Antibiotic resistance among gram-negative bacteria is increasingly becoming a problem of global concern. Particularly problematic is the emergence of resistance to last-resort antibiotics such as carbapenems and colistin. The increasing number of reports on the plasmid-mediated colistin resistance gene mcr-1 in isolates worldwide is raising concerns for the future usefulness of this class of antibiotics. Dissemination of mcr-1 is believed to have originated mainly from animal breeding, however, the role of the environment as a transmission source is not yet fully understood. In the current study, 89 extended-spectrum β-lactamase-producing Escherichia coli isolated from 231 samples from different environmental sources in 12 villages in a rural area of Shandong, China, were screened for mcr-1. 17 (19.1%) mcr-1-positive isolates were found from different environmental sources, aggregated in 6 villages. Plasmids of three different Inc-groups carrying mcr-1 were confirmed, indicating that the widespread geographical distribution of mcr-1 in the local area is due to a number of different plasmids. Additionally, almost a third (29.4%) of the isolates carried virulence factors associated to intestinal pathogenic E. coli. These results illustrate the high complexity of the transmission patterns of mcr-1 among different environmental matrices on a local scale and the potential for the environment to facilitate dissemination and emergence of antibiotic-resistant and virulent strains of bacteria.

World soils are subjected to a number of anthropogenic global change factors. Although many previous studies contributed to understand how single global change factors affect soil properties, there have been few studies aimed at understanding how two naturally co-occurring global change drivers, nitrogen (N) deposition and increased precipitation, affect critical soil properties. In addition, most atmospheric N deposition and precipitation increase studies have been simulated by directly adding N solution or water to the forest floor, and thus largely neglect some key canopy processes in natural conditions. These previous studies, therefore, may not realistically simulate natural atmospheric N deposition and precipitation increase in forest ecosystems. In a field experiment, we used novel canopy applications to investigate the effects of N deposition, increased precipitation, and their combination on soil chemical properties and the microbial community in a temperate deciduous forest. We found that both soil chemistry and microorganisms were sensitive to these global change factors, especially when they were simultaneously applied. These effects were evident within 2 years of treatment initiation. Canopy N deposition immediately accelerated soil acidification, base cation depletion, and toxic metal accumulation. Although increased precipitation only promoted base cation leaching, this exacerbated the effects of N deposition. Increased precipitation decreased soil fungal biomass, possible due to wetting/re-drying stress or to the depletion of Na. When N deposition and increased precipitation occurred together, soil gram-negative bacteria decreased significantly, and the community structure of soil bacteria was altered. The reduction of gram-negative bacterial biomass was closely linked to the accumulation of the toxic metals Al and Fe. These results suggested that short-term responses in soil cations following N deposition and increased precipitation could change microbial biomass and community structure.

The green turtle (Chelonia mydas) is listed as a globally endangered species and is vulnerable to anthropogenic threats, including environmental pollution. This study investigated the antimicrobial resistance of Gram-negative bacteria isolated from wild green turtles admitted to a sea turtle rehabilitation center in Taiwan. For this investigation, cloacal and nasal swab samples were collected from 28 green turtles between 2018 and 2020, from which a total of 47 Gram-negative bacterial isolates were identified. Among these, Vibrio spp. were the most dominant isolate (31.91%), and 89.36% of the 47 isolates showed resistance to at least one of 18 antimicrobial agents tested. Isolates resistant to one (6.38%), two (8.51%), and multiple (74.47%) antimicrobials were observed. The antimicrobial agents to which isolates showed the greatest resistance were penicillin (74.47%), followed by spiramycin, amoxicillin, and cephalexin. The antimicrobial-resistance profiles identified in this study provide useful information for the clinical treatment of sea turtles in rehabilitation facilities. The results of our study also imply that wild green turtles may be exposed to polluting effluents containing antimicrobials when the turtles traverse migratory corridors or forage in feeding habitats. To benefit sea turtle conservation, future research should focus on (1) how to prevent pollution from antimicrobials in major green turtle activity areas and (2) identifying sources of antimicrobial-resistant bacterial strains in coastal waters of Taiwan.

Our knowledge of the concentrations of bioaerosols in residential micro-environments in low income countries is scanty. The present investigation was conducted to assess the culturable concentration and size distribution of bacteria, gram negative bacteria and fungi in two rural and an urban site in Pakistan. The highest indoor culturable bacteria concentration was found at Rural Site II (14,650 CFU/m³) while the outdoor maximum occurred at the urban site (16,416 CFU/m³). With reference to fungi, both indoor and outdoor concentrations were considerably higher at Rural Site I than the other sites. The size distribution of culturable bacteria at all sites showed greater variability than that of culturable fungi. At all sites more than the half (55–93%) of the culturable bacterial and fungal counts were observed in the respirable fraction (<4.7 μm) and so had the potential to penetrate into lower respiratory system.

Spread of antibiotic resistance genes (ARGs) poses a worldwide threat to public health and food safety. However, ARG spread by plasmid mobilization, a broad host range transfer system, in agricultural soil has received little attention. Here, we investigated the spread of chloramphenicol resistance gene (CRG) and tetracycline resistance gene (TRG) in agricultural soil by mobilization of pSUP106 under different conditions, including different concentrations of nutrients, temperatures, soil depths, rhizosphere soils, and soil types. The number of resistant bacteria isolated in non-sterilized soil from the experiments was approximately 10⁴ to 10⁷ per gram of soil, belonging to 5–10 species from four genera, including nonpathogen, opportunistic pathogen, pathogen bacteria, and gram-positive and gram-negative bacteria, depending on the experiment conditions. In sterilized soil, higher levels of nutrients and higher temperatures promoted plasmid mobilization and ARG expression. Topsoil and deep soil might not support the spread of antibiotic resistance, while ARG dissemination by plasmid mobilization was better supported by maize rhizosphere and loam soils. All these factors might change bacterial growth and the activity of bacteria and lead to the above influence. Introduction of only the donor and helper, or the donor alone also resulted in the transfer of ARGs and large numbers of antibiotic resistant bacteria (ARB), indicating that some indigenous bacteria contain the elements necessary for plasmid mobilization. Our results showed that plasmid mobilization facilitated dissemination of ARGs and ARB in soil, which led to the disturbance of indigenous bacterial communities. It is important to clear ARG dissemination routes and inhibit the spread of ARGs.

Environmental health is increasingly compromised by persistent toxic substances, which may have serious implications in food safety and, thus, in human health. Polybrominated diphenyl ethers (PBDEs) are anthropogenic contaminants with endocrine disruption abilities and are commonly found in seafood, the main route of human exposure. Growing evidence points out that the human gut microbiota interacts with xenobiotics, which may lead to impairment of host homeostasis if functions of microbiota become compromised. The aim of this study was to ascertain if the physiological balance of human gut microbiome is affected by the presence and degree of exposure to PBDEs. Fermentation was performed in a batch closed-system using an inoculum made from fresh human stool. The volatolomic profile was analysed by solid-phase microextraction coupled to gas chromatography-mass spectrometry. Mesophilic, Gram-negative bacteria and coliforms were quantified by classic plating methods. Changes in the gut microbiome were evaluated after DNA extraction followed by deep sequencing of the 16S rDNA region. The exposure to PBDEs resulted in an imbalance in sulfur, short-chain fatty acids and aromatic organic compounds, changing the microbial volatolome in a dose- and time-dependent manner. Slight deviations in the microbial structure of human gut occurred in the presence of PBDEs, especially for high doses of exposure. For the first time, the impact of PBDEs on the microbial homeostasis of human gut microbiota was taken into consideration, revealing noteworthy modifications with serious health implications even at oral exposure doses considered as safe by worldwide regulatory entities.

Oxytetracycline (OTC) is one of the most used antibiotics in aquaculture. The main concern related to its use is the bacterial resistance, when ineffective treatments are applied for its removal or inactivation. OTC photo-degradation has been suggested as an efficient complementary process to conventional methods used in intensive fish production (e.g.: ozonation). Despite this, and knowing that the complete mineralization of OTC is difficult, few studies have examined the antibacterial activity of OTC photoproducts. Thus, the main aim of this work is to assess whether the OTC photoproducts retain the antibacterial activity of its parent compound (OTC) after its irradiation, using simulated sunlight. For that, three Gram-negative bacteria (Escherichia coli, Vibrio sp. and Aeromonas sp.) and different synthetic and natural aqueous matrices (phosphate buffered solutions at different salinities, 0 and 21‰, and three different samples from marine aquaculture industries) were tested. The microbiological assays were made using the well-diffusion method before and after OTC has been exposed to sunlight. The results revealed a clear effect of simulated sunlight, resulting on the decrease or elimination of the antibacterial activity for all strains and in all aqueous matrices due to OTC photo-degradation. For E. coli, it was also observed that the antibacterial activity of OTC is lower in the presence of sea-salts, as demonstrated by comparison of halos in aqueous matrices containing or not sea-salts.

Previous studies worldwide have suggested the potential role of bioaerosols as ice-nuclei and cloud-condensation nuclei. Furthermore, their participation in regulating the global carbon cycle urges systematic studies from different environmental conditions throughout the globe. Towards this through one-year study, conducted from June 2015–May 2016, we report on atmospheric abundance and variability of viable bioaerosols, organic carbon (OC) and particles number and deduced mass concentrations from Indo-Gangetic Plain (IGP; at Kanpur). Among viable bioaerosols, the highest concentrations of Gram-positive bacteria (GPB), Gram-negative bacteria (GNB) and Fungi were recorded during December–January (Avg.: 189 CFU/m³), November (244 CFU/m³) and September months (188 CFU/m³), respectively. Annual average concentration of GPB, GNB and Fungi were 105 ± 58, 144 ± 82 and 116 ± 51 CFU/m³. Particle number concentration (PNC) associated with fine-fraction aerosols (FFA) predominates throughout the year. However, mineral dust (coarser particle) remains a perennial constituent of atmospheric aerosols over the IGP. Temporal variability records and significant positive linear relationship (p < 0.05) of GPB and GNB with OC and biomass burning derived potassium (K⁺BB) indicates their association with massive emissions from paddy-residue burning (PRB) and bio-fuel burning. Influence of meteorological parameters on viable bioaerosols abundance has been rigorously investigated herein. Accordingly, ambient temperature seems to be more affecting the bacteria (anti-correlation), whereas wet-precipitation (1–4 mm) relates to higher abundance of Fungi. High abundance of GNB during large-scale biomass burning emissions has implications to endotoxin exposure on human health. Field-based data-set of bioaerosols, OC, PNC and deduced mass concentrations reported herein could serve to better constraint their role in human health and climate relevance.

Very few studies reported the potential of arbuscular mycorrhizal symbiosis to dissipate hydrocarbons in aged polluted soils. The present work aims to study the efficiency of arbuscular mycorrhizal colonized wheat plants in the dissipation of alkanes and polycyclic aromatic hydrocarbons (PAHs). Our results demonstrated that the inoculation of wheat with Rhizophagus irregularis allowed a better dissipation of PAHs and alkanes after 16 weeks of culture by comparison to non-inoculated condition. These dissipations observed in the inoculated soil resulted from several processes: (i) a light adsorption on roots (0.5% for PAHs), (ii) a bioaccumulation in roots (5.7% for PAHs and 6.6% for alkanes), (iii) a transfer in shoots (0.4 for PAHs and 0.5% for alkanes) and mainly a biodegradation. Whereas PAHs and alkanes degradation rates were respectively estimated to 12 and 47% with non-inoculated wheat, their degradation rates reached 18 and 48% with inoculated wheat. The mycorrhizal inoculation induced an increase of Gram-positive and Gram-negative bacteria by 56 and 37% compared to the non-inoculated wheat. Moreover, an increase of peroxidase activity was assessed in mycorrhizal roots. Taken together, our findings suggested that mycorrhization led to a better hydrocarbon biodegradation in the aged-contaminated soil thanks to a stimulation of telluric bacteria and hydrocarbon metabolization in mycorrhizal roots.

With increasing production of carbon nanoparticles (CNPs), environmental release of these entities becomes an ever-greater inevitability. However, many questions remain regarding their impact on soil microorganisms. This study examined the effects of long or short multiwalled carbon nanotubes (MWCNTs), C60 fullerene and fullerene soot in Gram-negative bacteria. Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy was applied to derive signature spectral fingerprints of effects. A concentration-dependent response in spectral alterations was observed for each nanoparticle type. Long or short MWCNTs and fullerene soot gave rise to similar alterations to lipids, Amide II and DNA. The extent of alteration varies with nanoparticle size, with smaller short MWCNTs resulting in greater toxicity than long MWCNTs. Fullerene soot was the least toxic. C60 results in the most distinct and largest overall alterations, notably in extensive protein alteration. This work demonstrates a novel approach for assaying and discriminating the effects of CNPs in target systems.