infections which can quickly become lethal. 

  11. Jim Carver says:


    Pretty low chance of that though Rajini, unless your immune system is highly compromised through AIDS, chemotherapy or the overuse of said antibiotics. 

  12. Azlin Bloor says:


    Fascinating read, Rajini! Is it acceptable to say congratulations on the paper?!

  13. Rajini Rao says:


    Yes, definitely Azlin Bloor . Each paper goes through trial by fire and we emerge charred at the edges and somewhat victorious at the end 😛

  14. Rajini Rao says:


    Jim Carver , yes of course (as was made clear in the post), but I want to emphasize that systemic infections (once it enters the blood stream) are quite distinct from surface/cutaneous infections and all the yogurt in the world won’t help when that happens. This research is focused on the systemic infections where mortality rates are very high. 

  15. Azlin Bloor says:


    I always thought there was a touch of the phoenix in you, Rajini! Congratulations! xx

  16. Jim Carver says:


    Rajini Rao Yeah, I wasn’t trying to address the emergency room patients. I was trying to state some healthwise statements that might be more applicable to a wider audience.


    And your diet does affect pH values in the bloodstream…it’s not a closed system ya know.


    Sure, throw some more drugs at it and then deal with that many more complications later.


    You know I don’t think that way.

  17. Rajini Rao says:


    Jim Carver , the pH of blood is tightly controlled between 7.35 and 7.45 otherwise respiratory or metabolic acidosis or alkalosis sets in. We are discussing a completely different range of pH here: 5.5-6.6, or up to two orders of magnitude lower, that is required inside the fungal vacuole for fungal virulence. You would be instantly dead if your blood pH was that low 🙂 


    Also, minor clarification, this is not about emergency room patients but more about prolonged hospitalizations when the so called “nosocomial” infections set in. 


  18. I’s amazing how much of ‘us’ is not made specifically of ‘us’ yet helps ‘us’. We are truly connected with our biosphere!

  19. Rajini Rao says:


    Leland Maurello , the new findings on our “commensals” that live within us, continue to break all expectations! 

  20. Vlad Levin says:


    I found one bit a little confusing: if the candida changes when it is in the bloodstream, would these drugs not change the ph of the blood too?

  21. Jim Carver says:


    Vlad Levin That was the argument. The blood pH doesn’t change very much. It’s the compounds in the blood that change the cellular pH.


  22. A very interesting study and result. 

  23. Mary T says:


    This is fantastic Rajini Rao ~ Congratulations!  Wonderful news.


    Excellent write up in Science Daily.


  24. Great piece. Congratulations Rajini Rao


  25. congratulations on your extensive work and valuable information.

  26. Chad Haney says:


    Congratulations Rajini Rao it’s nice to read about your work. I’ll check the JBC article when I get to my desktop, although I doubt I can understand half of it.

  27. Rajini Rao says:


    Vlad Levin , in answer to your question, pH is playing many roles in this story. First, when Candida encounters the relatively alkaline pH of blood, it switches into filament mode. Of course, pH is not the only signal: blood calcium is also known to be a trigger along with some components of serum itself. The new finding in our story is that the pH of an internal compartment (which has absolutely nothing to do with blood pH…do you get that Jim Carver ?) must be acidic (i.e., opposite from the alkaline signal from blood) for these filaments to form. The pH of these compartments is set by proton pumps and transporters that move the charged H+ across the membrane. 


    The final point is that some chemicals/drugs are weak bases that become trapped inside acidic compartments where they end up raising the pH of that compartment. They don’t alter the pH of blood at all, but they will make acidic vacuoles more alkaline. For the aficionados, these are known as lysomotropic drugs (the antimalarial drug chloroquine is one). They also have a high affinity for membranes which allows them to accumulate inside cells. But their free concentration in blood is very low. These properties are usually secondary to their medicinal action..like a side effect. We have shown that some of these drugs act as antifungals both in a culture dish and in a  mouse infected with Candida. Perhaps they can be included in the antifungal treatment as combination therapy. 

  28. Mary T says:


    I remember giving IV amphotericin B to immuno-compromised patients with systemic fungal infections.  It’s a brutal drug for patients to endure.  It’s exciting to see that there will be kinder options in the future.

  29. Rajini Rao says:


    Mara Rose , these are small and slow steps, I’m afraid. But that is the way of most progress. I’m so delighted to be able to share some of this with you guys here on G+. 


  30. Rajini Rao So the photos aren’t quite “spaghetti and meatballs” (mycelia and spores)… do we call these brussel sprouts? Maybe green beans 😛


    I knew fluconazole affected ergosterol synthesis, but I didn’t know loss of vacuolar membrane affecting V-ATPase was the actual mechanism, so that’s interesting. I guess this also explains why fluconazole is primarily fungistatic, not fungicidal. I also wasn’t aware amiodarone had any antifungal properties since it is mainly used as an anti-arrhythmic agent. Lots of good info 🙂


    To reiterate for others, fungal colonization and mucocutaneous presence are relatively benign in the otherwise healthy population. Invasive candidiasis and acute disseminated candidiasis (a sepsis-like syndrome) are the most concerning and require prompt intervention. Candidemia is the fourth most common cause of nosocomial bloodstream infections in much of the developed world. Complications can be difficult to treat, and thus it has a high mortality rate.


    Immunocompromised individuals are not only those with a specific illness, as Jim mentioned, but also refers to neonates and elderly too. It does occur in non-neutropenic patients. More commonly, others who are at risk are those with diabetes, AIDS, cancer, autoimmune disorders requiring immunomodulators, inflammatory diseases requiring corticosteroids, solid-organ or stem cell transplant recipients, surgical patients and prostheses, ICU patients (because of their critical status but also because of all the indwelling catheters), etc.


    Fluconazole is first-line therapy in most adults with clinically stable (mild) disease without recent azole exposure. For more serious cases of moderate-to-severe illness, involvement of sites like heart valves or CNS, or suspected C. glabrata or C. krusei (not C. albicans), alternative and more aggressive fungicidal agents are preferred (including Amphotericin B, which has the nickname of “Ampho-terrible” because of its awful side-effect profile).


    Some of the more insidious cases are osteomyelitis (bone infections) sometimes requiring treatment for a year and endocarditis (heart valve infections) of a prosthetic valve in someone who can no longer undergo surgery to replace it, in which case the patient must be placed on chronic suppressive antifungal therapy for the rest of his life.


    Suffice to say, invasive Candida is not a very good dance partner to have, and any investments to improve treatment selectivity and efficacy are welcomed. This is a nice step in that direction.

  31. Rajini Rao says:


    Johnathan Chung , thank you for that very informative and helpful commentary about Candida!


    Regarding amiodarone, although it is not a particularly effective antifungal by itself, it is synergistic with the azole drugs, particularly against azole resistant variants of Candida (we don’t have an explanation for that last part). So it might be useful in treating drug resistant infections. There is a group in Venezuela that has shown its effectiveness against Trypanosoma in combination with posaconazole (Chagas disease; http://www.ncbi.nlm.nih.gov/pubmed/16451055). I believe there is also a case report of a patient on amiodarone for anti-arrhythmia who was cured of his protozoan infection. Fungi and protozoa share similarities in their sterol profiles (ergosterol in place of cholesterol), among other things. All very intriguing! 


  32. That is pretty cool, and it shows how complex all these interactions are. Always more to discover 🙂


  33. Rajini Rao Buddhini Samarasinghe Many doctors do not think of Candida as lethal when we say fungal infections. Mucor and Aspergillus are thought of as worse but if you look at infections in the real world, Candida kills more and faster than the rest. 

  34. Rajini Rao says:


    Able Lawrence , they are all pretty terrible. I just got an email from a gentleman in India who was telling me how his father struggled with pulmonary Candida infections arising from chronic asthma and heart conditions for 16 years before succumbing to the disease. It must be frustrating, as a physician, to have no good medications for people like him. 


  35. Rajini Rao Issue is that of affordability. Anything other than Fluconazole or ordinary amphotericin B is too expensive. Hopefully, whatever results from your work will be affordable. There are patients who can’t take treatment due to unaffordability. 


    Once we had a Lupus girl with Cryptococcal meningiitis (with the rare variable resistance strain). After more than an year of treatment and no response family decided to stop treatment and we dont know what happened afterwards.


  36. This is marching ahead one step at a time…but today is always better than yesterday and tomorrow will be better than today. Right Rajini Rao?


    I know there are comments about cost, complexity and side effects but knowing at a fundamental level how chemical scenarios actually develop conditions is far better than giving a drug with only past subjective effectiveness.


    There are many conditions which we have very little understanding and there are no commercial interests to fund those. It will take years or decades for those conditions (many are called today psychological but they are neurological that we just don’t know how those work) to get understood and a viable treatment available.


    It is more likely that many treatments will be found as part of side effect of a research than a targeted efforts.


    Congratulations Rajini Rao for such a good work for your team. We should never forget to remember the team worked with you. There are many unnamed heroes in your team. Right?


    If you don’t mind, can you share how your team came to work on the problem and give us storyline. I know sometimes it is hard to write but you are such a good writer.


    G+ is different than medical publication because we want to give it a bit more for common people like us. So, when did your team started working at it and how did it go…


  37. May your team live long and prosper, and never have a sour vacuole.

  38. Aasim Wani says:


    thanks for sharing

  39. Rahul Joshi says:


    Sounds like a breakthrough. Kudos!

  40. naveen kumar says:


    not dance is virulence love is so

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