Targets on our Backs

Ashley Chenoweth (11 AM Micro) found this article about one of the molecules that acts as a virulence factor with pathogenic patient isolates of Salmonella typhi, a common cause of severe gastroenteritis. Here is Ashley’s summary:

Salmonella Typhi. This microorganism is of the Enterobacteriaceae family and the Salmonella genes along with the commonly known microorganism Salmonella typhimurium which is known to cause food poisoning. This organism is also a gram negative, rod-shaped bacterium. It is also the pathogen that causes the commonly known disease, typhoid fever. Many people have heard of typhoid fever. It kills hundreds of thousands of people every year. In fact, there is a twenty percent death rate for untreated cases! People get this pathogen by contaminated water or food. The pathogen can also be carried for years in a human. This disease causes diarrhea and constipation, fever, headaches, abdominal pain and sometimes even internal bleeding. However, many people do not know that humans are the only species that are susceptible to the typhoid pathogen. But what does our body not do that other animals do?  Why are we the only species susceptible to this deadly pathogen?

Rab32. Rab32 is a molecular courier that helps arm our anti-microbial defenses against the invading pathogen. It is actually part of the IgG antibodies that we learned so much about in microbiology class. According to the study done on November 16, the Rab32 in rabbits is more potent towards the pathogen then ours are. How did they figure this out? By introducing a gene from another microorganism of the Salmonella genes into Salmonella typhi, Jorge E. Galan, Markley Professor of Microbial Pathogenesis and Steffani Sparo were able to make the pathogen survive in the immune system of mice, which in normal circumstances would completely destroy the pathogen before it can cause disease. The gene they introduced to the pathogen was one that caused disease in other species, for example, Salmonella typhimurium. This small change allowed the pathogen to destroy the Rab32 antibody in the rabbits, like it does on its own in humans. So what exactly is going on?

It seems as though the pathogen has become resistant to our body’s immune system defenses! “The immune system is still firing it’s bullets, but this pathogen has learned how to dodge them in humans but apparently not in other animals.” says Galan. There is no for sure answer yet to why our immune systems do not fight this pathogen like the rest of the world’s animals. And there is still more bad news. Unfortunately, these microorganisms are very resistant against many commonly used antibiotics. This could be a very bad thing for us. Why? Because having deficiencies in Rab32 can also leave people more susceptible to leprosy and tuberculosis. But this did come with some good news.

Now that we have learned why we are the only species susceptible to this pathogen, we can work on an antibiotic which can either enhance our Rab32 antibodies, or create an antibody that will target only Salmonella typhi. Another option we have is that we can dismember the pathogen to see what gene makes it avoid our defenses and cause disease in our bodies. Besides, isn’t that what makes it non-virulent to other species? The loss of one gene can make the difference between disease, and just another microorganism infecting our bodies.


About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on November 30, 2012, in Guest Post, Microbes in the News and tagged , . Bookmark the permalink. Comments Off on Targets on our Backs.

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