Legionella oakridgensis: unusual new species isolated from cooling tower water

Presence of Viable, Clinically Relevant Legionella Bacteria in Environmental Water and Soil Sources of China

The distribution of pathogenic Legionella in the environmental soil and water of China has not been documented yet. In this study, Legionella was detected in 129 of 575 water (22.43%) and 41 of 442 soil samples (9.28%) by culture. Twelve Legionella species were identified, of which 11 were disease-associated. Of the Legionella-positive samples, 109 of 129 (84.50%) water and 29 of 41 (70.73%) soil were positive for L. pneumophila, which accounted for about 75% of Legionella isolates in both water and soil, suggesting L. pneumophila was the most frequent species. Soil showed a higher diversity of Legionella spp. as compared with water (0.6279 versus 0.4493). In contrast, serogroup (sg) 1 was more prevalent among L. pneumophila isolates from water than from soil (26.66% versus 12.21%). Moreover, many disease-associated sequence types (STs) of L. pneumophila were found in China. Intragenic recombination was acting on L. pneumophila from both water and soil. Phylogeny, population structure, and molecular evolution analyses revealed a probable existence of L. pneumophila isolates with a special genetic background that is more adaptable to soil or water sources and a small proportion of genetic difference between water and soil isolates. The detection of viable, clinically relevant Legionella demonstrates soil as another source for harboring and dissemination of pathogenic Legionella bacteria in China. Future research should assess the implication in public health with the presence of Legionella in the soil and illustrate the genetic and pathogenicity difference of Legionella between water and soil, particularly the most prevalent L. pneumophila. IMPORTANCE Pathogenic Legionella spp. is the causative agent of Legionnaires' disease (LD), and L. pneumophila is the most common one. Most studies have focused on L. pneumophila from water and clinical samples. However, the soil is another important reservoir for this bacterium, and the distribution of Legionella spp. in water and soil sources has not been compared and documented in China yet. Discovering the distribution of Legionella spp. and L. pneumophila in the two environments may help a deep understanding of the pathogenesis and molecular evolution of the bacterium. Our research systematically uncovered the distributions of Legionella spp. in different regions and sources (e.g., water and soil) of China. Moreover, phylogeny, population structure, and molecular evolution study revealed the possible existence of L. pneumophila with a special genetic background that is more adaptable to soil or water sources, and genetic difference may exist.

Legionella spp. All Ears? The Broad Occurrence of Quorum Sensing Elements outside Legionella pneumophila

Legionella spp. are ubiquitous bacteria principally found in water networks and ∼20 species are implicated in Legionnaire’s disease. Among them, Legionella pneumophila is an intracellular pathogen of environmental protozoa, responsible for ∼90% of cases in the world. Legionella pneumophila regulates in part its virulence by a quorum sensing system named “Legionella quorum sensing,” composed of a signal synthase LqsA, two histidine kinase membrane receptors LqsS and LqsT and a cytoplasmic receptor LqsR. To date, this communication system was only found in L. pneumophila. Here, we investigated 58 Legionella genomes to determine the presence of a lqs cluster or homologous receptors using TBlastN. This analysis revealed three categories of species: 19 harbored a complete lqs cluster, 20 did not possess lqsA but maintained the receptor lqsR and/or lqsS, and 19 did not have any of the lqs genes. No correlation was observed between pathogenicity and the presence of a quorum sensing system. We determined by RT-qPCR that the lqsA gene was expressed at least in four strains among different species available in our laboratory. Furthermore, we showed that the lqs genomic region was conserved even in species possessing only the receptors of the quorum sensing system, indicating an ancestral acquisition and various loss dynamics during evolution. This system could therefore function in interspecific communication as well.

The Flagellar Regulon of Legionella-A Review

The Legionella genus comprises more than 60 species. In particular, Legionella pneumophila is known to cause severe illnesses in humans. Legionellaceae are ubiquitous inhabitants of aquatic environments. Some Legionellaceae are motile and their motility is important to move around in habitats. Motility can be considered as a potential virulence factor as already shown for various human pathogens. The genes of the flagellar system, regulator and structural genes, are structured in hierarchical levels described as the flagellar regulon. Their expression is modulated by various environmental factors. For L. pneumophila it was shown that the expression of genes of the flagellar regulon is modulated by the actual growth phase and temperature. Especially, flagellated Legionella are known to express genes during the transmissive phase of growth that are involved in the expression of virulence traits. It has been demonstrated that the alternative sigma-28 factor is part of the link between virulence expression and motility. In the following review, the structure of the flagellar regulon of L. pneumophila is discussed and compared to other flagellar systems of different Legionella species. Recently, it has been described that Legionella micdadei and Legionella fallonii contain a second putative partial flagellar system. Hence, the report will focus on flagellated and non-flagellated Legionella strains, phylogenetic relationships, the role and function of the alternative sigma factor (FliA) and its anti-sigma-28 factor (FlgM).

Functional Analysis of the Alternative Sigma-28 Factor FliA and Its Anti-Sigma Factor FlgM of the Nonflagellated Legionella Species L. oakridgensis

Legionella oakridgensis causes Legionnaires' disease but is known to be less virulent than Legionella pneumophilaL. oakridgensis is one of the Legionella species that is nonflagellated. The genes of the flagellar regulon are absent, except those encoding the alternative sigma-28 factor (FliA) and its anti-sigma-28 factor (FlgM). Similar to L. oakridgensis, Legionella adelaidensis and Legionella londiniensis, located in the same phylogenetic clade, have no flagellar regulon, although both are positive for fliA and flgM Here, we investigated the role and function of both genes to better understand the role of FliA, the positive regulator of flagellin expression, in nonflagellated strains. We demonstrated that the FliA gene of L. oakridgensis encodes a functional sigma-28 factor that enables the transcription start from the sigma-28-dependent promoter site. The investigations have shown that FliA is necessary for full fitness of L. oakridgensis Interestingly, expression of FliA-dependent genes depends on the growth phase and temperature, as already shown for L. pneumophila strains that are flagellated. In addition, we demonstrated that FlgM is a negative regulator of FliA-dependent gene expression. FlgM seems to be degraded in a growth-phase- and temperature-dependent manner, instead of being exported into the medium as reported for most bacteria. The degradation of FlgM leads to an increase of FliA activity.IMPORTANCE A less virulent Legionella species, L. oakridgensis, causes Legionnaires' disease and is known to not have flagella, even though L. oakridgensis has the regulator of flagellin expression (FliA). This protein has been shown to be involved in the expression of virulence factors. Thus, the strain was chosen for use in this investigation to search for FliA target genes and to identify putative virulence factors of L. oakridgensis One of the five major target genes of FliA identified here encodes the anti-FliA sigma factor FlgM. Interestingly, in contrast to most homologs in other bacteria, FlgM in L. oakridgensis seems not to be transported from the cell so that FliA gets activated. In L. oakridgensis, FlgM seems to be degraded by protease activities.

The life stage-specific pathometabolism of Legionella pneumophila

The genus Legionella belongs to Gram-negative bacteria found ubiquitously in aquatic habitats, where it grows in natural biofilms and replicates intracellularly in various protozoa (amoebae, ciliates). L. pneumophila is known as the causative agent of Legionnaires' disease, since it is also able to replicate in human alveolar macrophages, finally leading to inflammation of the lung and pneumonia. To withstand the degradation by its host cells, a Legionella-containing vacuole (LCV) is established for intracellular replication, and numerous effector proteins are secreted into the host cytosol using a type four B secretion system (T4BSS). During intracellular replication, Legionella has a biphasic developmental cycle that alternates between a replicative and a transmissive form. New knowledge about the host-adapted and life stage-dependent metabolism of intracellular L. pneumophila revealed a bipartite metabolic network with life stage-specific usages of amino acids (e.g. serine), carbohydrates (e.g. glucose) and glycerol as major substrates. These metabolic features are associated with the differentiation of the intracellular bacteria, and thus have an important impact on the virulence of L. pneumophila.

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.

Legionella oakridgensis ATCC 33761 genome sequence and phenotypic characterization reveals its replication capacity in amoebae

Legionella oakridgensis is able to cause Legionnaires' disease, but is less virulent compared to L. pneumophila strains and very rarely associated with human disease. L. oakridgensis is the only species of the family legionellae which is able to grow on media without additional cysteine. In contrast to earlier publications, we found that L. oakridgensis is able to multiply in amoebae. We sequenced the genome of L. oakridgensis type strain OR-10 (ATCC 33761). The genome is smaller than the other yet sequenced Legionella genomes and has a higher G+C-content of 40.9%. L. oakridgensis lacks a flagellum and it also lacks all genes of the flagellar regulon except of the alternative sigma-28 factor FliA and the anti-sigma-28 factor FlgM. Genes encoding structural components of type I, type II, type IV Lvh and type IV Dot/Icm, Sec- and Tat-secretion systems could be identified. Only a limited set of Dot/Icm effector proteins have been recognized within the genome sequence of L. oakridgensis. Like in L. pneumophila strains, various proteins with eukaryotic motifs and eukaryote-like proteins were detected. We could demonstrate that the Dot/Icm system is essential for intracellular replication of L. oakridgensis. Furthermore, we identified new putative virulence factors of Legionella.

Regulation, integrase-dependent excision, and horizontal transfer of genomic islands in Legionella pneumophila

Legionella pneumophila is a Gram-negative freshwater agent which multiplies in specialized nutrient-rich vacuoles of amoebae. When replicating in human alveolar macrophages, Legionella can cause Legionnaires' disease. Recently, we identified a new type of conjugation/type IVA secretion system (T4ASS) in L. pneumophila Corby (named trb-tra). Analogous versions of trb-tra are localized on the genomic islands Trb-1 and Trb-2. Both can exist as an episomal circular form, and Trb-1 can be transferred horizontally to other Legionella strains by conjugation. In our current work, we discovered the importance of a site-specific integrase (Int-1, lpc2818) for the excision and conjugation process of Trb-1. Furthermore, we identified the genes lvrRABC (lpc2813 to lpc2816) to be involved in the regulation of Trb-1 excision. In addition, we demonstrated for the first time that a Legionella genomic island (LGI) of L. pneumophila Corby (LpcGI-2) encodes a functional type IV secretion system. The island can be transferred horizontally by conjugation and is integrated site specifically into the genome of the transconjugants. LpcGI-2 generates three different episomal forms. The predominant episomal form, form A, is generated integrase dependently (Lpc1833) and transferred by conjugation in a pilT-dependent manner. Therefore, the genomic islands Trb-1 and LpcGI-2 should be classified as integrative and conjugative elements (ICEs). Coculture studies of L. pneumophila wild-type and mutant strains revealed that the int-1 and lvrRABC genes (located on Trb-1) as well as lpc1833 and pilT (located on LpcGI-2) do not influence the in vivo fitness of L. pneumophila in Acanthamoeba castellanii.

Identification of legionella in the environment

Legionella is ubiquitous in freshwater systems worldwide and can also be found in soil. Legionellosis may be caused by inhalation of aerosolized water or soil particles containing Legionella. Isolation of Legionella from the environment is an essential step in outbreak investigation and may also be performed within the context of a hazard analysis and control risk management plan. Culture remains the gold standard for detection of Legionella in environmental samples. Specific properties of environmental sites that could be a source of Legionella contamination, collection of samples from such sites, and procedures for culture of these samples for Legionella are described in this chapter.

Legionella cardiaca sp. nov., isolated from a case of native valve endocarditis in a human heart

A Gram-negative, rod-shaped bacterium, designated H63(T), was isolated from aortic valve tissue of a patient with native valve endocarditis. 16S rRNA gene sequencing revealed that H63(T) belongs to the genus Legionella, with its closest neighbours being the type strains of Legionella brunensis (98.8% similarity), L. londiniensis (97.0%), L. jordanis (96.8%), L. erythra (96.2%), L. dresdenensis (96.0%) and L. rubrilucens, L. feeleii, L. pneumophila and L. birminghamensis (95.7%). DNA-DNA hybridization studies yielded values of <70% relatedness between strain H63(T) and its nearest neighbours in terms of 16S rRNA gene sequence similarity, indicating that the strain represents a novel species. Phylogenetic analysis of the 16S rRNA, macrophage infectivity potentiator (mip) and RNase P (rnpB) genes confirmed that H63(T) represents a distinct species, with L. brunensis being its closest sister taxon. Fatty acid composition and biochemical traits, such as the inability to ferment glucose and reduce nitrate, supported the affiliation of H63(T) to the genus Legionella. H63(T) was distinguishable from its neighbours based on it being positive for hippurate hydrolysis. H63(T) was further differentiated by its inability to grow on BCYE agar at 17 °C, its poor growth on low-iron medium and the absence of sliding motility. Also, H63(T) did not react with antisera generated from type strains of Legionella species. H63(T) replicated within macrophages. It also grew in mouse lungs, inducing histopathological evidence of pneumonia and dissemination to the spleen. Together, these results confirm that H63(T) represents a novel, pathogenic Legionella species, for which the name Legionella cardiaca sp. nov. is proposed. The type strain is H63(T) ( = ATCC BAA-2315(T)  = DSM 25049(T)  = JCM 17854(T)).

Legionella nagasakiensis sp. nov., isolated from water samples and from a patient with pneumonia

A novel Legionella species was identified based on analysis of 16S rRNA and mip (macrophage infectivity potentiator) gene sequences, cellular fatty acids, isoprenoid quinones, biochemical reactions, antigens and quantitative DNA–DNA hybridization. Strain CDC-1796-JAP-ET was isolated from well water at the Nagasaki Municipal Medical Center, Japan. Two strains, CDC-3041-AUS-E and CDC-3558-AUS-E, were isolated from water samples during an outbreak of legionellosis in South Australia. Strain CDC-5427-OH-H was isolated from a 66-year-old female patient diagnosed with Legionnaires’ disease in the US. Cells from these four strains were Gram-negative, non-fluorescent, rod-shaped, and positive for alkaline phosphatase, esterase, leucine arylamidase, catalase, gelatinase, β-lactamase and tyrosine browning assay. Phylogenetic analysis of 16S rRNA and mip genes revealed that the four strains formed a distinct cluster within the genus Legionella. The bacteria contained branched-chain fatty acids and quinones that are typical of members of the genus Legionella. Slide agglutination tests demonstrated no cross-reaction with 52 previously described members of the Legionellaceae. DNA–DNA hybridization studies indicated that DNAs from the four strains were highly related (78–84 %) but they showed 29 % relatedness to Legionella oakridgensis ATCC 33761T and less than 10 % to strains of other Legionella species tested. These characterizations suggest that the isolates represent a novel species, for which the name Legionella nagasakiensis sp. nov. is proposed; the type strain is CDC-1796-JAP-ET ( = ATCC BAA-1557T = JCM 15315T).

The first case of Legionella nagasakiensis isolation from hot spring water

In August, 2010, strain HYMO-6 was isolated from a sample of hot spring water in Aomori, Japan. The 16S rDNA sequences (1,496bp) of this strain (accession number: AB597175) had a similarity of less than 96.6% to other Legionella species, prompting us to hypothesize that this strain might be a novel species belonging to the genus Legionella. However, in March of 2011, it was became clear that the HYMO-6 strain (=JCM 17450 =KCTC 23560 =DSM 24727) was Legionella nagasakiensis CDC-1796-JAP-E(T) (=ATCC BAA-1557(T) =JCM 15315(T)). When this strain was cultured on BCYEα agar at 36°C for 7 d, no long cells were observed. The dominant fatty acids of strain HYMO-6 were 16:1ω7c (32.4%), and the DNA G+C content was 42.0 mol%.

Potentially pathogenic amoeba-associated microorganisms in cooling towers and their control

Cooling towers provide a favorable environment for the proliferation of microorganisms. Cooling towers generate a biofilm and often aerosolize contaminated water, thereby increasing the risk of microorganism dissemination by human inhalation. This pathogen dissemination was first revealed by the epidemics of Legionnaires’ disease that were directly related to the presence of cooling towers, and since then, the ecology of Legionella pneumophila has been well studied. Each country has specific standards regarding the acceptable amount of microorganisms in cooling tower systems. However, those standards typically only concern L. pneumophila, even though many other microorganisms can also be isolated from cooling towers, including protozoa, bacteria and viruses. Microbiological control of the cooling tower system can be principally achieved by chemical treatments and also by improving the system’s construction. Several new treatments are being studied to improve the efficiency of disinfection. However, as most of these treatments continue to focus solely on L. pneumophila, reports of other types of pathogens continue to increase. Therefore, how their dissemination affects the human populous health should be addressed now.

Role of bacterial adhesion in the microbial ecology of biofilms in cooling tower systems

The fate of the three heterotrophic biofilm forming bacteria, Pseudomonas aeruginosa, Klebsiella pneumoniae and Flavobacterium sp. in pilot scale cooling towers was evaluated both by observing the persistence of each species in the recirculating water and the formation of biofilms on steel coupons placed in each cooling tower water reservoir. Two different cooling tower experiments were performed: a short-term study (6 days) to observe the initial bacterial colonization of the cooling tower, and a long-term study (3 months) to observe the ecological dynamics with repeated introduction of the test strains. An additional set of batch experiments (6 days) was carried out to evaluate the adhesion of each strain to steel surfaces under similar conditions to those found in the cooling tower experiments. Substantial differences were observed in the microbial communities that developed in the batch systems and cooling towers. P. aeruginosa showed a low degree of adherence to steel surfaces both in batch and in the cooling towers, but grew much faster than K. pneumoniae and Flavobacterium in mixed-species biofilms and ultimately became the dominant organism in the closed batch systems. However, the low degree of adherence caused P. aeruginosa to be rapidly washed out of the open cooling tower systems, and Flavobacterium became the dominant microorganism in the cooling towers in both the short-term and long-term experiments. These results indicate that adhesion, retention and growth on solid surfaces play important roles in the bacterial community that develops in cooling tower systems.

Importance of type II secretion for survival of Legionella pneumophila in tap water and in amoebae at low temperatures

Legionella pneumophila type II secretion mutants showed reduced survival in both tap water at 4 to 17 degrees C and aquatic amoebae at 22 to 25 degrees C. Wild-type supernatants stimulated the growth of these mutants, indicating that secreted factors promote low-temperature survival. There was a correlation between low-temperature survival and secretion function when 12 additional Legionella species were examined.

Cysteine metabolism in Legionella pneumophila: characterization of an L-cystine-utilizing mutant

Growth of Legionella pneumophila on buffered charcoal-yeast extract (BCYE) medium is dependent on L-cysteine (but not L-cystine), which is added in excess over what is required for nutrition. We investigated the biochemical and genetic bases for this unusual requirement and determined that much of the L-cysteine in BCYE medium is rapidly oxidized to L-cystine and is unavailable to the bacteria. Analysis of cysteine consumption during bacterial growth indicated that of the 11% consumed, 3.85% (approximately 0.1 mM) was incorporated into biomass. The activities of two key cysteine biosynthetic enzymes (serine acetyltransferase and cysteine synthase) were not detected in cell extracts of L. pneumophila, and the respective genes were not present in the genome sequences, confirming cysteine auxotrophy. Kinetic studies identified two energy-dependent cysteine transporters, one with high affinity (apparent Km, 3.29 microM) and the other with low affinity (apparent Km, 93 microM), each of which was inhibited by the uncoupling agent carbonyl cyanide m-chlorophenylhydrazone. Cystine was not transported by L. pneumophila; however, a mutant strain capable of growth on L-cystine (CYS1 mutant) transported L-cystine with similar kinetics (Km, 4.4 microM and 90 microM). Based on the bipartite kinetics, requirement for proton motive force, and inhibitor studies, we suggest that a high-affinity periplasmic binding protein and a major facilitator/symporter (low affinity) mediate uptake. The latter most likely is functional at high cysteine concentrations and most likely displays altered substrate specificity in the CYS-1 mutant. Our studies provide biochemical evidence to support a general view that L. pneumophila is restricted to an intracellular lifestyle in natural environments by an inability to utilize cystine, which most likely ensures that the dormant cyst-like transmissible forms do not germinate outside suitable protozoan hosts.

Legionella confirmation using real-time PCR and SYTO9 is an alternative to current methodology

The currently accepted culture techniques for the detection of Legionella spp. in water samples (AS/NZS 3896:1998 and ISO 11731 standard methods) are slow and laborious, requiring from 7 to 14 days for a result. We describe a fully validated rapid confirmation technique that uses real-time PCR incorporating the intercalating dye SYTO9 for the direct identification of primary cultures, significantly decreasing turnaround time and allowing faster remedial action to be taken by the industry.

Gamma-proteobacteria Aquicella lusitana gen. nov., sp. nov., and Aquicella siphonis sp. nov. infect protozoa and require activated charcoal for growth in laboratory media

Several isolates, belonging to two new species of the same novel genus of gamma-proteobacteria, were recovered from drilled well (borehole) and spa water at São Gemil in central Portugal. These organisms are phylogenetically most closely related to the strictly intracellular uncultured species of the genus Rickettsiella, which cause disease in arthropods, and to the facultatively intracellular species of the genus Legionella, some of which cause Legionnaires' disease and Pontiac fever. The São Gemil strains grew only on media containing charcoal, as is also true of the species of the genus LEGIONELLA: Unlike the vast majority of Legionella isolates, the new isolates did not require L-cysteine or ferric pyrophosphate for growth but like the legionellae had an absolute requirement for alpha-ketoglutarate. Strains SGT-39(T) and SGT-56 grew consistently between 30 and 43 degrees C, while strains SGT-108(T) and SGT-109 grew between 30 and 40 degrees C. The pH ranges for growth of these organisms were surprisingly narrow: strains SGT-39(T) and SGT-56 grew between pH 6.3 and 7.3, while strains SGT-108(T) and SGT-109 grew between pH 6.3 and 7.0. Both organisms proliferated in the amoeba Hartmannella vermiformis but did not grow in U937 human cells. Based on 16S rRNA gene sequence analysis and physiological, biochemical, and chemical analysis we describe two new species of one novel genus; one species is represented by strain SGT-39(T), for which we propose the name Aquicella lusitana, while strain SGT-108(T) represents a second species of the same genus, for which we propose the name Aquicella siphonis.

Isolation of Legionella oakridgensis from two patients with pleural effusion living in the same geographical area

Two cases of Legionnaire's disease caused by Legionella oakridgensis were diagnosed at the university hospital in Nantes, France. The two patients' isolates were identified by means of phenotyping and genotyping methods. Epidemiological investigations concluded that the first case was hospital acquired while the second case was considered community acquired.

Dictyostelium discoideum: a new host model system for intracellular pathogens of the genus Legionella

The soil amoeba Dictyostelium discoideum is a haploid eukaryote that, upon starvation, aggregates and enters a developmental cycle to produce fruiting bodies. In this study, we infected single-cell stages of D. discoideum with different Legionella species. Intracellular growth of Legionella in this new host system was compared with their growth in the natural host Acanthamoeba castellanii. Transmission electron microscopy of infected D. discoideum cells revealed that legionellae reside within the phagosome. Using confocal microscopy, it was observed that replicating, intracellular, green fluorescent protein (GFP)-tagged legionellae rarely co-localized with fluorescent antibodies directed against the lysosomal protein DdLIMP of D. discoideum. This indicates that the bacteria inhibit the fusion of phagosomes and lysosomes in this particular host system. In addition, Legionella infection of D. discoideum inhibited the differentiation of the host into the multicellular fruiting stage. Co-culture studies with profilin-minus D. discoideum mutants and Legionella resulted in higher rates of infection when compared with infections of wild-type amoebae. Because the amoebae are amenable to genetic manipulation as a result of their haploid genome and because a number of cellular markers are available, we show for the first time that D. discoideum is a valuable model system for studying intracellular pathogenesis of microbial pathogens.

Infection of macrophage-like cells by Legionella species that have not been associated with disease

We assessed the ability of Legionella species that have not been associated with disease to infect macrophage-like U937 cells. Two of fourteen species tested exhibited a 50% infective dose that was within I log unit of that of virulent L. pneumophila. Indeed, intracellular CFU of L. jamestowniensis and L. parisiensis increased 100-fold over a 72-h period. These data indicate that additional legionellae can flourish within phagocytes and therefore, can, if given the opportunity, cause disease.

Detection of flagella in 278 Legionella strains by latex reagent sensitized with antiflagellum immunoglobulins

To determine whether all Legionella species show common flagellum antigen properties, we developed a reagent using latex beads sensitized with flagellin-specific immunoglobulins that could be used in a simple and rapid agglutination reaction to identify Legionella colonies. A total of 278 strains (68 Legionella reference strains and 210 patient and environmental isolates) were tested. The results were compared with those obtained by a direct immunofluorescence assay using an antiflagellum serum and by morphological observations by electron microscopy. The immunological methods based on the use of a flagellum-specific serum have confirmed the presence of a common flagellum antigen for all Legionella species described to date. Flagella were detected for all the legionellae studied except four species: L. oakridgensis, confirmed as a nonflagellate species; L. brunensis; L. cincinnatiensis; and L. longbeachae serogroup 1. However, we noted a remarkable variability in flagellum expression, of greater or lesser degree, according to the species and their origin. A combination of all three methods of flagellum detection revealed that 86.3% of Legionella strains studied were flagellate. The latex test identified 89.6% of these strains, 97.5% of L. pneumophila, and 100% of L. pneumophila serogroup 1.

Further development of simple tests to differentiate the legionellas

Current methods for the identification of the Legionellaceae to species level are suitable only for the specialist or research laboratory. As part of a continuing taxonomic study 42 simple biochemical tests were screened for their ability to differentiate species of Legionella. Only 23 of these were of practical use. These tests are able to differentiate 21 of 23 recognized species of Legionella and six new species. Phenotypic screening with these tests may prove useful to the routine microbiologist and be a viable alternative to identification techniques currently employed.

First isolation of Legionella gormanii from human disease

Legionella gormanii, previously isolated only from the environment, was grown from the bronchial brush specimen of a patient with pneumonia. The organism was characterized by serologic, biochemical, and DNA hybridization studies.

Legionnaires disease: historical perspective

In the summer of 1976, a mysterious epidemic of fatal respiratory disease in Philadelphia launched an intensive investigation that resulted in the definition of a new family of pathogenic bacteria, the Legionellaceae. In retrospect, members of the family had been isolated from clinical specimens as early as 1943. Unsolved epidemics of acute respiratory disease dating to the 1950s were subsequently attributed to the newly described pathogens. In the intervening years, the Legionellaceae have been firmly established as important causes of sporadic and epidemic respiratory disease. The sources of the infecting bacteria are environmental, and geographic variation in the frequency of infection has been documented. Airborne dissemination of bacteria from cooling towers and evaporative condensers has been responsible for some epidemics, but potable water systems are perhaps more important sources. The mode of transmission from drinking water is unclear. The Legionellaceae are gram-negative, facultative, intracellular pathogens. The resident alveolar macrophage, usually an effective antibacterial defense, is the primary site of growth. Cell-mediated immunity appears to be the most important immunological defense; the role of humoral immunity is less clear. Erythromycin remains the antibiotic of choice for therapy of infected patients, but identification and eradication of environmental sources are also essential for the control of infection.

An alkaline approach to treating cooling towers for control of Legionella pneumophila

Earlier field and laboratory studies have shown that Legionella species survive and multiply in the pH range 5.5 to 9.2. Additionally, the technical feasibility of operating cooling towers at elevated alkalinities and pH has previously been documented by published guidelines. The guidelines indicate that these conditions facilitate corrosion control and favor chlorine persistence which enhances the effectiveness of continuous chlorination in biofouling control. This information suggests that control of Legionella species in cooling towers can be accomplished by operating the towers under alkaline conditions. To test this possibility, we collected water samples over a period of months from a hospital cooling tower. The samples were analyzed for a variety of chemical parameters. Subsamples were pasteurized and inoculated with non-agar-passaged Legionella pneumophila which had been maintained in tap water. Correlation of subsequent Legionella growth with corresponding pH and alkalinity values revealed statistically significant inverse associations. These data support the hypothesis that operating cooling towers outside of the optimal conditions for Legionella growth (e.g., at elevated alkalinities and a pH greater than 9) may be a useful approach to controlling growth in this habitat.

Second serogroup of Legionella feeleii strains isolated from humans

Three strains of Legionella feeleii from patients with pneumonia (425-MI-H, 691-WI-H, and 693-WI-H) and one environmental strain (713-MI-E) received at the Centers for Disease Control for reference diagnostic testing were compared with the type strain WO-44C-C3 (ATCC 35072) by DNA hybridization, chemical analysis of cellular fatty acids and ubiquinones, biochemical tests, and serological characteristics. All four isolates were assigned to the L. feeleii species on the basis of DNA hybridization results. However, strains 691-WI-H and 693-WI-H were serologically distinct from strain WO-44C-C3, as shown by their minimal reactivity (1 to 2+) with a direct immunofluorescence conjugate prepared against L. feeleii serogroup 1 (strain WO-44C-C3). Therefore, strains 691-WI-H and 693-WI-H were placed in a new L. feeleii serogroup (serogroup 2). The reference strain of L. feeleii serogroup 2 is 691-WI-H (ATCC 35849).

Growth of Legionella pneumophila in continuous culture

A method was developed to grow Legionella pneumophila in continuous culture. A chemostat was used to simulate nutrient-limited, submaximal growth in the natural environmental and to provide a precisely controlled growth regimen. Cultures grew under forced aeration under conditions yielding up to 38% saturation of dissolved oxygen; supplemental CO2 (5%) at the same gas flow rates as ambient air had no effect on culture growth. Pleomorphism was observed during growth under all conditions. Pigment was produced only at D less than 0.03 h-1. Catalase was produced at higher growth rates but not at higher temperatures. The pathogenicity was unaffected by altering either the growth rate or the growth temperature.

Identification of 22 Legionella species and 33 serogroups with the slide agglutination test

We used the slide agglutination test to determine the serologic relationships of 22 Legionella spp. representing 33 serogroups. Antisera prepared against 14 of the Legionella spp. contained cross-reactive antibodies (1+ or greater) at their working dilutions. Numerous cross-reactions were observed for the blue-white fluorescing Legionella spp. With only three exceptions in the latter group, cross-reactive antibodies were removed by absorption, thereby producing serogroup-specific antisera. For screening tests or for identification only to the genus level, nine polyvalent antiserum pools were prepared. Routine use of slide agglutination test reagents should expand the number of Legionella spp. that can be identified in the clinical laboratory and, at the same time, provide a simpler, less costly test procedure.

Photoreactivation of UV-irradiated Legionella pneumophila and other Legionella species

Shortwave UV light was assessed as a feasible modality for the control of Legionnaires disease bacterium in water. The results of this study show that Legionella pneumophila and six other Legionella species are very sensitive to low doses of UV. However, all Legionella species tested effectively countered the germicidal effect of UV when subsequently exposed to photoreactiving light.

Legionella oakridgensis: laboratory diagnosis of a human infection

We report the laboratory diagnosis of a case of pneumonia caused by Legionella oakridgensis. L. oakridgensis, originally isolated from industrial cooling towers, has not previously been associated with human disease.

Legionella anisa: a new species of Legionella isolated from potable waters and a cooling tower

Between March 1980 and June 1981, five strains of Legionella-like organisms were isolated from water. Four were recovered from potable water collected from hospitals in Chicago, Ill., and Los Angeles, Calif., during outbreaks of nosocomial legionellosis. The fifth strain was isolated from water collected from an industrial cooling tower in Jamestown, N.Y. The strains exhibited biochemical reactions typical of Legionella species and were gram-negative motile rods which grew on buffered charcoal-yeast extract agar but not on blood agar, required cysteine, and were catalase positive, urease negative, nitrate negative, hippurate negative, and nonfermentative. All strains were positive for oxidase and beta-lactamase and produced a brown, diffusible pigment. Of the five strains, four exhibited blue-white autofluorescence under long-wavelength UV light. The fatty-acid composition and ubiquinone content of these strains were consistent with those of other Legionella species. Direct fluorescent-antibody examination of the five strains with conjugates to previously described Legionella species demonstrated no cross-reactions except with the conjugates to L. longbeachae serogroup 2 and L. bozemanii serogroup 2. Four strains gave a 4+ reaction to the L. longbeachae serogroup 2 conjugate and the fifth strain gave a 1+ reaction. Each of the five strains gave a 4+ reaction with the conjugate to L. bozemanii serogroup 2. DNAs from the five strains were highly related (84 to 99%) and showed 5 to 57% relatedness to other Legionella species. These strains constitute a new species in the genus Legionella, and the name Legionella anisa sp. nov. is proposed. The type strain of L. anisa is WA-316-C3 (ATCC 35292).

Legionella and Legionnaires' disease: a review with emphasis on environmental studies and laboratory diagnosis

Legionella pneumophila and related species are important causes of epidemic bacterial pneumonia and nosocomial infection. This review will discuss this new family of bacteria and the diseases they produce. The classification, general microbiologic characteristics, and ecology of the bacteria will be reviewed and the epidemiology and clinical aspects of the infection will be discussed. More emphasis will be given to issues that are more directly related to laboratory workers and with which the author has had more direct experience: pathology, laboratory diagnosis of human infection, pathogenesis of the infection, and virulence mechanisms of the bacterium. Therapy and prevention of the infection will be discussed more briefly.

Isolation of Legionella species from drinking water

Three different species of Legionella were recovered from samples of water taken from chlorinated public water supplies where no coliform bacteria were simultaneously detected. Five of 856 samples yielded Legionella isolates. Three isolates were identified as Legionella pneumophila serogroup 1, the fourth was identified as Legionella dumoffii, and the fifth was identified as Legionella jordanis. Studies to determine the survival of L. pneumophila Flint 1 serogroup 1 in tap water at various temperatures and in tap water with added sodium hypochlorite were done. These organisms were found to survive for 299 days in tap water at 24 and 5 degrees C but not at 35 degrees C. A concentration of at least 0.2 mg of residual chlorine per ml was required to eliminate at least 90% of L. pneumophila and Escherichia coli inocula in 2 h.

Determination of catalase, peroxidase, and superoxide dismutase within the genus Legionella

We examined 40 strains of Legionella for reduced-oxygen scavenging enzymes. Using a simple reaction chamber with a Swinney filter for the Beers and Sizer assay, we determined the catalase activity of live cells grown on buffered charcoal-yeast extract agar. For 29 strains of Legionella pneumophila, the apparent first-order rate constants for catalase ranged from 0.000 to 0.005. Similarly, low values ranging from 0.001 to 0.005 were observed for Legionella wadsworthii, Legionella oakridgensis, and Legionella gormanii. High catalase activities were found for Legionella jordanis, Legionella longbeachae, Legionella micdadei, and Legionella bozemanii, with first-order rate constant values of 0.010 to 0.035. Cell-free extracts were analyzed for catalase, peroxidase, and superoxide dismutase. Cell-free extracts of all strains had superoxide dismutase levels ranging from 8.2 to 30.5 U per mg of protein. The species could be characterized by their catalase and peroxidase since L. pneumophila and L. gormanii had only peroxidase (relative molecular weight [Mr], 150,000); L. dumoffii had a peroxidase (Mr, 150,000) plus a catalase (Mr, 174,000); and all remaining species had catalase only (Mr, 300,000, 220,000, or 150,000).

Vaccination against Legionella pneumophila: serum antibody correlates with protection induced by heat-killed or acetone-killed cells against intraperitoneal but not aerosol infection in guinea pigs

An aerosol model of Legionella infection has been established in guinea pigs. Infected animals showed growth of Legionella in their lungs, dissemination of organisms to the spleen, development of pneumonia and fever, and weight loss. Vaccination studies using heat-killed or acetone-killed cells were carried out, and guinea pigs were challenged intraperitoneally or by using the aerosol model of infection. Both vaccines were shown to give moderately high levels of protection against intraperitoneal challenge (28 to 145 50% lethal doses). Protection was found to be dose dependent and correlated with antibody levels as measured by enzyme-linked immunosorbent assay to an outer membrane antigen and by indirect immunofluorescence to heat-killed cells. In contrast, the same vaccination regimens that protected against intraperitoneal challenge failed to protect guinea pigs against aerosol challenge with comparable doses of Legionella, despite the presence of serum antibody. The results are discussed in terms of the possible requirements for immunity to aerosolized Legionella, including secretory immunoglobulin or cell-mediated immunity.

Clinical laboratory differentiation of Legionellaceae family members with pigment production and fluorescence on media supplemented with aromatic substrates

A systematic study of pigment production (browning) and fluorescence (extracellular yellow-green and intracellular blue-white) by nine Legionellaceae species was performed. A total of 56 strains representing Tatlockia micdadei (Pittsburgh pneumonia agent), Legionella pneumophila, Legionella jordanis, Legionella longbeachae, Legionella oakridgensis, Legionella wadsworthii, Fluoribacter bozemanae, Fluoribacter gormanii, and Fluoribacter dumoffii could be separated on media supplemented with tyrosine plus cystine, 3,4-diaminobenzoic acid, 3,5-diaminobenzoic acid, and 3-aminotyrosine. Parallel testing by hippurate hydrolysis and the bromocresol purple spot test enabled the identification of Legionellaceae species 24 to 72 h after primary isolation. This schema may be a practical alternative to species-specific antisera methods (slide agglutination or direct immunofluorescence) in the identification of members of the family Legionellaceae.

Retrospective examination of lung tissue specimens for the presence of Legionella organisms: comparison of an indirect fluorescent-antibody system with direct fluorescent-antibody testing

Although direct fluorescent-antibody (DFA) testing has been used successfully for a number of years to detect legionellae in clinical specimens, the number of known species and serogroups of Legionella has now increased to such an extent that the performance of DFA testing for all serological variants is impractical. Lung homogenates that were submitted to the Centers for Disease Control, Atlanta, Ga., from patients with suspected legionellosis, from November 1977 through May 1982, were originally screened by DFA testing. In our study 498 of these lung homogenates were screened by indirect fluorescent-antibody (IFA) testing, using a panvalent antiserum pool containing antibodies to 25 serological variants of Legionella spp. Fluorescein isothiocyanate-labeled goat anti-rabbit immunoglobulin was used as the second antibody of the sandwich system. For positive homogenates, i.e., those containing Legionella organisms, species and serogroup identification was made by IFA staining with polyvalent serum pools and then with monovalent antiserum. Of the 498 homogenates screened, 39 (7.8%) were positive by IFA testing. Four (0.8% of total; 10.3% of positive homogenates) of these had previously been negative by DFA testing, but subsequent testing showed that they contained Legionella organisms for which DFA reagents were not available at the initial screening. All specimens that were positive by DFA testing were also positive by IFA testing. IFA testing with polyvalent antisera is a simple, efficient method which is at least as sensitive as DFA testing and which can be used by clinical laboratories to cope with the increasing number of known serological variants of Legionella spp.

Legionella sainthelensi: a new species of Legionella isolated from water near Mt. St. Helens

Six strains of a new species, Legionella sainthelensi, were isolated from freshwater in areas affected by the volcanic eruptions of Mt. St. Helens in the state of Washington. Strains of L. sainthelensi are culturally and biochemically similar to other legionellae. They grow on buffered charcoal yeast agar but not on media that lack cysteine. They are gram-negative, nonsporeforming, motile rods that are positive in reactions for catalase, oxidase, gelatin liquefaction, and beta-lactamase. They are negative in reactions for urease, hydrolysis of hippurate, reduction of nitrates, fermentation of glucose, and blue-white autofluorescence. Their cell wall fatty acid composition is qualitatively similar to those of other legionellae, with 50 to 62% branched-chain fatty acids. They contain the isobranched-chain 14- and 16-carbon acids and anteisobranched-chain 15- and 17-carbon acids and relatively large amounts of straight-chain 16-carbon acid. All strains of L. sainthelensi contain approximately equal amounts of ubiquinones Q9, Q10, Q11, and Q12, a pattern similar to those of Legionella bozemanii, Legionella dumoffi, and Legionella longbeachae. Serological cross-reactions were observed between L. sainthelensi, both serogroups of L. longbeachae, and Legionella oakridgensis. Three strains of L. sainthelensi were greater than 90% related by DNA hybridization. The type strain of L. sainthelensi, Mt. St. Helens 4, was 36% related to the type strain of L. longbeachae and 3 to 14% related to the other nine described Legionella species.

Legionella bozemanii serogroup 2: a new etiological agent

A newly discovered bacterium, Toronto 3, isolated from a lung aspirate of a patient with pneumonia, has been characterized. The isolate was identified as Legionella bozemanii by chemical data from cellular fatty acid and ubiquinone analyses and by DNA relatedness studies. The isolate, however, differs phenotypically from L. bozemanii by its colonial characteristics and strong interspecies serological cross-reactions, which are unique among clinical isolates of legionellae. The name L. bozemanni serogroup 2 is proposed. The reference strain is Toronto 3. The clinical illness caused by L. bozemanii serogroup 2 was not distinguishable from other Legionella infections. L. bozemanii is the third Legionella species with more than one serogroup. Rapid laboratory diagnosis of this strain by direct fluorescent antibody test may be complicated in the absence of culture isolation.

Comparison of the effects of acid and base hydrolyses on hydroxy and cyclopropane fatty acids in bacteria

The cellular fatty acid compositions of Legionella oakridgensis, Brucella suis, Pseudomonas aeruginosa, and Francisella tularensis were compared after base hydrolysis (saponification), acid hydrolysis, and acid methanolysis procedures were used to release the fatty acids. The branched-chain, unsaturated, saturated, and ester-linked hydroxy acids were released as effectively with saponification at 100 degrees C for 30 min as with acid hydrolysis or acid methanolysis at 85 degrees C for 16 h. Although the amide-linked hydroxy acids were released more effectively by acid hydrolysis or acid methanolysis, these methods degraded the cyclopropane fatty acids, producing a number of new peaks or artifacts in the chromatograms. Cyclopropane fatty acids were not degraded by saponification, and at least 50% of the hydroxy acids were released when the cells were saponified with 15% NaOH in 50% aqueous methanol. Thus, the results show that saponification for 30 min at 100 degrees C with 15% NaOH, followed by methylation is an excellent method for routine fatty acid analysis of bacteria and for screening cultures whose identity and fatty acid composition are unknown.

Comparison of slide agglutination test and direct immunofluorescence assay for identification of Legionella isolates

It is technically impractical for many clinical laboratories to use the direct immunofluorescence assay for identifying and serogrouping clinical isolates of Legionella. We compared the results obtained with the direct immunofluorescence assay with the results of a simple and less-demanding slide agglutination test for identifying 15 serogroups representing seven Legionella species. The slide agglutination test was in complete agreement with the direct immunofluorescence assay, and the serogroup to which 64 clinical isolates of Legionella belonged was correctly identified. With polyvalent, pooled antisera and absorbed, serogroup-specific antisera, the slide agglutination test is a useful alternative to the direct immunofluorescence assay in the diagnosis of Legionella infections and for studying the serological relationships of Legionella-like organisms.

Cellular fatty acid composition and ubiquinone content of Legionella feeleii sp. nov

The cellular fatty acid composition of Legionella feeleii was determined by capillary gas-liquid chromatography, and the ubiquinone content was determined by reverse-phase high-pressure liquid chromatography. As in other Legionella species, this new species is characterized by relatively large amounts of branched-chain fatty acids and by major amounts of ubiquinones with more than 10 isoprene units in the side chain.