Why are Gram negative bacteria such significant pathogens?

The picture to the right, borrowed from Chapter 20 in Bauman, illustrates the prevalence of Gram-negative nosocomial infections. These infections are huge in the United States, averaging around 5% of all hospitalizations (1 in 20 frequency) with the higher risk peds patients at over 10%. Total hospital acquired infections in 2002 was 1.7 million cases, with almost 100,000 deaths from them. That’s over a one in twenty mortality rate for something that we have learned is best controlled at the point of patient contact. As we can see from the graphic, over half of these nosocomial infections are due to the Gram negatives, followed by Gram-positives (primarily S. aureus,) then various fungi (primarily C. albicans.)

We’ll make this an opportunity to foster a discussion answering the question of the posting title, in the comment thread below. Again, bonus points are my bribe to you to promote participation. Here are the rules: one bonus per person here, and to get a bonus, it needs to not be something somebody has already said in the comment thread. I also require you not just quote me from lecture, say something interesting so we all can learn!


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 10, 2010, in Bonus!, Lecture. Bookmark the permalink. 3 Comments.

  1. Gram negative bacteria are significat pathogens because of their outer membrane. The outer membrane protects the bacterium from detergents, which are described as having “cleaning properties in dilue solutions.” Soaps are a type of detergent. In a clinical setting, even if there is proper hand hygiene, the soap may not be able to penetrate the outer membrane, and nosocomial infections may occur.


  2. Gram negative bacteria are so significant because they multiple virulence factors. The most significant factors contributing to their virulence include endotoxins, antibiotic resistance, and capsules. It is nearly impossible to destroy endotoxins which may be found on materials coming into contact with patients. Once a patient has come into contact with gram negative bacteria, it is hard to destroy via the immune system or antibiotics. The immune system has difficulty destroying it because the capsules that some gram negative bacteria exhibit make it resistant to phagocytosis. Gram negative bacteria are hard to kill via antibiotics because of the complex structure surrounding them, specifically the outer membrane.

  3. Gram-Negative bacteria infection leads to endotoxemia in which the endotoxin come in contact with blood streams and gets mixed with blood. Once the endotoxin is mixed in blood, it becomes very hard to stop the toxic substance from harming/destroying healthy tissues and also causing inflammation of the tissues. The substance can reach any part of the body and start harm to the tissues. This is a very significant part of gram negative bacteria because it is difficult to treat because of its outer membrane.

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