Networking and co-occurrence of virulent and multidrug resistant environmental bacteria in different aquatic systems: A gap in MDR-virulence transfer?

Co-occurrence of resistance and virulence is often overlooked in aquatic bacteria as environmental reservoirs, while transmission of these characteristics to clinically significant strains present unforeseen problems in future. In this investigation, environmental bacteria identified concurrently from multiple aquatic habitats viz., groundwater, canal, river and coastal waters were profiled for antibiotic resistance, metal tolerance, virulence factors and genes coding for these determinants. Strains from polluted river and canal exhibited higher resistance and virulence, especially Pseudomonas gessardii and P. fluorescens displayed high antibiotic resistance index (ARI > 0.6-0.8) with Alkaline Protease and Phospholipase production. Opportunistic pathogens including Vibrio parahaemolyticus, V. alginolyticus, V. vulnificus, Corynebacterium and Comamonas testosteroni expressed all three virulence factors with relatively low resistance. However, V. vulnificus and V. alginolyticus exhibited multiclass antibiotic resistance (5/6 classes). Metagenomic analysis revealed that genes corresponding to beta-lactam resistance were significantly higher (p < 0.05) in freshwater than seawater, while multidrug resistance gene were higher (p < 0.05) in seawater. In all aquatic bodies, abundant virulence genes belonged to secretion system proteins followed by motility related genes. Culturable bacteria revealed differential distribution of positive and negative correlation between 31 targeted genes with expressed resistance and virulence. Among Acinetobacter, significant positive correlation was found between Phospholipase production, other virulence genes (OVGs) and resistance to DNA Synthesis Inhibitors (DSI). In Pseudomonas, positive correlation was detected between toxin genes (toxA, eta, hlyA and stx) and resistance to cell wall synthesis inhibitors (CSI) as well as with OVGs and adhesion genes (eae, afa, papC and papA). Network analysis displayed unique clustering of genes ncc, arsB, strA, merA and intI dominated by non-pathogens and distinct clustering of genes pho, erm, nfsA, trh, lasB, tdh and invA by Vibrio. This investigation extends insight on co-occurring resistance and virulence in aquatic reservoir bacteria that could pose serious threats to public health in future.

Arsenic resistance and horizontal gene transfer are associated with carbon and nitrogen enrichment in bacteria

Coastal waters are confluences receiving large amounts of point and non-point sources of pollution. An attempt was made to explore microbial community interactions in response to carbon, nitrogen and metal pollution. Additionally, experiments were designed to analyze the influence of these factors on horizontal gene transfer (HGT). Shift in bacterial diversity dynamics by arsenic stress and nutrient addition in coastal waters was explored by metagenomics of microcosm setups. Phylogenetic analysis revealed equal distribution of Gammaproteobacteria (29%) and Betaproteobacteria (28%) in control microcosm. This proportional diversity from control switched to unique distribution of Gammaproteobacteria (44.5%)> Flavobacteria (17.7%)> Bacteriodia (11.92%)> Betaproteobacteria (11.52%) in microcosm supplemented with carbon, nitrogen and metal (C + N + M). Among metal-stressed systems, alpha diversity analysis indicated highest diversity of genera in C + N + M followed by N + M > C+M> metal alone. Arsenic and ampicillin sensitive E. coli XL1 blue and environmental strains (Vibrio tubiashii W85 and E. coli W101) were tested for efficiency of uptake of plasmid (P) pUCminusMCS (arsB^Ramp^R) under varying stress conditions. Transformation experiments revealed that combined effect of carbon, nitrogen and metal on horizontal gene transfer (HGT) was significantly higher (p < 0.01) than individual factors. The effect of carbon on HGT was proved to be superior to nitrogen under metal stressed conditions. Presence of arsenic in experimental setups (P + M, P + N + M and P + C + M) enhanced the HGT compared to non-metal counterparts supplemented with carbon or nitrogen. Arsenic resistant bacterial isolates (n = 200) were tested for the ability to utilize various carbon and nitrogen substrates and distinct positive correlation (p < 0.001) was found between arsenic resistance and utilization of urea and nitrate. However, evident positive correlation was not found between carbon sources and arsenic resistance. Our findings suggest that carbon and nitrogen pollution in aquatic habitats under arsenic stress determine the microbial community dynamics and critically influence uptake of genetic material from the surrounding environment.

COVID-19 restrictions and their influences on ambient air, surface water and plastic waste in a coastal megacity, Chennai, India

Anthropogenic activities experienced a pause due to the nationwide lockdown, imposed to contain the rapid spread of COVID-19 in the third week of March 2020. The impacts of suspension of industrial activities, vehicular transport and other businesses for three months (25 March-30 June) on the environmental settings of Chennai, a coastal megacity was assessed. A significant reduction in the key urban air pollutants [PM_2.5 (66.5%), PM₁₀ (39.5%), NO₂ (94.1%), CO (29%), O₃ (45.3%)] was recorded as an immediate consequence of the reduced anthropogenic activities. Comparison of water quality of an urban river Adyar, between pre-lockdown and lockdown, showed a substantial drop in the dissolved inorganic N (47%) and suspended particulate matter (41%) during the latter period. During the pandemic, biomedical wastes in India showed an overall surge of 17%, which were predominantly plastic. FTIR-ATR analysis confirmed the polymers such as polypropylene (25.4%) and polyester (15.4%) in the personal protective equipment.

Heavy-metal resistance in Gram-negative bacteria isolated from Kongsfjord, Arctic

Isolation and characterization of heterotrophic Gram-negative bacteria was carried out from the sediment and water samples collected from Kongsfjord, Arctic. In this study, the potential of Arctic bacteria to tolerate heavy metals that are of ecological significance to the Arctic (selenium (Se), mercury (Hg), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn)) was investigated. Quantitative assay of 130 isolates by means of plate diffusion and tube dilution methods was carried out by incorporation of different concentrations of metals. Growth in Se and Pb at a concentration of 3000 μg/L was significantly lower (P≤0.0001) than at 2000 μg/L. The minimum inhibitory concentration for Cd and Hg was 50 μg/L (P≤0.0001, F=264.23 and P≤0.0001, F=291.08, respectively) even though in the tube dilution test, Hg-containing tubes showed much less growth, revealing its superior toxicity to Cd. Thus, the level of toxicity of heavy metals was found to be in the order of Hg>Cd>Cu>Zn>Pb>Se. Multiple-metal-resistant isolates were investigated for their resistance against antibiotics, and a positive correlation was observed between antibiotic and metal resistance for all the isolates tested. The resistant organisms thus observed might influence the organic and inorganic cycles in the Arctic and affect the ecosystem.