Identifying the "smell" of different types of lung bacteria could lead to a simple breath test to diagnose infections, a mouse study in the Journal of Breath Research, suggests.
According to the paper, bacteria produce unique combinations of volatiles that can be used to identify the genus and species, and in many cases the strain. The ability to identify bacteria by their volatilomes has generated great expectations for rapid and non-invasive clinical tests that are able to diagnose and identify infections in situ, particularly for diagnosing lung infections via breath analysis.
The authors note that the development and implementation of clinical tests based on volatile biomarkers have been limited due to the historical reliance on small numbers of volatile compounds for detection. Tests that rely on few biomarkers suffer from poor sensitivity and/or specificity because of variations in human metabolism, infectious species and strains, and the patient's environment .
An accurate breath analysis method could reduce lung infection diagnosis times from weeks to minutes, the researchers said. Scientists have already researched breath tests to diagnose asthma and cancer.
Traditionally diagnosing bacterial infections means collecting a sample that is used to grow bacteria in the lab, then testing it to see how it responds to antibiotics.
The detection of Pseudomonas aeruginosa, a common, opportunistic Gram-negative bacterium that frequently infects the cystic fibrosis (CF) lung, has been attempted via the use of several single biomarkers in breath. However, these studies and others have concluded that both external and environmental factors can confound the reliability of single biomarkers.
The researchers say that "while confounding factors such as diet or environmental background concentrations of putative biomarkers can be controlled for when known, identifying all potential interferences for single biomarkers is a labor-intensive approach".
Breath analysis is seen as a fast and non-invasive method of diagnosing diseases.
How the study was done
For the study, researchers from the University of Vermont analysed volatile organic compounds (VOCs) given off in exhaled breath by different bacteria as well as different strains of the same bacterium. They infected mice with two bacteria that are both common in lung infections - Pseudomonas aeruginosa and Staphylococcus aureus - and sampled their breath after 24 hours.
The compounds in their breath were analysed using a technique called secondary electrospray ionisation mass spectrometry (SESI-MS), which is capable of detecting extremely small elements of the chemicals present in their breath.
The researchers said they found a "statistically significant" difference between the breath profiles of the mice infected with the bacteria and the mice that were uninfected.
They also said they were able to differentiate between two species of bacteria and two different strains of the same P. aeruginosa bacterium.
Challenges that lie ahead
But Jane Hill, co-author of the study, from the University of Vermont College of Medicine, said there were still some challenges to overcome with "breath-prints".
"We are now collaborating with colleagues to sample patients in order to demonstrate the strengths, as well as limitations, of breath analysis more comprehensively," she said.
Richard Hubbard, professor of respiratory epidemiology at Nottingham City Hospital and a spokesman for the British Lung Foundation, said breath analysis was already being used to diagnose children with asthma.
"Breath analysis is an emerging field and is likely to take off across the board. It could be a very useful tool for children with cystic fibrosis, for example, as a guide on how to treat them," he said.
(Sources: IOP Science, BBC)
(Health24, January 2013)