Diversity of legionellae strains from Tunisian hot spring water

Legionella pneumophila Presence in Dental Unit Waterlines: A Cultural and Molecular Investigation in the West Bank, Palestine

A Legionella pneumophila bacterium is ubiquitous in water distribution systems, including dental unit waterlines (DUWLs). Legionellosis is atypical pneumonia, including Legionnaires' disease (LD) and the less acute form of Pontiac fever. Legionellosis occurs as a result of inhalation/aspiration of aerosolized Legionella-contaminated water by susceptible patients, health workers, and dentists. In this study, we undertook to determine the prevalence of Legionella in water and biofilm samples from Tap and DUWLs collected from five sites of dental clinics and faculties across the West Bank. Water samples were tested for physical and chemical parameters. The study samples included 185 samples, 89 (48%) water samples, and 96 (52%) biofilm swabs, which were analyzed by cultivation-dependent analysis (CDA) and by the cultivation-independent technique (CIA). Also, partial sequencing of the 16S rRNA gene for fifteen L. pneumophila isolates was performed for quality assurance and identification. L. pneumophila was isolated from 28 (15%) of 185 samples using CDA and was detected in 142 (77%) of 185 samples using CIA. The abundance of culturable L. pneumophila was low in DUWL of the sampling sites (range: 27-115 CFU/Liter). PCR was 5× more sensitive than the culture technique. L. pneumophila Sg 1 was detected in (75%) of the isolates, while (25%) isolates were L. pneumophila Sg 2-14. All fifteen sequenced Legionella isolates were identified as L. pneumophila ≥ 94.5%. The analysis of phylogenetic tree showed that L. pneumophila branch clearly identified and distinguished from other branches. These results show that DUWLs of the examined dental clinics and faculties are contaminated with L. pneumophila. This finding reveals a serious potential health risk for infection of immunocompromised patients and dentists' post-exposure.

Sodium levels and grazing pressure shape natural communities of the intracellular pathogen Legionella

BACKGROUND

Legionella are parasites of freshwater protozoa, responsible for Legionellosis. Legionella can be found in a variety of aquatic environments, including rivers, lakes, and springs, as well as in engineered water systems where they can potentially lead to human disease outbarks. Legionella are considered to be predominantly freshwater organisms with a limited ability to proliferate in saline environments. Exposure of Legionella to high sodium concentrations inhibits growth and virulence of laboratory strains, particularly under elevated temperatures. Nonetheless, Legionella have been identified in some saline environments where they likely interact with various protozoan hosts. In this work, we examine how these selection pressures, sodium and grazing, help shape Legionella ecology within natural environments. Utilizing Legionella-specific primers targeting a variable region of the Legionella 16S rRNA gene, we characterized Legionella abundance, diversity, and community composition in natural spring clusters of varying sodium concentrations, focusing on high sodium concentrations and elevated temperatures.

RESULTS

We observed the highest abundance of Legionella in spring clusters of high salinity, particularly in combination with elevated temperatures. Legionella abundance was strongly related to sodium concentrations. The Legionella community structure in saline environments was characterized by relatively low diversity, compared to spring clusters of lower salinity. The community composition in high salinity was characterized by few dominant Legionella genotypes, not related to previously described species. Protozoan microbial community structure and composition patterns resembled those of Legionella, suggesting a common response to similar selection pressures. We examined Legionella co-occurrence with potential protozoan hosts and found associations with Ciliophora and Amoebozoa representatives.

CONCLUSIONS

Our results indicate that selection forces in saline environments favor a small yet dominant group of Legionella species that are not closely related to known species. These novel environmental genotypes interact with various protozoan hosts, under environmental conditions of high salinity. Our findings suggest that alternative survival mechanisms are utilized by these species, representing mechanisms distinct from those of well-studied laboratory strains. Our study demonstrate how salinity can shape communities of opportunistic pathogens and their hosts, in natural environments, shedding light on evolutionary forces acting within these complex environments. Video Abstract.

Identification of Responders to Balneotherapy among Adults over 60 Years of Age with Chronic Low Back Pain: A Pilot Study with Trajectory Model Analysis

Balneotherapy may be a relevant treatment for chronic low back pain (LBP) in individuals > 60 years old. This pilot study aimed to determine the effectiveness of balneotherapy for chronic LBP in people > 60 years old and to determine profiles of responders with trajectory model analysis. This was a pilot prospective open cohort study, with repeated measurements using validated questionnaires; participants were their own controls. The primary endpoint was the proportion of participants with a change in pain intensity between the start of treatment and 3 months after treatment assessed with a numeric scale (NS) from 0 to 100 mm, with an effect size (ES) > 0.5. The assessments involved questionnaires that were self-administered on days (D) 1 and 21 and at months 3 and 6. The secondary objective was to determine the profile of responders to balneotherapy. We included 78 patients (69.2% women), mean age 68.3 ± 5.3 years. The mean pain score on the NS was 48.8 ± 19.9 at D1 and 39.1 ± 20.5 at 3 months (p < 0.001). The ES was 0.47 [95% confidence interval [CI] 0.25 to 0.69] for the whole sample; 36% (28/78) had an ES > 0.5; 23% (18/78) had a moderate ES (0 to 0.5); and 41% (32/78) had an ES of zero (14/78) or < 0 (18/78), corresponding to increased pain intensity. The pain trajectory model showed that the change in pain between D1 and D21 for trajectory A (larger reduction in pain intensity) was -50% [95% CI -60 to -27], and for trajectory B (smaller reduction in pain intensity), it was -13% [-33 to 0] (p < 0.001). Between Day 1 and month 3, the change for trajectory A was -33% [-54; 0] and for trajectory B was -13% [-40 to 0] (p = 0.14). Finally, between D1 and month 6, the change for trajectory A was -50% [-60 to 0] and for trajectory B was -6% [-33 to 17] (p = 0.007). The patients in trajectory A reported performing more physical activity than those in trajectory B (p = 0.04). They were also less disabled, with a mean Oswestry Disability Index of 40.4 versus 45.7 for those in trajectory A and B, respectively, (p = 0.03) and had a higher total Arthritis Self-Efficacy Scale score. This real-life study of the effectiveness of balneotherapy on chronic LBP identified distinct pain trajectories and predictive variables for responders. These criteria could be used in decision-making regarding the prescription of balneotherapy, to ensure personalized management of chronic LBP.

Legionella Occurrence beyond Cooling Towers and Premise Plumbing

Legionella is an environmental pathogen that is responsible for respiratory disease and is a common causative agent of water-related outbreaks. Due to their ability to survive in a broad range of environments, transmission of legionellosis is possible from a variety of sources. Unfortunately, a disproportionate amount of research that is devoted to studying the occurrence of Legionella in environmental reservoirs is aimed toward cooling towers and premise plumbing. As confirmed transmission of Legionella has been linked to many other sources, an over-emphasis on the most common sources may be detrimental to increasing understanding of the spread of legionellosis. This review aims to address this issue by cataloguing studies which have examined the occurrence of Legionella in less commonly investigated environments. By summarizing and discussing reports of Legionella in fresh water, ground water, saltwater, and distribution system drinking water, future environmental and public health researchers will have a resource to aid in investigating these pathogens in relevant sources.

Dynamic modelling of Legionella pneumophila thermal inactivation in water

A predictive mathematical model describing the effect of temperature on the inactivation of Legionella pneumophila in water was developed. Thermal inactivation of L. pneumophila was monitored under isothermal conditions (51 - 61°C). A primary log-linear model was fitted to the inactivation data and the estimated D values ranged from 0.23 to 25.31 min for water temperatures from 61 to 51°C, respectively. The effect of temperature on L. pneumophila inactivation was described using a secondary model, and the model parameters z value and D_ref (D-value at 55°C) were estimated at 5.54°C and 3.47 min, respectively. The developed model was further validated under dynamic temperature conditions mimicking various conditions of water thermal disinfection in plumbing systems. The results indicated that the model can satisfactorily predict thermal inactivation of the pathogen at dynamic temperature environments and effectively translate water temperature profiles to cell number reduction. The application of the model in combination with effective temperature monitoring could provide the basis of an integrated preventive approach for the effective control of L. pneumophila in plumbing systems.

Characterization of Legionella pneumophila Populations by Multilocus Variable Number of Tandem Repeats (MLVA) Genotyping from Drinking Water and Biofilm in Hospitals from Different Regions of the West Bank

The West Bank can be considered a high-risk area for Legionnaires' disease (LD) due to its hot climate, intermittent water supply and roof storage of drinking water. Legionella, mostly L. pneumophila, are responsible for LD, a severe, community-acquired and nosocomial pneumonia. To date, no extensive assessment of Legionella spp and L. pneumophila using cultivation in combination with molecular approaches in the West Bank has been published. Two years of environmental surveillance of Legionella in water and biofilms in the drinking water distribution systems (DWDS) of eight hospitals was carried out; 180 L. pneumophila strains were isolated, mostly from biofilms in DWDS. Most of the isolates were identified as serogroup (Sg) 1 (60%) and 6 (30%), while a minor fraction comprised Sg 8 and 10. Multilocus Variable number of tandem repeats Analysis using 13 loci (MLVA-8(12)) was applied as a high-resolution genotyping method and compared to the standard Sequence Based Typing (SBT). The isolates were genotyped in 27 MLVA-8(12) genotypes (Gt), comprising four MLVA clonal complexes (VACC 1; 2; 5; 11). The major fraction of isolates constituted Sequence Type (ST)1 and ST461. Most of the MLVA-genotypes were highly diverse and often unique. The MLVA-genotype composition showed substantial regional variability. In general, the applied MLVA-method made it possible to reproducibly genotype the isolates, and was consistent with SBT but showed a higher resolution. The advantage of the higher resolution was most evident for the subdivision of the large strain sets of ST1 and ST461; these STs were shown to be highly pneumonia-relevant in a former study. This shows that the resolution by MLVA is advantageous for back-tracking risk sites and for the avoidance of outbreaks of L. pneumophila. Overall, our results provide important insights into the detailed population structure of L. pneumophila, allowing for better risk assessment for DWDS.

Legionella pneumophila OxyR Is a Redundant Transcriptional Regulator That Contributes to Expression Control of the Two-Component CpxRA System

Nominally an environmental organism, Legionella pneumophila is an intracellular parasite of protozoa but is also the causative agent of the pneumonia termed Legionnaires' disease, which results from inhalation of aerosolized bacteria by susceptible humans. Coordination of gene expression by a number of identified regulatory factors, including OxyR, assists L. pneumophila in adapting to the stresses of changing environments. L. pneumophila OxyR (OxyR_Lp) is an ortholog of Escherichia coli OxyR; however, OxyR_Lp was shown elsewhere to be functionally divergent, such that it acts as a transcription regulator independently of the oxidative stress response. In this study, the use of improved gene deletion methods has enabled us to generate an unmarked in-frame deletion of oxyR in L. pneumophila Lack of OxyR_Lp did not affect in vitro growth or intracellular growth in Acanthamoeba castellanii protozoa and U937-derived macrophages. The expression of OxyR_Lp does not appear to be regulated by CpxR, even though purified recombinant CpxR bound a DNA sequence similar to that reported for CpxR elsewhere. Surprisingly, a lack of OxyR_Lp resulted in elevated activity of the promoters located upstream of icmR and the lpg1441-cpxA operon, and OxyR_Lp directly bound to these promoter regions, suggesting that OxyR_Lp is a direct repressor. Interestingly, a strain overexpressing OxyR_Lp demonstrated reduced intracellular growth in A. castellanii but not in U937-derived macrophages, suggesting that balanced expression control of the two-component CpxRA system is necessary for survival in protozoa. Taken together, this study suggests that OxyR_Lp is a functionally redundant transcriptional regulator in L. pneumophila under the conditions evaluated herein.IMPORTANCELegionella pneumophila is an environmental pathogen, with its transmission to the human host dependent upon its ability to replicate in protozoa and survive within its aquatic niche. Understanding the genetic factors that contribute to L. pneumophila survival within each of these unique environments will be key to limiting future point-source outbreaks of Legionnaires' disease. The transcriptional regulator L. pneumophila OxyR (OxyR_Lp) has been previously identified as a potential regulator of virulence traits warranting further investigation. This study demonstrated that oxyR is nonessential for L. pneumophila survival in vitro and in vivo via mutational analysis. While the mechanisms of how OxyR_Lp expression is regulated remain elusive, this study shows that OxyR_Lp negatively regulates the expression of the cpxRA two-component system necessary for intracellular survival in protozoa.

Legionella species diversity and dynamics from surface reservoir to tap water: from cold adaptation to thermophily

Water samples of the Drinking Water Supply System (DWSS) of the city of Braunschweig were analysed for its Legionella species composition using genus-specific PCR amplicons and single-strand conformation polymorphism (SSCP) fingerprint analyses based on 16S rRNA genes. These analyses comprised the whole supply chain including raw water, treatment process and large-scale storage, and a seasonal study of finished drinking water sampled monthly from cold and hot tap water. Treatment of raw water had a major impact on Legionella species by reducing their diversity and abundances. The Legionella species composition of the tap water was highly distinct from that of both source waters. In cold water, 8-14 different phylotypes of Legionella (PTLs) were observed per sample with relative abundances ranging from >1% to 53%. In hot water, L. pneumophila was present during all seasons at high relative abundances (8-40%) accompanied by 5-14 other PTLs of which 6 PTLs were in common with cold water. This thermophilic Legionella community, including L. pneumophila, was able to grow in the hot water above 50 °C. Such thermophilic Legionella populations are of general relevance for drinking water management and public health, but also for the ecology and evolution of the genus Legionella.

Confirmed and Potential Sources of Legionella Reviewed

Legionella bacteria are ubiquitous in natural matrices and man-made systems. However, it is not always clear if these reservoirs can act as source of infection resulting in cases of Legionnaires' disease. This review provides an overview of reservoirs of Legionella reported in the literature, other than drinking water distribution systems. Levels of evidence were developed to discriminate between potential and confirmed sources of Legionella. A total of 17 systems and matrices could be classified as confirmed sources of Legionella. Many other man-made systems or natural matrices were not classified as a confirmed source, since either no patients were linked to these reservoirs or the supporting evidence was weak. However, these systems or matrices could play an important role in the transmission of infectious Legionella bacteria; they might not yet be considered in source investigations, resulting in an underestimation of their importance. To optimize source investigations it is important to have knowledge about all the (potential) sources of Legionella. Further research is needed to unravel what the contribution is of each confirmed source, and possibly also potential sources, to the LD disease burden.