Wednesday, 9 April 2008

Micro-organisms munching on antibiotics

Recent and alarming news from the world of microbiology is the finding that bacteria are able to utilise antibiotics as their sole carbon source. On top of the pre-existing problem of antibiotic resistance in medicine, this study has been widely publicised and given much hype due to the potential of antibiotic resistance becoming much more prevalent. Although the phenomenon of bacteria thriving on antibiotics has been previously reported in the medical literature, the cases were limited to a small number of micro-organisms and antibiotics. This study is the first of its kind to establish the level of resistance amongst a wide range of micro-organisms.

Methods: The researchers examined 18 different antibiotics ranging from natural, semi-synthetic to synthetic which could target a wide range of bacterial families and included ciprofloxacin, penicillin and kanamycin which are some of the more commonly prescribed antibiotics in medicine. Seventy-five bacterial samples were isolated from 11 diverse soil samples ranging from farm soil (cornfields fertilised with manure from cows fed with antibiotics), urban soil and pristine soil (untouched forest areas). This method ensured that the bacteria were isolated from areas with varying degrees of exposure to human-made antibiotics. More than half of the samples included bacteria from the phylogenetic order of Burkholderiales and Pseudomonadales, both capable of inflicting disease in humans. Two antibiotic concentrations (20 mg/L and 1 g/L) were tested with one concentration (1 g/L) being 50 times greater than standard antibiotic resistance concentrations.

Some of the alarming results: As there was no break-down on which phylogenetic order each of the 75 individual samples came from, the results when examined as a whole showed that 32 of the 75 bacterial samples (42%) were resistant to almost 100% of the antibiotics at 1 g/L and 17 of the 75 bacterial samples (22%) were resistant to over 50% of the antibiotics at 1 g/L. Ciprofloxacin, penicillin and kanamycin at 1 g/L, which get notable mentions for their widespread use in medicine, had 34, 73 and 54 of the 75 bacterial samples, respectively, come up resistant.

The findings of this study are a cause for concern because: (1) the wide range of bacterial families examined are closely related to clinically-relevant bacteria and (2) the antibiotic classes examined are commonly used in medicine and the occurrence of lateral transfer of genes between distantly related bacteria is highly possible which could potentially lead to greater levels of antibiotic resistance. Although disconcerting, these findings remind us of the capabilities of these microscopic organisms that go unnoticed and consequences when antibiotics are misused.

(1) Dantas G. et al. (2008) Bacteria Subsisting on Antibiotics. Science. 320: p100-103.
(2) Leslie M. (2008) Germs Take a Bite Out of Antibiotics. Science. 320: p 33.

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