Legionella co-infection in HIV-associated pneumonia

Case report: The value of early application of mNGS technology in the diagnosis and treatment of severe Legionnaires' disease: reports of two cases with different outcomes

Background

Legionnaires' disease has a high clinical mortality rate, and early diagnosis and treatment are critical. Increasing evidence shows that metagenomic next-generation sequencing (mNGS) has excellent potential for the early identification of pathogens. To help clinicians better recognize Legionnaires' disease in its early stage and to illustrate the diagnostic value of mNGS technology, we reviewed and summarized two cases of severe Legionnaires' disease.

Methods and analysis

We selected two patients with severe Legionnaires' disease who were admitted to our department in recent years. We discuss experience with them and the shortcomings in their treatment by summarizing their medical history, disease evolution, tests, and diagnostic and therapeutic processes.

Results

In both patients, the diagnosis of Legionnaires' disease was confirmed through analysis of the bronchoalveolar lavage fluid (BALF). The middle-aged male patient was cured and discharged due to early detection and diagnosis. The elderly immunocompromised patient died due to a delay in diagnosis.

Conclusion

This study highlights the importance of the early recognition and diagnosis of severe Legionnaires' disease and the advantages of mNGS in identifying the pathogen.

The Adequacy of Current Legionnaires' Disease Diagnostic Practices in Capturing the Epidemiology of Clinically Relevant Legionella: A Scoping Review

Legionella is an underdiagnosed and underreported etiology of pneumonia. Legionella pneumophila serogroup 1 (LpSG1) is thought to be the most common pathogenic subgroup. This assumption is based on the frequent use of a urinary antigen test (UAT), only capable of diagnosing LpSG1. We aimed to explore the frequency of Legionella infections in individuals diagnosed with pneumonia and the performance of diagnostic methods for detecting Legionella infections. We conducted a scoping review to answer the following questions: (1) "Does nucleic acid testing (NAT) increase the detection of non-pneumophila serogroup 1 Legionella compared to non-NAT?"; and (2) "Does being immunocompromised increase the frequency of pneumonia caused by non-pneumophila serogroup 1 Legionella compared to non-immunocompromised individuals with Legionnaires' disease (LD)?". Articles reporting various diagnostic methods (both NAT and non-NAT) for pneumonia were extracted from several databases. Of the 3449 articles obtained, 31 were included in our review. The most common species were found to be L. pneumophila, L. longbeachae, and unidentified Legionella species appearing in 1.4%, 0.9%, and 0.6% of pneumonia cases. Nearly 50% of cases were caused by unspecified species or serogroups not detected by the standard UAT. NAT-based techniques were more likely to detect Legionella than non-NAT-based techniques. The identification and detection of Legionella and serogroups other than serogroup 1 is hampered by a lack of application of broader pan-Legionella or pan-serogroup diagnostics.

The Contribution of Legionella anisa to Legionella Contamination of Water in the Built Environment

Legionella bacteria can proliferate in poorly maintained water systems, posing risks to users. All Legionella species are potentially pathogenic, but Legionella pneumophila (L. pneumophila) is usually the primary focus of testing. However, Legionella anisa (L. anisa) also colonizes water distribution systems, is frequently found with L. pneumophila, and could be a good indicator for increased risk of nosocomial infection. Anonymized data from three commercial Legionella testing laboratories afforded an analysis of 565,750 water samples. The data covered July 2019 to August 2021, including the COVID-19 pandemic. The results confirmed that L. anisa commonly colonizes water distribution systems, being the most frequently identified non-L. pneumophila species. The proportions of L. anisa and L. pneumophila generally remained similar, but increases in L. pneumophila during COVID-19 lockdown suggest static water supplies might favor its growth. Disinfection of hospital water systems was effective, but re-colonization did occur, appearing to favor L. pneumophila; however, L. anisa colony numbers also increased as a proportion of the total. While L. pneumophila remains the main species of concern as a risk to human health, L. anisa's role should not be underestimated, either as a potential infection risk or as an indicator of the need to intervene to control Legionella's colonization of water supplies.

Structural basis for substrate recognition by a S-adenosylhomocysteine hydrolase Lpg2021 from Legionella pneumophila

S-Adenosyl-l-homocysteine hydrolase (SAHH) is a crucial enzyme that governs S-adenosyl methionine (SAM)-dependent methylation reactions within cells and regulates the intracellular concentration of SAH. Legionella pneumophila, the causative pathogen of Legionnaires' disease, encodes Lpg2021, which is the first identified dimeric SAHH in bacteria and is a promising target for drug development. Here, we report the structure of Lpg2021 in its ligand-free state and in complexes with adenine (ADE), adenosine (ADO), and 3-Deazaneplanocin A (DZNep). X-ray crystallography, isothermal titration calorimetry (ITC), and molecular docking were used to elucidate the binding mechanisms of Lpg2021 to its substrates and inhibitors. Virtual screening was performed to identify potential Lpg2021 inhibitors. This study contributes a novel perspective to the understanding of SAHH evolution and establishes a structural framework for designing specific inhibitors targeting pathogenic Legionella pneumophila SAHH.

Inflammatory Patterns Associated with Legionella in HIV and Pneumonia Coinfections

Legionella infections have a propensity for occurring in HIV-infected individuals, with immunosuppressed individuals tending to present with more severe disease. However, understanding regarding the Legionella host response in immune compromised individuals is lacking. This study investigated the inflammatory profiles associated with Legionella infection in patients hospitalized with HIV and pneumonia in Medellín, Colombia from February 2007 to April 2014, and correlated these profiles with clinical outcomes. Sample aliquots from the Colombian cohort were shipped to Canada where Legionella infections and systemic cytokine profiles were determined using real-time PCR and bead-based technology, respectively. To determine the effect of Legionella coinfection on clinical outcome, a patient database was consulted, comparing laboratory results and outcomes between Legionella-positive and -negative individuals. Principal component analysis revealed higher plasma concentrations of eotaxin, IP-10 and MCP-1 (p = 0.0046) during Legionella infection. Individuals with this immune profile also had higher rates of intensive care unit admissions (adjusted relative risk 1.047 [95% confidence interval 1.027-1.066]). Results demonstrate that systemic markers of monocyte/macrophage activation and differentiation (eotaxin, MCP-1, and IP-10) are associated with Legionella infection and worse patient outcomes. Further investigations are warranted to determine how this cytokine profile may play a role in Legionella pneumonia pathogenesis or immunity.

Legionella anisa or Legionella bozemanii? Traditional and molecular techniques as support in the environmental surveillance of a hospital water network

Understanding the actual distribution of different Legionella species in water networks would help prevent outbreaks. Culture investigations followed by serological agglutination tests, with poly/monovalent antisera, still represent the gold standard for isolation and identification of Legionella strains. However, also MALDI-TOF and mip-gene sequencing are currently used. This study was conducted to genetically correlate strains of Legionella non pneumophila (L-np) isolated during environmental surveillance comparing different molecular techniques. Overall, 346 water samples were collected from the water system of four pavilions located in a hospital of the Apulia Region of Italy. Strains isolated from the samples were then identified by serological tests, MALDI-TOF, and mip-gene sequencing. Overall, 24.9% of water samples were positive for Legionella, among which the majority were Legionella pneumophila (Lpn) 1 (52.3%), followed by Lpn2-15 (20.9%), L-np (17.4%), Lpn1 + Lpn2-15 (7.1%), and L-np + Lpn1 (2.3%). Initially, L-np strains were identified as L. bozemanii by monovalent antiserum, while MALDI-TOF and mip-gene sequencing assigned them to L. anisa. More cold water than hot water samples were contaminated by L. anisa (p < 0.001). PFGE, RAPD, Rep-PCR, and SAU-PCR were performed to correlate L. anisa strains. Eleven out of 14 strains identified in all four pavilions showed 100% of similarity upon PFGE analysis. RAPD, Rep-PCR, and SAU-PCR showed greater discriminative power than PFGE.

Increased susceptibility to pneumonia due to tumour necrosis factor inhibition and prospective immune system rescue via immunotherapy

Immunomodulators such as tumour necrosis factor (TNF) inhibitors are used to treat autoimmune conditions by reducing the magnitude of the innate immune response. Dampened innate responses pose an increased risk of new infections by opportunistic pathogens and reactivation of pre-existing latent infections. The alteration in immune response predisposes to increased severity of infections. TNF inhibitors are used to treat autoimmune conditions such as rheumatoid arthritis, juvenile arthritis, psoriatic arthritis, transplant recipients, and inflammatory bowel disease. The efficacies of immunomodulators are shown to be varied, even among those that target the same pathways. Monoclonal antibody-based TNF inhibitors have been shown to induce stronger immunosuppression when compared to their receptor-based counterparts. The variability in activity also translates to differences in risk for infection, moreover, parallel, or sequential use of immunosuppressive drugs and corticosteroids makes it difficult to accurately attribute the risk of infection to a single immunomodulatory drug. Among recipients of TNF inhibitors, Mycobacterium tuberculosis has been shown to be responsible for 12.5-59% of all infections; Pneumocystis jirovecii has been responsible for 20% of all non-viral infections; and Legionella pneumophila infections occur at 13-21 times the rate of the general population. This review will outline the mechanism of immune modulation caused by TNF inhibitors and how they predispose to infection with a focus on Mycobacterium tuberculosis, Legionella pneumophila, and Pneumocystis jirovecii. This review will then explore and evaluate how other immunomodulators and host-directed treatments influence these infections and the severity of the resulting infection to mitigate or treat TNF inhibitor-associated infections alongside antibiotics.

Case report of arthritis caused by Legionella anisa and review of the literature

BACKGROUND

Legionella spp. is recognized as a common cause of community acquired pneumonia, with Legionella pneumophila serogroup 1 being the most prevalent. At least 70 species are described so far but few are identified in pathogenic conditions. Data on extrapulmonary infections are scarce.

CASE PRESENTATION

A 73-yar-old male with chronic lymphoid leukemia was hospitalized for an insidious wrist arthritis. Ultrasound of the wrist showed a carpal and radiocarpal fluid effusion with positive Doppler signal. While routine bacterial cultures remained sterile, 16S rRNA PCR identified Legionella anisa. Ciprofloxacin 500 mg twice a day for a period of six weeks improved arthritis with full recovery at the end of the treatment.

CONCLUSION

Legionella non pneumophila are a rare cause of septic arthritis especially found in immunosuppressed patients and identification of species could help clinician to adapt antibiotherapy.

Dynamics of Legionella Community Interactions in Response to Temperature and Disinfection Treatment: 7 Years of Investigation

In man-made water distribution systems, Legionella community interactions remain unknown, due to their ability to change from sessile to planktonic states or live in viable but non-culturable forms, in response to anthropic and environmental stress. During 7 years of hospital Legionella surveillance, in 191 hot water positive samples, the interactions among the Legionella species, temperature, and disinfection treatment were evaluated. Legionella was isolated following ISO 11731:2017, and identification was performed by mip gene sequencing and sequence-based typing (SBT) for L. anisa or L. rubrilucens and L. pneumophila, respectively. The species with the higher frequency of isolation was L. pneumophila serogroup 1 (78.53%; 4865.36 ± 25,479.11 cfu/L), followed by L. anisa (54.45%; 558.79 ± 2637.41 cfu/L) and L. rubrilucens (21.99%; 307.73 ± 1574.95 cfu/L), which were sometimes present together. Spearman's rho correlation test was conducted among the species with respect to temperature and disinfectant (H₂O₂/Ag⁺). The results showed a generally positive interaction among these species sharing the same environment, except for competition between L. anisa and L. rubrilucens. High temperature (48.83 ± 2.59 °C) and disinfection treatment (11.58 ± 4.99 mg/L) affected the presence of these species. An exception was observed with L. anisa, which showed disinfection treatment resistance. For the purposes of environmental surveillance, it is fundamental to better understand the interactions and dynamic of the Legionella community in man-made water systems in order to choose the proper physical or chemical treatments. The simultaneous presence of different Legionella species could result in an increased resistance to high temperature and disinfectant treatment, leading to changes in contamination level and species diversity.

New Insight regarding Legionella Non-Pneumophila Species Identification: Comparison between the Traditional mip Gene Classification Scheme and a Newly Proposed Scheme Targeting the rpoB Gene

The identification of Legionella non-pneumophila species (non-Lp) in clinical and environmental samples is based on the mip gene, although several studies suggest its limitations and the need to expand the classification scheme to include other genes. In this study, the development of a new classification scheme targeting the rpoB gene is proposed to obtain a more reliable identification of 135 Legionella environmental isolates. All isolates were sequenced for the mip and rpoB genes, and the results were compared to study the discriminatory power of the proposed rpoB scheme. Complete concordance between the mip and rpoB results based on genomic percent identity was found for 121/135 (89.6%) isolates; in contrast, discordance was found for 14/135 (10.4%) isolates. Additionally, due to the lack of reference values for the rpoB gene, inter- and intraspecies variation intervals were calculated based on a pairwise identity matrix that was built using the entire rpoB gene (∼4,107 bp) and a partial region (329 bp) to better evaluate the genomic identity obtained. The interspecies variation interval found here (4.9% to 26.7%) was then proposed as a useful sequence-based classification scheme for the identification of unknown non-Lp isolates. The results suggest that using both the mip and rpoB genes makes it possible to correctly discriminate between several species, allowing possible new species to be identified, as confirmed by preliminary whole-genome sequencing analyses performed on our isolates. Therefore, starting from a valid and reliable identification approach, the simultaneous use of mip and rpoB associated with other genes, as it occurs with the sequence-based typing (SBT) scheme developed for Legionella pneumophila, could support the development of multilocus sequence typing to improve the knowledge and discovery of Legionella species subtypes. IMPORTANCELegionella spp. are a widely spread bacteria that cause a fatal form of pneumonia. While traditional laboratory techniques have provided valuable systems for Legionella pneumophila identification, the amplification of the mip gene has been recognized as the only useful tool for Legionella non-pneumophila species identification both in clinical and environmental samples. Several studies focused on the mip gene classification scheme showed its limitations and the need to improve the classification scheme, including other genes. Our study provides significant advantages on Legionella identification, providing a reproducible new rpoB gene classification scheme that seems to be more accurate than mip gene sequencing, bringing out greater genetic variation on Legionella species. In addition, the combined use of both the mip and rpoB genes allowed us to identify presumed new Legionella species, improving epidemiological investigations and acquiring new understanding on Legionella fields.

Development of a Fluorescent Tool for Studying Legionella bozemanae Intracellular Infection

Legionnaires' disease incidence is on the rise, with the majority of cases attributed to the intracellular pathogen, Legionella pneumophila. Nominally a parasite of protozoa, L. pneumophila can also infect alveolar macrophages when bacteria-laden aerosols enter the lungs of immunocompromised individuals. L. pneumophila pathogenesis has been well characterized; however, little is known about the >25 different Legionella spp. that can cause disease in humans. Here, we report for the first time a study demonstrating the intracellular infection of an L. bozemanae clinical isolate using approaches previously established for L. pneumophila investigations. Specifically, we report on the modification and use of a green fluorescent protein (GFP)-expressing plasmid as a tool to monitor the L. bozemanae presence in the Acanthamoeba castellanii protozoan infection model. As comparative controls, L. pneumophila strains were also transformed with the GFP-expressing plasmid. In vitro and in vivo growth kinetics of the Legionella parental and GFP-expressing strains were conducted followed by confocal microscopy. Results suggest that the metabolic burden imposed by GFP expression did not impact cell viability, as growth kinetics were similar between the GFP-expressing Legionella spp. and their parental strains. This study demonstrates that the use of a GFP-expressing plasmid can serve as a viable approach for investigating Legionella non-pneumophila spp. in real time.

Evaluation of MALDI-TOF Mass Spectrometry in Diagnostic and Environmental Surveillance of Legionella Species: A Comparison With Culture and Mip-Gene Sequencing Technique

Legionella spp. are widespread bacteria in aquatic environments with a growing impact on human health. Between the 61 species, Legionella pneumophila is the most prevalent in human diseases; on the contrary, Legionella non-pneumophila species are less detected in clinical diagnosis or during environmental surveillance due to their slow growth in culture and the absence of specific and rapid diagnostic/analytical tools. Reliable and rapid isolate identification is essential to estimate the source of infection, to undertake containment measures, and to determine clinical treatment. Matrix-assisted laser desorption ionization–time-of-flight mass spectrometry (MALDI–TOF MS), since its introduction into the routine diagnostics of laboratories, represents a widely accepted method for the identification of different bacteria species, described in a few studies on the Legionella clinical and environmental surveillance. The focus of this study was the improvement of MALDI–TOF MS on Legionella non-pneumophila species collected during Legionella nosocomial and community surveillance. Comparative analysis with cultural and mip-gene sequencing results was performed. Moreover, a phylogenetic analysis was carried out to estimate the correlations amongst isolates. MALDI–TOF MS achieved correct species-level identification for 45.0% of the isolates belonging to the Legionella anisa, Legionella rubrilucens, Legionella feeleii, and Legionella jordanis species, displaying a high concordance with the mip-gene sequencing results. In contrast, less reliable identification was found for the remaining 55.0% of the isolates, corresponding to the samples belonging to species not yet included in the database. The phylogenetic analysis showed relevant differences inside the species, regruped in three main clades; among the Legionella anisa clade, a subclade with a divergence of 3.3% from the main clade was observed. Moreover, one isolate, identified as Legionella quinlivanii, displayed a divergence of 3.8% from the corresponding reference strain. However, these findings require supplementary investigation. The results encourage the implementation of MALDI–TOF MS in routine diagnostics and environmental Legionella surveillance, as it displays a reliable and faster identification at the species level, as well as the potential to identify species that are not yet included in the database. Moreover, phylogenetic analysis is a relevant approach to correlate the isolates and to track their spread, especially in unconventional reservoirs, where Legionella prevention is still underestimated.

How Molecular Typing Can Support Legionella Environmental Surveillance in Hot Water Distribution Systems: A Hospital Experience

In this study, we aimed to associate the molecular typing of Legionella isolates with a culture technique during routine Legionella hospital environmental surveillance in hot water distribution systems (HWDSs) to develop a risk map able to be used to prevent nosocomial infections and formulate appropriate preventive measures. Hot water samples were cultured according to ISO 11731:2017. The isolates were serotyped using an agglutination test and genotyped by sequence-based typing (SBT) for Legionella pneumophila or macrophage infectivity potentiator (mip) gene sequencing for non-pneumophila Legionella species. The isolates' relationship was phylogenetically analyzed. The Legionella distribution and level of contamination were studied in relation to temperature and disinfectant residues. The culture technique detected 62.21% of Legionella positive samples, characterized by L. pneumophila serogroup 1, Legionella non-pneumophila, or both simultaneously. The SBT assigned two sequence types (STs): ST1, the most prevalent in Italy, and ST104, which had never been isolated before. The mip gene sequencing detected L. anisa and L. rubrilucens. The phylogenetic analysis showed distinct clusters for each species. The distribution of Legionella isolates showed significant differences between buildings, with a negative correlation between the measured level of contamination, disinfectant, and temperature. The Legionella molecular approach introduced in HWDSs environmental surveillance permits (i) a risk map to be outlined that can help formulate appropriate disinfection strategies and (ii) rapid epidemiological investigations to quickly identify the source of Legionella infections.