Modern molecular methods can reveal abundant airborne microbes where conventional culture methods used to assess cleanliness do not, say researchers. Their conclusion is based on a study of a hospital therapy pool which made nine lifeguards sick.
The team is now calling for the use of the molecular techniques to ensure safety in healthcare, describing existing methods as 鈥渟eriously inadequate鈥�.
The workers tending the warm indoor pool at a hospital in the US Midwest fell ill in 2000 with an occupational lung disease resembling pneumonia called hypersensitivity pneumonitis. Culturing samples from the workers revealed the culprit to be a bacterium called Mycobacterium avium.
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The pool was equipped with a 鈥渟tate-of-the-art鈥� disinfection system but the incident prompted Largus Angenent, at Washington University in St Louis, US, and colleagues to survey the bugs present in the pool and its surroundings using molecular techniques.
Bugs on plates
Angenent says airborne microbes are particularly hard to identify using traditional culture techniques, which involve growing bugs on agar plates in the lab. 鈥淚f something has been aerosolised it鈥檚 really hard to grow 鈥� or even if it鈥檚 not, only 1% of soil organisms can be grown in the lab,鈥� he notes.
This means that when healthcare organisations test for contamination, they 鈥渁re really only going after a small percentage of organisms鈥�, says Angenent. 鈥淭he approach we took goes after everything.鈥�
He believes the results of the study will reflect the situation in other hospital pools and in private hot tubs. 鈥淚 don鈥檛 want people to start panicking, but we need to be aware of what鈥檚 really there 鈥� and not base everything on culture studies,鈥� he told New 杏吧原创. The molecular technique the team used samples the germs鈥� DNA.
The researchers tested the pool water, the film on the pool walls and the air above the pool. A sterile filter was used to take a sample and then DNA was extracted and tested for a particular gene that is present in all life forms. This gene codes for a section of ribosomal RNA (called 16s) that has changed little through evolution.
Angenent and colleagues amplified the different forms of the gene they found, each of which represented a different strain of organism.
Infecting humans
A drawback of this molecular approach is that it does not reveal whether a bug can infect a human. But for certain conditions 鈥� such as hypersensitivity pneumonitis 鈥� this is irrelevant as the symptoms are caused simply by a biological reaction to the presence of the bug in the lungs.
The new study also found relatively greater numbers of certain bacteria, called Gram positive bacteria, in the warm air above the pool than in the water itself. Ironically, these bacteria, including Mycobacterium, can be inadvertently amplified by disinfecting systems.
Angenent explains that such bacteria have very waxy cell coats which makes them resistant to disinfectants such as chlorine or hydrogen peroxide in pools. 鈥淲hat can happen is that we kill everything else except these very resistant organisms. And then they have no competition,鈥� he told New 杏吧原创.
Molecular techniques are rarely used to identify bugs in public health settings, says Angenent. 鈥淎lthough many different water quality conditions may exist in public pools, inadequate disinfection may be more widespread than is indicated by conventional culture assays used for regulatory criteria,鈥� the researchers write.
Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0501235102)
