Environment, animals, and food as reservoirs of antibiotic-resistant bacteria for humans: One health or more?

Antimicrobial resistance (AMR) is a major public health challenge. For several years, AMR has been addressed through a One Health approach that links human health, animal health, and environmental quality. In this review, we discuss AMR in different reservoirs with a focus on the environment. Anthropogenic activities produce effluents (sewage, manure, and industrial wastes) that contaminate soils and aquatic environments with antibiotic-resistant bacteria (ARB), antibiotic-resistant genes (ARGs), and selective agents such as antibiotics, biocides, and heavy metals. Livestock treated with antibiotics can also contaminate food with ARB. In high-income countries (HICs), effective sanitation infrastructure and limited pharmaceutical industries result in more controlled discharges associated with human activities. Hence, studies using genome-based typing methods have revealed that, although rare inter-reservoir transmission events have been reported, human acquisition in HICs occurs primarily through person-to-person transmission. The situation is different in low- and middle-income countries (LMICs) where high population density, poorer sanitation and animal farming practices are more conducive to inter-reservoir transmissions. In addition, environmental bacteria can be a source of ARGs that, when transferred to pathogenic species under antibiotic selection pressure in environmental hotspots, produce new antibiotic-resistant strains that can potentially spread in the human community through human-to-human transmission. The keys to reducing AMR in the environment are (i) better treatment of human waste by improving wastewater treatment plants (WWTPs) in HICs and improving sanitation infrastructure in LMICs, (ii) reducing the use of antibiotics by humans and animals, (iii) prioritizing the use of less environmentally harmful antibiotics, and (iv) better control of pharmaceutical industry waste.

Effect of a karst system (France) on extended spectrum beta-lactamase (ESBL)-producing Escherichia coli

Karst aquifers are an important water resource worldwide particularly exposed to anthropogenic pollution, including antibiotic-resistance. The release of antibiotic-resistant bacterial pathogens in the environment is a major public health challenge worldwide. In this One Health study, we aimed to determine the effect of karst on antibiotic-resistant bacteria. For this purpose, we determined the concentrations of extended-spectrum β-lactamases-producing Escherichia coli (ESBL-Ec) for 92 weeks in a rural karst hydrosystem providing drinking water. ESBL-Ec isolates (n = 130) were sequenced by whole genome sequencing. We analysed the isolates at different levels of granularity, i.e., phylogroup, sequence type, presence of antibiotic-resistance genes, mutations conferring antibiotic-resistance, and virulence genes. The ESBL-Ec concentrations were spatially and temporally heterogeneous in the studied karst hydrosystem. ESBL-Ec isolates survived in the karst and their concentrations were mostly explained by the hydrodynamic of the hydrosystem. We demonstrate that the studied karst has no filtration effect on ESBL-Ec, either quantitatively (i.e., in the ESBL-Ec concentrations) or qualitatively (i.e., in the genetic characteristics of ESBL-Ec isolates).

Origin, fluxes, and reservoirs of Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa in aquatic ecosystems of a French floodplain

The release and spread of opportunistic pathogens - some of which are resistant to antibiotics - in the environment is a major public health challenge worldwide. In this study, we found evidence of the origin of such microorganisms and characterized their dispersal and survival in floodplain ecosystems to understand their fate in the environment. We determined the concentrations of Escherichia coli, extended-spectrum β-lactamases (ESBL)-producing E. coli, Klebsiella pneumoniae, ESBL-producing K. pneumoniae, and Pseudomonas aeruginosa in a floodplain of Eastern France using a culture-based method. Furthermore, we assessed the population structure of E. coli isolates by quadruplex PCR, their plasmid replicon content by PCR-based replicon typing, and the nature of their bla_ESBL genes by PCR and sequencing. The main aquatic ecosystems of the floodplain (river, tributaries, riverine wetlands, and groundwater) were sampled monthly over a one-year cycle. The majority of E. coli isolates retrieved in the studied floodplain were likely of human origin. Moreover, contamination of floodplain aquatic ecosystems by opportunistic pathogens mainly resulted from hydrological fluxes during high-flow periods, suggesting that dispersal and dilution predominated. During low-flow periods, E. coli may be able to survive for several months in isolated ecosystems in which it may find favourable conditions to thrive. The most nutrient-rich and isolated wetlands are consequently potential pathogen reservoirs. The production of ESBL was not a disadvantage for E. coli in low-anthropized floodplain ecosystems.

Populations of extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae are different in human-polluted environment and food items: a multicentre European study

OBJECTIVES

To assess the extent to which food items are a source of extended-spectrum β-lactamase (ESBL) -producing Escherichia coli (ESBL-Ec) and ESBL-producing Klebsiella pneumoniae (ESBL-Kp) for humans in five European cities.

METHODS

We sampled 122 human polluted (hp)-environments (sewers and polluted rivers, as a proxy of human contamination) and 714 food items in Besançon (France), Geneva (Switzerland), Sevilla (Spain), Tübingen (Germany) and Utrecht (The Netherlands). A total of 254 ESBL-Ec and 39 ESBL-Kp isolates were cultured. All genomes were fully sequenced to compare their sequence types (ST) and core genomes, along with the distribution of bla_ESBL genes and their genetic supports (i.e. chromosome or plasmid).

RESULTS

Sequence data revealed that ESBL-Ec and ESBL-Kp isolates from hp-environments were genetically different from those contaminating food items. ESBL-Ec ST131 was widespread in the hp-environment (21.5% of the isolates) but absent from the food items tested. ESBL-Ec ST10 was in similar proportions in hp-environments and food items (15 and 10 isolates, respectively) but mostly carried reservoir-specific bla_ESBL. bla_CTX-M-1 and bla_SHV-12 predominated in food-related E. coli isolates (32% and 34% of the isolates, respectively), whereas bla_CTX-M-15 and bla_CTX-M-27 predominated in isolates from hp-environments (52% and 15% of the isolates, respectively).

CONCLUSIONS

We found a very limited connection between ESBL-Ec and ESBL-Kp populations retrieved in food items and from hp-environments and bla_ESBL. This suggests that human-to-human contamination, rather than the food chain, is possibly the most frequent route of ESBL-Ec and ESBL-Kp transmission in high-income countries.

High Prevalence of Human-Associated Escherichia coli in Wetlands Located in Eastern France

Escherichia coli that are present in the rivers are mostly brought by human and animal feces. Contamination occurs mostly through wastewater treatment plant (WWTP) outflows and field amendment with sewage sludge or manure. However, the survival of these isolates in river-associated wetlands remains unknown. Here, we assessed E. coli population structure in low-anthropized wetlands located along three floodplains to identify the major source of contamination of wetlands, whose functioning is different from the rivers. We retrieved 179 E. coli in water samples collected monthly from 19 sites located in eastern France over 1 year. Phylogroups B1 and B2 were dominant in the E. coli population, while phylogroup A was dominant in isolates resistant to third-generation cephalosporins, which harbored the extended-spectrum β-lactamase (ESBL) encoding genes bla_CTX–M–15 and bla_CTX–M–27 in half of the cases. The high proportion of isolates from human source can be attributed to WWTP outflows and the spread of sewage sludge. We analyzed the distribution of the isolates belonging to the most human-associated phylogroups (B2 and D) on a phylogenetic tree of the whole species and compared it with that of isolates retrieved from patients and from WWTP outflows. The distribution of the three E. coli populations was similar, suggesting the absence of a specific population in the environment. Our results suggest that a high proportion of E. coli isolates that reach and survive in low-anthropized environments such as wetlands are from human source. To the best of our knowledge, this is the first study assessing E. coli contamination and resistance genes in natural freshwater wetlands.

Using GFP-Tagged Escherichia coli to Investigate the Persistence of Fecal Bacteria in Vegetated Wetlands: An Experimental Approach

The contamination of surface water by pathogenic bacteria of human origin is an important public health issue. Wetlands can be contaminated with fecal bacteria by water originating from different sources, such as wastewater treatment plants and agriculture. Escherichia coli is a commensal of the human gut flora and the major indication of fecal contamination in surface water. Little is known about the association between fecal bacteria and submerged macrophytes and how this may influence the water quality. We questioned whether macrophytes enhance or inhibit the bacterial growth in wetlands. For this purpose, we grew four different species of macrophytes (Mentha aquatica, Baldellia ranunculoides, Sparganium emersum and Elodea canadensis, in mono- or multispecies cultures) in aquatic rhizotrons and inoculated the devices with a fluorescent strain of Escherichia coli (producing a green fluorescent protein) to simulate the fecal contamination of wetlands. Bacterial survival was monitored by measuring the fluorescence for 19 days. We found (i) that contaminated sediments did not release E. coli in the water column in lentic conditions and (ii) that monocultures of E. canadensis, M. aquatica and S. emersum reduced the E. coli concentration in the water column. This suggests that aquatic plant species may be used in constructed wetlands to clear surface freshwater from bacteria of fecal origin.

Occurrence and ecological determinants of the contamination of floodplain wetlands with Klebsiella pneumoniae and pathogenic or antibiotic-resistant Escherichia coli

The survival and multiplication of human pathogenic and antibiotic-resistant bacteria in ecosystems is of increasing concern but has been little explored. Wetlands can be contaminated by water fluxes from rivers and may present environmental conditions leading to bacterial survival and multiplication. To test this hypothesis, we sampled 16 wetlands located along three rivers of the Jura Massif, France. The bacterial contamination of the wetland and river waters was measured monthly over a one-year cycle together with the water physico-chemical characteristics. We assessed the abundance of three pathogenic species: Escherichia coli,Klebsiella pneumoniaeand Pseudomonas aeruginosa. The concentrations of E. coli producing extended-spectrum β-lactamase (ESBL E. coli) or belonging to the phylogenetic group B2 (E. coli B2–more pathogenic) were also measured. We found that rivers carried total E. coli, ESBL E. coli, and K. pneumoniae to wetlands. ESBL E. coli poorly survived in wetlands, whereas total E. coli and K. pneumoniae possibly met favourable physico-chemical conditions for survival and multiplication in these habitats. K. pneumoniae peaked in summer in warm and shallow wetlands. Total E. coli and E. coli B2 potentially reached wetlands through sources other than rivers (hillslope groundwater or leaching from contaminated fields).

Relationships between key functional traits of the waterlily Nuphar lutea and wetland nutrient content

Little attention has been paid to how aquatic habitat characteristics affect the traits of plant species. Nuphar lutea (L.) Sm. is a keystone species distributed across temperate regions of Europe, northwest Africa and western Asia. Its apparently low phenotypic variability compared to other aquatic plants led us to test whether the species exhibited significant phenotypic variability and whether trait values correlated to environmental parameters. The hypotheses were that (1) the environmental variation within our set of wetlands (both water and sediment characteristics) led to significant variation among four sets of traits related respectively to growth, reproduction, defence and storage and (2) that nutrient limitation (nitrogen and especially phosphorus) should affect plant traits towards a higher investment in storage and defence and a lower investment in growth and reproduction, thereby negatively affecting the success of N. lutea. To test these hypotheses, 11 populations of N. lutea were sampled in wetlands differing in physicochemical characteristics and spread along three rivers. A total of 15 traits, grouped into four sets (growth, reproduction, storage and defence), were measured during the growing season. Most N. lutea traits were related to the environmental characteristics of wetlands. The growth and reproduction traits were mostly positively related to habitat resource conditions, whereas the defence traits were positively correlated with both ammonium concentration and temperature, outlining possible anoxic stress (habitat adversity). Nitrogen or phosphorus limitation led to the variation of only a few traits: the rhizome starch content was higher in phosphorus-limited wetlands, while the rhizome length and volume, and the number of flowers were higher in nitrogen-limited wetlands.