Comparison of detection methods for Legionella species in environmental water by colony isolation, fluorescent antibody staining, and polymerase chain reaction

A Combined Immunofluorescence and Fluorescent Viability Cocktail Staining Procedure for Rapid Microscopic Detection and Enumeration of Live Legionella pneumophila

This report describes a combined immunofluorescence and fluorescence viability stain applied as one staining solution for rapid detection of live Legionella pneumophila in mixed bacterial populations. Instead of sequential viability staining with the Invitrogen BacLight LIVE/DEAD staining kit followed by antibody-Alexa Fluor (AF) 647 conjugate staining to identify live L. pneumophila, a combined single cocktail solution staining protocol was developed to simplify and accelerate the time to detection of viable L. pneumophila serogroup-1 (SG-1) in mixed species populations on a filter membrane. The stain cocktail will aid in accelerating fluorescence microscopic analysis of cooling tower, air conditioner and water fountain or other liquid samples for the presence of L. pneumophila and its viability status. Visibly red stained cells were identified as dead non-L. pneumophila SG-1 cells, while green fluorescing cells represented viable non-L. pneumophila SG-1 cells. Due to also staining red with antibody-AF 647, L. pneumophila SG-1 cells were pseudocolorized as blue to distinguish them from other dead cells. Fluorescence color emission mixing from the viability dyes (SYTO 9 and propidium iodide) with antibody-AF 647 stained L. pneumophila led to other fluorescent colors. For example, green plus pseudocolorized blue AF 647-antibody- labeled cells were identified as live cyan-colored L. pneumophila SG-1 cells. Magenta-colored cells resulted from dead L. pneumophila cells that combined red propidium iodide with blue pseudocolorized AF 647-antibody emissions. Analysis of measured RGB (red, green, blue) color values in microscopic images of mixed bacterial populations suggests the possibility of facile automated discrimination of subpopulations of live and dead L. pneumophila and non-L. pneumophila species by computers in 3-dimensional RGB color space after staining in the combined cocktail which will save time for more rapid microscopic detection of potential sources of Legionnaire's disease.

Phylogenetic Characterization of Viable but-not-yet Cultured Legionella Groups Grown in Amoebic Cocultures: A Case Study using Various Cooling Tower Water Samples

　Legionella spp. exist naturally in association with amoeba in water environments and are known to be the etiological agent of a severe form of pneumonia. To detect diverse Legionella populations in cooling tower water systems, amoebic coculturing was performed for 15 water samples obtained from five different kinds of facilities in six geographically different locations. The growth of Legionella in coculture with Acanthamoeba sp. cells was monitored by quantitative PCR targeting Legionella-specific 16S rRNA genes. Seven out of the 15 samples were positive for Legionella growth and subjected to clone library analysis. A total of 333 clones were classified into 14 operational taxonomic units composed of seven known species and seven previously undescribed groups. Four of the seven Legionella-growth-positive samples harbored detectable levels of free-living amoeba and were predominated by either L. drozanskii or L. lytica, by both L. bozemanii and L. longbeachae, or by a not-yet-described group named OTU 4. The Legionella-growth- positive samples contained higher ATP levels (>980 pM) than the growth-negative samples (<160 pM) , suggesting that ATP content would be a good indicator of the presence of viable but nonculturable Legionella populations able to grow with amoeba.

Preventing legionellosis outbreaks by a quick detection of airborne Legionella pneumophila

Legionellosis is a severe pneumonic infection caused by inhaling bacteria of the genus Legionella. Most cases reported in the USA and Europe are associated with the species Legionella pneumophila. This Gram-negative bacterium can survive within a wide spectrum of temperatures, and be transmitted via aerosols from multiple aquatic sources: fountains, thermal spas and other water systems. Although the PCR is one of the most popular methods to verify its presence in environmental or clinical samples, the direct application of this technique to ambient air samples is unusual because of the scarce material in the specimens. Here, we have developed a two-PCR assay, carried out over the V3 and V5 hypervariable regions of the 16S rRNA gene, to detect specifically the pathogenic bacteria Legionella pneumophila in outdoor air samples with low concentration of DNA. The application of this protocol does not require culture and retrieves quick results to activate the corresponding public alerts to prevent legionellosis outbreaks.

Comprehensive detection of pathogens in immunocompromised children with bloodstream infections by next-generation sequencing

Bloodstream infection (BSI) is a severe complication in immunocompromised patients. Next-generation sequencing (NGS) allows us to analyze comprehensively and quantitatively all microorganisms present in a clinical sample. Thirty-five pediatric patients (12 with BSI and 23 with suspected BSI/negative blood culture) were enrolled. Plasma/serum samples were used for sequencing and the results were compared with those from blood culture. Sequencing reads of bacteria isolated in blood culture were identified by NGS in all plasma/serum samples at disease onset. Bacteria isolated in blood culture were identical to the dominant bacteria by NGS in 8 of 12 patients. Bacterial reads per million reads of the sequence depth (BR) > 200 and relative importance values of the dominant bacteria (P1) > 0.5 were employed to determine causative pathogens. Causative pathogens were detected using these criteria in 7 of 12 patients with BSI. Additionally, causative bacteria were detected in the plasma/serum at 7 days before disease onset in two patients with catheter-related BSI. Causative pathogens, including virus, were identified in three patients with suspected BSI. Lastly, a total of 62 resistance genes were detected by NGS. In conclusion, NGS is a new method to identify causative microorganisms in BSI and may predict BSI in some patients.

Molecular characterization of viable Legionella spp. in cooling tower water samples by combined use of ethidium monoazide and PCR

Viable Legionella spp. in environmental water samples were characterized phylogenetically by a clone library analysis combining the use of ethidium monoazide and quantitative PCR. To examine the diversity of Legionella spp., six cooling tower water samples and three bath water samples were collected and analyzed. A total of 617 clones were analyzed for their 16S rRNA gene sequences and classified into 99 operational taxonomic units (OTUs). The majority of OTUs were not clustered with currently described Legionella spp., suggesting the wide diversity of not-yet-cultured Legionella groups harbored in cooling tower water environments.

Current and emerging Legionella diagnostics for laboratory and outbreak investigations

Legionnaires' disease (LD) is an often severe and potentially fatal form of bacterial pneumonia caused by an extensive list of Legionella species. These ubiquitous freshwater and soil inhabitants cause human respiratory disease when amplified in man-made water or cooling systems and their aerosols expose a susceptible population. Treatment of sporadic cases and rapid control of LD outbreaks benefit from swift diagnosis in concert with discriminatory bacterial typing for immediate epidemiological responses. Traditional culture and serology were instrumental in describing disease incidence early in its history; currently, diagnosis of LD relies almost solely on the urinary antigen test, which captures only the dominant species and serogroup, Legionella pneumophila serogroup 1 (Lp1). This has created a diagnostic "blind spot" for LD caused by non-Lp1 strains. This review focuses on historic, current, and emerging technologies that hold promise for increasing LD diagnostic efficiency and detection rates as part of a coherent testing regimen. The importance of cooperation between epidemiologists and laboratorians for a rapid outbreak response is also illustrated in field investigations conducted by the CDC with state and local authorities. Finally, challenges facing health care professionals, building managers, and the public health community in combating LD are highlighted, and potential solutions are discussed.

Overestimation of the Legionella spp. load in environmental samples by quantitative real-time PCR: pretreatment with propidium monoazide as a tool for the assessment of an association between Legionella concentration and sanitary risk

Quantitative polymerase chain reaction (qPCR) offers rapid, sensitive, and specific detection of Legionella in environmental water samples. In this study, qPCR and qPCR combined with propidium monoazide (PMA-qPCR) were both applied to hot-water system samples and compared to traditional culture techniques. In addition, we evaluated the ability of PMA-qPCR to monitor the efficacy of different disinfection strategies. Comparison between the quantification obtained by culture and by qPCR or PMA-qPCR on environmental water samples confirms that the concentration of Legionella estimated by GU/L is generally higher than that estimated in CFU/L. Our results on 57 hot-water-system samples collected from 3 different sites show that: i) qPCR results were on average 178-fold higher than the culture results (Δ log10=2.25), ii) PMA-qPCR results were on average 27-fold higher than the culture results (Δ log10=1.43), iii) propidium monoazide-induced signal reduction in qPCR were nearly 10-fold (Δ log10=0.95), and that iv) different degrees of correlations between the 3 methods might be explained by different matrix properties, but also by different disinfection methods affecting cultivability of Legionella. In our study, we calculated the logarithmic differences between the results obtained by PMA-qPCR and those obtained by culture, and we suggested an algorithm for the interpretation of PMA-qPCR results for the routine monitoring of healthcare water systems using a commercial qPCR system (iQ-check real-time PCR kit; Bio-Rad, Marnes-la-Coquette, France).

Identification of Legionella spp. in Environmental Water Samples by ScanVIT-Legionella™ Method in Spain

Rapid and more sensitive methods for the detection and quantification of viable Legionella cells have been developed. In this paper, a comparative analysis of environmental water samples using the ScanVIT-Legionella™ method and the traditional "gold standard" method of culturing is realised indicating the usefulness of the ScanVIT method. The ScanVIT-Legionella™ method was performed on environmental water samples from different locations of Huesca region (Spain). Legionella micro-colonies should appear green colour and Legionella pneumophila micro-colonies appear red. Twenty-one environmental water samples analysed by standard culture plus five control samples (Two sterile water samples with Legionella as positive controls and three sterile water samples as negative controls). All of them were used to apply ScanVIT-Legionella™ method. From of 21 environmental samples eleven were positive, six negative with both methods and four samples were negative for culture method and positive for ScanVIT-Legionella™ method. The positive control samples were positive and the negative were negative for both methods. A comparative analysis of the results obtained with two methods showed a strong positive determination coefficient (R(2) = 0.99753). The results demonstrate the usefulness of the ScanVIT-Legionella™ method as a rapid diagnostic tool in order to provide a diagnosis as quick as possible. ScanVIT-Legionella™ method offers a series of advantages such as quickly diagnosis, higher sensitivity and the possibility to identify Legionella spp. and L. pneumophila simultaneously.

Rapid monitoring of Pseudomonas aeruginosa in hospital water systems: a key priority in prevention of nosocomial infection

Pseudomonas aeruginosa has emerged as a major pathogen in nosocomial infections. Biofilm formation allows the microorganism to persist in hospital water systems for extended periods, which have been associated with nosocomial infections. The aim of this study was to evaluate the frequency of P. aeruginosa colonization of hospital tap waters by nested PCR assay. A total of 44 water samples were collected from 11 hospitals and analyzed for the presence of Pseudomonas spp. and P. aeruginosa by specific primer sets of 16S rRNA gene. Some physicochemical parameters and heterotrophic plate count (HPC) of samples for possible association with P. aeruginosa contamination were also determined. The nested PCR revealed 32% of the water samples being positive for P. aeruginosa. From the 11 hospitals surveyed, 82% (9 of 11) of the hospitals water systems were positive for P. aeruginosa. No correlation was seen between the presence of P. aeruginosa and HPC as well as physicochemical parameters. Identification of contaminated sources could be a key priority in waterborne nosocomial infections. PCR assay was used in the study provides simple, rapid, and reliable identification of P. aeruginosa in hospital water systems, which could eliminate the infections of P. aeruginosa through implementation of immediate control measures.

Outbreak investigations and identification of legionella in contaminated water

To avoid further cases arising from an infectious source it is essential to ensure the early identification of all potential source(s) within an identified area, or buildings, to determine if they are being managed safely; to take appropriate samples and ensure appropriate remedial actions are taken to remove the risk of further cases. If samples are to give representative results of the system at the time of sampling it is essential to ensure that they are processed appropriately using methods which are both sensitive and specific. It is also imperative that results are interpreted in context and transmitted as soon as possible to the outbreak control team to ensure appropriate and timely action is taken on sites which still pose a risk of infection. A multidisciplinary team approach and forward planning are essential to ensure that there are sufficiently trained and competent personnel and resources. Recognition of sources is dependent on many factors including thorough epidemiological investigations to narrow down the potential geographical area or water system that maybe common to the patients as agreed within the outbreak case definition. qPCR can be useful in both the elimination and identification of suspect systems/sites. However, it requires expert interpretation of results in the context of the sample site and factors which may affect the results such as the use of biocides together with the use of an algorithm for interpretation and actions to be taken to put the results in context.

Liver cirrhosis as a predisposing condition for Legionnaires' disease: a report of four laboratory-confirmed cases from China

Here, we describe four cases of laboratory-confirmed Legionella infection. Case 1 was a culture-confirmed case of Legionella infection in a patient with liver cirrhosis. Following this, three other liver cirrhosis cases (cases 2-4) were diagnosed with Legionella infection as confirmed by quantitative real-time PCR. The cause of the pneumonia was determined as Legionella pneumophila by positive direct fluorescence assay and isolation of the causative agent. The infections were successfully treated by administering appropriate antibiotics. These cases highlight the importance of considering Legionella as a cause of pneumonia in patients with liver disease and lung infections. The strain of L. pneumophila isolated from Case 1 was characterized as being closely related to strain Philadelphila-1 (ATCC 33152(T)), which is the type strain of the species, belonging to serogroup 1 and sequence type 36 (ST36), and is known to be distributed worldwide. To our knowledge, this is the first report of Legionella infection on the Chinese mainland for a decade and highlights the need to raise awareness of diagnostic methods for Legionnaires' disease in China and the requirement for further epidemiological surveillance strategies to monitor this disease.

Total and viable Legionella pneumophila cells in hot and natural waters as measured by immunofluorescence-based assays and solid-phase cytometry

A new method was developed for the rapid and sensitive detection of viable Legionella pneumophila. The method combines specific immunofluorescence (IF) staining using monoclonal antibodies with a bacterial viability marker (ChemChrome V6 cellular esterase activity marker) by means of solid-phase cytometry (SPC). IF methods were applied to the detection and enumeration of both the total and viable L. pneumophila cells in water samples. The sensitivity of the IF methods coupled to SPC was 34 cells liter(-1), and the reproducibility was good, with the coefficient of variation generally falling below 30%. IF methods were applied to the enumeration of total and viable L. pneumophila cells in 46 domestic hot water samples as well as in cooling tower water and natural water samples, such as thermal spring water and freshwater samples. Comparison with standard plate counts showed that (i) the total direct counts were always higher than the plate counts and (ii) the viable counts were higher than or close to the plate counts. With domestic hot waters, when the IF assay was combined with the viability test, SPC detected up to 3.4 × 10(3) viable but nonculturable L. pneumophila cells per liter. These direct IF methods could be a powerful tool for high-frequency monitoring of domestic hot waters or for investigating the occurrence of viable L. pneumophila in both man-made water systems and environmental water samples.

Usefulness of real-time PCR as a complementary tool to the monitoring of Legionella spp. and Legionella pneumophila by culture in industrial cooling systems

AIMS

This study was designed to evaluate the usefulness of quantification by real-time PCR as a management tool to monitor concentrations of Legionella spp. and Legionella pneumophila in industrial cooling systems and its ability to anticipate culture trends by the French standard method (AFNOR T90-431).

METHODS AND RESULTS

Quantifications of Legionella bacteria were achieved by both methods on samples from nine cooling systems with different water qualities. Proportion of positive samples for L. pneumophila quantified by PCR was clearly lower in deionized or river waters submitted to a biocide treatment than in raw river waters, while positive samples for Legionella spp. were quantified for almost all the samples. For some samples containing PCR inhibitors, high quantification limits (up to 4·80 × 10(5) GU l(-1) ) did not allow us to quantify L. pneumophila, when they were quantified by culture. Finally, the monitoring of concentrations of L. pneumophila by both methods showed similar trends for 57-100% of the samples.

CONCLUSIONS

These results suggest that, if some methodological steps designed to reduce inhibitory problems and thus decrease the quantification limits, could be developed to quantify Legionella in complex waters, the real-time PCR could be a valuable complementary tool to monitor the evolution of L. pneumophila concentrations.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows the possibility of using real-time PCR to monitor L. pneumophila proliferations in cooling systems and the importance to adapt nucleic acid extraction and purification protocols to raw waters.

An international trial of quantitative PCR for monitoring Legionella in artificial water systems

AIMS

  To perform an international trial to derive alert and action levels for the use of quantitative PCR (qPCR) in the monitoring of Legionella to determine the effectiveness of control measures against legionellae.

METHODS AND RESULTS

  Laboratories (7) participated from six countries. Legionellae were determined by culture and qPCR methods with comparable detection limits. Systems were monitored over ≥10 weeks. For cooling towers (232 samples), there was a significant difference between the log mean difference between qPCR (GU l(-1) ) and culture (CFU l(-1) ) for Legionella pneumophila (0·71) and for Legionella spp. (2·03). In hot and cold water (506 samples), the differences were less, 0·62 for Leg. pneumophila and 1·05 for Legionella spp. Results for individual systems depended on the nature of the system and its treatment. In cooling towers, Legionella spp. GU l(-1) always exceeded CFU l(-1) , and usually Legionella spp. were detected by qPCR when absent by culture. The pattern of results by qPCR for Leg. pneumophila followed the culture trend. In hot and cold water, culture and qPCR gave similar results, particularly for Leg. pneumophila. There were some marked exceptions with temperatures ≥50°C, or in the presence of supplementary biocides. Action and alert levels for qPCR were derived that gave results comparable to the application of the European Guidelines based on culture. Algorithms are proposed for the use of qPCR for routine monitoring.

CONCLUSIONS

  Action and alert levels for qPCR can be adjusted to ensure public health is protected with the benefit that remedial actions can be validated earlier with only a small increase in the frequency of action being required.

SIGNIFICANCE AND IMPACT OF THE STUDY

  This study confirms it is possible to derive guidelines on the use of qPCR for monitoring the control of legionellae with consequent improvement to response and public health protection.

Isolation of Legionella rubrilucens from a pneumonia patient co-infected with Legionella pneumophila

We report what we believe to be the first clinical isolation of Legionella rubrilucens from a pneumonia patient co-infected with Legionella pneumophila. L. rubrilucens strains were found in both a patient's sputum and the water of a hot spring in which the patient bathed, and DNA analysis by PFGE showed that they were indistinguishable.

Presence of potential bacterial pathogens in a municipal drinking water supply system

The quality of drinking water is a major public concern, but the detection of most potential pathogens is not always included in drinking water hygienic monitoring or is only assessed with highly biased cultivation-based methods. In this study, the occurrence of Pseudomonas aeruginosa and Legionella spp. was examined with taxon-specific PCRs in samples taken at ten points of a municipal drinking water supply system in three months. Sequence analysis confirmed the positivity of samples and revealed a diverse community of legionellae. The results showed that chlorination was an important and effective disinfection method against pathogenic bacteria in drinking water, but pathogenic bacteria could reoccur in the system farther away from the chlorination point. No strong correlation was found between the presence of the investigated potentially pathogenic bacteria and the measured abiotic and biotic parameters within the investigated range. It is hypothesized that instead of physicochemical parameters, the main factors influencing the presence of pathogens in the drinking water were rather the composition of the microbial community, the biotic interactions between individual non-pathogenic and pathogenic microorganisms (competition or promotion of growth) and the structure of biofilm grown on the inner surface of the supply system.

Detection of potentially pathogenic bacteria in the drinking water distribution system of a hospital in Hungary

The drinking water distribution system of a hospital was investigated using standard cultivation techniques, taxon-specific PCRs targeting pathogenic bacteria, denaturing gradient gel electrophoresis, cloning and sequencing. The results obtained verify the higher sensitivity of PCR compared to cultivation for detecting Legionella and Pseudomonas aeruginosa. Moreover, several other opportunistic pathogenic bacteria, such as Escherichia albertii, Acinetobacter lwoffi and Corynebacterium tuberculostrearicum, were detected, emphasizing that drinking water systems, especially those with stagnant water sections, could be the source of nosocomial infections.

Two-step scheme for rapid identification and differentiation of Legionella pneumophila and non-Legionella pneumophila species

A rapid two-step scheme based on PCR amplification and enzymatic digestion analysis of a 226-bp fragment of the 16S rRNA gene was developed to identify the Legionella genus by PCR amplification and to differentiate the Legionella pneumophila and non-Legionella pneumophila species by enzymatic digestion analysis. Among 42 ATCC strains (16 strains of L. pneumophila and 26 strains of non-L. pneumophila) and 200 Legionella isolates from environmental water samples, including pools, rivers, lakes, and cooling towers in Guangdong province, 99.59% of L. pneumophila and non-L. pneumophila strains were correctly identified and differentiated by this scheme. The procedure of this two-step identification and differentiation scheme is simple and takes only about 4 h. These results suggest that this two-step scheme provides a simple and convenient method for the rapid identification and differentiation of L. pneumophila and non-L. pneumophila species.

Specific detection of viable Legionella cells by combined use of photoactivated ethidium monoazide and PCR/real-time PCR

Legionella organisms are prevalent in manmade water systems and cause legionellosis in humans. A rapid detection method for viable Legionella cells combining ethidium monoazide (EMA) and PCR/real-time PCR was assessed. EMA could specifically intercalate and cleave the genomic DNA of heat- and chlorine-treated dead Legionella cells. The EMA-PCR assay clearly showed an amplified fragment specific for Legionella DNA from viable cells, but it could not do so for DNA from dead cells. The number of EMA-treated dead Legionella cells estimated by real-time PCR exhibited a 10(4)- to 10(5)-fold decrease compared to the number of dead Legionella cells without EMA treatment. Conversely, no significant difference in the numbers of EMA-treated and untreated viable Legionella cells was detected by the real-time PCR assay. The combined assay was also confirmed to be useful for specific detection of culturable Legionella cells from water samples obtained from spas. Therefore, the combined use of EMA and PCR/real-time PCR detects viable Legionella cells rapidly and specifically and may be useful in environmental surveillance for Legionella.

Real-time PCR assay for the detection and quantification of Legionella pneumophila in environmental water samples: utility for daily practice

We developed a quantitative real-time PCR assay targeting the mip gene of Legionella pneumophila for a prospective study from September 2004 to April 2005. It was compared with a standard culture method (French guideline AFNOR T90-431), analysing 120 water samples collected to monitor the risk related to Legionellae at Nantes hospital and to investigate a case of legionellosis acquired from hospital environment. Samples from six distinct water distribution systems were analysed by DNA extraction, amplification and detection with specific primers and FRET probes. The detection limit was 100 genomic units of L. pneumophila per liter (GU/l), the positivity threshold about 600 GU/l and the quantification limit 800 GU/l. PCR results were divided into three groups: negative (n=63), positive but non-quantifiable (n=22) or positive (n=35). PCR showed higher sensitivity than culture, whereas four culture-positive samples appeared negative by PCR (PCR inhibitor detected for two of them). Although no correlation was observed between both methods and real-time PCR cannot substitute for the reference method, it represents an interesting complement. Its sensitivity, reproducibility and rapidity appear particularly interesting in epidemic contexts in order to identify the source of contamination or to evaluate critical points of contamination in water distribution systems.

Integrated real-time PCR for detection and monitoring of Legionella pneumophila in water systems

We evaluated a ready-to-use real-time quantitative Legionella pneumophila PCR assay system by testing 136 hot-water-system samples collected from 55 sites as well as 49 cooling tower samples collected from 20 different sites, in parallel with the standard culture method. The PCR assay was reproducible and suitable for routine quantification of L. pneumophila. An acceptable correlation between PCR and culture results was obtained for sanitary hot-water samples but not for cooling tower samples. We also monitored the same L. pneumophila-contaminated cooling tower for 13 months by analyzing 104 serial samples. The culture and PCR results were extremely variable over time, but the curves were similar. The differences between the PCR and culture results did not change over time and were not affected by regular biocide treatment. This ready-to-use PCR assay for L. pneumophila quantification could permit more timely disinfection of cooling towers.

Quantitative real-time Legionella PCR for environmental water samples: data interpretation

Quantitative Legionella PCRs targeting the 16S rRNA gene (specific for the genus Legionella) and the mip gene (specific for the species Legionella pneumophila) were applied to a total of 223 hot water system samples (131 in one laboratory and 92 in another laboratory) and 37 cooling tower samples (all in the same laboratory). The PCR results were compared with those of conventional culture. 16S rRNA gene PCR results were nonquantifiable for 2.8% of cooling tower samples and up to 39.1% of hot water system samples, and this was highly predictive of Legionella CFU counts below 250/liter. PCR cutoff values for identifying hot water system samples containing >10(3) CFU/liter legionellae were determined separately in each laboratory. The cutoffs differed widely between the laboratories and had sensitivities from 87.7 to 92.9% and specificities from 77.3 to 96.5%. The best specificity was obtained with mip PCR. PCR cutoffs could not be determined for cooling tower samples, as the results were highly variable and often high for culture-negative samples. Thus, quantitative Legionella PCR appears to be applicable to samples from hot water systems, but the positivity cutoff has to be determined in each laboratory.

Development of an improved PCR-ICT hybrid assay for direct detection of Legionellae and Legionella pneumophila from cooling tower water specimens

A novelly improved polymerase chian reaction and immunochromatography test (PCR-ICT) hybrid assay comprising traditional multiplex-nested PCR and ICT, (a lateral-flow device) was developed for direct detection of Legionella bacteria from environmental cooling tower samples. The partial 16S rDNA (specific for Legionella spp.) and dnaJ (specific for Legionella pneumophila) genes from Legionella chromosome were first specifically amplified by multiplex-nested PCR, respectively, followed by detection using ICT strip. Reading of results was based on presence or absence of the two test lines on the strips. Presence of test line 1 indicated existence of Legionella spp. specific 16S rDNA and identified Legionella spp. Presence of test line 2 further indicated existence of dnaJ and thus specifically identified L. pneumophila. In contrast, for non-Legionellae bacteria no test line formation was observed. Results of direct detection of Legionella bacteria and L. pneumophila from water tower specimens by this assay showed 100% sensitivity, and 96.6% and 100% specificity, respectively compared with traditional culture, biochemical and serological identification methods. The PCR-ICT hybrid assay does not require sophisticated equipment and was proved to be practically useful in rapid and direct Legionellae detection from environmental water samples.

Rapid method for enumeration of viable Legionella pneumophila and other Legionella spp. in water

A sensitive and specific method has been developed to enumerate viable L. pneumophila and other Legionella spp. in water by epifluorescence microscopy in a short period of time (a few hours). This method allows the quantification of L. pneumophila or other Legionella spp. as well as the discrimination between viable and nonviable Legionella. It simultaneously combines the specific detection of Legionella cells using antibodies and a bacterial viability marker (ChemChrome V6), the enumeration being achieved by epifluorescence microscopy. The performance of this immunological double-staining (IDS) method was investigated in 38 natural filterable water samples from different aquatic sources, and the viable Legionella counts were compared with those obtained by the standard culture method. The recovery rate of the IDS method is similar to, or higher than, that of the conventional culture method. Under our experimental conditions, the limit of detection of the IDS method was <176 Legionella cells per liter. The examination of several samples in duplicates for the presence of L. pneumophila and other Legionella spp. indicated that the IDS method exhibits an excellent intralaboratory reproducibility, better than that of the standard culture method. This immunological approach allows rapid measurements in emergency situations, such as monitoring the efficacy of disinfection shock treatments. Although its field of application is as yet limited to filterable waters, the double-staining method may be an interesting alternative (not equivalent) to the conventional standard culture methods for enumerating viable Legionella when rapid detection is required.

Alkali-resistant bacteria in root canal systems

The aim of this study was to isolate and identify alkali-resistant bacteria from the dentin of infected root canals. Bacteria from homogenized dentin powder made up from infected root canal walls from human teeth were cultured on buffer-enriched Brain Heart Infusion agar supplemented with 4% sheep blood (BHI-blood agar), adjusted to pH 7.0, 9.0 or 10.0. Incubation took place for 7 days at 37 degrees C in an anaerobic glove box. Bacterial strains selected according to colony and morphology were subcultured in buffer-enriched BHI broth adjusted to pH 9.0, 10.0 or 11.0 to confirm their growth as alkali-resistant bacteria. Polymerase chain reaction amplification using specific primer sets and 16S rDNA sequence analysis was performed for identification of alkali-resistant isolates. In the present study, 37 teeth extracted from 37 patients were used for preparation of the dentin powder samples. Bacteria were detected in 25 samples when standard BHI-blood agars (pH 7.0) were used. Of these, 29 strains from 15 samples were alkali resistant, 25 strains growing at pH 9.0 and 4 at pH 10.0. The alkali-resistant strains included Enterococcus faecium (10 strains) and Enterococcus faecalis (2 strains), Enterobacter cancerogenus (1 strains), Fusobacterium nucleatum (1 strains), Klebsiella ornithinolytica (2 strains), Lactobacillus rhamnosus (2 strains), Streptococcus anginosus (2 strains), Streptococcus constellatus (3 strains), and Streptococcus mitis (2 strains). Three strains were also identified as bacteria of genus Firmicutes or Staphylococcus at the genus level. The present study showed that many bacterial species in infected root canal dentin were alkali-resistant at pH 9.0 and/or pH 10.0, and belonged mainly to the genus Enterococcus.

Evaluation of a real-time PCR hybridization assay for rapid detection of Legionella pneumophila in hospital and environmental water samples

A real-time LightCycler assay for Legionella pneumophila was evaluated with 120 water samples potentially contaminated with PCR inhibitors. Results were obtained within five hours, with a detection limit equivalent to 800 cells/L. However, 11 of 22 culture-positive samples containing < 100 CFU/L were also positive by LightCycler assay, indicating the presence of significant numbers of non-viable cells. Following extraction, amplification inhibitors remained in four culture-positive samples, but only one contained > 800 CFU/L. The assay seemed suitable for rapidly screening large sample numbers for heavy contamination with L. pneumophila, but conventional culture should continue to be used to detect low contamination levels.

Detection of Legionella pneumophila in water samples by quantitative culture and an antigen detection assay

We evaluated the new Legionella pneumophila antigen detection assay Binax Equate for quantitative determination of legionellae in potable water samples. Seventy-seven water samples from different sources were investigated by Binax Equate and quantitative culture. Our culture assay is able to detect 20 to 40 cfu per 100 ml water. The rates of detection of legionellae were 1% (1 of 77) for the antigen detection assay and 25% (19 of 77) by culture. We were able to detect antigen in one water sample with 28 cfu per ml L. pneumophila serogroup 1. In in-vitro experiments the antigen assay had a sensitivity of about 333 cfu per ml when the bacteria were added directly to the test tubes and about 1000 cfu per ml when a simulated water sample was investigated. None of the water samples positive for L. pneumophila serogroup 2 to 14 was positive in the Binax Equate. The new antigen assay proved to be a valuable tool for investigating heavy L. pneumophila Serogroup 1 contamination in potable water systems but lacks sufficient sensitivity to be used in the surveillance of water supplies.

Detection of legionellae in hospital water samples by quantitative real-time LightCycler PCR

Contamination of hospital water systems with legionellae is a well-known cause of nosocomial legionellosis. We describe a new real-time LightCycler PCR assay for quantitative determination of legionellae in potable water samples. Primers that amplify both a 386-bp fragment of the 16S rRNA gene from Legionella spp. and a specifically cloned fragment of the phage lambda, added to each sample as an internal inhibitor control, were used. The amplified products were detected by use of a dual-color hybridization probe assay design and quantified with external standards composed of Legionella pneumophila genomic DNA. The PCR assay had a sensitivity of 1 fg of Legionella DNA (i.e., less than one Legionella organism) per assay and detected 44 Legionella species and serogroups. Seventy-seven water samples from three hospitals were investigated by PCR and culture. The rates of detection of legionellae were 98.7% (76 of 77) by the PCR assay and 70.1% (54 of 77) by culture; PCR inhibitors were detected in one sample. The amounts of legionellae calculated from the PCR results were associated with the CFU detected by culture (r = 0.57; P < 0.001), but PCR results were mostly higher than the culture results. Since L. pneumophila is the main cause of legionellosis, we further developed a quantitative L. pneumophila-specific PCR assay targeting the macrophage infectivity potentiator (mip) gene, which codes for an immunophilin of the FK506 binding protein family. All but one of the 16S rRNA gene PCR-positive water samples were also positive in the mip gene PCR, and the results of the two PCR assays were correlated. In conclusion, the newly developed Legionella genus-specific and L. pneumophila species-specific PCR assays proved to be valuable tools for investigation of Legionella contamination in potable water systems.

Development of 16S rDNA-based PCR assay for detecting centipeda periodontii and selenomonas sputigena

To detect oral motile bacteria directly from dental plaque, specific PCR primers for Centipeda periodontii and Selenomonas sputigena were designed based on the sequence analysis of their 16S rDNA. The primers were specific and sensitive enough to amplify DNA fragments from the available oral bacteria. The detection limit was fewer than 10 bacterial cells per sample. It was also possible to detect these bacteria in dental plaque. The prevalence of these bacteria varied in each sample. The specific primers designed in this study may clarify the epidemiology of periodontal disease.

Abundance and distribution of bacteria carrying sltII gene in natural river water

Direct in situ PCR with HNPP/Fast Red TR was used to enumerate bacteria carrying the sltII gene in river water. By direct in situ PCR with a sltII-specific EVS primer, 10(2)-10(5) cells ml-1 of bacteria carrying the sltII gene were detected from all sampling sites, except the site nearest to the source of the river, while 10(2)-10(4) cells ml-1 of Escherichia coli O157:H7 were detected using a direct fluorescent antibody staining method. These results indicate that such bacteria are commonly distributed in natural river water. Direct in situ PCR with HNPP/Fast Red TR is a useful tool for detecting cells carrying specific genes, such as verotoxin-producing bacteria in natural environments.

Amplification of rfbE and fliC genes by polymerase chain reaction for identification and detection of Salmonella serovar Enteritidis, Dublin and Gallinarum-Pullorum

Polymerase chain reaction (PCR) primers for O9 antigen (rfbE) and phase 1 flagellin antigen (fliC) were designed for the rapid identification and detection of Salmonella serovar Enteritidis and Dublin. The rfbE primer pairs selectively amplified the rfbE region of group O9 Salmonella serovars. The fliC primer pairs amplified the DNAs of g,m and g,p-type flagellar antigen; Salmonella serovar Enteritidis, Dublin, and Essen. However, DNA from flagellar-negative Salmonella serovar Gallinarum-Pullorum was also amplified. The sensitivity of PCR primer pairs was 10(4) CFU/assay by boiled DNA preparation and 10(2) CFU/assay by proteinase K-treated DNA preparation.

Development of a new seminested PCR method for detection of Legionella species and its application to surveillance of legionellae in hospital cooling tower water

The presence of PCR inhibitors in water samples is well known and contributes to the fact that a practical PCR assay has not been developed for legionella surveillance. In this study, we devised a new seminested PCR assay for detection of Legionella spp. in water samples as a means of overriding the PCR inhibitors without loss of sensitivity. The seminested PCR assay utilized primers to amplify the 16S rRNA gene (LEG primers) of 39 Legionella spp. The assay was specific to legionellae, and the sensitivity was 1 fg of extracted Legionella DNA in laboratory examination. To evaluate the feasibility and sensitivity of the PCR assay in identifying the presence of legionellae, it was used to survey Legionella contamination in the water of 49 cooling towers of 32 hospitals. A commercially available EnviroAmp Legionella kit and a culture method were also used in the survey for comparison with the seminested PCR assay. The detection rates of legionellae in the samples were 91.8% (45 of 49) by the PCR assay and 79.5% (39 of 49) by the culture method. The EnviroAmp kit revealed that 30.6% of the water samples (15 of 49) contained inhibitors of the PCR amplification. However, the seminested PCR assay could produce the Legionella-specific DNA bands in 14 of the 15 samples. Although 8 of the 14 samples were positive in the first-step PCR, 6 of the 14 samples became positive in the second-step PCR. These results suggest that the effect of PCR inhibitors in samples, if any, can be reduced because of the dilution of the sample in the second-step PCR and that sensitivity of detection can be increased by the second-step PCR. Thus, the seminested PCR assay with LEG primers to amplify the 16S rRNA gene of 39 Legionella spp. was a practical and sensitive method to detect Legionella spp. in water samples.

Enzyme-linked immunoassay for detection of PCR-amplified DNA of legionellae in bronchoalveolar fluid

A nonradioactive method is described that detects 10 to 100 legionellae in 1 ml of bronchoalveolar lavage fluid. DNA is purified by a proteinase K-phenol protocol or with a commercial DNA preparation kit and amplified by PCR with amplimers specific for the 16S rRNA gene of Legionella pneumophila. The upstream primer is 5' biotinylated. The amplification product is immobilized on streptavidin-coated microtiter plates. Because of the high binding capacity, no removal of nonincorporated biotin from the PCR product is required. After alkaline denaturation, the single-stranded PCR product is hybridized with a 5' digoxigenin-labeled probing oligomer. The amplification product is then detected by using peroxidase-labeled anti-digoxigenin antibodies in a luminescence or colorimetric reaction. The assay detects as few as 10 legionellae in 1-ml bronchoalveolar lavage fluid specimens. It is specific for medically relevant Legionella species, including Legionella pneumophila, L. bozemanii, and L. longbeachae. Of over 250 clinical specimens examined, 8 were positive for legionellae by both culture and the PCR assay. Six further specimens were culture negative but PCR positive for legionellae; of these, five specimens were from patients receiving high-dose erythromycin therapy for suspected or previously diagnosed legionella pneumonia. None of the remaining 240 specimens that were culture negative for legionellae yielded a positive PCR test, although a total of over 30 different bacterial species were cultured from these specimens. The PCR assay therefore appears to exhibit high sensitivity and specificity and thus could prove suitable for use in the routine microbiological diagnostic laboratory.

Development of nested PCR based on the ViaB sequence to detect Salmonella typhi

For a rapid diagnosis of typhoid fever, we developed a nested PCR based on the nucleotide sequence encoding the Vi antigen. All Salmonella typhi strains along with a Salmonella paratyphi C strain were PCR positive. This assay was able to detect S. typhi at the single-cell level.