Isolation of Legionella pneumophila from water supplies: comparison of methods based on the guinea-pig and culture media

Confirming the Presence of Legionella pneumophila in Your Water System: A Review of Current Legionella Testing Methods

Legionnaires' disease has been recognized since 1976 and Legionella pneumophila still accounts for more than 95% of cases. Approaches in countries, including France, suggest that focusing risk reduction specifically on L. pneumophila is an effective strategy, as detecting L. pneumophila has advantages over targeting multiple species of Legionella. In terms of assays, the historically accepted plate culture method takes 10 days for confirmed Legionella spp. results, has variabilities which affect trending and comparisons, requires highly trained personnel to identify colonies on a plate in specialist laboratories, and does not recover viable-but-non-culturable bacteria. PCR is sensitive, specific, provides results in less than 24 h, and determines the presence/absence of Legionella spp. and/or L. pneumophila DNA. Whilst specialist personnel and laboratories are generally required, there are now on-site PCR options, but there is no agreement on comparing genome units to colony forming units and action limits. Immunomagnetic separation assays are culture-independent, detect multiple Legionella species, and results are available in 24 h, with automated processing options. Field-use lateral flow devices provide presence/absence determination of L. pneumophila serogroup 1 where sufficient cells are present, but testing potable waters is problematic. Liquid culture most probable number (MPN) assays provide confirmed L. pneumophila results in 7 days that are equivalent to or exceed plate culture, are robust and reproducible, and can be performed in a variety of laboratory settings. MPN isolates can be obtained for epidemiological investigations. This accessible, non-technical review will be of particular interest to building owners, operators, risk managers, and water safety groups and will enable them to make informed decisions to reduce the risk of L. pneumophila.

Ecology of Legionella: From Data to Knowledge with a Little Wisdom

The respiratory diseases produced by the Legionella genus of bacteria are collectively called Legionellosis. Presently more than 34 species of Legionella have been identified, 20 of which have been isolated from both environmental and clinical sources. The diseases produced by Legionella include the pneumonic form, Legionnaires' disease, and the flu-like form, Pontiac fever. Because the vast majority of Legionellosis is caused by the L. pneumophila species, this bacterium is the thrust of the discussion.Legionella is a global bacterium. The relationship of the bacterium to its environment has told us many things about infectious diseases. Not until Legionellosis and the discovery of its etiologic agent, Legionella, has such a successful modern-day marriage been consummated between the agent and its environment. Nearly two decades have passed since the term Legionellosis found its way into the vocabulary of the scientific journals, the popular press, and courtroom proceedings. Too often the scientific development, engineering implementation, and societal acceptance are disconnected. The focus of scientific research sometimes does not reflect engineering or societal needs and thus contributes little to the solution of immediate and important problems. At other times, scientific knowledge that could contribute to solutions is overlooked because of poor communication between the problem holders, the scientific community, regulatory agencies, the problem makers, and the public. The scope of this paper provides insights on the ecological niche of Legionella, describes the organism's ecological relationships in the natural world, and provides wisdom for effective control of the bacterium for the industrial and user communities.

Comparison of culture methods and an immunofluorescence assay for the detection ofLegionella pneumophila in domestic hot water devices

The objective of this study was to compare an indirect immunofluorescence assay with culture methods for the identification of Legionella pneumophila serogroups 1 to 6 in hot water samples taken from domestic environments. Hot water samples were obtained from the water heater, the shower heads, and the most frequently used faucet of 211 private houses. Concentrated water samples were inoculated on buffered charcoal yeast extract agar (BCYE) and on a semi-selective culture medium (GPV). Colonies with a morphology similar to that of Legionellaceae were subcultured on BCYE and on blood agar plates; those that grew on the former but not the latter were further characterized and identified by direct immunofluorescence techniques. The concentrated samples were also smeared on multiple-well microscope slides and tested by indirect immunofluorescence with monoclonal antibodies against L. pneumophila, serogroups 1 to 6. Of the houses studied, 30% were found to contain culturable L. pneumophila in at least one water sample, whereas 63% were positive by indirect immunofluorescence. The sensitivity of this assay compared with culture varied from 16.7-21.1%, and its specificity was between 76.7% and 88.3% depending on the sample source (water heater, shower heads, or faucet). In the 38 houses with at least one positive sample found by both immunofluorescence and culture, total or partial agreement between serogroups identified by both techniques was only 34%. The results obtained in this study strongly suggest that indirect immunofluorescence is not an adequate alternative for the identification of L. pneumophila in hot water systems.

Incubation of water samples containing amoebae improves detection of legionellae by the culture method

Some protozoans isolated from aquatic habitats, including domestic water supplies, can support the intracellular replication of autochthonous legionellae in vitro. We studied the effect of incubating water samples containing amoebae on the sensitivity of culture for legionellae. Samples collected during investigations of legionellosis epidemics and shown by conventional culture procedures to contain amoebae, but not legionellae, were incubated at 35 degrees C and replated. Legionellae were recovered from 59 of 144 such samples. Species isolated included L. pneumophila, L. anisa, L. bozemanii, L. gormanii, L. micdadei, L. rubrilucens, L. sainthelensi, L. steigerwaltii, and an unnamed species. Acanthamoeba polyphaga, Acanthamoeba hatchetti, a Rosculus sp., Hartmannella vermiformis, and Vahlkampfia spp. were among the autochthonous amoebae identified. Legionellae were recovered by this procedure from only 3 of 63 samples that were negative for amoebae by conventional culture procedures. These results show that water samples negative for legionellae, but positive for amoebae, by standard culture techniques should be incubated and replated to maximize the sensitivity of culture for legionellae.

Polymerase chain reaction-gene probe detection of microorganisms by using filter-concentrated samples

To detect low levels of microorganisms in environmental samples by using polymerase chain reaction (PCR)-gene probe detection, samples were concentrated by filtration. Fluoropore (Millipore Corp.) filters were compatible with PCR DNA amplification, whereas various other filters including nitrocellulose and cellulose acetate filters inhibited PCR amplification. By concentrating cells on Fluoropore filters and releasing the DNA by freeze-thaw cycling, PCR DNA amplification could be performed without removing the filter. Concentration with Fluoropore FHLP and FGLP filters permitted the detection of single cells of microorganisms in 100-ml samples by PCR-gene probes.

Detection of Legionella with polymerase chain reaction and gene probe methods

Methods were developed for the detection of Legionella in environmental water sources, based upon the polymerase chain reaction (PCR) and gene probes. All species of Legionella, including all 15 serogroups of L. pneumophila tested, were detected by PCR amplification of a 104 bp DNA sequence that codes for a region of 5S rRNA followed by radiolabelled oligoprobe hybridization to an internal region of the amplified DNA. Strains of L. pneumophila (all serogroups) were specifically detected based upon amplification of a portion of the coding region of the macrophage infectivity potentiator (mip) gene. Pseudomonas spp. that exhibit antigenic cross-reactivity in serological detection methods did not produce positive signals in the PCR-gene probe method using Southern blot analyses. Single cell, single gene Legionella detection was achieved with the PCR-gene probe methods.

Epidemiology, prevention and control of legionellosis: memorandum from a WHO meeting

This Memorandum describes the following aspects of legionellosis: clinical presentations of legionella infection, general epidemiology (including nosocomial outbreaks and travel-associated legionnaires' disease), surveillance and reporting of cases, the organism and its environment, and measures for prevention and control. These topics were discussed by experts at a meeting in Geneva on 27-29 November 1989. This article also includes their conclusions and recommendations for research in critical areas including surveillance and preventive activities that have been found to be effective.

A comparison of virulence of two strains of Legionella pneumophila based on experimental aerosol infection of guinea-pigs

Two strains of Legionella pneumophila (LP) serogroup I, of differing virulence, were examined in terms of numbers of viable organisms in tissues, pyrexia and mortality following aerosol infection. The Corby strain was the more virulent, with pyrexia and deaths of guinea-pigs 3 to 6 days after infection. This strain multiplied very rapidly in the lungs to reach a peak of 5 X 10(11) viable organisms/lung. Organisms were present in the blood, liver, spleen and kidney. The Philadelphia-1 strain (NCTC 11192) was unable to replicate in the lung and was cleared between 14 and 21 days after infection. Pyrexia was not observed. No guinea-pigs died and viable LP was not found in any organ other than the lung. Lung lavages on aerosol infected animals were performed and the virulent Corby strain was found to be mainly intracellular. The avirulent Philadelphia-1 strain was found predominantly in the extracellular location. There were approximately 10 times the number of viable virulent LP in the lung macrophage fraction than in the lung PMNL fraction. In comparison, there were approximately equal numbers of the viable avirulent strain in the macrophages and the PMNL. Experimental evidence suggests that the macrophage preferentially supports the growth of the virulent Corby strain compared with the PMNL. The avirulent strain on the other hand appears to be destroyed by both the macrophages and the PMNL.

Legionella pneumophila and water temperatures in Australian hospitals

Thirty-four samples of warm waters from 12 psychiatric centres in Victoria and New South Wales were examined for legionellae by guinea-pig inoculation. Legionella pneumophila was isolated from 20 of the samples collected from ten of the establishments investigated. The detected prevalence proportion of L. pneumophila in waters of temperatures 36 to 43 degrees C was 0.9 (18/20), whereas the prevalence in waters of temperatures 45 to 54.2 degrees C was 0.14 (2/14). The two 'positive' waters within the latter range showed evidence of low numbers of L. pneumophila. No significant antibody titres to relevant serogroups were detected in the 112 exposed residents tested from seven psychiatric hospitals in New South Wales. The findings show that the temperature range with the greatest prevalence of L. pneumophila in warm waters is 36 to 43 degrees C. The presence of legionellae in these warm water-distribution systems contrasts with their absence from the water-distribution systems of Victorian hospitals in an earlier survey and underlines the value and simplicity of the usual Australian practice of maintaining hospital hot water temperatures at about 70 degrees C in the control of L. pneumophila.