Farming continues to endanger us all

The structure of a typical bacteriophage

A bacteriophage, Image via Wikipedia

I’ve perhaps overstated the case with the title here, but a recent report in the October issue of Antimicrobial Agents and Chemotherapy, and summarized on Science Daily, is quite alarming. We spoke of how antibiotic resistance is increasing in frequency, due to a number of factors such as non-medical use in the agriculture industry. Our very simplified mechanism for this occurrence began with mutation: a chance event in a single organism allowed that bacterium to survive in the presence of an antibiotic, until eventually the majority of the population possessed resistance to the antibiotic. The implication in this is that only the progeny of a single cell in which a given mutational event has occurred will produce the resulting population of resistant bacteria through the process of binary fission.

Antibiotic resistance can also move between bacteria in the same species via conjugation (basically, bacterial sex), and also between species via transformation. DNA encoding antibiotic resistance genes can also be passed between a resistant and a susceptible bacterium by using a viral intermediate. Viruses of bacteria, called bacteriophages, are extremely efficient at transferring specific pieces of DNA between bacteria, and turn out to play a tremendously significant role in the transfer of antibiotic resistance.

The report linked above describes the presence of antibiotic resistance genes, specifically of the beta-lactamase family of resistance genes involved in resistance to the penicillin class of antibiotics. The authors from the University of Barcelona examined water sources polluted by farm animal fecal matter for the presence of bacteriophages, and found significant numbers of phage genomes, which contained copies of the beta-lactamase genes. The bacterial viruses are able to carry the beta-lactamase gene, and transfer those resistance genes into susceptible bacteria. The authors propose that these bacterial viruses play a huge role in the horizontal transfer of antibiotic resistance between two bacteria, as opposed to the vertical transfer of resistance from a mother cell to two daughter cells during cellular division.

The upshot of the study is that the role of viruses in spreading antibiotic resistance is now clearer, and this may mean that resistance to a specific antibiotic may actually be able to spread through a population of microorganisms (and perhaps between species as well), much more quickly than we would have anticipated without this mechanism. The main recourse to combat this spread continues to be to reduce and eliminate the very prevalent non-medical use of antibiotics. Remember: if the antibiotics are not present, antibiotic resistance won’t spread through the population!


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 October 25, 2011, in Danger danger danger!, Microbes in the News, You are what you eat and tagged , , . Bookmark the permalink. Comments Off on Farming continues to endanger us all.

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