Preferential feeding in Naegleria fowleri; intracellular bacteria isolated from amoebae in operational drinking water distribution systems

Spatiotemporal distribution of thermophilic free-living amoebae in recreational waters: A 5-year survey in Guadeloupe (French West Indies)

Free-living amoebae (FLA) such as Acanthamoeba, Balamuthia mandrillaris, Naegleria fowleri and Sappinia pedata are naturally widespread in freshwater, causing rare but fatal and debilitating infections in humans. Although recent studies have shown an increase in infection rates, there is a paucity of epidemiological studies regarding the presence of these emerging pathogens in water. Herein, we studied the diversity and relative abundance of thermophilic FLA in different recreational baths in a tropical climate for 5 years. From 2018 to 2022, a total of 96 water samples were collected from 7 recreational baths (natural, tiled, regularly cleaned or not, and with temperatures ranging from 27 to 40 °C). DNA was extracted from FLA cultivated at 37 °C to detect thermophilic culturable FLA. Metabarcoding studies were conducted through FLA 18S rRNA gene amplicons sequencing; amplicon sequence variants (ASV) were extracted from each sample and taxonomy assigned against PR2 database using dada2 and phyloseq tools. We also searched for Naegleria sp. and N. fowleri using PCR targeting ITS and NFITS genes (respectively) and we quantified them using an optimized most probable number (MPN) method for FLA. Our results showed that differences in FLA diversity and abundance were observed amongst the 7 baths, but without a clear seasonal distribution. Naegleria, Vermamoeba and Stenamoeba were the most represented genera, while the genera Acanthamoeba and Vahlkampfia were mainly found in 2 baths. The MPN values for Naegleria sp. (NT/l) increased between 2018 and 2022, but the MPN values for N. fowleri (NF/l) seemed to decrease. Globally, our results showed that since we cannot establish a seasonal distribution of FLA, the regular presence of FLA (namely Naegleria and Acanthamoeba) in recreational waters can pose a potential threat in terms of neuroinfections as well as Acanthamoeba keratitis. It is thus imperious to perform the regular control of these baths as a preventive health measure.

Prokaryotic microbial ecology as an ecosurveillance tool for eukaryotic pathogen colonisation: Meiothermus and Naegleria fowleri

Naegleria fowleri has been detected in drinking water distribution systems (DWDS) in Australia, Pakistan and the United States and is the causative agent of the highly fatal disease primary amoebic meningoencephalitis. Previous small scale field studies have shown that Meiothermus may be a potential biomarker for N. fowleri. However, correlations between predictive biomarkers in small sample sizes often breakdown when applied to larger more representative datasets. This study represents one of the largest and most rigorous temporal investigations of Naegleria fowleri colonisation in an operational DWDS in the world and measured the association of Meiothermus and N. fowleri over a significantly larger space and time in the DWDS. A total of 232 samples were collected from five sites over three-years (2016-2018), which contained 29 positive N. fowleri samples. Two specific operational taxonomic units assigned to M. chliarophilus and M. hypogaeus, were significantly associated with N. fowleri presence. Furthermore, inoculation experiments demonstrated that Meiothermus was required to support N. fowleri growth in field-collected biofilms. This validates Meiothermus as prospective biological tool to aid in the identification and surveillance of N. fowleri colonisable sites.

Bacterial microbiota management in free-living amoebae (Heterolobosea lineage) isolated from water: The impact of amoebae identity, grazing conditions, and passage number

Free-living amoebae (FLA) are ubiquitous protozoa mainly found in aquatic environments. They are well-known reservoirs and vectors for the transmission of amoeba-resistant bacteria (ARB), most of which are pathogenic to humans. Yet, the natural bacterial microbiota associated with FLA remains largely unknown. Herein, we characterized the natural bacterial microbiota of different FLA species isolated from recreational waters in Guadeloupe. Monoxenic cultures of Naegleria australiensis, Naegleria sp. WTP3, Paravahlkampfia ustiana and Vahlkampfia sp. AK-2007 (Heterolobosea lineage) were cultivated under different grazing conditions, during successive passages. The whole bacterial microbiota of the waters and the amoebal cysts was characterized using 16S rRNA gene metabarcoding. The culturable subset of ARB was analyzed by mass spectrometry (MALDI-TOF MS), conventional 16S PCR, and disk diffusion method (to assess bacterial antibiotic resistance). Transmission electron microscopy was used to locate the ARB inside the amoebae. According to alpha and beta-diversity analyses, FLA bacterial microbiota were significantly different from the ones of their habitat. While Vogesella and Aquabacterium genera were detected in water, the most common ARB belonged to Pseudomonas, Bosea, and Escherichia/Shigella genera. The different FLA species showed both temporary and permanent associations with differentially bacterial taxa, suggesting host specificity. These associations depend on the number of passages and grazing conditions. Additionally, Naegleria, Vahlkampfia and Paravahlkampfia cysts were shown to naturally harbor viable bacteria of the Acinetobacter, Escherichia, Enterobacter, Pseudomonas and Microbacterium genera, all being pathogenic to humans. To our knowledge, this is the first time Paravahlkampfia and Vahlkampfia have been demonstrated as hosts of pathogenic ARB in water. Globally, the persistence of these ARB inside resistant cysts represents a potential health risk. To ensure the continued safety of recreational waters, it is crucial to (i) regularly control both the amoebae and their ARB and (ii) improve knowledge on amoebae-bacteria interactions to establish better water management protocols.

Naegleria fowleri outbreak in Pakistan: unveiling the crisis and path to recovery

The outbreak of Naegleria fowleri in Pakistan presents a significant public health concern due to its high fatality rate and limited treatment options. This review explores the impact of the outbreak on communities and the challenges faced in combating the disease. It evaluates available treatment options and highlights the need for early diagnosis and intervention. The study proposes recommendations to improve public health preparedness, including public awareness campaigns, enhanced healthcare infrastructure, and robust water surveillance systems. Collaboration between research institutions and public health organizations is emphasized to develop effective outbreak response strategies.

Behaviors and mechanisms of microbially-induced corrosion in metal-based water supply pipelines: A review

Microbially-induced corrosion (MIC) is unstoppable and extensively spread throughout drinking water distribution systems (DWDSs) as the cause of pipe leakage and deteriorating water quality. For maintaining drinking water safety and reducing capital inputs in pipe usage, the possible consequences from MIC in DWDSs is still a research hotspot. Although most studies have investigated the effects of changing environmental factors on MIC corrosion, the occurrence of MIC in DWDSs has not been discussed sufficiently. This review aims to fill this gap by proposing that the formation of deposits with microbial capture may be a source of MIC in newly constructed DWDSs. The microbes early attaching to the rough pipe surface, followed by chemically and microbially-induced mineral deposits which confers resistance to disinfectants is ascribed as the first step of MIC occurrence. MIC is then activated in the newly-built, viable, and accessible microenvironment while producing extracellular polymers. With longer pipe service, oligotrophic microbes slowly grow, and metal pipe materials gradually dissolve synchronously with electron release to microbes, resulting in pipe-wall damage. Different corrosive microorganisms using pipe material as a reaction substrate would directly or indirectly cause different types of corrosion. Correspondingly, the formation of scale layers may reflect the distribution of microbial species and possibly biogenic products. It is therefore assumed that the porous and loose layer is an ideal microbial-survival environment, capable of providing diverse and sufficient ecological niches. The usage and chelation of metabolic activities and metabolites, such as acetic, oxalic, citric and glutaric acids, may lead to the formation of a porous scale layer. Therefore, the microbial interactions within the pipe scale reinforce the stability of microbial communities and accelerate MIC. Finally, a schematic model of the MIC process is presented to interpret MIC from its onset to completion.

Environmental abiotic and biotic factors affecting the distribution and abundance of Naegleria fowleri

Naegleria fowleri is a free-living protozoan that resides in soil and freshwater. Human intranasal amoebae exposure through water or potentially dust particles can culminate in primary amoebic meningoencephalitis, which generally causes death. While many questions remain regarding pathogenesis, the microbial ecology of N. fowleri is even less understood. This review outlines current knowledge of the environmental abiotic and biotic factors that affect the distribution and abundance of N. fowleri. Although the impacts of some abiotic factors remain poorly investigated or inconclusive, N. fowleri appears to have a wide pH range, low salinity tolerance and thermophilic preference. From what is known about biotic factors, the amoebae preferentially feed upon bacteria and are preyed upon by other free-living amoebae. Additional laboratory and environmental studies are needed to fill in knowledge gaps, which are crucial for surveillance and management of N. fowleri in freshwaters. As surface water temperatures increase with climate change, it is likely that this amoeba will pose a greater threat to human health, suggesting that identifying its abiotic and biotic preferences is critical to mitigating this risk.

Molecular detection of opportunistic premise plumbing pathogens in rural Louisiana's drinking water distribution system

Opportunistic premise plumbing pathogens (OPPPs) in drinking water distribution systems are responsible for causing numerous infections such as Legionnaires' disease and pneumonia through the consumption of contaminated drinking water. The incidence of opportunistic pathogens and the number of individuals at risk of contracting infections caused by these OPPPs in drinking water has risen drastically in the past decade. Preflush and postflush water samples were collected from 64 houses in a rural town in northeast Louisiana to determine drinking water quality in terms of understanding abiotic and biotic factors on potential proliferation of OPPPs. Physical and chemical water quality parameters, such as pH, temperature, dissolved oxygen, salinity, and specific conductance were also measured. The quantitative polymerase chain reaction (qPCR) results indicated that Legionella spp. had the highest prevalence and was found in 46/64 samples (72%), followed by Mycobacterium spp. which was found in 43/64 samples (67%), E. coli in 31/64 samples (48%) and, Naegleria fowleri in 4/64 samples (6%) respectively. The results indicate the persistence of Legionella spp. DNA marker in these water samples.