The hunt for Legionella pneumophila
The Legionella bacteria was discovered as recently as the mid-seventies, by which time we had already been able to observe and control thousands of other water-borne bacteria from similar water sources. Why did it take such a long time to discover this particular bacterium?
The first observations of the Legionella bacterium were made in the lung tissue of persons who died as a result of the major fatal outbreak of acute pulmonary disease among members of the American Legion (military veterans) in Atlanta in 1976. At first, the bacterium was called LDB (Legionnaires’ Disease Bacterium), but it was subsequently named for the outbreak itself: Legionella pneumophila.
In 1977, the scientists realised that they were faced with a new bacterium. At that time, it could only be demonstrated by cultivating it in hamster tissue or in fertilised hens’ eggs, but now the hunt started for a simpler, more user-friendly method of detecting it. The first artificial culture medium for laboratory use was presented in 1978 by Feeley, who reported using 17 different bacteriological agar compositions before the key was found: L-cysteine and iron pyrophosphate. Further modification gave us what is now the well-known and thoroughly tested BCYE-agar (Feeley et al, 1979). All this means that none of the usual culture media are capable of demonstrating the presence of Legionella bacteria, even when they are present in large amounts.
Cultures of L. pneumophila on germ-count agar (TGE), blood agar and BCYE agar, showing how the bacterium grows only on BCYE. | 
A dipslide to which the same L. pneumophila culture has been added; nor does this substrate support growth of the bacterium. |
Process water with a normal bacterial flora, with and without additions of L. pneumophila (upper row without; lower row withL. pneumophila) |
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Screening for Legionella
SINTEF’s Department of Microbiology can offer direct demonstration of occurrences of Legionella pneumophila and can draw up strategies for monitoring specific sources of outbreaks:
- On-site survey and registration of all relevant sampling points (potential points of growth and infection)
- Sampling of all relevant sampling points (this number will vary from site to site)
- Analysis by means of real-time PCR (DNA) and preliminary reporting the following day (in Norway)
If the analyses are negative, i.e. no evidence of L. pneumophila is found, the following control regime is recommended:
- Selection of a limited number of sampling points
- Weekly L. pneumophila checks for about two months - if results continue to be negative
- Monthly checks continuing for about one year
- If Legionella pneumophila are not demonstrated on the basis of this protocol, the site may be regarded as low-risk
- Regular checks on a quarterly basis at most.
If the analyses are positive, i.e. they detect genetic material from L. pneumophila, the following measures are recommended:
- Cleaning and disinfection
- Identification of potential contamination vectors
- The positive finds to be cultured in order to confirm or reject the presence of live infectious vectors, which are a premise for infection - answers within three to four days
- Follow-up samples collected from all sampling points in the wake of the above measures
- Frequent checks until the situation has been brought under control.
We suggest that this stage should be followed up by the regime for negative findings as proposed above.