Conjugative plasmids in multi-resistant bacterial isolates from Indian soil

Vertical distribution characteristics and transport paths of antibiotic resistance genes in constructed wetland system

Although the migration and diffusion of antibiotic resistance genes (ARGs) in soil-plant systems have attracted much attention, the migration and diffusion characteristics between constructed wetlands and soil-plant systems differ greatly. Therefore, it is necessary to conduct research on vertical transmission and diffusion of ARGs in constructed wetlands. The vertical distribution and transmission of ARGs in constructed wetlands were explored via metagenomic analysis. The results showed that the proportion of multidrug ARGs was the largest, ranging from 24.2% to 47.5%. The shared characteristics of ARGs were similar to those of bacteria, and there were fewer unique ARGs and microbial species in mesophyll tissue. Sourcetracker analysis revealed that ARGs transfer between plants and atmosphere was bidirectional, but the diffusion of ARGs to atmosphere through plants was relatively weak. ARGs were mainly transmitted to atmosphere/surrounding environment through substrate and influent, and the contributions of substrate to ARGs in atmosphere/surrounding environment were 59.2% and 78.6%, respectively. ARGs involved in foliar attachment mainly originated from peripheral inputs. ARGs showed nonspecific selection for the host at phylum, class and order levels. These findings suggest that more attention should be given to the potential risks of ARGs in constructed wetlands, to formulate effective control and management strategies.

Horizontal transmission of a multidrug-resistant IncN plasmid isolated from urban wastewater

Wastewater treatment plants (WWTPs) are considered reservoirs of antibiotic resistance genes (ARGs). Given that plasmid-mediated horizontal gene transfer plays a critical role in disseminating ARGs in the environment, it is important to inspect the transfer potential of transmissible plasmids to have a better understanding of whether these mobile ARGs can be hosted by opportunistic pathogens and should be included in One Health's considerations. In this study, we used a fluorescent-reporter-gene based exogenous isolation approach to capture extended-spectrum beta-lactamases encoding mobile determinants from sewer microbiome samples that enter an urban water system (UWS) in Denmark. After screening and sequencing, we isolated a ∼73 Kbp IncN plasmid (pDK_DARWIN) that harboured and expressed multiple ARGs. Using a dual fluorescent reporter gene system, we showed that this plasmid can transfer into resident urban water communities. We demonstrated the transfer of pDK_DARWIN to microbiome members of both the sewer (in the upstream UWS compartment) and wastewater treatment (in the downstream UWS compartment) microbiomes. Sequence similarity search across curated plasmid repositories revealed that pDK_DARWIN derives from an IncN backbone harboured by environmental and nosocomial Enterobacterial isolates. Furthermore, we searched for pDK_DARWIN sequence matches in UWS metagenomes from three countries, revealing that this plasmid can be detected in all of them, with a higher relative abundance in hospital sewers compared to residential sewers. Overall, this study demonstrates that this IncN plasmid is prevalent across Europe and an efficient vector capable of disseminating multiple ARGs in the urban water systems.

Enzymatic Activity and Horizontal Gene Transfer of Heavy Metals and Antibiotic Resistant Proteus vulgaris from Hospital Wastewater: An Insight

Globally, the issue of microbial resistance to medicines and heavy metals is getting worse. There are few reports or data available for Proteus vulgaris (P. vulgaris), particularly in India. This investigation intends to reveal the bacteria's ability to transmit genes and their level of resistance as well. The wastewater samples were taken from several hospitals in Lucknow City, India, and examined for the presence of Gram-negative bacteria that were resistant to antibiotics and heavy metals. The microbial population count in different hospital wastewaters decreases with increasing concentrations of metal and antibiotics. Among all the examined metals, Ni and Zn had the highest viable counts, whereas Hg, Cd, and Co had the lowest viable counts. Penicillin, ampicillin, and amoxicillin, among the antibiotics, demonstrated higher viable counts, whereas tetracycline and erythromycin exhibited lower viable counts. The MIC values for the P. vulgaris isolates tested ranged from 50 to 16,00 μg/ml for each metal tested. The multiple metal resistance (MMR) index, which ranged from 0.04 to 0.50, showed diverse heavy metal resistance patterns in all P. vulgaris isolates (in the case of 2-7 metals in various combinations). All of the tested isolates had methicillin resistance, whereas the least number of isolates had ofloxacin, gentamycin, or neomycin resistance. The P. vulgaris isolates displayed multidrug resistance patterns (2-12 drugs) in various antibiotic combinations. The MAR indexes were shown to be between (0.02-0.7). From the total isolates, 98%, 84%, and 80% had urease, gelatinase, and amylase activity, whereas 68% and 56% displayed protease and beta-lactamase activity. Plasmids were present in all the selected resistant isolates and varied in size from 42.5 to 57.0 kb and molecular weight from 27.2 to 37.0 MD. The transmission of the antibiotic/metal resistance genes was evaluated between a total of 7 pairs of isolates. A higher transfer frequency (4.4 × 10-1) was observed among antibiotics, although a lower transfer frequency (1.0 × 10-2) was observed against metals in both the media from the entire site tested. According to exponential decay, the population of hospital wastewater declined in the following order across all sites: Site II > Site IV > Site III > Site I for antibiotics and site IV > site II > site I >site III for metal. Different metal and antibiotic concentrations have varying effects on the population. The metal-tolerant P. vulgaris from hospital wastewater was studied in the current study had multiple distinct patterns of antibiotic resistance. It could provide cutting-edge methods for treating infectious diseases, which are essential for managing and assessing the risks associated with hospital wastewater, especially in the case of P. vulgaris.

Does Irrigation with Treated and Untreated Wastewater Increase Antimicrobial Resistance in Soil and Water: A Systematic Review

Population growth and water scarcity necessitate alternative agriculture practices, such as reusing wastewater for irrigation. Domestic wastewater has been used for irrigation for centuries in many historically low-income and arid countries and is becoming more widely used by high-income countries to augment water resources in an increasingly dry climate. Wastewater treatment processes are not fully effective in removing all contaminants, such as antimicrobial resistant bacteria (ARB) and antimicrobial resistance genes (ARGs). Literature reviews on the impact of wastewater irrigation on antimicrobial resistance (AMR) in the environment have been inconclusive and mostly focused on treated wastewater. We conducted the first systematic review to assess the impact of irrigation with both treated or untreated domestic wastewater on ARB and ARGs in soil and adjacent water bodies. We screened titles/abstracts of 3002 articles, out of which 41 were screened in full text and 26 were included in this review. Of these, thirteen investigated irrigation with untreated wastewater, and nine found a positive association with ARB/ARGs in soil. Out of thirteen studies focused on treated wastewater, six found a positive association with ARB/ARGs while six found mixed/negative associations. Our findings demonstrate that irrigation with untreated wastewater increases AMR in soil and call for precautionary action by field workers, their families, and consumers when untreated wastewater is used to irrigate crops. The effect of irrigation with treated wastewater was more variable among the studies included in our review, highlighting the need to better understand to what extent AMR is disseminated through this practice. Future research should assess factors that modify the effect of wastewater irrigation on AMR in soil, such as the degree and type of wastewater treatment, and the duration and intensity of irrigation, to inform guidelines on the reuse of wastewater for irrigation.

Bioaerosol is an important transmission route of antibiotic resistance genes in pig farms

Although pig farms are hotspots of antibiotic resistance due to intensive use of antibiotics, little is known about the abundance, diversity and transmission of airborne antibiotic resistance genes (ARGs). This study reports that bioaerosol is an important spread route of ARGs in pig farms. ARGs, mobile genetic elements (MGEs), and bacterial communities were investigated in both air and feces samples during winter and summer. The average concentration of airborne ARGs and MGEs during winter is higher than that during summer when using the ventilation system. The tetM is identified as the predominant airborne ARG with abundance of 6.3 ± 1.2 log copies/m³. Clostridium and Streptococcus are two dominant bacteria and several opportunistic pathogens are detected in air samples. High temperature is favorable for more diverse bacterial communities, but relative humidity has negative effects. The wind speed promotes the spread of airborne ARGs. The network analysis results show the average fecal contribution to airborne bacteria is 19.9% and 59.4% during summer and winter, respectively. Horizontal gene transfer plays an important role in the dissemination of airborne ARGs during winter (77.8% possibility), while a lower possibility of 12.0% in summer.

An insight into the exploration of proliferation of antibiotic resistance genes in high-fat diet induced obesity mice

Using mice as an animal model, we first demonstrated the significant proliferation of ARGs and the change of mobile genetic elements (MGEs) in high-fat diet induced obesity (DIO) mice, which the ermB and tnpA-03 genes mostly increased, illuminating that DIO could enrich the abundance of ARGs. Additionally, Lactobacillus sharply increased in the DIO mice and might contribute to the proliferation of ARGs and dramatical change of MGEs in the HFD groups. Finally, procrustes analysis showed the explanatory variables of the MGEs, the metabolites, and the microbial communities for the ARGs accounted for 94.3%, 53.4%, and 68.1%, respectively, and implying that MGEs might be the most direct factor affecting ARGs, and microbiota could be the main driver of the proliferation of ARGs in the DIO mice.

Prevalence of multi-resistant plasmids in hospital inhalable particulate matter (PM) and its impact on horizontal gene transfer

Antibiotic resistance is exacerbated by the exchange of antibiotic resistance genes (ARGs) between microbes from diverse habitats. Plasmids are important ARGs mobile elements and are spread by horizontal gene transfer (HGT). In this study, we demonstrated the presence of multi-resistant plasmids from inhalable particulate matter (PM) and its effect on gene horizontal transfer. Three transferable multi-resistant plasmids were identified from PM in a hospital, using conjugative mating assays and nanopore sequencing. pTAir-3 contained 26 horizontal transfer elements and 10 ARGs. Importantly pTAir-5 harbored carbapenem resistance gene (blaOXA) which shows homology to plasmids from human and pig commensal bacteria, thus indicating that PM is a media for antibiotic resistant plasmid spread. In addition, 125 μg/mL PM_2.5 and PM₁₀ significantly increased the conjugative transfer rate by 110% and 30%, respectively, and augmented reactive oxygen species (ROS) levels. Underlying mechanisms were revealed by identifying the upregulated expressional levels of genes related to ROS, SOS, cell membranes, pilus generation, and transposition via genome-wide RNA sequencing. The study highlights the airborne spread of multi-resistant plasmids and the impact of inhalable PM on the horizontal transfer of antibiotic resistance.

Dissemination of antibiotic resistance genes (ARGs) via integrons in Escherichia coli: A risk to human health

With the induction of various emerging environmental contaminants such as antibiotic resistance genes (ARGs), environment is considered as a key indicator for the spread of antimicrobial resistance (AMR). As such, the ARGs mediated environmental pollution raises a significant public health concern worldwide. Among various genetic mechanisms that are involved in the dissemination of ARGs, integrons play a vital role in the dissemination of ARGs. Integrons are mobile genetic elements that can capture and spread ARGs among environmental settings via transmissible plasmids and transposons. Most of the ARGs are found in Gram-negative bacteria and are primarily studied for their potential role in antibiotic resistance in clinical settings. As one of the most common microorganisms, Escherichia coli (E. coli) is widely studied as an indicator carrying drug-resistant genes, so this article aims to provide an in-depth study on the spread of ARGs via integrons associated with E. coli outside clinical settings and highlight their potential role as environmental contaminants. It also focuses on multiple but related aspects that do facilitate environmental pollution, i.e. ARGs from animal sources, water treatment plants situated at or near animal farms, agriculture fields, wild birds and animals. We believe that this updated study with summarized text, will facilitate the readers to understand the primary mechanisms as well as a variety of factors involved in the transmission and spread of ARGs among animals, humans, and the environment.

Heavy metal and antibiotic co-resistance in Vibrio parahaemolyticus isolated from shellfish

Vibrio parahaemolyticus is a major gastroenteritis-causing pathogen in Korea. Recent studies have reported that heavy metal and antimicrobial resistance in bacteria are related. In this study, we investigated heavy metal and antimicrobial resistance in wild strains of V. parahaemolyticus. First, we isolated and characterized 38 V. parahaemolyticus strains (toxR-positive) from shellfish collected from the West Sea of Korea between May and November 2018. Antibiotic and heavy metal resistance in the 38 strains were tested by disk diffusion assay and broth dilution assay, respectively. Then, we selected seven strains that showed resistance to cobalt (Co²⁺) and copper (Cu²⁺), to examine the relationship between heavy metal resistance and antimicrobial resistance. After heavy metal (Co²⁺ and Cu²⁺) pretreatment, the seven strains exhibited increased resistance to kanamycin, streptomycin, tetracycline, and gentamycin. Likewise, antimicrobial pretreatment resulted in increased heavy metal tolerance.

Co-occurrence of Antibiotic and Heavy Metal Resistance and Sequence Type Diversity of Vibrio parahaemolyticus Isolated From Penaeus vannamei at Freshwater Farms, Seawater Farms, and Markets in Zhejiang Province, China

Vibrio parahaemolyticus is the leading cause of seafood-borne bacterial poisoning in China and is a threat to human health worldwide. The aim of this study was to assess the antibiotic resistance profiles and distribution of heavy metal resistance of V. parahaemolyticus isolates from Penaeus vannamei from freshwater farms, seawater farms, and their corresponding markets in Zhejiang, China and to assess the relationship between multidrug resistance (MDR) and multi-heavy metal resistance (MHMR). Of the 360 P. vannamei samples that we tested, 90 (25.00%) were V. parahaemolyticus positive, but the occurrence of pathogenic isolates carrying the toxin genes tdh (4.44%) and trh (3.33%) was low. None of the tested isolates harbored both the tdh and trh genes. However, antibiotic resistance profiles varied among different sampling locations, levels of resistance to the antibiotics ampicillin (76.67%) and streptomycin (74.44%) were high overall, and MDR isolates were common (40.00% of all isolates). Heavy metal resistance patterns were similar among the different sampling locations. Overall, the majority of V. parahaemolyticus isolates displayed tolerance to Cd²⁺ (60.00%), and fewer were resistant to Cu²⁺ (40.00%), Zn²⁺ (38.89%), Ni²⁺ (24.44%), Cr³⁺ (14.44%), and Co²⁺ (8.89%). In addition, 34.44% (31/90) of isolates tested in this study were found to be MHMR. Using Pearson's correlation analysis, MDR and MHMR were found to be positively correlated (P = 0.004; R = 0.759). The 18 V. parahaemolyticus isolates that were both MDR and MHMR represented 18 sequence types, of which 12 were novel to the PubMLST database, and displayed a high level of genetic diversity, suggesting that dissemination may be affected by mobile genetic elements via horizontal gene transfer. However, a low percentage of class 1 integrons without gene cassettes and no class 2 or 3 integrons were detected in the 18 MDR and MHMR isolates or in the 90 V. parahaemolyticus isolates overall. Thus, we suggest that future research focus on elucidating the mechanisms that lead to a high prevalence of resistance determinants in V. parahaemolyticus. The results of this study provide data that will support aquatic animal health management and food safety risk assessments in the aquaculture industry.

Screening of Metal and Antibiotic Resistance in Beta-lactamase Producing Coliform Bacteria from Hospital Wastewater of Northern India

AIMS

Our exploration work has uncovered the different anti-toxin/metal tolerance and patterns against the heavy metal resistant coliform microscopic organisms from the aquatic waste of the hospital. It might give new routes for the treatment of irresistible ailments particularly by coliform and critical for hazard evaluation as well as hazard management associated with the effluents of the hospital.

BACKGROUND

The higher use of pharmaceuticals, Radionuclides, and other antimicrobial solvents are the major source of metals in hospital wastewater. The hospital aquatic environment has a high content of both organic and inorganic matter with living organisms. Bacteria can resist an antimicrobial agent by producing extracellular enzymes that eliminate antibiotics and metal toxicity. In this study, we covered the existing patent literature in this area. New patents in the areas of topically applied antibiotics and agents that can potentiate the achievement of existing antibiotics may extend their helpful lifetime.

METHODS

Samples were collected from three different Departments of King George Medical University, Lucknow during the month of December to May (2015-16). Isolation and metal tolerance of coliform isolates were done on metal amended plates. The antibiotic sensitivity test was done by disc diffusion method. The plasmid DNA of bacterial isolates was done by the alkaline lysis method. The conjugation study was also performed in wastewater as well as a nutrient medium.

RESULTS

Maximum isolates demonstrated their MICs at 400, 800 and 1600 μg/ml against all the metals, respectively. The high level of resistance was observed against Methicillin (88.32%, 80.60%) followed by penicillin (75%, 76%), Cephradin (59.52%, 28.84%) and least to Gentamycine (1.92%, 5.76) in E. coli and Enterobacter, respectively. Of 70%, 78% E. coli and Enterobacter isolates produce beta-lactamase activity. Six amino acid residues namely, Glu104, Tyr105, Asn132, Asn170, Ala237, and Gly238 of the beta-lactamase were found in the common interaction with the selected drugs. Plasmid DNA size ranged between 48-58.8 kb. The conjugation experiments showed a higher transfer frequency (5.5×10-1 and 3.6×10-1) rate among antibiotics and metals tested.

CONCLUSION

The finding of this study presents a potential health problem as the predominant coliform species have increasingly been associated with outbreaks of hospital infections. It is recommended that hospital waste must be properly treated before its release into the environment.

Screening of polycyclic aromatic hydrocarbon degrading bacterial isolates from oil refinery wastewater and detection of conjugative plasmids in polycyclic aromatic hydrocarbon tolerant and multi-metal resistant bacteria

Wastewater were collected from the effluent channel in the vicinity of Mathura oil refinery, U.P. (India) and analysed for physicochemical characteristics, heavy metals as well as organic compounds including PAHs. The interaction of PAHs and heavy metals with various group of microorganisms revealed the viable count of aerobic heterotrophs, asymbiotic nitrogen fixers, actinomycetes and fungi were found to be 2.38 × 10⁶, 1.89 × 10⁴, 2.20 × 10⁴ CFU/mL and 8.76 × 10³ CFU/mL respectively. We have selected and screened 50 bacterial isolates for their resistance/tolerance to heavy metal and PAHs. Out of 25 multi-metal resistant isolates, 6 were able to tolerate PAHs at the concentration of 5000 μg/mL (50μg/disc) to naphthalene, anthracene, phenanthrene and pyrene. The PAH degradation efficiency of the isolates was assessed using spectrophotometer with 100 μg/mL of phenanthrene and observed different degree of degradation ranging from 34-66% after 96 h of incubation. One of the bacterial isolates KWB3 (identified as Enterobacter ludwigii by 16S rDNA sequencing) exhibited maximum degradation efficiency (66%) was further tested for phenanthrene degrading ability in the presence and absence of a co-substrate (glucose) in a mineral salt medium; and a number of metabolites were produced and detected by GC-MS which revealed the presence of benzocoumarin, phthalic acid, catechol and several low molecular weight compounds. The DNA derived from multi-metal and PAHs tolerant bacteria were PCR amplified using Inc specific primers and positive PCR products were obtained with oriT and trfA2 of the IncP group; indicates that these bacteria have gene-mobilizing capacity.

Antibiotic and heavy-metal resistance of Vibrio parahaemolyticus isolated from oysters in Korea

Vibrio parahaemolyticus, found frequently in oysters and other seafoods, is the most prevalent gastroenteritis-causing pathogen in Korea and other Asian countries. It is associated exclusively with the consumption of raw or improperly cooked contaminated seafood, especially oysters. In this study, we isolated and characterized 59 V. parahaemolyticus strains (toxR-positive) from May to October 2016 in shellfish-harvesting areas off the west coast of Korea. The results revealed that none of the isolates contained the tdh and trh toxicity genes. The multiple antibiotic resistance (MAR) value of most isolates was 0.32, but it was as high as 0.69 in one isolate strain. Moreover, when resistance to heavy metals was examined, the majority of the isolates displayed resistance to Ba²⁺ (98.3%), Co³⁺ (28.8%), Cd²⁺ (16.9%), and Cu²⁺ (13.6%). Interestingly our data revealed that tolerance to heavy metals was prevalent in the V. parahaemolyticus strains with more than two antibiotic resistance phenotypes.

Virulence and Antibiotic and Heavy Metal Resistance of Vibrio parahaemolyticus Isolated from Crustaceans and Shellfish in Shanghai, China

Vibrio parahaemolyticus can cause serious human seafoodborne gastroenteritis and even death. In this study, we isolated and characterized 208 V. parahaemolyticus strains from 10 species of commonly consumed crustaceans and shellfish available in fish markets in Shanghai, People's Republic of China, in 2014. Most of these aquatic species had not been detected previously. The results revealed an extremely low occurrence of pathogenic V. parahaemolyticus carrying the toxin gene trh (1.9%). However, a high level of resistance to the antibiotics ampicillin (94.2%), rifampin (93.3%), and streptomycin (77.9%) was found. Approximately 74.5% of the isolates had multidrug-resistant phenotypes. Tolerance to the heavy metals Cu(2+), Pb(2+), and Cd(2+) was detected in the majority of antibiotic resistant isolates. The resistance patterns differed depending on the tested samples. The crustaceans Penaeus monodon and Marsupenaeus japonicus harbored more antibiotic-resistant bacteria, whereas the isolates from the crustacean Litopenaeus vannamei and the shellfish Busycon canaliculatus had high tolerance to eight heavy metals tested. In contrast to the wide distribution of multidrug resistance and tolerance to heavy metals, lower percentages of plasmid DNA (22.6%) and SXT/R391-like integrative and conjugative elements (4.8%) were detected in the isolates, suggesting that V. parahaemolyticus in these aquatic species may have adopted some other molecular mechanisms that mediated the high prevalence of resistance determinants. The results of this study support the need for food safety risk assessment of aquatic products.

Antibiotic and heavy-metal resistance of Vibrio parahaemolyticus isolated from fresh shrimps in Shanghai fish markets, China

Vibrio parahaemolyticus is a causative agent of human serious seafood-borne gastroenteritis disease and even death. Shrimps, often eaten raw or undercooked, are an important reservoir of the bacterium. In this study, we isolated and characterized a total of 400 V. parahaemolyticus strains from commonly consumed fresh shrimps (Litopenaeus vannamei, Macrobrachium rosenbergii, Penaeus monodon, and Exopalaemon carinicauda) in Shanghai fish markets, China in 2013-2014. The results revealed an extremely low occurrence of pathogenic V. parahaemolyticus carrying two major toxic genes (tdh and trh, 0.0 and 0.5 %). However, high incidences of antibiotic resistance were observed among the strains against ampicillin (99 %), streptomycin (45.25 %), rifampicin (38.25 %), and spectinomycin (25.50 %). Approximately 24 % of the strains derived from the P. monodon sample displayed multidrug resistant (MDR) phenotypes, followed by 19, 12, and 6 % from the E. carinicauda, L. vannamei, and M. rosenbergii samples, respectively. Moreover, tolerance to heavy metals of Cr(3+) and Zn(2+) was observed in 90 antibiotic resistant strains, the majority of which also displayed resistance to Cu(2+) (93.3 %), Pb(2+) (87.8 %), and Cd(2+)(73.3 %). The pulsed-field gel electrophoresis (PFGE)-based genotyping of these strains revealed a total of 71 distinct pulsotypes, demonstrating a large degree of genomic variation among the isolates. The wide distribution of MDR and heavy-metal resistance isolates in the PFGE clusters suggested the co-existence of a number of resistant determinants in V. parahaemolyticus population in the detected samples. This study provided data in support of aquatic animal health management and food safety risk assessment in aquaculture industry.

The zoonotic potential of daptomycin non-susceptible enterococci

Daptomycin non-susceptible Enterococcus (DNSE) is an emerging clinical problem. Little is known about how de novo DNSE infections develop or the risk factors associated with them. Determining risk factors associated with de novo DNSE infections will aid in understanding the mechanisms of daptomycin non-susceptibility. Humans in contact with animals worldwide are at risk of carriage of multidrug-resistant bacteria. Herein, I review the scientific evidence that supports the hypothesis that transport of daptomycin non-susceptibility genes between animals and humans may be a possible mechanism for development of de novo daptomycin non-susceptibility in enterococci.

Detection and fate of antibiotic resistant bacteria in wastewater treatment plants: a review

Antibiotics are among the most successful group of pharmaceuticals used for human and veterinary therapy. However, large amounts of antibiotics are released into municipal wastewater due to incomplete metabolism in humans or due to disposal of unused antibiotics, which finally find their ways into different natural environmental compartments. The emergence and rapid spread of antibiotic resistant bacteria (ARB) has led to an increasing concern about the potential environmental and public health risks. ARB and antibiotic resistant genes (ARGs) have been detected extensively in wastewater samples. Available data show significantly higher proportion of antibiotic resistant bacteria contained in raw and treated wastewater relative to surface water. According to these studies, the conditions in wastewater treatment plants (WWTPs) are favourable for the proliferation of ARB. Moreover, another concern with regards to the presence of ARB and ARGs is their effective removal from sewage. This review gives an overview of the available data on the occurrence of ARB and ARGs and their fate in WWTPs, on the biological methods dealing with the detection of bacterial populations and their resistance genes, and highlights areas in need for further research studies.

Broad-host-range IncP-1 plasmids and their resistance potential

The plasmids of the incompatibility (Inc) group IncP-1, also called IncP, as extrachromosomal genetic elements can transfer and replicate virtually in all Gram-negative bacteria. They are composed of backbone genes that encode a variety of essential functions and accessory genes that have implications for human health and environmental bioremediation. Broad-host-range IncP plasmids are known to spread genes between distinct phylogenetic groups of bacteria. These genes often code for resistances to a broad spectrum of antibiotics, heavy metals, and quaternary ammonium compounds used as disinfectants. The backbone of these plasmids carries modules that enable them to effectively replicate, move to a new host via conjugative transfer and to be stably maintained in bacterial cells. The adaptive, resistance, and virulence genes are mainly located on mobile genetic elements integrated between the functional plasmid backbone modules. Environmental studies have demonstrated the wide distribution of IncP-like replicons in manure, soils and wastewater treatment plants. They also are present in strains of pathogenic or opportunistic bacteria, which can be a cause for concern, because they may encode multiresistance. Their broad distribution suggests that IncP plasmids play a crucial role in bacterial adaptation by utilizing horizontal gene transfer. This review summarizes the variety of genetic information and physiological functions carried by IncP plasmids, which can contribute to the spread of antibiotic and heavy metal resistance while also mediating the process of bioremediation of pollutants. Due to the location of the resistance genes on plasmids with a broad-host-range and the presence of transposons carrying these genes it seems that the spread of these genes would be possible and quite hazardous in infection control. Future studies are required to determine the level of risk of the spread of resistance genes located on these plasmids.

Accumulation of pharmaceuticals, Enterococcus, and resistance genes in soils irrigated with wastewater for zero to 100 years in central Mexico

Irrigation with wastewater releases pharmaceuticals, pathogenic bacteria, and resistance genes, but little is known about the accumulation of these contaminants in the environment when wastewater is applied for decades. We sampled a chronosequence of soils that were variously irrigated with wastewater from zero up to 100 years in the Mezquital Valley, Mexico, and investigated the accumulation of ciprofloxacin, enrofloxacin, sulfamethoxazole, trimethoprim, clarithromycin, carbamazepine, bezafibrate, naproxen, diclofenac, as well as the occurrence of Enterococcus spp., and sul and qnr resistance genes. Total concentrations of ciprofloxacin, sulfamethoxazole, and carbamazepine increased with irrigation duration reaching 95% of their upper limit of 1.4 µg/kg (ciprofloxacin), 4.3 µg/kg (sulfamethoxazole), and 5.4 µg/kg (carbamazepine) in soils irrigated for 19–28 years. Accumulation was soil-type-specific, with largest accumulation rates in Leptosols and no time-trend in Vertisols. Acidic pharmaceuticals (diclofenac, naproxen, bezafibrate) were not retained and thus did not accumulate in soils. We did not detect qnrA genes, but qnrS and qnrB genes were found in two of the irrigated soils. Relative concentrations of sul1 genes in irrigated soils were two orders of magnitude larger (3.15×10⁻³±0.22×10⁻³ copies/16S rDNA) than in non-irrigated soils (4.35×10⁻⁵±1.00×10⁻⁵ copies/16S rDNA), while those of sul2 exceeded the ones in non-irrigated soils still by a factor of 22 (6.61×10^–4±0.59×10⁻⁴ versus 2.99×10⁻⁵±0.26×10⁻⁵ copies/16S rDNA). Absolute numbers of sul genes continued to increase with prolonging irrigation together with Enterococcus spp. 23S rDNA and total 16S rDNA contents. Increasing total concentrations of antibiotics in soil are not accompanied by increasing relative abundances of resistance genes. Nevertheless, wastewater irrigation enlarges the absolute concentration of resistance genes in soils due to a long-term increase in total microbial biomass.

Vehicles, replicators, and intercellular movement of genetic information: evolutionary dissection of a bacterial cell

Prokaryotic biosphere is vastly diverse in many respects. Any given bacterial cell may harbor in different combinations viruses, plasmids, transposons, and other genetic elements along with their chromosome(s). These agents interact in complex environments in various ways causing multitude of phenotypic effects on their hosting cells. In this discussion I perform a dissection for a bacterial cell in order to simplify the diversity into components that may help approach the ocean of details in evolving microbial worlds. The cell itself is separated from all the genetic replicators that use the cell vehicle for preservation and propagation. I introduce a classification that groups different replicators according to their horizontal movement potential between cells and according to their effects on the fitness of their present host cells. The classification is used to discuss and improve the means by which we approach general evolutionary tendencies in microbial communities. Moreover, the classification is utilized as a tool to help formulating evolutionary hypotheses and to discuss emerging bacterial pathogens as well as to promote understanding on the average phenotypes of different replicators in general. It is also discussed that any given biosphere comprising prokaryotic cell vehicles and genetic replicators may naturally evolve to have horizontally moving replicators of various types.

Prediction of biosorption of total chromium by Bacillus sp. using artificial neural network

An artificial neural network (ANN) model was developed to predict the biosorption efficiency of Bacillus sp. for the removal of total chromium from aqueous solution based on 360 data sets obtained in a laboratory batch study. Experimental parameters affecting the biosorption process such as pH, contact time and initial concentration of chromium were studied. A contact time of 2 h was generally sufficient to achieve equilibrium. At optimal conditions, metal ion uptake increased with increasing initial metal ion concentration. The Freundlich model was applied to describe the biosorption isotherm. Chromium biosorption was most significantly influenced by pH, followed by the initial metal concentration of the solution. The findings indicated that the ANN model provided reasonable predictive performance (R(2) = 0.971) of chromium biosorption.

Incidence of metal and antibiotic resistance in Pseudomonas spp. from the river water, agricultural soil irrigated with wastewater and groundwater

A total of 144 isolates of Pseudomonas spp. (48 each from the Yamuna River water, wastewater irrigated soil and groundwater irrigated soil) were tested for their resistance against certain heavy metals and antibiotics. Minimum inhibitory concentrations (MICs) of Hg(2+ ), Cd(2+ ), Cu(2+ ), Zn(2+ ), Ni(2+ ), Pb(2+ ), Cr(3+ ) and Cr(6+ ) for each isolate were also determined. A maximum MIC of 200 μg/ml for mercury and 3,200 μg/ml for other metals were observed. The incidences of metal resistance and MICs of metals for Pseudomonas isolates from the Yamuna water and wastewater irrigated soil were significantly different to those of groundwater irrigated soil. A high level of resistance against tetracycline and polymyxin B (81.2%) was observed in river water isolates. However, 87.5% of Pseudomonas isolates from soil irrigated with wastewater showed resistance to sulphadiazine, whereas 79.1% were resistant to both ampicillin and erythromycin. Isolates from soil irrigated with groundwater exhibited less resistance towards heavy metals and antibiotics as compared to those of river water and wastewater irrigated soil. Majority of the Pseudomonas isolates from water and soil exhibited resistance to multiple metals and antibiotics. Resistance was transferable to recipient Escherichia coli AB2200 strains by conjugation. Plasmids were cured with the curing agent ethidium bromide and acridine orange at sub-MIC concentration.

Hexavalent chromium reduction by Bacillus sp. strain FM1 isolated from heavy-metal contaminated soil

A Cr(VI) reducing bacterial strain FM1 was isolated from heavy metal contaminated agricultural soil irrigated with tannery effluents of Jajmau, Kanpur (India), and was identified as Bacillus sp. on the basis of biochemical methods and 16S rDNA gene sequence analysis. FM1 strain was found to be resistant to some toxic heavy metals (Cr(VI), Cr(III), Cu²+, Co²+, Cd²+, Ni²+ and Zn²+) up to several fold concentrations to the normal levels occurring in highly polluted region. FM1 was resistant to very high concentration of Cr(VI) (1,000 mg/L) and completely reduced 100 mg/L Cr(VI) within 48 h. Factors (pH, temperature, initial Cr(VI) concentration) affecting Cr(VI) reduction under culture condition were also evaluated. Reduction was optimum at 37 °C and pH 8. Cr(VI) reduction was enhanced by addition of glucose. The presence of heavy metal cations, such as Cu²+, Co²+, Cd²+, Ni²+ and Zn²+ showed differential effect on reduction. Since strain FM1 could grow in the presence of significant concentrations of metals and due to high Cr(VI) reduction ability, this bacterium may be potentially applicable in Cr(VI) detoxification.

Seasonal variation of different microorganisms with nickel and cadmium in the industrial wastewater and agricultural soils

Wastewater and soil samples were collected from the industrial area of Ghaziabad City, India from January 2005 to December 2007 and were analyzed for the presence of heavy metals by atomic absorption spectrophotometry. Test samples revealed high levels of Fe, Cr, Cu, Ni, Zn, and Cd as 967.03, 34.63, 27.97, 19.7, 16.70, and 3.20 mg/L of wastewater, respectively. The concentrations of inorganic minerals were higher in the soil samples irrigated with wastewater. Total coliforms were found to be maximum (1,133x10(4) most probable number per 100 mL) during spring and summer followed by winter and postmonsoon in the wastewater samples. The microbial count in soil as well as in wastewater decreases as the metal concentration increases. The concentration 200 microg/mL of nickel and cadmium inhibits majority of the population, while, at some points, it inhibits 100% of the population. The exponential decay model for microbial count at the increasing metal concentrations indicate that asymbiotic N2 fixers were best fitted to the model. In all the seasons, the order of decline in terms of exponential decay of the population of different microbial groups in soil was asymbiotic N2 fixers>actinomycetes>fungi>aerobic heterotrophic bacteria. The different microbial groups that have different values of slope in different seasons indicate that the resistant population of microorganisms was variable with seasons.

Wastewater bacterial communities bring together broad-host range plasmids, integrons and a wide diversity of uncharacterized gene cassettes

To investigate the mobile gene pool present in wastewater environments, total community DNA was obtained from two distinct raw effluents: urban and slaughterhouse wastewaters. Bacterial community structure was evaluated by DGGE analysis of 16S rRNA gene fragments. Detection of broad-host-range plasmid sequences and integrase encoding genes was carried out through PCR and Southern hybridization. Gene cassette libraries were obtained using primers targeting consensus sequences that flank gene cassettes. Analysis of DGGE profiles revealed a complex and distinct bacterial community among effluents (similarity<25%). Despite that, All plasmid-specific sequences searched (rep for IncN, trfA for IncP-1 and oriV for IncQ and IncW) and integrase genes were present in both effluents. Gene cassettes recovered from clone libraries showed low homology with genes encoding putative enzymes involved in the metabolism of amino sugars, cell wall synthesis, motility, gene regulation, intercellular signalling and secretion pathways and in the synthesis of cellulose, folic acid and antibiotics. Additionally, in the majority of clones, no identifiable open reading frames homologues were found in the databases. According to our results, wastewater environments promote the development of bacterial communities that support and bring together different types of molecular elements that, in association, play a major role in bacterial adaptation and evolution.