Hospital Killer: Methicillin-resistant Staphylococcus aureus

Author: Kevin Meek
Date: 5/16/2010




Introduction:

There are over 30 different types of Staphylococci that can infect humans, but most infections are caused by Staphylococcus aureus. Staphylococci can be found normally in the nose and on the skin in roughly a quarter of all healthy adults. They don't cause harm unless there is damage to the skin or other injury, in which case the bacteria can overcome the protective mechanisms of the body, leading to infection. While Staphylococcus can cause many types of infections, staph infections are caused specifically by Staphylococcus aureus. The worst types of staph infections are caused by Methicillin-resistant Staphylococcus aureus (MRSA). While all staph infections are dangerous, MRSA has the highest mortality rate and is the most common hospital aquired infection in the country. MRSA is broken into two different categories: hospital associated MRSA and community associated MRSA, the former being far more common (Stoppler 2006).


http://www.youtube.com/watch?v=Yb-e4cPNn7s&feature=related



Why you should know about it:

In the United States, staphylococcus aureus is the most common cause of skin and soft-tissue infections, as well as of invasive infections acquired in hospitals. The strains that are methicillin resistant still have a mortality rate is still between 20 and 25 percent despite antimicrobial against available (Joelving 2010). This should be a major cause for concern considering In 1974, MRSA infections accounted for two percent of the total number of staph infections; in 1995 it was 22%; in 2004 it was 63%. On top of the fact that the MRSA is becoming more common, the occurrences of staph infections in general have been increasing every year for the last decade (Enright et al. 2002).



Why it is resistant:

While MRSA is a type of gram- positive bacteria, there is nothing special about its structure that makes it resistant. “Methicillin was introduced in 1959 to treat infections caused by penicillin-resistant Staphylococcus aureus.” Within 2 years there were reports from Europe of MRSA. Since then it has been discovered that there is a single gene (mecA) that encodes for the methicillin resistant protein. Scientists believe that this gene came from a distant related species and may not necessarily come from a mutation. On top of that many types of MRSA are multiply resistant to drugs such as oxacillin, penicillin, and amoxicillin, and are usually only susceptible to glycopeptide antibiotics (Enright et al. 2002).

Identification:

A MRSA staph infection. Taken from http://www.lib.uiowa.edu/hardin/md/pictures22/staph/7824_lores.jpg
A MRSA staph infection. Taken from http://www.lib.uiowa.edu/hardin/md/pictures22/staph/7824_lores.jpg

MRSA doesn’t necessarily look any different than other types of staph infections. These infections are usually skin infections and can come in the form of such as abscesses, boils, and other pus-filled lesions. If you ever get any symptoms like this you should contact your doctor immediately (Boyles 2007). The CDC says these are a few key things to for if you feel you might have a staph infection. Look at the affected area and notice if it is:

  • Red
  • Swollen
  • Painful
  • Warm to the touch
  • Full of pus or other drainage
  • Accompanied by a fever



Who it affects:

MRSA viewed under an SEM microscope. Taken from http://www.sciencedaily.com/images/2007/10/071030163137-large.jpg
MRSA viewed under an SEM microscope. Taken from http://www.sciencedaily.com/images/2007/10/071030163137-large.jpg

One reason why MRSA is so dangerous is that up until recently it has only affected those will established risk factors like a weakened immune system, frequent hospital visits, or the fact that they just had surgery. However, it is started to appear in patients living among the general population with no significant risk factors at all (Klevens 2007).

While MRSA can infect perfectly healthy people it tends to affect those with a weakened immune system. This is why the majority of individuals who obtain MRSA are found in health care facilities. This includes hospitals, health clinics, nursing homes, etc. It also seems to affect the elderly (those 65 years old and older), African Americans, and men more than the rest of the population. Out of 100,000 elderly people it is estimated that there will be 127.7 infections, out of 100,000 African Americans there will be 66.5 infections, and out of 100,000 men there will be 37.5 infections, which is slightly higher than the average of 31.8 per 100,000 (Enright et al. 2002).

While this may not seem like a lot it adds up. In 2005 there were an estimated 94,360 infections in the United States alone. Of these an estimated 18,650 resulted in death (Todar 2010). While this may not seem like much these deaths are only a result of MRSA and there are many more types of drug resistance bacteria in hospitals killing patients.


Infection:

Another reason MRSA is so dangerous is because it can be spread so easily. Not only can you get it from touching a person that has it, or coming in contact with something that an infected person came in contact with, but it is possible to contract an infection from bacteria that are already living on your own skin. It is also thought that it is so common in hospitals due to bed overcrowding and the fact that the beds were not contaminated by MRSA, but also that when a bed was needed the sterilization process was rushed (Borg, 2003).This is why in Europe they test patients when they first arrive and if they test positive they are kept in isolation. A prime example of why is that a hospital in Seattle got a burn patient who had the disease. The patient was in the burn unit and the ICU and after that person left other patients continued to get infected during their stay in the hospital. They eventually had to close the burn unit and ICU and built new ones so the bacteria would stop infecting patients (Joelving 2010).


Treatment:

Although MRSA is resistant to many drugs, most remain susceptible to some older antibiotics like vancomycin and teicoplanin (Targocid). However some forms of MRSA are even resistant to these drugs. Linezolid (Zyvox) and daptomycin (Cubicin) are newer drugs that have been approved to treat MRSA. Because Zyvox is so effective at treating it doctor’s only use it in extreme cases to prolong the time before MRSA becomes resistant to it (Ge 1999).

Vancomycin is the usually the first drug used against gram-positive bacterial infections. They work by binding to proteins that help synthesize and make peptidoglycan. This in turn makes it so the bacteria cannot form cell walls (Ge 1999). Unlike many of the other drugs used to treat MRSA, Linezolid has a unique mechanism of action whereby it selectively binds to the 50S ribosomal unit and prevents formation of the initiation complex (Todar 2008). This action is thought to prevent cross-resistance with other antimicrobial agents.


Literature Cited
  • Borg, M. "Bed Occupancy and Overcrowding as Determinant Factors in the Incidence of MRSA Infections within General Ward Settings." Journal of Hospital Infection
  • Boyles, Salynn. "MRSA: Experts Answer Your Questions." WebMD - Better Information. Better Health. 27 Oct. 2007. Web. 18 May 2010. <http://www.webmd.com/skin-problems-and-treatments/news/20071024/mrsa-experts-answer-your-questions>.
  • Enright, Mark, D. Robinson, Gaynor Randle, Edward Feil, Hajo Grundmann, and Brian Spratt. "The Evolutionary History of Methicillin-resistant Staphylococcus Aureus (MRSA)." Proceeding of the National Academy of Sciences of the United States of America 99.11 (2002): 7687-692. Web.Ge, Min. "Vancomycin Derivatives That Inhibit Peptidoglycan Biosynthesis Without Binding D-Ala-D-Ala." Science 284.5413 (1999): 507-11. Web. 15 May 2010.
  • Joelving, Frederik. "Faster, Stronger, Deadlier: the MRSA Superbug | Reuters." 14 May 2010. Web. 15 May 2010. <http://www.reuters.com/article/idUSTRE64D66L20100514>.
  • Klevens, Monina. "Invasive Methicillin-Resistant Staphylococcus Aureus Infections in the United States." The Journal of the American Medical Association 298.15 (2007): 1763-771. Web. 15 May 2010.
  • Stoppler, Melissa. "Staph Infection (Staphylococcus Aureus) Symptoms, Causes, Picture and Treatment by MedicineNet.com." 23 Apr. 2006. Web. 18 May 2010. <http://www.medicinenet.com/staph_infection/article.htm>.
  • Todar, Kenneth. "Staphylococcus Aureus." Online Textbook of Bacteriology. 2008. Web. 15 May 2010. <http://www.textbookofbacteriology.net/staph.html>. 54 (2003): 316-18. Web. 15 May 2010.