Bacterial isolates harboring antibiotics and heavy-metal resistance genes co-existing with mobile genetic elements in natural aquatic water bodies

A One Health exploration of antimicrobial resistance in Escherichia coli originated from urban and rural lakes ecosystem

Antimicrobial resistance (AMR) has become one of the most serious threats to One Health. Aquatic environments are an ideal non-clinical AMR reservoir and can act as a key battlefront for tackling the AMR. However, AMR data using the One Health approach remain scarce in aquatic environments worldwide. Here, we extensively assessed AMR in Escherichia coli isolated from urban and rural lake ecosystems using the One Health perspective. A total of 162 E. coli isolates obtained from lakes were tested against 25 antimicrobials using an in-vitro antimicrobial susceptibility testing method. A low (2%) to moderate (45%) drug resistance rate was found for all antimicrobials used in human/veterinary medicine or animal/plant agriculture. However, <80% E. coli isolates exhibited multidrug resistance (MDR) phenotype to highly important (amikacin, gentamicin, trimethoprim) or critically important (amoxicillin, ampicillin, colistin) drugs of both human and veterinary medicine. Of concern, >50% of E. coli isolates exhibited MDR to drugs used as last-resorts (chloramphenicol, colistin) or as frontline (nitrofurantoin, sulfamethoxazole, ampicillin, gentamicin) against E. coli infections. In conclusion, the presence of MDR E. coli strains in urban or rural lake ecosystems highlights their possible role as AMR reservoirs with potential One Health risks.

Multiple antibiotic resistance and herbicide catabolic profiles of bacteria isolated from Lake Villarrica surface sediments (Chile)

Antibiotics and herbicides are contaminants of emerging concern in aquatic environments. Lake Villarrica is a relevant freshwater body in Chile and was recently designated a 'saturated nutrient zone'. Here, we investigated the occurrence of multiple antibiotic resistance (MAR) and herbicide catabolic profiles among bacteria present in the surface sediments of Lake Villarrica. The occurrence of antibiotic-resistant genes (ARGs; blaTEM, catA and tetM) and herbicide-catabolic genes (HCGs; phnJ and atzA) was investigated by qPCR. Subsequently, the presence of culturable bacteria with multiple resistance to amoxicillin (AMX), chloramphenicol (CHL) and oxytetracycline (OXT) was studied. Forty-six culturable MAR (AMX + CHL + OXT) strains were isolated and characterized with respect to their resistance to 11 antibiotics by using a disc diffusion assay and testing their ability to use herbicides as a nutrient source. qPCR analyses revealed that ARGs and HCGs were present in all sediment samples (101 to 103 gene copies g-1), with significant (P ≤ 0.05) higher values in sites near Villarrica city and cattle pastures. The plate method was used to recover MAR isolates from sediment (103-106 CFU g-1), and most of the 46 isolates also showed resistance to oxacillin (100%), cefotaxime (83%), erythromycin (96%) and vancomycin (93%). Additionally, 54 and 57% of the MAR isolates were able to grow on agar supplemented (50 mg L-1) with atrazine and glyphosate as nutrient sources, respectively. Most of the MAR isolates were taxonomically close to Pseudomonas (76.1%) and Pantoea (17.4%), particularly those isolated from urbanized sites (Pucón city). This study shows the presence of MAR bacteria with herbicide catabolic activity in sediments, which is valuable for conservation strategies and risk assessments of Lake Villarrica. However, major integrative studies on sediments as reservoirs or on the fate of MAR strains and traces of antibiotics and herbicides as a result of anthropic pressure are still needed.

Snapshot of resistome, virulome and mobilome in aquaculture

Aquaculture environments can be hotspots for resistance genes through the surrounding environment. Our objective was to study the resistome, virulome and mobilome of Gram-negative bacteria isolated in seabream and bivalve molluscs, using a WGS approach. Sixty-six Gram-negative strains (Aeromonadaceae, Enterobacteriaceae, Hafniaceae, Morganellaceae, Pseudomonadaceae, Shewanellaceae, Vibrionaceae, and Yersiniaceae families) were selected for genomic characterization. The species and MLST were determined, and antibiotic/disinfectants/heavy metals resistance genes, virulence determinants, MGE, and pathogenicity to humans were investigated. Our study revealed new sequence-types (e.g. Aeromonas spp. ST879, ST880, ST881, ST882, ST883, ST887, ST888; Shewanella spp. ST40, ST57, ST58, ST60, ST61, ST62; Vibrio spp. ST206, ST205). >140 different genes were identified in the resistome of seabream and bivalve molluscs, encompassing genes associated with β-lactams, tetracyclines, aminoglycosides, quinolones, sulfonamides, trimethoprim, phenicols, macrolides and fosfomycin resistance. Disinfectant resistance genes qacE-type, sitABCD-type and formA-type were found. Heavy metals resistance genes mdt, acr and sil stood out as the most frequent. Most resistance genes were associated with antibiotics/disinfectants/heavy metals commonly used in aquaculture settings. We also identified 25 different genes related with increased virulence, namely associated with adherence, colonization, toxins production, red blood cell lysis, iron metabolism, escape from the immune system of the host. Furthermore, 74.2 % of the strains analysed were considered pathogenic to humans. We investigated the genetic environment of several antibiotic resistance genes, including blaTEM-1B, blaFOX-18, aph(3″)-Ib, dfrA-type, aadA1, catA1-type, tet(A)/(E), qnrB19 and sul1/2. Our analysis also focused on identifying MGE in proximity to these genes (e.g. IntI1, plasmids and TnAs), which could potentially facilitate the spread of resistance among bacteria across different environments. This study provides a comprehensive examination of the diversity of resistance genes that can be transferred to both humans and the environment, with the recognition that aquaculture and the broader environment play crucial roles as intermediaries within this complex transmission network.

Study of heavy metal resistance genes in Escherichia coli isolates from a marine ecosystem with a history of environmental pollution (arsenic, cadmium, copper, and mercury)

We analyzed whole genome sequences of 308 Escherichia coli isolates from a marine ecosystem to determine the prevalence and relationships of heavy metal resistance genes (HMRGs) and antibiotic resistance genes (ARGs), as well as the presence of plasmid sequences. We screened all genomes for presence of 18 functional HMRGs conferring resistance to arsenic, cadmium, copper, or cadmium/mercury. In subset analyses, we examined geographic variations of HMRG carriage patterns in 224 isolates from water sources, and sought genetic linkages between HMRGs and ARGs in 25 genomes of isolates resistant to antibiotics. We found high carriage rates of HMRGs in all genomes, with 100% carrying at least one copy of 11 out of 18 HMRGs. A total of 173 (56%) of the isolates carried both HMRGs and plasmid sequences. In the 25 genomes of antibiotic-resistant isolates, 80% (n = 20) carried HMRGs, ARGs, and plasmid sequences, while 40% (n = 10) had linked HMRGs and ARGs on their assembled genomes. We found no evidence of geographic variation in HMRG frequency, nor any association between locational proximity to Superfund sites and co-carriage of HMRGs and ARGs. Our study findings indicate that HMRGs are common among E. coli in marine ecosystems, suggesting widespread heavy metal presence in water sources of a region with history of environmental pollution. Further research is needed to determine the role HMRGs play in driving antimicrobial resistance in human pathogens through genetic linkage and the value their detection in environmental bacterial genomes may offer as an indicator of environmental heavy metal pollution.

Investigation of antibiotic resistance genotypic and phenotypic characteristics of marine aquaculture fish carried in the Dalian area of China

Due to the long-term and irrational use of antibiotics for the prevention and control of bacterial diseases in aquaculture, antibiotic resistance genes have become a new source of pollution in aquatic products. Factors such as the spread of drug-resistant strains and the horizontal transfer of drug-resistant genes have led to multi-drug resistance in fish-infecting bacteria, which seriously affects the quality and safety of aquatic products. In this study, 50 samples of horse mackerel and puffer fish sold in Dalian aquatic products market and seafood supermarket were collected, and the phenotypic characteristics of the bacteria carried by the fish for drugs such as sulfonamides, amide alcohols, quinolones, aminoglycosides and tetracyclines were tested and analyzed, and the resistance genes carried by fish samples were detected by SYBG qPCR. Our statistical analyses demonstrated that the drug resistance phenotypes and genotypes of bacteria carried by mariculture horse mackerel and puffer fish in the Dalian area of China were complex, and the multi-drug resistance rate reached 80%. Among the examined antibiotics, the resistance rates to cotrimoxazole, tetracycline, chloramphenicol, ciprofloxacin, norfloxacin, levofloxacin, kanamycin, and florfenicol exceeded 50%, whereas the resistance rates to gentamicin and tobramycin were 26 and 16%, respectively. The detection rate of the drug resistance genes tetA, sul1, sul2, qnrA, qnrS, and floR exceeded 70% and all samples carried more than three drug resistance genes. The correlation analysis of drug resistance genes and drug resistance phenotypes showed that the detection of the drug resistance genes sul1, sul2, floR, and qnrD was correlated with the detection of drug resistance phenotypes (p < 0.01). However, the correlation between the resistance genes cmlA, cfr, tetA, qnrA, qnrS, and aac(6')-Ib-cr and the corresponding resistance phenotype was not significant (p > 0.05). In general, our findings indicated that the multi-drug resistance of bacteria carried by marine horse mackerel and puffer fish in the Dalian area was serious. From the perspective of drug resistance rate and drug resistance gene detection rate, the aminoglycosides gentamicin and tobramycin are still considered effective in controlling bacterial infection in marine fish in the study area. Collectively, our findings provide a scientific basis for the management of drug use in mariculture, which can prevent the transmission of drug resistance through the food chain and minimize the associated human health risks.

Reduced Antibiotic Resistance in the Rhizosphere of Lupinus albus in Mercury-Contaminated Soil Mediated by the Addition of PGPB

The emergence of antibiotic resistance (AR) poses a threat to the "One Health" approach. Likewise, mercury (Hg) pollution is a serious environmental and public health problem. Its ability to biomagnify through trophic levels induces numerous pathologies in humans. As well, it is known that Hg-resistance genes and AR genes are co-selected. The use of plant-growth-promoting bacteria (PGPB) can improve plant adaptation, decontamination of toxic compounds and control of AR dispersal. The cenoantibiogram, a technique that allows estimating the minimum inhibitory concentration (MIC) of a microbial community, has been postulated as a tool to effectively evaluate the evolution of a soil. The present study uses the metagenomics of 16S rRNA gene amplicons to understand the distribution of the microbial soil community prior to bacterial inoculation, and the cenoantibiogram technique to evaluate the ability of four PGPB and their consortia to minimize antibiotic resistance in the rhizosphere of Lupinus albus var. Orden Dorado grown in Hg-contaminated soils. Results showed that the addition of A1 strain (Brevibacterium frigoritolerans) and its consortia with A2, B1 and B2 strains reduced the edaphic community´s MIC against cephalosporins, ertapenem and tigecycline. The metagenomic study revealed that the high MIC of non-inoculated soils could be explained by the bacteria which belong to the detected taxa,. showing a high prevalence of Proteobacteria, Cyanobacteria and Actinobacteria.

Draft genome of Raoultella planticola, a high lead resistance bacterium from industrial wastewater

Isolation of heavy metals-resistant bacteria from their original habitat is a crucial step in bioremediation. Six lead (Pb) resistant bacterial strains were isolated and identified utilizing 16S rRNA to be Enterobacter ludwigii FACU 4, Shigella flexneri FACU, Microbacterium paraoxydans FACU, Klebsiella pneumoniae subsp. pneumonia FACU, Raoultella planticola FACU 3 and Staphylococcus xylosus FACU. It was determined that all these strains had their Minimum inhibitory concentration (MIC) to be 2500 ppm except R. planticola FACU 3 has a higher maximum tolerance concentration (MTC) up to 2700 ppm. We evaluated the survival of all six strains on lead stress, the efficiency of biosorption and lead uptake. It was found that R. planticola FACU 3 is the highest MTC and S. xylosus FACU was the lowest MTC in this evaluation. Therefore, transmission electron microscopy (TEM) confirmed the difference between the morphological responses of these two strains to lead stress. These findings led to explore more about the genome of R. planticola FACU 3 using illumine Miseq technology. Draft genome sequence analysis revealed the genome size of 5,648,460 bp and G + C content 55.8% and identified 5526 CDS, 75 tRNA and 4 rRNA. Sequencing technology facilitated the identification of about 47 genes related to resistance to many heavy metals including lead, arsenic, zinc, mercury, nickel, silver and chromium of R. planticola FACU 3 strain. Moreover, genome sequencing identified plant growth-promoting genes (PGPGs) including indole acetic acid (IAA) production, phosphate solubilization, phenazine production, trehalose metabolism and 4-hydroxybenzoate production genes and a lot of antibiotic-resistant genes.

Aquatic Environments as Hotspots of Transferable Low-Level Quinolone Resistance and Their Potential Contribution to High-Level Quinolone Resistance

The disposal of antibiotics in the aquatic environment favors the selection of bacteria exhibiting antibiotic resistance mechanisms. Quinolones are bactericidal antimicrobials extensively used in both human and animal medicine. Some of the quinolone-resistance mechanisms are encoded by different bacterial genes, whereas others are the result of mutations in the enzymes on which those antibiotics act. The worldwide occurrence of quinolone resistance genes in aquatic environments has been widely reported, particularly in areas impacted by urban discharges. The most commonly reported quinolone resistance gene, qnr, encodes for the Qnr proteins that protect DNA gyrase and topoisomerase IV from quinolone activity. It is important to note that low-level resistance usually constitutes the first step in the development of high-level resistance, because bacteria carrying these genes have an adaptive advantage compared to the highly susceptible bacterial population in environments with low concentrations of this antimicrobial group. In addition, these genes can act additively with chromosomal mutations in the sequences of the target proteins of quinolones leading to high-level quinolone resistance. The occurrence of qnr genes in aquatic environments is most probably caused by the release of bacteria carrying these genes through anthropogenic pollution and maintained by the selective activity of antimicrobial residues discharged into these environments. This increase in the levels of quinolone resistance has consequences both in clinical settings and the wider aquatic environment, where there is an increased exposure risk to the general population, representing a significant threat to the efficacy of quinolone-based human and animal therapies. In this review the potential role of aquatic environments as reservoirs of the qnr genes, their activity in reducing the susceptibility to various quinolones, and the possible ways these genes contribute to the acquisition and spread of high-level resistance to quinolones will be discussed.

Microbial silver resistance mechanisms: recent developments

In this mini-review, after a brief introduction into the widespread antimicrobial use of silver ions and nanoparticles against bacteria, fungi and viruses, the toxicity of silver compounds and the molecular mechanisms of microbial silver resistance are discussed, including recent studies on bacteria and fungi. The similarities and differences between silver ions and silver nanoparticles as antimicrobial agents are also mentioned. Regarding bacterial ionic silver resistance, the roles of the sil operon, silver cation efflux proteins, and copper-silver efflux systems are explained. The importance of bacterially produced exopolysaccharides as a physiological (biofilm) defense mechanism against silver nanoparticles is also emphasized. Regarding fungal silver resistance, the roles of metallothioneins, copper-transporting P-type ATPases and cell wall are discussed. Recent evolutionary engineering (adaptive laboratory evolution) studies are also discussed which revealed that silver resistance can evolve rapidly in bacteria and fungi. The cross-resistance observed between silver resistance and resistance to other heavy metals and antibiotics in bacteria and fungi is also explained as a clinically and environmentally important issue. The use of silver against bacterial and fungal biofilm formation is also discussed. Finally, the antiviral effects of silver and the use of silver nanoparticles against SARS-CoV-2 and other viruses are mentioned. To conclude, silver compounds are becoming increasingly important as antimicrobial agents, and their widespread use necessitates detailed understanding of microbial silver response and resistance mechanisms, as well as the ecological effects of silver compounds. Figure created with BioRender.com.

Molecular characterization of resistance determinants and mobile genetic elements of ESBL producing multidrug-resistant bacteria from freshwater lakes in Kashmir, India

BACKGROUND

Antibiotic resistance conceded as a global concern is a phenomenon that emerged from the bacterial response to the extensive utilization of antimicrobials. The expansion of resistance determinants through horizontal transfer is linked with mobile genetic elements (MGEs) like transposons, insertion sequences, and integrons. Heavy metals also create consequential health hazards. Metal resistance gene in alliance with antibiotic resistance genes (ARGs) and MGEs is assisting bacteria to attain exalted quantity of resistance.

METHODOLOGY

The present work was carried out to study ARGs blaCTX-M, AmpC, qnrS, MGEs like ISecp1, TN3, TN21, and Int I by performing PCR and sequencing from Wular and Dal lakes of Kashmir; India. The genetic environment analysis of blaCTX-M-15 was carried out using PCR amplification, and sequencing approach followed by in-silico docking and mutational studies. Co-occurrence of ARGs and HMRGs was determined. Plasmid typing was done using PCR-based replicon typing (PBRT) and conjugation assay was also performed.

RESULTS

Out of 201 isolates attained from 16 locations, 33 were ESBLs producers. 30 ESBL displaying isolates were perceived positive for CTX-M gene, followed by AmpC (17), qnrS (13), ISecp1 (15), TN3 (11), TN21 (11), Int I (18), and SulI (14). The genetic environment of blaCTX-M-15 was observed as (ISEcp1-blaCTX-M-15-orf477), classical promoter-10 TACAAT and -35 TTGAA was found at the 3' region. The 3D structure of CTX-M-15 and ISEcp1 was generated and CTX-M-15-ISEcp1 (R299L) docking and mutation showed a reduction in hydrogen bonds. Co-occurrence of antibiotics and HMRGs (mer, sil, and ars) was found in 18, 14, and 8 isolates. PBRT analysis showed the presence of Inc. groups- B/O, F, I1, HI1, FIA, HI2, N, FIB, L/M. Molecular analysis of transconjugants showed the successful transfer of ARGs, MGEs, and HMRGs in the E. coli J53 AZ^R strain.

CONCLUSION

This study highlights the occurrence of ESBL producing bacteria in the aquatic environment of Kashmir India that can serve as a reservoir of ARGs. It also discussed the molecular mechanisms of MGEs which can help in containing the spread of antibiotic resistance.

Integrated approaches to mitigate threats from emerging potentially toxic elements: A way forward for sustainable environmental management

Potentially toxic elements (PTEs) such as toxic metal (loid)s and other emerging hazardous contaminants, exist in the environment and poses a serious threat. A large amount of wastewater containing PTEs such as cadmium, chromium, copper, nickel, arsenic, lead, zinc, etc. Release from industries during production process. Besides these, chemical-based fertilizers used in soils during crop production have become one of the crucial sources of PTEs. Various techniques are being employed for the mitigation of PTEs like chemical precipitation, ion exchange, coagulation, activated carbon, adsorption, membrane filtration, and bioremediation. Among these mitigation strategies, biological processes such as bioremediation, phytoremediation etc. Are extensively used, as they are economic have high-efficiency rate and are eco-friendly. This review intends to provide information on PTEs contamination through various sources; along with the toxicity of metal (loid)s with respect to their patterns of transmission and risks in the changing environment. Various remediation methods for the management of these pollutants along with their techno-economic perspective are also summarized in this review.

Genomic features of a multidrug-resistant and mercury-tolerant environmental Escherichia coli recovered after a mining dam disaster in South America

Mining dam disasters contribute to the contamination of aquatic environments, impacting associated ecosystems and wildlife. A multidrug-resistant Escherichia coli strain (B2C) was isolated from a river water sample in Brazil after the Mariana mining dam disaster. The genome was sequenced using the Illumina MiSeq platform, and de novo assembled using Unicycler. Resistome, virulome, and plasmidome were predicted using bioinformatics tools. Data analysis revealed that E. coli B2C belonged to sequence type ST219 and phylogroup E. Strikingly, a broad resistome (antibiotics, hazardous heavy metals, and biocides) was predicted, including the presence of the clinically relevant bla_CTX-M-2 extended-spectrum β-lactamase (ESBL) gene, qacE∆1 efflux pump gene, and the mer (mercury resistance) operon. SNP-based analysis revealed that environmental E. coli B2C was clustered along to ESBL-negative E. coli strains of ST219 isolated between 1980 and 2021 from livestock in the United States of America. Acquisition of clinically relevant genes by ST219 seems to be a recent genetic event related to anthropogenic activities, where polluted water environments may contribute to its dissemination at the human-animal-environment interface. In addition, the presence of genes conferring resistance to heavy metals could be related to environmental pollution from mining activities. Antimicrobial resistance genes could be essential biomarkers of environmental exposure to human and mining pollution.

The changing water quality of lakes-a case study of Dal Lake, Kashmir Valley

Lakes throughout the globe have been gravely altered or degraded at a pace much more significant than their restoration. In the heart of Srinagar, the summer capital of Jammu and Kashmir, Dal Lake, has witnessed extreme loss in water quality during the last four decades because of anthropogenic pressures. The lake is unique in that over 50,000 people inhabit the lake itself in houseboats, dongas, or islands within the lake. These people derive their livelihood from the lake in terms of tourism, agriculture, fishing, and vegetable farming. The countless ways people use the lake have led to an extreme load of pollution in the lake. Encroachment in and around the lake has led to the loss of volume of water in the lake and consequently increased the concentration of pollutants. Discharge of untreated sewage, agricultural runoff, and sediments from adjoining catchments have further degraded the lake water quality. The changes in water quality are clear from the physio-chemical properties of the lake waters. While transparency and dissolved oxygen in the lake have decreased drastically during the last 40 years, the concentration of harmful substances like phosphates, nitrates, and chlorides has increased. The hardness of water has also increased due to higher levels of carbonates and bicarbonates in the lake. This paper details the changes in the water quality of Dal Lake over the recent past. The paper analyses the strategies that can be implemented to manage the lake and restore its quality if appropriately implemented.

Bacterial Genes Encoding Resistance Against Antibiotics and Metals in Well-Maintained Drinking Water Distribution Systems in Finland

Information on the co-occurrence of antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) among bacterial communities in drinking water distribution systems (DWDSs) is scarce. This study characterized ARGs and MRGs in five well-maintained DWDSs in Finland. The studied DWDSs had different raw water sources and treatment methods. Two of the waterworks employed artificially recharged groundwater (ARGW) and used no disinfection in the treatment process. The other three waterworks (two surface and one groundwater source) used UV light and chlorine during the treatment process. Ten bulk water samples (two from each DWDS) were collected, and environmental DNA was extracted and then sequenced using the Illumina HiSeq platform for high-throughput shotgun metagenome sequencing. A total of 430 ARGs were characterized among all samples with the highest diversity of ARGs identified from samples collected from non-disinfected DWDSs. Furthermore, non-disinfected DWDSs contained the highest diversity of bacterial communities. However, samples from DWDSs using disinfectants contained over double the ratio of ARG reads to 16S rRNA gene reads and most of the MRG (namely mercury and arsenic resistance genes). The total reads and types of ARGs conferring genes associated with antibiotic groups namely multidrug resistance, and bacitracin, beta-lactam, and aminoglycoside and mercury resistance genes increased in waterworks treating surface water with disinfection. The findings of this study contribute toward a comprehensive understanding of ARGs and MRGs in DWDSs. The occurrence of bacteria carrying antibiotic or metal resistance genes in drinking water causes direct exposure to people, and thus, more systematic investigation is needed to decipher the potential effect of these resistomes on human health.

Current Update on Intrinsic and Acquired Colistin Resistance Mechanisms in Bacteria

Colistin regained global interest as a consequence of the rising prevalence of multidrug-resistant Gram-negative Enterobacteriaceae. In parallel, colistin-resistant bacteria emerged in response to the unregulated use of this antibiotic. However, some Gram-negative species are intrinsically resistant to colistin activity, such as Neisseria meningitides, Burkholderia species, and Proteus mirabilis. Most identified colistin resistance usually involves modulation of lipid A that decreases or removes early charge-based interaction with colistin through up-regulation of multistep capsular polysaccharide expression. The membrane modifications occur by the addition of cationic phosphoethanolamine (pEtN) or 4-amino-l-arabinose on lipid A that results in decrease in the negative charge on the bacterial surface. Therefore, electrostatic interaction between polycationic colistin and lipopolysaccharide (LPS) is halted. It has been reported that these modifications on the bacterial surface occur due to overexpression of chromosomally mediated two-component system genes (PmrAB and PhoPQ) and mutation in lipid A biosynthesis genes that result in loss of the ability to produce lipid A and consequently LPS chain, thereafter recently identified variants of plasmid-borne genes (mcr-1 to mcr-10). It was hypothesized that mcr genes derived from intrinsically resistant environmental bacteria that carried chromosomal pmrC gene, a part of the pmrCAB operon, code three proteins viz. pEtN response regulator PmrA, sensor kinase protein PmrAB, and phosphotransferase PmrC. These plasmid-borne mcr genes become a serious concern as they assist in the dissemination of colistin resistance to other pathogenic bacteria. This review presents the progress of multiple strategies of colistin resistance mechanisms in bacteria, mainly focusing on surface changes of the outer membrane LPS structure and other resistance genetic determinants. New handier and versatile methods have been discussed for rapid detection of colistin resistance determinants and the latest approaches to revert colistin resistance that include the use of new drugs, drug combinations and inhibitors. Indeed, more investigations are required to identify the exact role of different colistin resistance determinants that will aid in developing new less toxic and potent drugs to treat bacterial infections. Therefore, colistin resistance should be considered a severe medical issue requiring multisectoral research with proper surveillance and suitable monitoring systems to report the dissemination rate of these resistant genes.

Lentic and effluent water of Delhi-NCR: a reservoir of multidrug-resistant bacteria harbouring blaCTX-M, blaTEM and blaSHV type ESBL genes

Antimicrobial resistance is not restricted to clinics but also spreading fast in the aquatic environment. This study focused on the prevalence and diversity of extended-spectrum β-lactamase (ESBL) genes among bacteria from lentic and effluent water in Delhi-NCR, India. Phenotypic screening of 436 morphologically distinct bacterial isolates collected from diverse sites revealed that 106 (∼24%) isolates were ESBL positive. Antibiotic profiling showed that 42, 60, 78 and 59% ESBL producing isolates collected from Ghazipur slaughterhouse, Lodhi garden pond, Hauz Khas lake and Jasola wastewater treatment plant, respectively, were multidrug-resistant (MDR). The multiple antibiotic resistance (MAR) index varied from 0.20 to 0.32 among selected locations. The prevalence of ESBL gene variants blaSHV, blaTEM and blaCTX-M were found to be 17.64, 35.29 and 64%, respectively. Furthermore, the analysis of obtained gene sequences showed three variants of blaCTX-M (15, 152 and 205) and two variants of blaTEM (TEM-1 and TEM-116) among ESBL producers. The co-existence of 2-3 gene variants was recorded among 48% ESBL positive isolates. New reports from this study include the blaCTX-M gene in Acinetobacter lwoffii, Enterobacter ludwigii, Exiguobacterium mexicanum and Aeromonas caviae. Furthermore, the identification of blaTEM and blaSHV in an environmental isolate of A. caviae is a new report from India.

Pharmaceutical disposal facilitates the mobilization of resistance determinants among microbiota of polluted environment

The emergence of resistance on exposure to pharmaceuticals among microorganisms has raised serious concern in the therapeutic approach against infectious diseases. Effluents discharge from hospitals, industries, and urban settlements containing pharmaceuticals and other toxic compounds into the aquatic ecosystem selects bacterial population against them; thereby promotes acquisition and dissemination of resistant traits among the inhabitant microbiota. The present study was aimed to determine the prevalence and multidrug resistance pattern of Extended Spectrum β-lactamase (ESBL) producing and non-producing bacterial isolates from the heavily polluted Delhi stretch of river Yamuna, India. Additionally, the role of abiotic factors in the dissemination of conjugative plasmids harbouring resistance genes was also studied using E. coli J53 as recipient and resistant E. coli isolates as donor strains. Of the 227 non-duplicate bacterial isolates, 60% (136) were identified as ESBL⁺ and 40% (91) as ESBL. ESBL⁺ isolates were found highly resistant to β-lactam and non-β-lactam classes of antibiotics compared with the ESBL^- isolates. 68% of ESBL⁺ and 24% of ESBL^- isolates showed an MAR index of ≥0.5. Surprisingly, multidrug resistance (MDR), extensively drug resistance (XDR), and pandrug resistance (PDR) phenotype were observed for 78.6%, 16.9%, and 0.7% of ESBL⁺ and 90%, 3%, and none for PDR among ESBL^- isolates. Conjugation under different conditions showed a higher mobilization rate at neutral pH (7-7.5) for ESBL⁺ isolates. Conjugation frequency was maximum at 40 °C for the isolate E. coli MRB6 (4.1 × 10^-5) and E. coli MRE32 (4.89 × 10^-4) and at 35 °C for E. coli MRA11 (4.89 × 10^-5). The transconjugants obtained were found tolerating different concentrations of mercuric chloride (0.0002-0.2 mg/L). Increased biofilm formation for ESBL⁺ isolates was observed on supplementing media with HgCl₂ (2 μg/mL) either singly or in combination with CTX (10 μg/mL). The present study demonstrates that anthropogenically influenced aquatic environments act as a reservoir of MDR, XDR, and even PDR strains; thereby posing a potent public health risk.