Thursday, November 17, 2011

Bacterial Resistance to Antibiotics – How does it Occur?

Although the emergence of bacterial antibiotic resistance has concerned those involved in public health for many years, the mechanism for this resistance is still poorly understood.  The magnitude of this problem is compounded by the global spread of the infectious agents that cause such diseases as gonorrhea and tuberculosis and that have become resistance to a broad spectrum of antibiotics.

Dr. Qiucen Zhang from the Department of Physics at Princeton University in a collaborative effort with others at various institutions has attempted to define the variables and quantify the nature of the development of bacterial immunity to antibiotics.

In previous work, resistant mutations in bacterial populations have been isolated and their genetic makeup successfully analyzed.  However, Zhang and his colleagues sought to understand how such mutations actually occur and spread within a given bacterial population when it is first subjected to antibiotics.

In order to elucidate this process, it was important to simulate the micro-environment that is present in nature – within a host organism, for example.  The candidate organism that was chosen for this study was Escherichia coli, a ubiquitous bacterial species.  A device was constructed for this purpose was designed to mimic a normal bacterial niche.  The antibiotic that was chosen for this study was ciprofloxacin, often used in a clinical setting.  This substance inhibits DNA replication and cell division but does not kill the bacterial cell target.

The findings from these experiments were that resistance of Escherichia coli to ciprofloxacin occurred within a mere ten hours of the introduction of the drug, and with as few as 100 bacteria.  In addition, DNA analysis of the resistant strain showed four unique single-nucleotide polymorphisms (SNPs) that could account for the antibiotic resistance.

These results are of immense importance in that they help elucidate the often rapid appearance of antibiotic resistance with the body of mammals, including humans.  These data may also be of used in improving the understanding of the emergence of drug resistance in patients undergoing cancer chemotherapy.    

Thursday, November 10, 2011

Meteorites and Prebiotic Organic Matter

It has been long understood that in the early history of the earth before the appearance of life, there were present organic substances that were the precursors to the complex compounds that are the essential ingredients for all living things.  These molecular precursors are referred to as prebiotic organic matter.  In addition, the cosmological data has established that the earth along with all the other planetary bodies within our solar system were formed from material expelled from the sun during its formation – the so-called “protoplanetary disk.”

A fundamental question that arises from these known occurrences is the actual origin of prebiotic organic matter.  One of the possible answers to this question is that these materials may have been seeded as a result of collisions of meteorites on the earth’s surface.  This postulate is made even more plausible if one takes into account the fact that in the early history of the planet collisions with meteorites were exceeding common.
Of particular interest is a class of meteorites referred to as the carbonaceous chondrite meteors that are believed to be samples of primitive meteorites that contain the material that was part of the formation of planet earth some 4.6 billion years ago.  These generally consist of insoluble organic matter (IOM) and soluble organic matter ((SOM). 

Dr. Christopher D. K. Herd from the Department of Earth and Atmospheric Sciences at the University of Albert, Canada and his colleagues systematically analyzed the Tagish Lake – in the Southwest region of the Yukon in Canada - meteorite specimens that fell on the frozen lake and were harvested within a few days.  The freshness of the samples effectively ruled out the possibility of contamination from the local environment – an issue that is always of major concern in these types of studies.  The investigative group chose four samples for detailed evaluation. 

Their findings were of extreme interest, for they discovered that the water extracts from these samples were dominated by monocarboxylic acids (MCAs) including formic and acetic acids that play key and ubiquitous roles in the biochemical metabolism of life on the planet.  They isolated eleven different examples of this class of organic compound.  In addition to these, amino acids were also identified.  Amino acids are the basic building blocks from which all proteins are constructed.  The evidence that was accumulated in these studies supports an extraterrestrial origin for these compounds.

This conclusion, if true, is of immense value in understanding the evolution of life on planet earth as well as encouraging speculation as to the possibility of life on other worlds or so-called “exoplanets.”

Thursday, November 3, 2011

Snowpack Declines in North America

The levels of snowpack in the mountains in the Western United States have a substantial impact upon the local natural environment.   This is due to the fact that increased runoff impacts temperature due to the loss of capacity of snow and ice to reflect heat back into the atmosphere – the so-called "albedo feedback."  This in turn influences a wide range of ecosystem processes.

It has been reported that snowpack in the Western United States has experienced a noticeable decline in recent decades.  Weather projections predict that this decline will continue to increase in the twenty-first century.  In order to quantify these changes Dr. Gregory T. Pederson and his colleagues from the U.S Geological Survey (USGS) at the Northern Rocky Mountain Science Center in Bozeman, Montana have developed snowpack reconstructions for the headwaters of the Columbia, Missouri and Colorado Rivers.  These reconstructions examine levels of snowpack that span from five hundred to a thousand years.  These findings are based upon an "extensive network of tree-ring sites," and elucidate patterns of water management and snow accumulations over extended periods of time.  The study of tree-rings has long been utilized to reconstruct patterns in regard to precipitation, drought and temperature.  Previous studies have clearly demonstrated that the amount of water available to trees during their growing cycle is largely dependent on the amount of snowpack that accumulated during prior winter seasons.

As a result of the data accumulated during this investigation, the author concluded that, "Over the past millennium, late 20th century snowpack reductions are almost unprecedented in magnitude across the northern Rocky Mountains."   This is a matter of serious concern in that it may well be a harbinger of future conditions of drought and establishes further relationships between the accumulation of greenhouse gases in the atmosphere, temperature and the global water cycle.