Friday, June 17, 2011

Antibiotic Resistance – A Cause for Global Concern

Penicillin was discovered and developed as the first widely-used anti-microbial (antibiotic) agent in 1928.   Ever since that time, bacteria have developed resistance to a wide range of antibiotics as they have been introduced.  This capability can be explained based on two important properties of bacteria.  These organisms divide approximately every twenty minutes; therefore, through the course of a single twenty-four hour day, seventy-two generations have been produced.  If bacteria are in an environment permeated with antibiotic some of the progeny may develop a resistance due to a spontaneous mutation in their genetic material (DNA).  If this should happen, all the susceptible bacteria will die off leaving behind those that are resistant.  This process can be regarded as natural selection.  Since resistance is conferred by a change in the genetic makeup of the organism, resistance can then be passed on to all the progeny.  There has always been a potential public health risk in regard to this ability of microorganisms to become resistant to these agents.


Bacteria are classified into two distinct groups – gram-negative and gram-positive.  This classification was created based on their ability or inability to take up a particular stain.  A well known example of gram-positive bacteria that is disease producing (pathogenic) is Staphylococcus aureus that is of a particular concern in a hospital setting.  An antibiotic that has been traditionally used to combat this kind of infection is methicillin.  As a result of its universal application, a highly resistance form of this bacteria referred to as methicillin resistant Staphylococcus aureus (MRSA) has arisen.  This has created a serious public health dilemma.


From a public health perspective, a far more problematic issue is antibiotic resistance among gram-negative bacteria.  These bacteria possess a double cell wall that makes them more challenging to eliminate.  An example of a pernicious variety of this kind of bacteria is Klebsiella pneumoniae; this strain is particularly prevalent in hospitalized patients and is a major cause of pneumonia and bloodstream infections (sepsis).  The antibiotics that have been found to be effective against gram-negative bacteria are referred to as the carbapenems.  As one would suspect, Klebsiella has now been shown to possess resistant to the action of carbapenems.


Doctor Timothy Walsh and his colleagues from the Cardiff University, United Kingdom have examined the nature of this resistance and have found that the resistant strain produces an enzyme (NDM-1) that effectively inactivates carbapenems.  This is particularly disturbing since gram negative bacteria, Klebsiella as an example, also possess the capacity to transfer antibiotic resistance to other kinds of bacteria including the ubiquitous Escherichia coli that normally inhabits the large intestines of most mammals.


Given the seriousness of this issue, it is considerably disturbing that there are no new kinds of antibiotics against gram-negative bacteria currently being developed.  This reality holds an ominous prospect for the future in regards to global public health.  

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