Diverse populations of Legionella pneumophila present in the water of geographically clustered institutions served by the same water reservoir

Legionella pneumophila and Protozoan Hosts: Implications for the Control of Hospital and Potable Water Systems

Legionella pneumophila is an opportunistic waterborne pathogen of public health concern. It is the causative agent of Legionnaires’ disease (LD) and Pontiac fever and is ubiquitous in manufactured water systems, where protozoan hosts and complex microbial communities provide protection from disinfection procedures. This review collates the literature describing interactions between L. pneumophila and protozoan hosts in hospital and municipal potable water distribution systems. The effectiveness of currently available water disinfection protocols to control L. pneumophila and its protozoan hosts is explored. The studies identified in this systematic literature review demonstrated the failure of common disinfection procedures to achieve long term elimination of L. pneumophila and protozoan hosts from potable water. It has been demonstrated that protozoan hosts facilitate the intracellular replication and packaging of viable L. pneumophila in infectious vesicles; whereas, cyst-forming protozoans provide protection from prolonged environmental stress. Disinfection procedures and protozoan hosts also facilitate biogenesis of viable but non-culturable (VBNC) L. pneumophila which have been shown to be highly resistant to many water disinfection protocols. In conclusion, a better understanding of L. pneumophila-protozoan interactions and the structure of complex microbial biofilms is required for the improved management of L. pneumophila and the prevention of LD.

Isolation and Identification of Legionella spp. in environmental water sources based on macrophage infectivity potentiator (mip) gene sequencing in southwest Iran

Legionella species are widespread in natural water sources and man-made aqueous environments, as well as fresh-water. The present study was conducted owing to the lack of research regarding the prevalence of Legionella spp in the water sources of Ahvaz city in southwest Iran. In this study the macrophage infectivity potentiator (mip) gene sequencing was used for identification of various Legionella species isolated from different water sources. In this study, 144 water samples were collected and inoculated on the buffered charcoal-yeast extract (BCYE) agar and modified Wadowsky-Yee (MWY) medium. The DNA was extracted from positive cultures. The Legionella species were confirmed by amplifying a 654 bp fragment of the 16S rRNA gene. The mip gene of all isolates were amplified by PCR and purified for sequencing. The mip gene sequences were analyzed by jPHYDIT software version 1. The results showed a 13.9% (20/144) prevalence of Legionella spp. in water sources of Ahvaz city, southwest Iran. Analyzing of the mip gene sequences showed, out of 20 Legionella isolates, 13 isolates (54.1%) were positive for L. pneumophila, 5 isolates (20.8%) were positive for L. worsleinsis, one isolates for each one of L. dumoffi and L. fairfieldensis, (4.1%). According to our research, the occurrence of Legionella spp in water sources could be a hazard for the health systems especially in the hospitals. The regular monitoring of these water sources by health planners may therefore be useful for decreasing the risk for Legionella spp. infections.

Presence and Chromosomal Subtyping ofLegionellaSpecies in Potable Water Systems in 20 Hospitals of Catalonia, Spain

Objective:

To investigate the presence and clonal distribution ofLegionellaspecies in the water supply of 20 hospitals in Catalonia, Spain.

Setting:

20 hospitals in Catalonia, an area of 32,000 km2, located in northeast Spain.

Methods:

Environmental cultures of 186 points of potable water supply and 10 cooling towers were performed for the presence ofLegionellaspecies. Following filtration and acid treatment, the samples were seeded in selective MWY (modified Wadowsky Yee)-buffered charcoal yeast extract-a agar. All isolates obtained were characterized microbiologically and genotyped bySfilpulsed-field gel electrophoresis (PFGE).

Results:

73 of 196 water samples, representing 17 of the 20 hospitals included in the study, were positive forLegionella pneumophila(serogroups 1, 2-14, or both). The degree of contamination ranged from 200 to 74,250 colony-forming units/L. Twenty-five chromosomal DNA subtypes were detected by PFGE. A single DNA subtype was identified in 10 hospitals, 2 DNA subtypes were observed in 6 hospitals, and 1 hospital exhibited 3 different DNA subtypes. Each hospital had its ownLegionellaDNA subtype, which was not shared with any other hospitals.

Conclusions:

Legionellawas present in the water of most of the hospitals studied; each such hospital had a unique, dominant chromosomal DNA subtype. The verification of several genomic DNA restriction profiles in such a small geographic area demonstrates the great genetic diversity ofLegionellain the aquatic environment.

Persistence and multiplication of obligate anaerobe bacteria in amebae under aerobic conditions

After co-cultivation of Mobiluncus curtisii, an obligate non-sporeforming anaerobe, with free living amebae from the Acanthamoeba spp. under aerobic conditions, internalization, multiplication and persistence of bacterial cells were established for at least 4-6 weeks. Under the same conditions and media without viable amebae, the cells of M. curtisii did not replicate and died in 4-7 days. The infection of amebae occurred with 10 to 100 bacteria per ml of co-cultivation media. In 7-14 days the amount of bacterial cells increased to 1x10(5)-1x10(6) CFU/mL. Electron microscopic examinations revealed bacteria within vacuoles in the amebae and intracellular replication. These results suggest a previously undescribed mechanism for spread, replication and persistence of obligately anaerobe bacteria in the environment and new possible sources, reservoirs and transfer mechanisms of infections caused by obligate anaerobe bacteria.

Distribution of 19 major virulence genes in Legionella pneumophila serogroup 1 isolates from patients and water in Queensland, Australia

The distribution of 19 major virulence genes and the presence of plasmids were surveyed in 141 Legionella pneumophila serogroup (SG) 1 isolates from patients and water in Queensland, Australia. The results showed that 16 of the virulence genes examined were present in all isolates, suggesting that they are life-essential genes for isolates in the environment and host cells. The 65 kb pathogenicity island identified originally in strain Philadelphia-1(T) was detected more frequently in isolates from water (44.2%) than in those from patients (2.7%), indicating that the 65 kb DNA fragment may aid the survival of L. pneumophila in the sampled environment. However, the low frequency of the 65 kb fragment in isolates from patients suggests that the pathogenicity island may not be necessary for L. pneumophila to cause disease. Plasmids were not detected in the L. pneumophila SG1 isolates from patients or water studied. There was an association of both lvh and rtxA with the virulent and predominant genotype detected by amplified fragment length polymorphism, termed AF1, whereas the avirulent common isolate from water termed AF16 did not have lvh or rtxA genes, with the exception of one isolate with rtxA. It was found that a PCR detection test strategy with lvh and rtxA as pathogenesis markers would be useful for determining the infection potential of an isolate.

icmT is essential for pore formation-mediated egress of Legionella pneumophila from mammalian and protozoan cells

The final step of the intracellular life cycle of Legionella pneumophila and other intracellular pathogens is their egress from the host cell after termination of intracellular replication. We have previously isolated five spontaneous mutants of L. pneumophila that replicate intracellularly similar to the wild-type strain but are defective in pore formation-mediated cytolysis and egress from mammalian and protozoan cells, and the mutants have been designated rib (release of intracellular bacteria). Here, we show that the rib mutants are not defective in the activity of enzymes secreted through the type II secretion system, including phospholipase A, lysophospholipase A, and monoacylglycerol lipase, although they are potential candidates for factors that lyse host cell membranes. In addition, the pilD and lspG mutants, which are defective in the type II secretion system, are not defective in the pore-forming toxin. We show that all five rib mutants have an identical point mutation (deletion) following a stretch of poly(T) in the icmT gene. Spontaneous revertants of the rib mutants, due to an insertion of a nucleotide following the poly(T) stretch in icmT, have been isolated and shown to have regained the wild-type phenotype. We constructed an icmT insertion mutant (AA100kmT) in the chromosome of the wild-type strain by allelic exchange. The AA100kmT mutant was as defective as the rib mutant in pore formation-mediated cytolysis and egress from mammalian and protozoan cells. Both the rib mutant and the AA100kmT mutant were complemented by the icmT gene for their phenotypic defect. rtxA, a gene that is thought to have a minor role in pore formation, was not involved in pore formation-mediated cytolysis and egress from mammalian and protozoan cells. We conclude that the icmT gene is essential for pore formation-mediated lysis of mammalian and protozoan cells and the subsequent bacterial egress.

Presence and chromosomal subtyping of Legionella species in potable water systems in 20 hospitals of Catalonia, Spain

OBJECTIVE

To investigate the presence and clonal distribution of Legionella species in the water supply of 20 hospitals in Catalonia, Spain.

SETTING

20 hospitals in Catalonia, an area of 32,000 km2, located in northeast Spain.

METHODS

Environmental cultures of 186 points of potable water supply and 10 cooling towers were performed for the presence of Legionella species. Following filtration and acid treatment, the samples were seeded in selective MWY (modified Wadowsky Yee)-buffered charcoal yeast extract-alpha agar. All isolates obtained were characterized microbiologically and genotyped by SfiI pulsed-field gel electrophoresis (PFGE).

RESULTS

73 of 196 water samples, representing 17 of the 20 hospitals included in the study, were positive for Legionella pneumophila (serogroups 1, 2-14, or both). The degree of contamination ranged from 200 to 74,250 colony-forming units/L. Twenty-five chromosomal DNA subtypes were detected by PFGE. A single DNA subtype was identified in 10 hospitals, 2 DNA subtypes were observed in 6 hospitals, and 1 hospital exhibited 3 different DNA subtypes. Each hospital had its own Legionella DNA subtype, which was not shared with any other hospitals.

CONCLUSIONS

Legionella was present in the water of most of the hospitals studied; each such hospital had a unique, dominant chromosomal DNA subtype. The verification of several genomic DNA restriction profiles in such a small geographic area demonstrates the great genetic diversity of Legionella in the aquatic environment.

Persistence of Legionella pneumophila in a hospital's water system: a 13-year survey

OBJECTIVE

To describe the molecular epidemiology of Legionella pneumophila infections in the University of Iowa Hospitals and Clinics (UIHC).

DESIGN

Molecular epidemiological study using pulsed-field gel electrophoresis (PFGE).

SETTING

A large university teaching hospital. ISOLATES: All surviving isolates obtained from culture-proven nosocomial L. pneumophila infections and all surviving isolates obtained from the University of Iowa Hospital and Clinics' water supply between 1981 and 1993.

RESULTS

Thirty-three isolates from culture-proven nosocomial cases of L. pneumophila pneumonia were available for typing. PFGE of genomic DNA from the clinical isolates identified six different strains. However, only strain C (16 cases) and strain D (13 cases) caused more than 1 case. Strain C caused clusters of nosocomial infection in 1981, 1986, and 1993 and also caused 4 sporadic cases. Strain D caused a cluster in 1987 and 1988 plus 4 sporadic cases. Of the six strains causing clinical infections, only strains C and D were identified in water samples. PFGE identified three strains in the water supply, of which strains C and D caused clinical disease and also persisted in the water supply during most of the study period.

CONCLUSION

Specific strains of L. pneumophila can colonize hospital water supplies and cause nosocomial infections over long periods of time.

Detecting legionellosis by unselected culture of respiratory tract secretions and developing links to hospital water strains

For a 13-month period, all respiratory tract secretions submitted for routine bacteriology from a large hospital complex were cultured for legionella, irrespective of clinical diagnosis and laboratory requests. Ten cases of legionellosis were detected in this manner, three of which met a strict epidemiological definition of hospital-acquired. Therefore, the 16 warm-water systems of the hospitals, spread out over two locations, were examined for the presence of legionella. Legionella pneumophila was found in 15 warm water systems, with a distinct pattern of serogroups between the two locations. Legionella of the same serogroups as those isolated from patients were present in each hospital water supply. The isolates were further typed by monoclonal antibodies and by genomic macrorestriction analysis. Similarity between clinical and environmental isolates was found in seven cases. In these cases, acquisition from the hospital water supply appears very likely. The strains of the remaining three patients did not match those in hospital water, suggesting that community-acquired legionellosis was occurring as well. This study suggests that routinely culturing respiratory tract secretions of pneumonia patients for legionella can help diagnose unsuspected cases of legionellosis. Typing legionella strains beyond the serogroup level with tools such as macrorestriction analysis is useful to define sources of infection, which can then be targeted for control measures.

Analysis of Legionella pneumophila serogroup 1 isolates by pulsed-field gel electrophoresis

At a hospital in Halifax, Nova Scotia, Canada, three strains of Legionella pneumophila were detectable based on plasmid content, while the isolates collected at another hospital in Halifax had no plasmids. Genomic DNA was digested with BssHII, SalI, and SpeI and subjected to pulsed-field gel electrophoresis (PFGE). We found no relationship between plasmid profile and PFGE pattern.

Nosocomial legionellosis outbreak over a three-year period: investigation and control

OBJECTIVE: To investigate the epidemiologic relatedness of nosocomial infections due to Legionella pneumophila serogroup 1 diagnosed between 1992 and 1994 in six immunocompromised patients of the same hospital and to describe the measures which were developed to control the outbreak. METHODS: Legionella strains isolated from patients and from potable hot water were compared using three typing methods: monoclonal antibody analysis, arbitrarily primed PCR and ribotyping. RESULTS: Environmental investigations revealed the presence of high levels of L. pneumophila serogroup 1 in hot water. The typing methods gave concordant results for demonstrating (1) the persistence of an epidemic strain of L. pneumophila serogroup 1 in the major water distribution circuit of the hospital over a 3-year period, and (2) the identity between patients' and environmental strains. Five of the six patients were probably infected via aerosols of hot tap water following inappropriate therapeutic procedures. Repetitive heat flushings associated with regular bacteriologic surveillance allowed correct disinfection of the water distribution systems. Specific recommendations concerning aerosol delivery and oxygen therapy were implemented in order to prevent further nosocomial legionellosis. CONCLUSIONS: The same strain of L. pneumophila had been able to colonize the main water circuit of the hospital for at least 3 years; the relatedness between clinical and environmental strains was easily confirmed by the use of molecular markers.

Epidemiological and environmental investigations of Legionella pneumophila infection in cattle and case report of fatal pneumonia in a calf

A fatal pneumonia due to Legionella pneumophila was diagnosed in a young calf reared in a dairy herd located in northern Italy. Clinical symptoms consisted of watery diarrhea, hyperthermia, anorexia, and severe dyspnea. The pathological and histological findings were very similar to those observed in human legionellosis. Legionella pneumophila serogroup 1 (SG1) and SG10 were isolated from the calfs lung, and L. pneumophila SG1 was isolated from the calfs liver. L. pneumophila SG1 was also demonstrated in the lung tissue by immunofluorescence and immunohistochemical examinations. Nine of 10 L. pneumophila SG1 isolates belonged to the Olda subtype, and 1 belonged to the Camperdown subtype. A very low prevalence of antibodies to Legionella was detected in cows and calves reared in the same herd. Cultures of aqueous sediment of an old electric water heater which supplied hot water for the feeding of the calves yielded L. pneumophila SG1. Four of the colonies tested belonged to the Olda subtype. Ten clinical and four environmental isolates were examined for the presence of plasmids. Nine of them were also examined by pulsed-field gel electrophoresis assay, and the same patterns were found for L. pneumophila SG1 Olda strains isolated from the calf and from the electric heater. This is the first report of a documented case of a naturally occurring Legionella pneumonia in an animal. Cattle probably act as accidental hosts for legionellae, much the same as humans.

Environmental investigation of a legionellosis outbreak in western Sydney: the role of molecular profiling

This investigation used DNA profiling in an attempt to identify the environmental source of a community outbreak of 11 cases of Legionnaires' disease. Nine of these cases were culture positive and a single strain (DNA profile) of Legionella pneumophila serogroup 1 was isolated from eight cases. Spot water samples were collected from 51 cooling towers implicated by case exposure histories; this same strain was isolated from four towers at three separate locations up to 6 km apart. None of these locations had been frequently implicated by case histories. Because we did not perform an analytic epidemiological investigation, we were unable to identify a single environmental source for the outbreak. It is also possible that this outbreak was multifocal. The use of molecular profiling should not overshadow the importance of epidemiological methods in these environmental investigations. More data is needed regarding the prevalence, distribution, and clinical significance (virulence) of environmental L. pneumophila strains. This would aid interpretation of molecular profiling used in investigations of community legionellosis outbreaks.

Characterization and cloning of a 37.6-kb plasmid carried by Legionella pneumophila recovered from patients and hospital water over a 12-year period

For 12 years, strains of Legionella pneumophila serogroup 1 harbouring a 37.6-kb (23 MDa) plasmid have predominated among patient and potable water isolates at the Victoria General Hospital, Halifax, N.S. Plasmid DNA recovered from 24 strains isolated between 1983 and 1995 was digested with the restriction endonucleases EcoRI, HindIII, KpnI, PvuII, XbaI, and BamHI. The distribution of cutting sites indicated that the 23-MDa size group had remained essentially unchanged during this period, suggesting the persistence of a single plasmid type. Further fragmentation pattern analysis permitted the construction of a physical map of the prototype 23-MDA plasmid, pLp4269. Double digestion with BamHI-HindIII enabled the cloning of 94.4% of pLp4269 into pBluescript vector. A 2.1-kb fragment was not clonable. Plasmid pLp4269 is the first of the smaller Legionella extrachromosomal DNAs to be characterized in this way.

Subtyping of Legionella pneumophila isolates by arbitrarily primed polymerase chain reaction

Arbitrarily primed polymerase chain reaction (AP-PCR) was used to differentiate strains of Legionella pneumophila isolated from different water sources in a resort hotel in Benidorm, Alicante, Spain, where an outbreak of Legionnaires' disease occurred among a group of tourists between 65 and 80 years of age. All isolates were L. pneumophila serogroup 1, subtype Pontiac (Knoxville 1). Five different patterns (P1 to P5) were obtained by AP-PCR. The number of bands per pattern varied between 4 and 11. Patterns P1 and P2 represented 60 and 20% of L. pneumophila isolates, respectively. Since different subpopulations of L. pneumophila coexisted (up to three different AP-PCR patterns were identified in a single room), it was not possible to link an individual L. pneumophila strain to the occurrence of this outbreak.

Potable water and nosocomial Legionnaires' disease--check water from all rooms in which patient has stayed

We studied 7 patients with nosocomial Legionnaires' disease to determine the relationship between isolates of Legionella pneumophila recovered from potable water and those recovered from patients. Potable water was cultured from all rooms in which patients had stayed prior to the diagnosis of Legionnaires' disease. The 38 isolates of L. pneumophila (31 environmental, 7 patient) were resolved into 9 distinct patterns by pulse-field gel electrophoresis (PFGE), 3 by plasmid content and 2 each with monoclonal antibodies and conventional agarose gel electrophoresis of small fragments of DNA. Using PFGE it was determined that 4 of the 7 patients were infected with L. pneumophila identical to an isolate recovered from the potable water supply in one of the rooms each had occupied prior to the diagnosis of Legionnaires' disease. Patients had resided in a mean of 3.57 rooms before a diagnosis of nosocomial Legionnaires' disease. We conclude that in the setting of contaminated potable water and nosocomial Legionnaires' disease water from all the rooms which the patient has occupied prior to this diagnosis should be cultured. PFGE of large DNA fragments discriminated best among the isolates of L. pneumophila.

Nested polymerase chain reaction for detection of Legionella pneumophila in water

A highly sensitive nested polymerase chain reaction (PCR) method was evaluated for detection of Legionella pneumophila in water. Two sets of primers homologous to the coding region of the L. pneumophila macrophage infectivity potentiator (mip) gene were used. Even when starting from minute amounts of L. pneumophila DNA, the double PCR products were readily detected by direct visualization in ethidium-bromide-stained agarose gels. The method was tested on 34 potable water samples from a hospital building and compared with standard culture isolation. L. pneumophila was isolated in only twelve samples, whereas, by nested PCR, 19 samples were positive, 12 of them coincidental with culturing. These results indicate that nested PCR permits detection of L. pneumophila in samples where culturing fails, with the advantage of a rapid turnaround time, simplicity and the ability to detect non-culturable cells, fulfilling the requirements of sensitivity and specificity for routine use in an environmental laboratory.

Legionnaires' disease outbreak, Fairfield 1992: public health aspects

An investigation of an outbreak of Legionnaires' disease in 1992 in Fairfield, a municipality of Sydney, was carried out to determine the source of the outbreak. Cases of Legionnaires' disease with onset of symptoms between 11 and 20 April 1992 were included. Definite cases were individuals with a history consistent with Legionnaires' disease, confirmed by direct fluorescent antibody testing plus serology or culture. There were two control groups: patients admitted to the same hospital as the cases, matched for age and sex, and patients admitted to hospital with a presumptive diagnosis of legionnaires' disease, in whom the diagnosis was subsequently excluded. There were 26 definite cases with onset of symptoms between 11 and 20 April 1992. Six (23 per cent) died. Twenty-two cases (85 per cent) reported visiting the Fairfield business district during the ten days prior to the onset of symptoms. They were 20 times more likely to have visited Fairfield than were matched controls. Matching of Legionella pneumophila serogroup 1 from environmental and clinical samples was achieved by cytogenetic fingerprinting. Fourteen cases were linked to a single environmental sample. The epidemiological findings were consistent with a point source of Legionella in the Fairfield business district. It is most likely that the exposure occurred on 10 April 1992.

Legionellaceae in the potable water of Nova Scotia hospitals and Halifax residences

Water was cultured from 39 of 48 hospitals (7 Halifax hospitals and 32 non-Halifax hospitals) in the province of Nova Scotia and from 90 residences (74 private dwellings, 16 apartments) in Halifax to determine the frequency of legionella contamination. Six of seven Halifax hospitals had Legionellaceae isolated from their potable water compared with 3 of 32 non-Halifax hospitals (P < 0.0001). Overall, 19 of 59 (32%) of the water samples from Halifax hospitals were positive for legionellae compared with 5 of 480 (1%) samples from non-Halifax hospitals (P < 0.0000). Five of the six positive Halifax hospitals had Legionella pneumophila serogroup 1 and 1 had L. longbeachae serogroup 2 recovered from their potable water. Legionella contamination was associated with older, larger (> or = 50 beds) hospitals with total system recirculation. These hospitals also had water with a higher pH and calcium content but lower sodium, potassium, nitrate, iron and copper content. Fourteen of the 225 (6.2%) water samples from Halifax residences were positive for legionellae -8% (6/74) of the single family dwellings were positive, compared with 25% (4/16) apartments. The positivity rate of 15.7% for the 19 electric hot-water heaters in Halifax homes was not significantly different from the 32% positivity for Halifax hospitals. L. longbeachae accounted for 2 of the 14 isolates of legionellae from Halifax homes.

Treatment of Legionnaires' disease. Current recommendations

Legionnaires' disease is a relatively common cause of community-acquired pneumonia and of some outbreaks of hospital-acquired pneumonia. Moreover, Legionella pneumophila is frequently involved in the aetiology of the subset of pneumonias that is characterised by severe clinical course and high mortality. No sure clinical, radiographical or analytical features are useful in differentiating Legionella infection from other aetiologies of pneumonia. On the basis of these data, a rational initial therapeutic approach to community-acquired pneumonia, as well as to nosocomial pneumonia in certain circumstances, has to include an antimicrobial agent that is clinically effective against Legionella spp. Clinical studies have provided evidence that erythromycin is the first-line treatment. An intravenous dosage of 1g every 6 hours as initial therapy will be effective in most cases. Parenteral treatment may be switched to oral administration only after clinical response is observed. In vitro susceptibilities and preliminary experimental and clinical results suggest that clarithromycin will most likely become the preferred treatment once an intravenous preparation is available worldwide. However, orally administered clarithromycin at the dosage of 500 mg every 12 hours may be recommended in those developing countries in which health systems cannot afford the costs of intravenous therapy. In the case of clinically severe illness or in seriously immunosuppressed hosts with confirmed legionellosis, a combined therapeutic approach is warranted. Rifampicin 600 mg every 12 hours intravenously or orally has to be added to the usual dosage of erythromycin. Other alternative therapies, but with less distinct clinical efficacy, that can be combined with erythromycin are doxycycline 100 mg every 12 hours intravenously or orally, and intravenous ciprofloxacin 200 mg every 6 hours.