Incidence of class 1 integrons in multiple antibiotic-resistant Gram-negative copiotrophic bacteria from the River Torsa in India

A metagenomic study of antibiotic resistance genes in a hypereutrophic subtropical lake contaminated by anthropogenic sources

Antibiotic resistance genes (ARGs) are a major threat to human and environmental health. This study investigated the occurrence and distribution of ARGs in Lake Cajititlán, a hypereutrophic subtropical lake in Mexico contaminated by anthropogenic sources (urban wastewater and runoff from crop and livestock production). ARGs (a total of 475 genes) were detected in 22 bacterial genera, with Pseudomonas (144 genes), Stenotrophomonas (88 genes), Mycobacterium (54 genes), and Rhodococcus (27 genes) displaying the highest frequencies of ARGs. Among these, Pseudomonas aeruginosa and Stenotrophomonas maltophilia showed the highest number of ARGs. The results revealed a diverse array of ARGs, including resistance to macrolides (11.55 %), aminoglycosides (8.22 %), glycopeptides (6.22 %), tetracyclines (4 %), sulfonamides (4 %), carbapenems (1.11 %), phenicols (0.88 %), fluoroquinolones (0.44 %), and lincosamides (0.22 %). The most frequently observed ARGs were associated with multidrug resistance (63.33 %), with MexF (42 genes), MexW (36 genes), smeD (31 genes), mtrA (25 genes), and KHM-1 (22 genes) being the most common. Lake Cajititlán is a recreational area for swimming, fishing, and boating, while also supporting irrigation for agriculture and potentially acting as a drinking water source for some communities. This raises concerns about the potential for exposure to antibiotic-resistant bacteria through these activities. The presence of ARGs in Lake Cajititlán poses a significant threat to both human and environmental health. Developing strategies to mitigate the risks of antibiotic resistance, including improving wastewater treatment, and promoting strategic antibiotic use and disposal, is crucial. This study represents a significant advancement in the understanding of antibiotic resistance dynamics in a hypereutrophic subtropical lake in a developing country, providing valuable insights for the scientific community and policymakers.

Fermented Polyherbal Formulation Ameliorates the Severity of Acute Multiple Antibiotics-Resistant Pseudomonas aeruginosa-Infected Burn Wound in a Rat Burn Model

Pseudomonas aeruginosa, a Gram-negative opportunistic bacterium, has emerged as a cause of life-threatening infections in burn wounds. Current therapeutic approaches through wound dressings and systemic medicines are far from satisfactory; resistance to more than two antibiotics shown by pathogens contributes to failures of therapy causing mortality. This animal study was conducted to check the efficacy of one Ayurveda-based fermented polyherbal preparation (AP 01) against multiple antibiotics-resistant (MAR) P. aeruginosa HW01-infected rat burn wounds. AP-01 was applied on artificially infected burn wound on a rat model infected with MAR P. aeruginosa to register the healing effects in terms of reduction in residual wound area percentage, the presence of C-reactive protein in blood, and the presence of viable bacteria colony. Topical application with conventional antibiotics served as a positive control. The polyherbal preparation had reduced the infected residual burn wound area at 40.63% ± 0.69 from the initial burn wound area within two weeks after a single intervention, whereas residual burn wound area remained much higher in the case of animals left untreated and in the case of the animals treated with control drug. Restoration to the normalcy of serum C-reactive protein level was also achieved earlier in the case of polyherbal AP-01-treated groups than in other groups. Fermented formulations using components of AP-01 singly or in different combinations had never been tested earlier for topical application in infected burn wound. The formulation of AP-01 was found superior in terms of the rate of healing and control of infection by MAR P. aeruginosa strains in burn wounds in rat models.

Enhanced removal of antibiotic and antibiotic resistance genes by coupling biofilm electrode reactor and manganese ore substrate up-flow microbial fuel cell constructed wetland system

Manganese ore substrate up-flow microbial fuel cell constructed wetland (UCW-MFC(Mn)) as an innovative wastewater treatment technology for purifying antibiotics and electricity generation with few antibiotic resistance genes (ARGs) generation has attracted attention. However, antibiotic purifying effects should be further enhanced. In this study, a biofilm electrode reactor (BER) that needs direct current driving was powered by a Mn ore anode (UCW-MFC(Mn)) to form a coupled system without requiring direct-current source. Removal efficiencies of sulfadiazine (SDZ), ciprofloxacin (CIP) and the corresponding ARGs in the coupled system were compared with composite (BER was powered by direct-current source) and anaerobic systems (both of BER and UCW-MFC were in open circuit mode). The result showed that higher antibiotic removal efficiency (94% for SDZ and 99.1% for CIP) in the coupled system was achieved than the anaerobic system (88.5% for SDZ and 98.2% for CIP). Moreover, electrical stimulation reduced antibiotic selective pressure and horizontal gene transfer potential in BER, and UCW-MFC further reduced ARG abundances by strengthening the electro-adsorption of ARG hosts determined by Network analysis. Bacterial community diversity continuously decreased in BER while it increased in UCW-MFC, indicating that BER mitigated the toxicity of antibiotic. Degree of modularity, some functional bacteria (antibiotic degrading bacteria, fermentative bacteria and EAB), and P450 enzyme related to antibiotic and xenobiotics biodegradation genes were enriched in electric field existing UCW-MFC, accounting for the higher degradation efficiency. In conclusion, this study provided an effective strategy for removing antibiotics and ARGs in wastewater by operating a BER-UCW-MFC coupled system.

Evolution and Emergence of Antibiotic Resistance in Given Ecosystems: Possible Strategies for Addressing the Challenge of Antibiotic Resistance

Antibiotics were once considered the magic bullet for all human infections. However, their success was short-lived, and today, microorganisms have become resistant to almost all known antimicrobials. The most recent decade of the 20th and the beginning of the 21st century have witnessed the emergence and spread of antibiotic resistance (ABR) in different pathogenic microorganisms worldwide. Therefore, this narrative review examined the history of antibiotics and the ecological roles of antibiotics, and their resistance. The evolution of bacterial antibiotic resistance in different environments, including aquatic and terrestrial ecosystems, and modern tools used for the identification were addressed. Finally, the review addressed the ecotoxicological impact of antibiotic-resistant bacteria and public health concerns and concluded with possible strategies for addressing the ABR challenge. The information provided in this review will enhance our understanding of ABR and its implications for human, animal, and environmental health. Understanding the environmental dimension will also strengthen the need to prevent pollution as the factors influencing ABR in this setting are more than just antibiotics but involve others like heavy metals and biocides, usually not considered when studying ABR.

Ti/PbO2 Electrode Efficiency in Catalytic Chloramphenicol Degradation and Its Effect on Antibiotic Resistance Genes

Livestock farming has led to the rapid accumulation of antibiotic resistance genes in the environment. Chloramphenicol (CAP) was chosen as a model compound to investigate its degradation during electrochemical treatment. Ti/PbO₂ electrodes were prepared using electrodeposition. The prepared Ti/PbO₂-La electrodes had a denser surface and a more complete PbO₂ crystal structure. Ti/PbO₂-Co electrodes exhibited improved electrochemical catalytic activity and lifetime in practice. The impact of different conditions on the effectiveness of CAP electrochemical degradation was investigated, and the most favorable conditions were identified (current density: I = 15.0 mA/cm, electrolyte concentration: c = 0.125 mol/L, solution pH = 5). Most importantly, we investigated the effects of the different stages of treatment with CAP solutions on the abundance of resistance genes in natural river substrates (intI1, cmlA, cmle3, and cata2). When CAP was completely degraded (100% TOC removal), no effect on resistance gene abundance was observed in the river substrate; incomplete CAP degradation significantly increased the absolute abundance of resistance genes. This suggests that when treating solutions with antibiotics, they must be completely degraded (100% TOC removal) before discharge into the environment to reduce secondary pollution. This study provides insights into the deep treatment of wastewater containing antibiotics and assesses the environmental impact of the resulting treated wastewater.

The removal of antibiotic resistant bacteria and genes and inhibition of the horizontal gene transfer by contrastive research on sulfidated nanoscale zerovalent iron activating peroxymonosulfate or peroxydisulfate

Antibiotic resistant bacteria (ARB) and the antibiotic resistance genes (ARGs) dissemination via plasmid-mediated conjugation have attracted considerable attentions. In this research, sulfidated nanoscale zerovalent iron (S-nZVI)/peroxymonosulfate (PMS) and S-nZVI/peroxydisulfate (PDS) process were investigated to inactivate ARB (Escherichia coli DH5α with RP4 plasmid, Pseudomonas. HLS-6 contains sul1 and intI1 on genome DNA sequence). S-nZVI/PMS system showed higher efficiency than S-nZVI/PDS on ARB inactivation. Thus, the optimal condition 28 mg/L S-nZVI coupled with 153.7 mg/L (0.5 mM) PMS was applied to remove both intracellular ARGs (iARGs) and ARB. The oxidative damage of ARB cell was systemically studied by cell viability, intracellular Mg²⁺ levels, the changes of extracellular and internal structure, integrity of cell walls and membranes and enzymatic activities. S-nZVI/PMS effectively inactivated ARB (~7.32 log) within 15 min. These effects were greatly higher than those achieved individually. Moreover, removal efficiencies of iARGs sul1, intI1 and tetA were 1.52, 1.79 and 1.56 log, respectively. These results revealed that S-nZVI and PMS have a synergistic effect against ARB and iARGs. The regrowth assays illustrated that the ARB were effectively inactivated. By verifying the inhibitory impacts of S-nZVI/PMS treatment on conjugation transfer, this work highlights a promising alternative technique for inhibiting the horizontal gene transfer.

Identification of carbapenems resistant genes on biofilm forming K. pneumoniae from urinary tract infection

The multi-drug resistant effect of the Gram negative bacteria K. pneumoniae was identified by disc diffusion method using specific UTI panel discs of Kleb 1 HX077 and Kleb 2 HX090 HEXA. Among the multi-drug resistant bacteria, the carbapenem resistant (CR) effect of the K. pneumoniae was screened by specific carbapenem detection antibiotics of HEXA HX066 and HX0103 HEXA by disc diffusion method. In addition, the effective antibiotics were further performed against K. pneumoniae by minimum inhibition concentration method. Further, the carbapenemase genes of VIM 1 and IMP 1 were detected from the isolated strains by multiplex PCR method. Furthermore, the biofilm forming ability of selected carbapenem resistant K. pneumoniae was initially identified by tissue culture plate method and confirmed by exopolysaccharide arrest ability of congo red agar assay. Finally, our result was proved that the identified K. pneumoniae is carbapenemase producing strain, and its virulence was extended with strong biofilm formation.

Selectively enrichment of antibiotics and ARGs by microplastics in river, estuary and marine waters

The partition of antibiotics and antibiotic resistant genes (ARGs) between the microplastics (MPs) and the surrounding water with various salinity are still unclear. In this study, we hypothesized that adsorption of antibiotics on MPs might cause a significant change of the structure of microbial communities, diversity and abundance of ARGs on MPs and this might be further affected by change of salinity. In this study, we investigated adsorption of four common antibiotics (sulfamerazine, tetracycline, chloramphenicol and tylosin) to polyethylene (PE) MPs in river, estuary and marine waters, and the differences of antibiotic resistant genes (ARGs) and bacterial communities on MPs and in the three waters. The results showed that MPs can enrich antibiotics, ARGs and microbes from the surrounding water. Elevated salinity could reduce adsorption of antibiotics to MPs and the abundance of ARGs. For example, MPs can concentrate more antibiotics and ARGs in the fresh river water than in the estuary and the marine waters. In addition, ARGs and bacterial communities on MPs at various salinity were significantly different under the pressure of four antibiotics. On MPs, sul1, sulA/folP-01, tetA, tetC, tetX and ermE increased significantly but a few new ARGs such as sulA/folP-01 and tetA appeared. The structure of the bacterial communities on MPs was different from the surrounding water since some bacteria species found on MPs were barely detected in the surrounding water while some genera on MPs vanished after exposure to antibiotics. As the antibiotics adsorbed and the ARGs on MPs decreased with the water salinity, the structure of the communities on MPs thus varied with salinity change. These findings are important to understand the effects of MPs on the transport, fate and ecological risk of antibiotics and ARGs in different aquatic environments.

Anaerobic/aerobic conditions determine antibiotic resistance genes removal patterns from leachate by affecting bacteria taxa-genes co-occurrence modules

Landfill treatment of municipal solid waste treatment produces a large amount of leachate, which has been an important hotspot of ARGs. This study aimed to investigate the ARGs removal potential, kinetics and mechanism from leachate in aerobic and anaerobic conditions. Simulated landfill reactors showed the efficacy in reducing ARGs, and the removal efficiencies depended on ARGs types and aerobic/anaerobic conditions. The ARGs tetQ and bla_CTX-M were more likely to attenuate with the log-removal efficiencies of 1.50-3 order of magnitude. The ARGs removal kinetic was well fitted by modified Collins-Selleck model, and aerobic condition showed better removal capacities and kinetics than anaerobic condition. Among the ARGs with great removal performance, sul2, aadA1and bla_CTX-M were eliminated from leachate and refuse simultaneously, but tetM, ermB, and mefA were removed from leachate but enriched in refuse. Aerobic/anaerobic states might drive the bacterial community shift of leachate and refuse, and topology property comparison of co-occurrence networks suggested that refuse had a closer non-random host relationship between ARGs and microbial taxa than leachate. Further module analyses revealed that ARGs removal efficiencies depended on the taxonomy of host bacteria in leachate, while the refuse taxa-ARGs correlation determined ARGs removal patterns. By selecting distinct bacteria cluster in different conditions, aerobic treatment benefited ARGs reduction in leachate and refuse, while anaerobic treatment enhanced the enrichment of ARGs in refuse. These findings can potentially foster the understanding of ARGs removal mechanism in biological treatment processes.

Distribution of antibiotic resistance genes in soils and crops. A field study in legume plants (Vicia faba L.) grown under different watering regimes

Social concern has raised during the last years due to the development of antibiotic resistance hotspots in different environmental compartments, including the edible parts of crops. To assess the influence of the water quality used for watering, we collected samples from soil, roots, leaves and beans from the legume plant Vicia faba (broad beans) in three agricultural peri-urban plots (Barcelona, NE Spain), irrigated with either groundwater, river water, or reclaimed water. Antibiotic resistance genes (ARGs) sul1, tetM, qnrS1, bla_CTX-M-32,bla_OXA-58, mecA, and bla_TEM were quantified by real-time PCR, along with 16S rDNA and intl1 sequences, as proxies for bacterial abundance and integron prevalence, respectively. Microbiome composition of all samples were analyzed by high-throughput DNA sequencing. Results show a gradient of bacterial species diversity and of ARG prevalence from highly diverse soil samples to microbially-poor beans and leaves, in which Rhizobiales essentially displaced all other groups, and that presented very small loads of ARGs and integron sequences. The data suggest that the microbiome and the associated resistome were likely influenced by agricultural practices and water quality, and that future irrigation water legal standards should consider the specific Physiology of the different crop plants.

Distribution and relationship between antimicrobial resistance genes and heavy metals in surface sediments of Taihu Lake, China

Heavy metals, pharmaceuticals, and other wastes released into the environment can significantly influence environmental antibiotic resistance. We investigated the occurrence of 22 antimicrobial resistance genes (ARGs) and 10 heavy metal concentrations, and the relationship between ARGs and heavy metals in surface sediment from seven sites of Lake Taihu. The results showed significant correlations (p < 0.05) between sediment ARG levels, especially for tetracycline and sulfonamides (e.g., tet(A), tet(D), tet(E), tet(O), sul1, sul2 and int-1) and specific heavy metals (Fe, Mn, Cr, Cu, Zn, among others) in the Lake. In the surface sediments, heavy metals showed an interaction with resistance genes, but the strength of interaction was diminished with increasing depth. For most of the heavy metals, the concentration of elements in the top sediments was higher than that in other depths. Tetracycline resistance genes (tet(A), tet(B), tet(D), tet(E) and tet(O), β-lactam resistance genes (SHV, TEM, CTX, OXA and OXY) and sulfonamide resistance genes (sulA, sul1, sul2, sul3 and int-1) were detected. They showed a trend which inferred a statistically significant increase followed by decreases in the relative abundance of these ARGs (normalized to 16S rRNA genes) with increasing depth. This study revealed that tet(A), tet(O), TEM, OXY, int-1, sul1 and sul3 were widespread in surface sediments with high abundance, indicating that these genes deserve more attention in future work.

Comparative network analysis revealing the mechanisms of antibiotic resistance genes removal by leachate recirculation under different hydraulic loadings

The wide dissemination of antibiotic resistance is a pervasive global health threat, and landfill leachate has been an important hotspot of antibiotic resistance genes (ARGs). This study aimed to investigate the removal performance and mechanism of ARGs from leachate under different hydraulic loadings. ARGs removal efficiencies were dependent on hydraulic loadings and ARGs types other than operating time, and reactors operated with hydraulic loadings of 25 and 50 L·m^-3·d^-1 exhibited greater removal potential than 100 L·m^-3·d^-1. ARGs removal patterns varied from different subtypes, for genes sul2, tetQ, aadA1 and bla_CTX-M were eliminated from both leachate and refuse, and tetM, ermB, mefA, and strB were removed from leachate but enriched in refuse. Under different hydraulic loadings, bacterial communities shift shaped ARGs fates in leachate, but refuse had more stable antibiotic resistome and community structure. The topology comparison analysis of co-occurrence network suggested a closer hosting relationship between ARGs and genera in refuse than leachate. Furthermore, taxonomic category of host bacteria other than diversity of host genera determined the ARGs removal, and the ARGs harbored in phyla Cyanobacteria, Tenericutes and Acidobacteria were more likely to be removed. These findings can potentially foster the understanding of ARGs removal mechanism in biological treatment processes under different operating conditions.

Characterization of Bacterial Communities and Their Antibiotic Resistance Profiles in Wastewaters Obtained from Pharmaceutical Facilities in Lagos and Ogun States, Nigeria

In Nigeria, pharmaceutical wastewaters are routinely disseminated in river waters; this could be associated with public health risk to humans and animals. In this study, we characterized antibiotic resistant bacteria (ARB) and their antibiotic resistance profile as well as screening for sul1 and sul2 genes in pharmaceutical wastewater effluents. Bacterial composition of the wastewater sources was isolated on non-selective media and characterized by the polymerase chain reaction (PCR) amplification of the 16S rRNA genes, with subsequent grouping using restriction fragment length polymorphism (RFLP) and sequencing. The antibiotics sensitivity profiles were investigated using the standard disk diffusion plate method and the minimum inhibitory concentrations (MICs) of selected antibiotics on the bacterial isolates. A total of 254 bacterial strains were isolated, and majority of the isolates were identified as Acinetobacter sp., Klebsiella pneumonia, Proteus mirabilis, Enterobacter sp. and Bacillus sp. A total of 218 (85.8%) of the bacterial isolates were multidrug resistant. High MICs values were observed for all antibiotics used in the study. The result showed that 31.7%, 21.7% and 43.3% of the bacterial isolates harbored sul1, sul2, and Intl1 genes, respectively. Pharmaceuticals wastewaters are potential reservoirs of ARBs which may harbor resistance genes with possible risk to public health.

Seasonal Variations in Water-Quality, Antibiotic Residues, Resistant Bacteria and Antibiotic Resistance Genes of Escherichia coli Isolates from Water and Sediments of the Kshipra River in Central India

OBJECTIVES

To characterize the seasonal variation, over one year, in water-quality, antibiotic residue levels, antibiotic resistance genes and antibiotic resistance in Escherichia coli isolates from water and sediment of the Kshipra River in Central India.

METHODS

Water and sediment samples were collected from seven selected points from the Kshipra River in the Indian city of Ujjain in the summer, rainy season, autumn and winter seasons in 2014. Water quality parameters (physical, chemical and microbiological) were analyzed using standard methods. High-performance liquid chromatography⁻tandem mass spectrometry was used to determine the concentrations of antibiotic residues. In river water and sediment samples, antibiotic resistance and multidrug resistance patterns of isolated E. coli to 17 antibiotics were tested and genes coding for resistance and phylogenetic groups were detected using multiplex polymerase chain reaction. One-way analysis of variance (ANOVA) and Fisher tests were applied to determine seasonal variation.

RESULTS

In river water, seasonal variation was significantly associated with various water quality parameters, presence of sulfamethoxazole residues, bacteria resistant to ampicillin, cefepime, meropenem, amikacin, gentamicin, tigecycline, multidrug resistance and CTX-M-1 gene. The majority of the Extended Spectrum Beta-Lactamase (ESBL)-producing E. coli isolates from river water and sediment in all different seasons belonged to phylogenetic group A or B1.

CONCLUSIONS

Antibiotic pollution, resistance and resistance genes in the Kshipra River showed significant seasonal variation. Guidelines and regulatory standards are needed to control environmental dissemination of these “pollutants” in this holy river.

On-site removal of antibiotics and antibiotic resistance genes from leachate by aged refuse bioreactor: Effects of microbial community and operational parameters

The abuse of antibiotics has raised the prevalence of antibiotic resistance, which will pose potential risk to human health. Leachate, generated during the landfill treatment of municipal solid waste, is the important hotspot of the antibiotics and antibiotic resistance genes (ARGs), and no effective on-site treatment has been put forward for preventing ARGs dissemination. Herein, the aged refuse bioreactor was employed to remove antibiotics and ARGs from leachate, and the great removal performance was observed. For the detected antibiotics, the total removal efficiency was about 76.75%, and sulfanilamide and macrolide were removed with high efficiencies (>80%). Among the target ARGs, tetracycline and macrolide resistance genes (tetM, tetQ and ermB) were eliminated with 1.2-2.0 orders of magnitude. The occurrences of ARGs did not correlated with water quality parameters such as COD, total nitrogen, ammonia, nitrate and nitrite, but closely linked to the variations of the bacterial community structure. Redundancy analysis (RDA) indicated the significant correlations between four genera and the distribution of ARGs, which implied that these key genera (including potential pathogens) drove the ARGs removal. Furthermore, the hydraulic loading test confirmed that the aged refuse bioreactor was capable of achieving high removal efficiencies even under shock loading for the higher loading was negative for the proliferations of potential ARGs hosts. This study suggested that aged refuse bioreactor could be a promising way for antibiotics and ARGs on-site removal from leachate.

Lignin-graft-Polyoxazoline Conjugated Triazole a Novel Anti-Infective Ointment to Control Persistent Inflammation

Lignin, one of the most abundant renewable feedstock, is used to develop a biocompatible hydrogel as anti-infective ointment. A hydrophilic polyoxazoline chain is grafted through ring opening polymerization, possess homogeneous spherical nanoparticles of 10-15 nm. The copolymer was covalently modified with triazole moiety to fortify the antimicrobial and antibiofilm activities. The hydrogel was capable of down regulating the expression level of IL-1β in LPS induced macrophage cells, and to cause significant reduction of iNOS production. It supported cellular anti-inflammatory activity which was confirmed with luciferase assay, western blot, and NF-κB analysis. This novel lignin-based hydrogel tested in-vivo has shown the abilities to prevent infection of burn wound, aid healing, and an anti-inflammatory dressing material. The hydrogel reported here provides a new material platform to introduce a cost-effective and efficient ointment option after undertaking further work to look at its use in the area of clinical practice.

Environmental dissemination of antibiotic resistance genes and correlation to anthropogenic contamination with antibiotics

Antibiotic resistance is a growing problem which threatens modern healthcare globally. Resistance has traditionally been viewed as a clinical problem, but recently non-clinical environments have been highlighted as an important factor in the dissemination of antibiotic resistance genes (ARGs). Horizontal gene transfer (HGT) events are likely to be common in aquatic environments; integrons in particular are well suited for mediating environmental dissemination of ARGs. A growing body of evidence suggests that ARGs are ubiquitous in natural environments. Particularly, elevated levels of ARGs and integrons in aquatic environments are correlated to proximity to anthropogenic activities. The source of this increase is likely to be routine discharge of antibiotics and resistance genes, for example, via wastewater or run-off from livestock facilities and agriculture. While very high levels of antibiotic contamination are likely to select for resistant bacteria directly, the role of sub-inhibitory concentrations of antibiotics in environmental antibiotic resistance dissemination remains unclear. In vitro studies have shown that low levels of antibiotics can select for resistant mutants and also facilitate HGT, indicating the need for caution. Overall, it is becoming increasingly clear that the environment plays an important role in dissemination of antibiotic resistance; further studies are needed to elucidate key aspects of this process. Importantly, the levels of environmental antibiotic contamination at which resistant bacteria are selected for and HGT is facilitated at should be determined. This would enable better risk analyses and facilitate measures for preventing dissemination and development of antibiotic resistance in the environment.

Antimicrobial resistance determinants of Escherichia coli isolates recovered from some rivers in Osun State, South-Western Nigeria: Implications for public health

The inevitable development of resistance has sunk the great success achieved in the discovery of antimicrobial agents and dashed the hope of man in the recovery from infections and illnesses, as diseases and disease agents that were once thought to be controlled by antimicrobials are now re-emerging in new leagues resistance to therapy. A total of 300 PCR confirmed Escherichia coli isolates recovered from different river sources in Osun State, Nigeria were evaluated for their antibiogram profiling by the disc diffusion method and the resistant isolates were further profiled for their genotypic antimicrobial resistance determinants by polymerase chain reaction assays. Among the 20 antimicrobials selected from 10 families, resistance among sulfonamides, β-lactams and tetracyclines were found to be most frequent than phenicols and aminoglycosides with a noticeable increase in the number of multi-drug resistance ranging from three to nine antimicrobials. A total of 19 resistance determinants were assessed with their prevalence and distributions obtained as follows; [sulfonamides sulI (8%), sulII (41%)], [β-lactams; ampC 22%; blaTEM, (21%), and blaZ (18%),], [tetracyclines tetA (24%), tetB (23%), tetC (18%), tetD (78%), tetK (15%), and tetM, (10%)], [phenicols; catI (37%), catII (28%), and cmIA1 (19%)] and [aminoglycosides; aacC2 (8%), aphA1 (80%), aphA2 (80%), aadA (79%) and strA (38%)]. The Pearson chi-square exact test revealed many strong significant associations among ampC, blaTEM, blaZ and tetA genes with some determinants screened. The findings signify high increase in the prevalence of multidrug resistant E. coli isolates and resistance determinants indicating increased public health risks associated with the ingestion of waters from untreated sources. Hence, a necessity for safe water supply, provision of proper sanitation facilities and good surveillance programmes to monitor antimicrobial resistance patterns in water bodies.

An Escherichia coli strain, PGB01, isolated from feral pigeon Faeces, thermally fit to survive in pigeon, shows high level resistance to trimethoprim

In this study, of the hundred Escherichia coli strains isolated from feral Pigeon faeces, eighty five strains were resistant to one or more antibiotics and fifteen sensitive to all the antibiotics tested. The only strain (among all antibiotic-resistant E. coli isolates) that possessed class 1 integron was PGB01. The dihydrofolate reductase gene of the said integron was cloned, sequenced and expressed in E. coli JM109. Since PGB01 was native to pigeon's gut, we have compared the growth of PGB01 at two different temperatures, 42°C (normal body temperature of pigeon) and 37°C (optimal growth temperature of E. coli; also the human body temperature), with E. coli K12. It was found that PGB01 grew better than the laboratory strain E. coli K12 at 37°C as well as at 42°C. In the thermal fitness assay, it was observed that the cells of PGB01 were better adapted to 42°C, resembling the average body temperature of pigeon. The strain PGB01 also sustained more microwave mediated thermal stress than E. coli K12 cells. The NMR spectra of the whole cells of PGB01 varied from E. coli K12 in several spectral peaks relating some metabolic adaptation to thermotolerance. On elevating the growth temperature from 37°C to 42°C, susceptibility to kanamycin (both strains were sensitive to it) of E. coli K12 was increased, but in case of PGB01 no change in susceptibility took place. We have also attempted to reveal the basis of trimethoprim resistance phenotype conferred by the dfrA7 gene homologue of PGB01. Molecular Dynamics (MD) simulation study of docked complexes, PGB01-DfrA7 and E. coli TMP-sensitive-Dfr with trimethoprim (TMP) showed loss of some of the hydrogen and hydrophobic interaction between TMP and mutated residues in PGB01-DfrA7-TMP complex compared to TMP-sensitive-Dfr-TMP complex. This loss of interaction entails decrease in affinity of TMP for PGB01-DfrA7 compared to TMP-sensitive-Dfr.

Characterization of integron-mediated antimicrobial resistance among Escherichia coli strains isolated from a captive population of Amur tigers in China

The present study was undertaken to identify and characterize integrons and integrated resistance gene cassettes among multidrug resistant Escherichia coli isolates from a captive population of Amur tigers (Panthera tigris altaica) in China. In addition, the prevalence of antimicrobial resistance and class I integrons was assessed in E. coli strains (n = 61) isolated from a captive population of Amur tigers in Heilongjiang Amur Tiger Park, China. Among the isolates, 52.46% (32 of 61) were positive for intI1, but no isolates carried intI2 or intI3. Most isolates were susceptible to amoxicillin/clavulanic acid, aztreonam, and polymyxin B, while they also exhibited high incidence rates of resistance to ampicillin, doxycycline, chloramphenicol, tetracycline, and dihydrofolate reductase. Sequencing analysis revealed three gene cassettes, which encoded resistance to dihydrofolate reductase (dfrA15), dihydrofolate reductase (dfrA12), and adenyltransferase (aadA2). The gene cassette arrays dfrA15 (31%) and dfrA12-aadA2 (19%) were most prevalent among these isolates.

Exploring variation of antibiotic resistance genes in activated sludge over a four-year period through a metagenomic approach

In this study, the profiles of ARGs in activated sludge from the Shatin WWTP of Hong Kong were investigated using metagenomic analysis over a four-year period. Forty giga base pairs of metagenomic data were generated from eight activated sludge samples collected biannually at two seasons (winter and summer) from July 2007 to January 2011. A structured database of ARGs was proposed and constructed to facilitate the classification of ARGs in the collected samples from metagenomic data using a customized script. Analysis of the data showed the existence of a broad-spectrum of different ARGs, some of which have never been reported in activated sludge before. The most abundant ARGs were aminoglycoside and tetracycline resistance genes, followed by resistance genes of sulfonamide, multidrug, and chloramphenicol. Seasonal fluctuations were observed for 3 types of ARGs, that is, resistance genes of tetracycline, sulfonamide, and vancomycin. The abundances of these resistance genes were generally higher in the samples collected in the winters than the samples collected in the contiguous summer. Further analyses were carried out for the presence of subtypes of ARGs for aminoglycoside, tetracycline, and beta-lactam. The abundances of some ARGs subtypes were inconsistent with those reported in previous studies of activated sludge using the PCR approach. Statistical analyses showed that the activated sludge data sets from this study can be distinguished from other types of samples based on their ARGs profiles. Furthermore, the results of this study demonstrate that a high throughput-based metagenomic approach combined with a structured database of ARGs provides a powerful tool for a comprehensive survey of the various ARGs not only in the activated sludge of a WWTP but in other environmental samples as well. Thus, the profiling of ARGs in other ecologically important environmental matrixes may help elucidate those environmental factors contributing to the spread of ARGs.

Diverse gene cassettes in class 1 integrons of facultative oligotrophic bacteria of River Mahananda,West Bengal, India

BACKGROUND

In this study a large random collection (n=2188) of facultative oligotrophic bacteria, from 90 water samples gathered in three consecutive years (2007-2009) from three different sampling sites of River Mahananda in Siliguri, West Bengal, India, were investigated for the presence of class 1 integrons and sequences of the amplification products.

METHODOLOGY/PRINCIPAL FINDINGS

Replica plating method was employed for determining the antibiotic resistance profile of the randomly assorted facultative oligotrophic isolates. Genomic DNA from each isolate was analyzed by PCR for the presence of class 1 integron. Amplicons were cloned and sequenced. Numerical taxonomy and 16S rRNA gene sequence analyses were done to ascertain putative genera of the class 1 integron bearing isolates. Out of 2188 isolates, 1667 (76.19%) were antibiotic-resistant comprising of both single-antibiotic resistance (SAR) and multiple-antibiotic resistant (MAR), and 521 (23.81%) were sensitive to all twelve different antibiotics used in this study. Ninety out of 2188 isolates produced amplicon(s) of varying sizes from 0.15 to 3.45 KB. Chi-square (χ(2)) test revealed that the possession of class 1 integron in sensitive, SAR and MAR is not equally probable at the 1% level of significance. Diverse antibiotic-resistance gene cassettes, aadA1, aadA2, aadA4, aadA5, dfrA1, dfrA5, dfrA7, dfrA12, dfrA16, dfrA17, dfrA28, dfrA30, dfr-IIe, blaIMP-9, aacA4, Ac-6'-Ib, oxa1, oxa10 and arr2 were detected in 64 isolates. The novel cassettes encoding proteins unrelated to any known antibiotic resistance gene function were identified in 26 isolates. Antibiotic-sensitive isolates have a greater propensity to carry gene cassettes unrelated to known antibiotic-resistance genes. The integron-positive isolates under the class Betaproteobacteria comprised of only two genera, Comamonas and Acidovorax of family Comamonadaceae, while isolates under class Gammaproteobacteria fell under the families, Moraxellaceae, Pseudomonadaceae, Aeromonadaceae and Enterobacteriaceae.

CONCLUSIONS

Oligotrophic bacteria are good sources of novel genes as well as potential reservoirs of antibiotic resistance gene casettes.

Association between the presence of class 1 integrons, virulence genes, and phylogenetic groups of Escherichia coli isolates from river water

Ninety-six class 1 integron-positive and 96 integron-negative Escherichia coli isolates cultured from the water of the Warta River, Poland, were characterized for their phylogenetic group affiliation and for the presence of genes associated with virulence. Most strains belonged to phylogenetic group A, but phylogenetic group affiliation was not related with the presence of integrons. The occurrence of heat-stable toxin gene of enterotoxigenic E. coli, S fimbriae subunit gene sfaS, and siderophore receptor genes, fyuA and iutA, was associated with the presence of class 1 integrons. Moreover, virulence factor score (the total number of virulence-associated genes) was associated with the presence of integrons in groups. The results bring new insight into relations between the presence of integrons in E. coli, virulence traits, as well as phylogenetic group affiliation.

New integron gene arrays from multiresistant clinical isolates of members of the Enterobacteriaceae and Pseudomonas aeruginosa from hospitals in Malaysia

This study investigated 147 multidrug-resistant Enterobacteriaceae and Pseudomonas aeruginosa isolates from hospitalized patients in Malaysia. Class 1 integrons were the most dominant class identified (45.6%). Three isolates were shown to contain class 2 integrons (2.0%), whilst one isolate harboured both class 1 and 2 integrons. No class 3 integrons were detected in this study. In addition, the sul1 gene was amplified in 35% of isolates and was significantly associated with the presence of integrase genes in an integron structure. RFLP and DNA sequencing analyses revealed the presence of 19 different cassette arrays among the detected integrons. The most common gene cassettes were those encoding resistance towards aminoglycosides (aad) and trimethoprim (dfr). As far as is known, this study is the first to identify integron-carrying cassette arrays such as aadA2-linF, aacC3-cmlA5 and aacA4-catB8-aadA1 in the Malaysian population. Patients' age was demonstrated as a significant risk factor for the acquisition of integrons (P=0.028). Epidemiological typing using PFGE also demonstrated a clonal relationship among isolates carrying identical gene cassettes in Klebsiella pneumoniae and P. aeruginosa but not in Escherichia coli isolates.

High frequency of integrons related to drug-resistance in clinical isolates of Acinetobacter baumannii

PURPOSE

As an opportunistic pathogen, Acinetobacter baumannii causes various nosocomial infections. In recent years, the increasing cumulative infection outbreaks involving A. baumannii have appeared worldwide. In addition, a perplexing trouble for clinical treatment is a severe drug-resistance problem with A. baumannii. In this study, we investigated the drug-resistance rates and integrons' distribution in A. baumannii clinical strains in East China. Furthermore, we explored the relationship between integrons and drug resistance.

MATERIALS AND METHODS

Strains were identified using non-fermenting bacteria identification cards by Vitek-32 system. Disk-diffusion method (Kirby-Bauer) was used to judge antimicrobial sensitivity. Integrons and the gene cassettes of integrons were identified by PCR, restriction enzyme digestion and DNA sequencing.

RESULTS

Except imipenem and cefoperazone/sulbactam, the drug-resistance rates of the A. baumannii clinical isolates to other 15 kinds of antibacterials, all surpassed 30%. Of 96 A. baumannii clinical isolates, 66 strains carried class 1 integrons (no class 2 or 3 integrons were found). Overall, the drug-resistance rates in integrons-positive A. baumannii to 14 kinds of antibacterials were higher than those in integrons-negative A. baumannii. Gene sequencing showed that 9 of 12 integrons contained seven different gene cassettes (aacA4, catB3, dfrA1, blam-1, orfX, aadA1, and sat2). The cassette arrays aacA4-catB3-dfrA1 was found in five detected integrons.

CONCLUSIONS

High resistances in A. baumannii clinical strains to most common antimicrobial agents have appeared in East China, which was closely related with high frequencies class 1 integrons. A. baumannii integrons cassettes carried multi-drug-resistant gene codes. We believe that integrons cassettes gene could be taken as a marker of prognosticating A. baumannii antimicrobial resistance, but only reveal partial drug resistance profiles.

Genetic diversity analyses of class 1 integrons and their associated antimicrobial resistance genes in Enterobacteriaceae strains recovered from aquatic habitats in China

AIMS

To characterize the molecular diversity of class 1 integrons and antibiotic resistance (AR) genes of Enterobacteriaceae strains recovered from aquatic habitats in Jinan, Shandong Province, China.

METHODS AND RESULTS

Six hundred and thirty-eight antimicrobial-resistant Enterobacteriaceae isolated from wastewater were examined for class 1 integron. Of these, 293 were positive for the class 1 integrase gene intI1; among these, 34 gene cassettes and 29 AR genes were detected. Twenty-nine distinct gene cassette arrays were identified by restriction fragment length polymorphism (RFLP). Seven strains harboring novel gene cassette arrays were subjected to further study, in which antimicrobial susceptibility profiles were determined, and the presence of other AR genes outside of the integrons was assayed. Several of the resistance determinants were found to be transferable by conjugation or transformation.

CONCLUSIONS

This study established the assessment of class 1 integron and antimicrobial resistance gene patterns among environmental Enterobacteriaceae. Also, a restriction enzyme EcoRII was employed to develop a rapid and simple method for characterizing gene cassette arrays by RFLP analysis, which facilitated further study of novel gene cassette arrays.

SIGNIFICANCE AND IMPACT OF STUDY

These data not only illustrated the diversity of class 1 integron gene cassettes but also provided direct evidence that integrons mobilized gene cassettes, generating new linkages of resistance genes, and they could be integrated in gene transfer units such as conjugative plasmids to contribute to the dissemination of AR genes by horizontal gene transfer (HGT) in aquatic environments.

A multiple antibiotic and serum resistant oligotrophic strain, Klebsiella pneumoniae MB45 having novel dfrA30, is sensitive to ZnO QDs

Background

The aim of this study was to describe a novel trimethoprim resistance gene cassette, designated dfrA30, within a class 1 integron in a facultatively oligotrophic, multiple antibiotic and human serum resistant test strain, MB45, in a population of oligotrophic bacteria isolated from the river Mahananda; and to test the efficiency of surface bound acetate on zinc oxide quantum dots (ZnO QDs) as bactericidal agent on MB45.

Methods

Diluted Luria broth/Agar (10^-3) media was used to cultivate the oligotrophic bacteria from water sample. Multiple antibiotic resistant bacteria were selected by employing replica plate method. A rapid assay was performed to determine the sensitivity/resistance of the test strain to human serum. Variable region of class 1 integron was cloned, sequenced and the expression of gene coding for antibiotic resistance was done in Escherichia coli JM 109. Identity of culture was determined by biochemical phenotyping and 16S rRNA gene sequence analyses. A phylogenetic tree was constructed based on representative trimethoprim resistance-mediating DfrA proteins retrieved from GenBank. Growth kinetic studies for the strain MB45 were performed in presence of varied concentrations of ZnO QDs.

Results and conclusions

The facultatively oligotrophic strain, MB45, resistant to human serum and ten antibiotics trimethoprim, cotrimoxazole, ampicillin, gentamycin, netilmicin, tobramycin, chloramphenicol, cefotaxime, kanamycin and streptomycin, has been identified as a new strain of Klebsiella pneumoniae. A novel dfr gene, designated as dfrA30, found integrated in class 1 integron was responsible for resistance to trimethoprim in Klebsiella pneumoniae strain MB45. The growth of wild strain MB45 was 100% arrested at 500 mg/L concentration of ZnO QDs. To our knowledge this is the first report on application of ZnO quantum dots to kill multiple antibiotics and serum resistant K. pneumoniae strain.

Five novel acid-tolerant oligotrophic thiosulfate-metabolizing chemolithotrophic acid mine drainage strains affiliated with the genus Burkholderia of Betaproteobacteria and identification of two novel soxB gene homologues

Five acid-tolerant thiosulfate-metabolizing bacteria were isolated from acid mine drainage samples from Garubathan, India. 16S rRNA gene analysis revealed that the strains were affiliated with the genus Burkholderia of the class of Betaproteobacteria. Comparative 16S rRNA gene sequence analyses indicated that the strains designated as GAH1 and GAH2 produced a separate phylogenetic branch having Burkholderia pyrrocinia ATCC 51958(T) (96-98%) as the closest relative. Strains GAH4 and Burkholderia tropica Ppe8(T) (93%) branched out separately in the phylogenetic tree. Strain GMX2 was most closely related to Burkholderia cepacia ATCC 25417(T) (99.6%) and Burkholderia vietnamiensis LMG 10929(T) (99%). Strain GAH5 was most closely related to B. pyrrocinia ATCC 51958(T) (98%). Oligotrophy has been demonstrated in all AMD strains of Burkholderia spp. All strains showed chemolithoautotrophic and mixotrophic growth in thiosulfate. Furthermore, cell-free extracts of all test strains possessed thiosulfate and sulfite dehydrogenase activities. Phylogenetic analysis of the soxB gene revealed that GAH4 and GAH2 strains formed a novel cluster, Betaproteobacteria II, having highest similarity with Allochromatium vinosum, a member of Gammaproteobacteria II.

The occurrence, spatial and temporal distribution, and environmental routes of tetracycline resistance and integrase genes in Crassostrea virginica beds

Rapid spread of antibiotic resistance genes has placed them under consideration as emerging environmental contaminants. The occurrence and distribution of tetracycline resistance genes (TRG) and integrons (INT) have been monitored for 2 years in seven oyster beds located in the Altamaha River (Georgia, USA) estuary. TRG/INT profiles varied both temporally (p<0.025) and spatially between oysters and their environment (p<0.005) suggesting shifts in sources of contamination and selection of TRG/INT carriers by oysters. The latter was confirmed via analysis of tet(D) and tet(G) distribution between oysters and their environment. Uncommon class 3 integrons dominated the integrons' profile in oysters. The frequency of TRG/INT incidents correlated (R(2) ≥ 0.9) to (i) dissolved solids, (ii) potential water density, and (iii) turbidity but not to the amount of local precipitation suggesting the watershed as the dominant source of TRG/INT contamination and other than directly rainfall-caused run-offs as its environmental route.

Class 1 integronase gene and tetracycline resistance genes tetA and tetC in different water environments of Jiangsu Province, China

Class 1 integronase gene (intI1) and tetracycline resistance genes (tetA and tetC) from various environmental sites in Jiangsu Province (China) were detected using qualitative PCR (polymerase chain reaction) and quantified with SYBR Green-based qRT-PCR (quantitative real-time PCR) in this study. Qualitative PCR assays demonstrated that intI1, tetA and tetC occurred in the water environments of Taihu Lake, the Nanjing section of the Yangtze River, a sewage treatment plant (STP) in Nanjing City, and two drinking water treating bioreactors. qRT-PCR results showed that abundance of intI1 in lake water and sediments was lower than the tet genes, for a given sample site and date (P < 0.05). On a volumetric basis, lake sediments contained higher concentrations of the three genes by four to five orders of magnitude than water samples, and lake water and sediments sampled in April contained fewer copies of all the genes than the samples collected in June and August (P < 0.05). The levels of intI1, tetA and tetC in the Yangtze River water increased significantly after the river flowed through Nanjing City (P < 0.05). 94.1% integron, 97.2% tetA and 98.3% tetC were removed by the activated sludge process in the STP, and more than 80% of each gene was removed in both of the two biofilters in terms of relative concentration based on sample volume. However, on the basis of DNA mass, lower removals were obtained for both the activated sludge and biofiltration processes.

Characterization and quantification of class 1 integrons and associated gene cassettes in sewage treatment plants

Class 1 integrons and gene cassettes containing antibiotic resistance genes (ARGs) in five different sewage treatment plants (STPs) were characterized and quantified using polymerase chain reaction (PCR), sequencing, and quantitative real-time PCR (qRT-PCR) in this study. Class 1 integronase gene (intI1) was found commonly occurring in all of activated sludge samples from the five STPs, as well as in influent and effluent of two STPs at Hong Kong. One hundred and nine lactose-fermenting Enterobacteriaceae (LFE) strains were isolated from activated sludge of Shatin STP. Among them, 36 strains (33.0%) were found to carry class 1 integrons. PCR assays showed that 11 of the 36 intI1-carrying isolates harbored a common type of gene cassette array of about 1,600 bps, as well as the static genes (sulI and qacEDelta1) on class 1 integrons. This gene cassette array was found phylogenetically close to antibiotic resistance genes dfr17 and aadA5, encoding dihydrofolate reductase conferring resistance to trimethoprim and adenylyltransferase conferring resistance to spectinomycin/streptomycin, respectively. Antimicrobial susceptibility analysis demonstrated that all the 11 LFEs carrying gene cassette were multi-resistant, especially having common resistance to trimethoprim and streptomycin. qRT-PCR assay showed that genes copies of both class 1 integron and the gene cassette varied significantly among the activated sludge sampled from different STPs, at different time points or different treatment steps. More than 90% of class 1 integrons and the gene cassette were removed by activated sludge processes in two STPs, while the disinfection process removed 94% integron and 77% gene cassette in one STP.

Antibiotic resistance genes in water environment

The use of antibiotics may accelerate the development of antibiotic resistance genes (ARGs) and bacteria which shade health risks to humans and animals. The emerging of ARGs in the water environment is becoming an increasing worldwide concern. Hundreds of various ARGs encoding resistance to a broad range of antibiotics have been found in microorganisms distributed not only in hospital wastewaters and animal production wastewaters, but also in sewage, wastewater treatment plants, surface water, groundwater, and even in drinking water. This review summarizes recently published information on the types, distributions, and horizontal transfer of ARGs in various aquatic environments, as well as the molecular methods used to detect environmental ARGs, including specific and multiplex PCR (polymerase chain reaction), real-time PCR, DNA sequencing, and hybridization based techniques.

Distribution of tetracycline and streptomycin resistance genes and class 1 integrons in Enterobacteriaceae isolated from dairy and nondairy farm soils

The prevalence of selected tetracycline and streptomycin resistance genes and class 1 integrons in Enterobacteriaceae (n = 80) isolated from dairy farm soil and nondairy soils was evaluated. Among 56 bacteria isolated from dairy farm soils, 36 (64.3%) were resistant to tetracycline, and 17 (30.4%) were resistant to streptomycin. Lower frequencies of tetracycline (9 of 24 or 37.5%) and streptomycin (1 of 24 or 4.2%) resistance were observed in bacteria isolated from nondairy soils. Bacteria (n = 56) isolated from dairy farm soil had a higher frequency of tetracycline resistance genes including tetM (28.6%), tetA (21.4%), tetW (8.9%), tetB (5.4%), tetS (5.4%), tetG (3.6%), and tetO (1.8%). Among 24 bacteria isolated from nondairy soils, four isolates carried tetM, tetO, tetS, and tetW in different combinations; whereas tetA, tetB, and tetG were not detected. Similarly, a higher prevalence of streptomycin resistance genes including strA (12.5%), strB (12.5%), ant(3'') (12.5), aph(6)-1c (12.5%), aph(3'') (10.8%), and addA (5.4%) was detected in bacteria isolated from dairy farm soils than in nondairy soils. None of the nondairy soil isolates carried aadA gene. Other tetracycline (tetC, tetD, tetE, tetK, tetL, tetQ, and tetT) and streptomycin (aph(6)-1c and ant(6)) resistance genes were not detected in both dairy and nondairy soil isolates. A higher distribution of multiple resistance genes was observed in bacteria isolated from dairy farm soil than in nondairy soil. Among 36 tetracycline- and 17 streptomycin-resistant isolates from dairy farm soils, 11 (30.6%) and 9 (52.9%) isolates carried multiple resistance genes encoding resistance to tetracycline and streptomycin, respectively, which was higher than in bacteria isolated from nondairy soils. One strain each of Citrobacter freundii and C. youngae isolated from dairy farm soils carried class 1 integrons with different inserted gene cassettes. Results of this small study suggest that the presence of multiple resistance genes and class 1 integrons in Enterobacteriaceae in dairy farm soil may act as a reservoir of antimicrobial resistance genes and could play a role in the dissemination of these antimicrobial resistance genes to other commensal and indigenous microbial communities in soil. However, additional longer-term studies conducted in more locations are needed to validate this hypothesis.

Conjugation potential and class 1 integron carriage of resident plasmids in river water copiotrophs

Plasmid content was investigated in hundred copiotrophic Gram-negative river water isolates that exhibited resistance to four or more antibiotics. A total of seventy-seven isolates were found to carry plasmids of varying sizes. These isolates were primarily grouped as Pseudomonads and members of Enterobacteriaceae on the basis of physiological and biochemical tests. Fifty-six isolates that were rifampicin-sensitive and belonged to Enterobacteriaceae family were chosen as donors for the conjugal transfer assay. Eighteen of the isolates successfully transferred conjugable plasmids to the E. coli DH5alpha recipient. Countable multiple antibiotic resistant transconjugants arose readily and conjugal transfer frequency was in the range of 3.75 x 10(-6) to 1.0 x 10(-1). The most common carriage of resistances conferred by transmissible R plasmids was against ampicillin, cefotaxim and cephalexin. The residence of class 1 integrons on conjugative R plasmids was confirmed in only six transconjugants. Gene cassettes borne on the integrons were identified to be dihydrofolate reductases (dhfrs). The major concern of this study was about the copiotrophs containing self-transmissible R plasmids which may be potential reservoirs of antibiotic-resistance genes and instrumental in dissemination of the same in the environment.

Antibacterial activity of some 3-(arylideneamino)-2-phenylquinazoline-4(3H)-ones: synthesis and preliminary QSAR studies

Synthesis of ten 3-(arylideneamino)-2-phenylquinazoline-4(3H)-ones is reported. All the compounds contained a common phenyl group at the 2-position, while the substituents on the arylideneamino group were varied. The compounds were investigated for their antimicrobial activity against both Gram-positive (Staphylococcus aureus 6571 and Bacillus subtilis) and Gram-negative bacteria (Escherichia coli K12 and Shigella dysenteriae 6) using a turbidometric assay method. It was found that the incorporation of the 3-arylideneamino substituent enhanced the anti-bacterial activity of the quinazolone system. The preliminary QSAR studies were done using some computer derived property descriptors, calculated values of partition coefficients as well as usual Hammett's sigma constants and the substituent's molar refractivity.

Emergence of multidrug-resistant Salmonella enterica serovar Typhi associated with a class 1 integron carrying the dfrA7 gene cassette in Nepal

A total of 121 Salmonella enterica serovars Typhi and Paratyphi A isolated from enteric fever patients at a university hospital in Nepal between February 2004 and January 2006 were tested for their antimicrobial susceptibility. The occurrence and cassette content of integrons as well as the molecular mechanisms of resistance among the multidrug-resistant (MDR) S. Typhi were evaluated. Thirty-nine percent of the isolates were susceptible to all the antimicrobial agents tested. Seven of the S. Typhi strains were MDR. None of the 121 S. enterica isolates were resistant to ciprofloxacin, cefazolin, rifampicin or kanamycin. All MDR S. Typhi isolates contained a class 1 integron with a single cassette, dfrA7, conferring resistance to trimethoprim. Pulsed-field gel electrophoresis (PFGE) of XbaI-generated genomic restriction fragments yielded 12 different patterns. Five of the seven MDR isolates containing class 1 integrons had an identical PFGE pattern. Resistance to sulfamethoxazole, streptomycin, ampicillin, tetracycline and chloramphenicol was mediated by sul1, strA-strB, blaTEM-like, tetB and catA genes, respectively. To the best of our knowledge, this is the first report of integron-associated multidrug resistance as well as the first molecular characterisation of the mechanism of resistance of S. Typhi isolated from Nepal. This study indicates the spread of integron-associated multidrug resistance in S. Typhi in Nepal.