Finding bugs in the drugs

Food may be a more favoured haunt, but bacteria are not above contaminating pharmaceutical preparations as well, especially aqueous preparations such as cough syrup. Common bacterial colonizers of such preparations include Escherichia coli, Bacillus subtilis and Salmonella enterica, which can both directly affect patients’ health and also reduce the effectiveness of the preparation.

Numerous techniques are available for detecting such bacterial contamination, but they all tend to be fairly involved and time-consuming. This made a team of Portuguese researchers led by Clara Sousa at the University of Minho in Braga wonder whether NIR spectroscopy might make a more convenient alternative.

To find out, they first tried detecting bacteria in saline solutions, as a simple stand-in for aqueous pharmaceutical preparations. This involved focusing on those spectral regions that stimulate the vibration of organic molecules such as alkanes, alkenes and aromatics, whole ignoring those that are absorbed by water, and then analysing the resultant NIR data with partial least squares discriminant analysis.

The results were impressive. As they report in the International Journal of Pharmaceutics, not only could NIR spectroscopy distinguish fresh saline from contaminated saline, but it could also accurately identify the species of contaminating bacteria and determine its concentration.

So Sousa and her team then moved on to trying to detect the same five species of bacteria in three aqueous pharmaceutical preparations: cough syrup, contact lens solution and a topical anti-inflammatory solution. The results were equally impressive: for all three aqueous preparations, NIR spectroscopy could detect bacterial contamination, identify the contaminating species and determine their concentration.

The same approach should work with many other species of bacteria, say the researchers, as well as possibly with other types of microbial contaminants such as yeasts and mould.