High clonal diversity of multidrug-resistant and extended spectrum beta-lactamase-producing Escherichia coli in a wastewater treatment plant

Occurrence of antibiotics and antibiotic-resistant bacteria in the Lebanese polluted Litani River

Antibiotic contamination in polluted rivers is well recognized as an environmental and public health challenge. In this study, the occurrence, distribution, and ecological risk assessment of three commonly used antibiotics (amoxicillin, ciprofloxacin, and azithromycin) were assessed in the Litani River, the most important and highly polluted river in Lebanon. Physicochemical and microbiological water quality parameters including the antibiotic-resistant ones were in parallel determined in the same sites. Water samples from five sites stretching across the river upper basin were analyzed for the antibiotics under study using high-performance liquid chromatography, with both fluorometric and UV detectors post-extraction using a solid-phase method with a hydrophilic-lipophilic balance cartridges. The disc diffusion method and standardized water quality methods were used for antibiotic-resistant bacteria and water quality assessment, respectively. Amoxicillin and ciprofloxacin were found at concentrations of 250 ng/L and 107.2 ng/L, while azithromycin was not detected in any of the sites under study. Varying levels of antibiotic resistance were detected with the isolated Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) while the total coliforms showed resistance to multiple antibiotics. COD, TP, PO43-, TN, NO3-, NH4 + , E. coli, total coliform, P. aeruginosa, and Cd levels surpassed permissible levels. Correlation analysis with water quality parameters (COD, total phosphate, phosphate, total nitrogen, and cadmium) showed a significant positive correlation with ciprofloxacin (r > 0.5, p value < 0.05). Also, the resistant P. aeruginosa showed a significant positive correlation with cadmium (r > 0.5, p value < 0.05) while the resistant E. coli was positively correlated with total nitrogen, nitrate, and lead levels (r > 0.5, p value < 0.05). The ecological risk assessment revealed that all the tested antibiotics pose low risks (ecological risk quotient RQ < 0.1) except ciprofloxacin, which could pose a medium risk (0.1 < RQ < 1). Future research concerning the long-term assessment of antibiotics' residues and the identification of resistance genes in the river is recommended.

Clinically Relevant β-Lactam Resistance Genes in Wastewater Treatment Plants

Antimicrobial resistance (AMR) is one of the largest global concerns due to its influence in multiple areas, which is consistent with One Health's concept of close interconnections between people, animals, plants, and their shared environments. Antibiotic-resistant bacteria (ARB) and antibiotic-resistance genes (ARGs) circulate constantly in various niches, sediments, water sources, soil, and wastes of the animal and plant sectors, and is linked to human activities. Sewage of different origins gets to the wastewater treatment plants (WWTPs), where ARB and ARG removal efficiency is still insufficient, leading to their transmission to discharge points and further dissemination. Thus, WWTPs are believed to be reservoirs of ARGs and the source of spreading AMR. According to a World Health Organization report, the most critical pathogens for public health include Gram-negative bacteria resistant to third-generation cephalosporins and carbapenems (last-choice drugs), which represent β-lactams, the most widely used antibiotics. Therefore, this paper aimed to present the available research data for ARGs in WWTPs that confer resistance to β-lactam antibiotics, with a particular emphasis on clinically important life-threatening mechanisms of resistance, including extended-spectrum β-lactamases (ESBLs) and carbapenemases (KPC, NDM).

Magnitude of Extended-Spectrum Beta-Lactamase-Producing Gram-Negative and Beta-Lactamase-Producing Gram-Positive Pathogens Isolated from Patients in Dar es Salaam, Tanzania: A Cross-Sectional Study

Background

The worldwide emergence of antibiotic-resistant bacteria threatens to overshadow the dramatic advances in medical sciences since the discovery of antibiotics. Antibiotic resistance has rendered some antibiotics obsolete, creating a reliance on synthetic drugs. In some instances, bacteria can be resistant to all antibiotics. The problem of antibiotic resistance is eminent in resource-limited countries like Tanzania, where systematic surveillance and routine susceptibility tests are rarely conducted. Therefore, this study aimed to investigate the magnitude of beta-lactamase-producing Gram-positive pathogens and Enterobacteriaceae with extended-spectrum beta-lactamase (ESBL) in Dar es Salaam, Tanzania.

Methodology

This multi-site cross-sectional study involved three private hospitals in Dar es Salaam, Tanzania. The study was conducted between July and September 2008. Bacterial isolates were collected, identified, and subjected to antibiotic-sensitivity testing against cephalosporins, including ceftriaxone, cefuroxime and cefotaxime, and clavulanic acid, which are antibiotics readily available on the Tanzanian market at the time of the study. The microdilution method was employed to determine beta-lactamase and ESBL production per the Clinical Laboratory and Standards Institute (CLSI) protocol. Cephalosporins, including ceftriaxone, cefuroxime and cefotaxime, the beta-lactamase inhibitor, and clavulanic acid, were serially diluted with concentrations ranging from 0.011 mg/ml to 200 mg/ml. Each of these antibiotics was subjected to sensitivity tests by determining the minimum inhibitory concentrations (MIC) of the clinical isolates of bacteria using a 96-well microdilution plate. Five microliters of bacterial suspension were inoculated into each well-containing 120µl of sterile Mueller-Hinton broth before incubation overnight.

Results

A total of 111 bacterial isolates were tested. Of the 111 tested bacterial isolates, 85 (76.6%) and 26 (23.4%) were Gram-negative and Gram-positive bacteria, respectively. Fifty-six clinical isolates (50.4%) were Escherichia coli, and 13 Salmonella species (11.7%) were among the Gram-negative isolates. On the other hand, 15 (13.5%) and 11 (9.9%) Gram-positive bacteria were Staphylococcus aureus and Streptococcus species, respectively, of all isolates. The majority of these clinical isolates, 71 (64.0%), were obtained from mid-stream urine, while the remaining were from stool, vaginal secretions, blood, pus, catheter sip, and urethra. A high proportion of tested Gram-negative bacteria, 58 (68.2%), were identified as ESBL producers, and 16 (61.5%) of the Gram-positive bacteria were identified as beta-lactamase producers. Cefuroxime was the least effective, exhibiting the largest MIC (18.47 ± 22.6 mg/ml) compared to clavulanic acid alone (5.28 ± 8.0 mg/ml) and clavulanic acid-cefuroxime (5.0± 12.32 mg/ml). Of all isolates, 78.2% were sensitive to chloramphenicol. Only five isolates had MIC larger than 32.23 mg/ml as opposed to cefotaxime and ampicillin, which had more isolates in that similar MIC range.

Conclusion

There is a high proportion of beta-lactamase, particularly ESBL-producing pathogens, in Dar es Salaam, Tanzania. Therefore, regular detection of beta-lactamase and ESBL production may help detect resistance to beta-lactam antibiotics.

Persistence of Antibiotic-Resistant Escherichia coli Strains Belonging to the B2 Phylogroup in Municipal Wastewater under Aerobic Conditions

Escherichia coli is classified into four major phylogenetic groups (A, B1, B2, and D) that are associated with antibiotic resistance genes. Although antibiotic-resistant E. coli is commonly detected in municipal wastewater, little is known about the relationship between the phylogenetic groups and antibiotic-resistant E. coli in wastewater. In this study, the survival of E. coli in wastewater and the changes to the relationships between each phylogroup and the antibiotic-resistant profiles of E. coli isolates from wastewater were investigated under aerobic conditions for 14 days. The isolates were classified into the phylogroups A, B1, B2, and D or others by multiplex PCR. In addition, the susceptibility of the isolates to 11 antibiotics was assessed with the minimum inhibitory concentration (MIC) assay. While E. coli counts decreased in the wastewater with time under aerobic conditions, the prevalence of phylogroup B2 had increased to 73% on day 14. Furthermore, the MIC assay revealed that the abundance of antibiotic-resistant E. coli also increased on day 14. After batch-mixing the experiments under aerobic conditions, the surviving antibiotic-resistant E. coli included mainly multidrug-resistant and beta-lactamase-producing isolates belonging to phylogroup B2. These results suggest that the phylogroup B2 isolates that have acquired antibiotic resistance had a high survivability in the treated wastewater.

Beta-lactam resistance development during the treatment processes of municipal wastewater treatment plants

This work monitored the effect of a municipal and a village wastewater treatment plant (WWTP) technology on the fate of beta-lactam resistance genes in bacterial populations in different phases of the wastewater treatment process. In case of the municipal WWTP1, the bacteria possessing a high ampicillin resistance (minimal inhibitory concentration (MIC) values of 20 mg/mL) accumulated in the sedimentation tank, which was accompanied with a higher concentration of ampicillin in the wastewater samples (28.09 ng/L) and an increase in the relative abundance of the blaTEM gene in the bacterial population. However, an opposite trend was revealed with the blaNDM-1 gene, making the sedimentation processes of WWTP1 crucial only for the accumulation of the blaTEM gene. Similarly, the comparison with the WWTP2 showed that the accumulation of the ampicillin resistance in bacterial population probably depended on the WWTP technology and wastewater composition. Out of the four tested resistance genes (blaTEM, blaKPC, blaNDM-1, and blaOXA-48), blaTEM and blaNDM-1 genes were the only two detected in this study. According to NGS analysis of bacterial 16 S rRNA gene, Gammaproteobacteria dominated the ampicillin-resistant bacteria of the WWTP sedimentation tanks. Their relative abundance in the bacterial population also increased during the sedimentation processes in WWTP1. It could indicate the role of the bacterial taxon in ampicillin resistance accumulation in this WWTP and show that only 9.29% of the original bacterial population from the nitrification tank is involved in the documented shifts in beta-lactam resistance of the bacterial population.

Climatological and Epidemiological Conditions Are Important Factors Related to the Abundance of bla KPC and Other Antibiotic Resistance Genes (ARGs) in Wastewater Treatment Plants and Their Effluents, in an Endemic Country

Several physicochemical and season factors have been related to the abundance of antibiotic resistance genes (ARGs) in wastewater treatment plants (WWTPs), considered hotspots of bacterial resistance. However, few studies on the subject have been carried out in tropical countries endemic for resistance mechanisms such as bla_KPC. In this study, the occurrence of ARGs, particularly bla_KPC, was determined throughout a WWTP, and the factors related to their abundance were explored. In 2017, wastewater samples were taken from a WWTP in Colombia every 15 days for 6 months, and a total of 44 samples were analyzed by quantitative real-time PCR. sul1, sul2, bla_KPC, and ermB were found to be the most prevalent ARGs. A low average reduction of the absolute abundance ARGs in effluent with respect to influent was observed, as well as a greater absolute abundance of ARGs in the WWTP effluent in the rainy season. Factors such as temperature, pH, oxygen, total organic carbon (TOC), chemical oxygen demand (COD), and precipitation were significantly correlated with the absolute abundance of several of the ARGs evaluated. A generalized linear mixed-effects model analysis showed that dissolved oxygen and precipitation in the sampling day were important factors related to the absolute concentration of bla_KPC over time. In conclusion, the abundance of ARGs in the WWTP could be influenced by endemic conditions and physicochemical and climatological parameters. Therefore, it is necessary to continuously monitor clinical relevant genes in WWTPs from different global regions, even more so in low-income countries where sewage treatment is limited.

Tracking antibiotic resistance genes and class 1 integrons in Escherichia coli isolates from wastewater and agricultural fields

Considering high concentrations of multidrug-resistant bacteria and antibiotic resistance genes (ARGs) in wastewater, agricultural reuse of treated wastewater may be a public health threat due to ARG dissemination in different environmental compartments, including soil and edible parts of crops. We investigated the presence of antibiotic-resistant Escherichia coli as an indicator bacterium from secondary treated wastewater (STWW), water- or wastewater-irrigated soil and crop samples. ARGs including bla_CTX-m-32, bla_OXA-23, tet-W, sul1, cml-A, erm-B, along with intI1 gene in E. coli isolates were detected via molecular methods. The most prevalent ARGs in 78 E. coli isolates were sul1 (42%), followed by bla_CTX-m-32 (19%), and erm-B (17%). IntI1 as a class 1 integrons gene was detected in 46% of the isolates. Cml-A was detected in STWW isolates but no E. coli isolate from wastewater-irrigated soil and crop samples contained this gene. The results also showed no detection of E. coli in water-irrigated soil and crop samples. Statistical analysis showed a correlation between sul1 and cml-A with intI1. The results suggest that agricultural reuse of wastewater may contribute to the transmission of antibiotic-resistant bacteria to soil and crop. Further research is needed to determine the potential risk of ARB associated with the consumption of wastewater-irrigated crops.

Emergence and Spread of Cephalosporinases in Wildlife: A Review

Simple Summary

Antimicrobial resistance (AMR) is one of the global public health challenges nowadays. AMR threatens the effective prevention and treatment of an ever-increasing range of infections, being present in healthcare settings but also detected across the whole ecosystem, including wildlife. This work compiles the available information about an important resistance mechanism that gives bacteria the ability to inactivate cephalosporin antibiotics, the cephalosporinases (extended-spectrum beta-lactamase (ESBL) and AmpC beta-lactamase), in wildlife. Through a rigorous systematic literature review in the Web of Science database, the available publications on this topic in the wildlife sphere were analysed. The emergence and spread of cephalosporinases in wildlife has been reported in 46 countries from all continents (52% in Europe), with descriptions mainly in birds and mammals. The most widely disseminated cephalosporinases in human-related settings (e.g. CTX-M-1, CTX-M-14, CTX-M-15 and CMY-2) are also the most reported in wildlife, suggesting that anthropogenic pressure upon natural environments have a strong impact on antimicrobial resistance spread, including the dissemination of genes encoding these enzymes. Our work highlights the urgence and importance of public and ecosystem health policies, including improved surveillance and control strategies that breakdown AMR transmission chains across wildlife, as part of an integrated strategy of the One Health approach.

Abstract

In the last decade, detection of antibiotic resistant bacteria from wildlife has received increasing interest, due to the potential risk posed by those bacteria to wild animals, livestock or humans at the interface with wildlife, and due to the ensuing contamination of the environment. According to World Health Organization, cephalosporins are critically important antibiotics to human health. However, acquired resistance to β-lactams is widely distributed and is mainly mediated by extended-spectrum beta-lactamase and AmpC beta-lactamases, such as cephalosporinases. This work thus aimed to compile and analyse the information available on the emergence and dissemination of cephalosporinases in wildlife worldwide. Results suggest a serious scenario, with reporting of cephalosporinases in 46 countries from all continents (52% in Europe), across 188 host species, mainly birds and mammals, especially gulls and ungulates. The most widely reported cephalosporinases, CTX-M-1, CTX-M-14, CTX-M-15 and CMY-2, were also the most common in wild animals, in agreement with their ubiquity in human settings, including their association to high-risk clones of Escherichia coli (E. coli), such as the worldwide distributed CTX-M-15/ST131 E. coli. Altogether, our findings show that anthropogenic activities affect the whole ecosystem and that public policies promoting animal and environmental surveillance, as well as mitigation measures to avoid antimicrobial misuse and AMR spread, are urgently needed to be out in practise.

A comprehensive bibliometric overview: antibiotic resistance and Escherichia coli in natural water

The environment is the most important reservoir for both resistance mechanisms and gene transfer in biological science studies. This study gives a bibliometric overview of studies of "antibiotic resistance" and "Escherichia coli" in the field of "Agricultural and Biological Sciences" from 2015 to 2019 to assess both research trends and scholarly networks in diverse research disciplines. The two keywords of "antibiotic resistance" and "Escherichia coli" were selected to search in the Scopus database. Each review article was categorized into materials, natural waters (i.e., seawater, freshwater) and wastewater, journal name, and quartile in category of the journal, the year of publication, and the country. Bibliometric indicators and visualization maps were utilized to analyse the retrieved data quantitatively and qualitatively. A total of 1376 publications in the field of agricultural and biological sciences over the last 5 years were obtained using the keywords of antibiotic resistance and Escherichia coli. With additional keywords of freshwater and wastewater, 4 and 24 studies were obtained, respectively. Wastewater was found to be the most common working environment for the keywords of antibiotic resistance and Escherichia coli. It is also found that the studies of antibiotic resistance are mainly conducted in wastewater environments, focusing on human and food health. Working under "One Health" consisting of human, animal and agriculture, and environmental health could be the only permanent and effective approach to solving antibiotic resistance-related issues.

Distinct Resistomes and Microbial Communities of Soils, Wastewater Treatment Plants and Households Suggest Development of Antibiotic Resistances Due to Distinct Environmental Conditions in Each Environment

The use of antibiotics in humans and animals results in a release of excess antibiotic residues into the environment through wastewaters and insufficient removal in wastewater treatment plants (WWTP), leading to increasing numbers of bacteria enriched in antibiotic resistance genes (ARG). However, the potential transfer of ARG and their host bacteria between different environments remains largely unexplored. Since many factors need to be fulfilled for a transfer between different environments, we hypothesized that antibiotic resistance (ABR) is less frequently transferred between environments in the same geographical region but rather develops and clusters in each distinct environment, leading to characteristic metagenome patterns in samples of different environments. We sampled agricultural soils, a WWTP and private households and performed metagenomic analyses to evaluate differences and potential overlaps in bacterial communities and resistomes of different environments. Wastewater revealed significantly higher richness of ARG (n = 40) and mobile genetic elements (n = 52) than soil and household samples. Bacterial communities differed between the environments and antibiotic resistance factors clustered distinctly. Overall, only few overlaps of ARG between the environments were observed, leading to the conclusion that ABR predominantly develops in individual environments as caused by environmental filtering for ARG, while a transfer between different environments is less likely.

Genetic characterization of extended-spectrum β-lactamase-producing Enterobacteriaceae from a biological industrial wastewater treatment plant in Tunisia with detection of the colistin-resistance mcr-1 gene

This study evaluated the occurrence of extended-spectrum β-lactamases (ESBL) and associated resistance genes, integrons, and plasmid types, as well as the genetic relatedness of enterobacterial isolates in the wastewater treatment plant (WWTP) of La Charguia, Tunis City (Tunisia). A total of 100 water samples were collected at different points of the sewage treatment process during 2017-2019. Antimicrobial susceptibility was conducted by the disc-diffusion method. blaCTX-M, blaTEM and blaSHV genes as well as those encoding non-β-lactam resistance, the plasmid types, occurrence of class1 integrons and phylogenetic groups of Escherichia coli isolates were determined by PCR/sequencing. Genomic relatedness was determined by multi-locus sequence typing (MLST) for selected isolates. In total, 57 ESBL-producer isolates were recovered (47 E. coli, eight Klebsiella pneumoniae, 1 of the Citrobacter freundii complex and 1 of the Enterobacter cloacae complex). The CTX-M-15 enzyme was the most frequently detected ESBL, followed by CTX-M-27, CTX-M-55 and SHV-12. One E. coli isolate harboured the mcr-1 gene. The following phylogroups/sequence types (STs) were identified among ESBL-producing E. coli isolates: B2/ST131 (subclade-C1), A/ST3221, A/ST8900, D/ST69, D/ST2142, D/ST38, B1/ST2460 and B1/ST6448. High numbers of isolates harboured the class 1 integrons with various gene cassette arrays as well as IncP-1 and IncFIB plasmids. Our findings confirm the importance of WWTPs as hotspot collectors of ESBL-producing Enterobacteriaceae with a high likelihood of spread to human and natural environments.

Structure of Bacterial Community with Resistance to Antibiotics in Aquatic Environments. A Systematic Review

Aquatic environments have been affected by the increase in bacterial resistant to antibiotics. The aim of this review is to describe the studies carried out in relation to the bacterial population structure and antibiotic resistance genes in natural and artificial water systems. We performed a systematic review based on the PRISMA guideline (preferred reporting items for systematic reviews and meta-analyzes). Articles were collected from scientific databases between January 2010 and December 2020. Sixty-eight papers meeting the inclusion criteria, i.e., "reporting the water bacterial community composition", "resistance to antibiotics", and "antibiotic resistance genes (ARG)", were evaluated according to pre-defined validity criteria. The results indicate that the predominant phyla were Firmicutes and Bacteroidetes in natural and artificial water systems. Gram-negative bacteria of the family Enterobacteraceae with resistance to antibiotics are commonly reported in drinking water and in natural water systems. The ARGs mainly reported were those that confer resistance to β-lactam antibiotics, aminoglycosides, fluoroquinolones, macrolides and tetracycline. The high influence of anthropogenic activity in the environment is evidenced. The antibiotic resistance genes that are mainly reported in the urban areas of the world are those that confer resistance to the antibiotics that are most used in clinical practice, which constitutes a problem for human and animal health.

Genotypic diversity in multi-drug-resistant E. coli isolated from animal feces and Yamuna River water, India, using rep-PCR fingerprinting

Genotypic diversity among multi-drug-resistant (MDR) aquatic E. coli isolated from different sites of Yamuna River was analyzed using repetitive element PCR (rep-PCR) methods viz. ERIC-PCR and (GTG)₅-PCR and compared with the MDR animal fecal isolates. The 97 E. coli isolates belonging to different serotypes, phylogroups, and multi-drug resistance patterns were analyzed. High genetic diversity was observed by both the methods; however, (GTG)₅ typing showed higher discriminating potential. Combination of ERIC types (E1-E32) and (GTG)₅ types (G1-G46) generated 77 genotypes. The frequency of genotypes ranged from 0.013 to 0.065. The genotype composition of E. coli isolates was highly diverse at all the sampling sites across Yamuna River except at its entry site in Delhi. The sampling sites under the influence of high anthropogenic activities showed an increase in number of unique genotype isolates. These sites also exhibited high multiple antibiotic resistance (MAR) indexes (above 0.25) suggesting high risk of contamination. Principal coordinate analysis (PCoA) showed limited clustering of genotypes based on the sampling sites. The most frequent genotypes were grouped in the positive zone of both the principal coordinates (PC1 and PC2). The genotypes of most of the animal fecal isolates were unique and occupied a common space in the negative PC1 area forming a separate cluster. High genotypic diversity among the aquatic E. coli and the drain isolates, discharging the untreated municipal waste in the river, was observed, suggesting that the sewage effluents contribute substantially to contamination of this river system than animal feces. The presence of such a high diversity among the MDR E. coli isolates in the natural river systems is of great public health significance and highlights the need of an efficient surveillance system for better management of Indian natural water bodies.

High frequency of gram-negative bacilli harboring blaKPC-2 in the different stages of wastewater treatment plant: A successful mechanism of resistance to carbapenems outside the hospital settings

Wastewater treatment plants (WWTPs) are considered to be a reservoir and a source of bacterial resistance. Worryingly, the presence of carbapenem-resistant Gram-negative bacilli (CRGNB) in WWTPs has recently been reported, but there are still many research gaps regarding its emergence and impact. The distribution of CRGNB in the different stages of a WWTP in Colombia and the relationship between the physicochemical factors involved with their presence are described in this paper. Additionally, given the impact on public health, the CRGNB detected were compared with isolates previously found in hospital patients. Residual water samples were taken from five different stages of a WWTP between January and July 2017. A total of 390 GNB were isolated, and a significant frequency of CRGNB harboring bla_KPC-2 (38.2%, n = 149/390) was detected, of which 57% were Enterobacteriaceae, 41.6% Aeromonadaceae, and 1.3% Pseudomonadaceae. The Enterobacteriaceae were more frequent in the raw effluent compared to the Aeromonadaceae, which in turn were more prevalent in the recycled activated sludge and final effluent. Environmental variables such as pH, oxygen, chemical oxygen demand, and temperature were significantly correlated with the quantification of carbapenem-resistant Enterobacteriaceae (CRE) at specific points in the WWTP. Interestingly, isolated K. pneumoniae harboring bla_KPC-2 from the WWTPs were diverse and did not relate genetically to the hospital strains with which they were compared. In conclusion, these results confirm the worrying scenario of the dissemination and persistence of emerging contaminants such as CRGNB harboring bla_KPC-2, and reinforce the need to establish strategies aimed at containing this problem using multifocal interventions.

Multiple draft tubes airlift loop membrane bioreactor as an efficient system for acidic 7-amino cephalosporanic acid (7-ACA) wastewater treatment

In this study, a lab-scale multiple draft tubes airlift loop membrane bioreactor (Mt-ALMBR) was used for treating acidic 7-amino cephalosporanic acid (7-ACA) wastewater under different pHs (3.54-6.20) and hydraulic retention time (HRT) (48 h, 36 h, 24 h and 16 h). During about 200 days operation, under HRT of 48 h and pH condition about 6.0, the optimum average COD and BOD₅ removal rates were reach to 84.4 ± 2.1% and 94.9 ± 0.8%, and the highest 7-ACA removal rate also observed as 77.6%. Biodegradation, membrane rejection, hydrolysis and sludge adsorption were the four main pathways of 7-ACA removal. With the increase of pH, biodegradation, membrane rejection and hydrolysis had significant positive impacts on 7-ACA removal, while adsorption had a negative impact. Moreover, mathematical models for 7-ACA removal rate and pH were calculated to guide the operation of Mt-ALMBR. Biodegradation was the main pathway to remove 7-ACA when pH was >4.17.

Winter is coming - Impact of temperature on the variation of beta-lactamase and mcr genes in a wastewater treatment plant

Wastewater treatment plants (WWTP) play a key role in the dissemination of antibiotic resistance and analyzing the abundance of antibiotic resistance genes (ARGs) and resistant bacteria is necessary to evaluate the risk of proliferation caused by WWTPs. Since few studies investigated the seasonal variation of antibiotic resistance, this study aimed to determine the abundance of beta-lactamase and mcr genes and to characterize phenotypic resistant strains in a WWTP in Germany over the seasons. Wastewater, sewage sludge and effluent samples were collected over a one year period and analyzed using quantitative real-time PCR. Resistant strains were isolated, followed by identification and antibiotic susceptibility testing using VITEK 2. The results show a significantly higher occurrence of nearly all investigated ARGs in the wastewater compared to sewage sludge and effluent. ARG abundance and temperature showed a negative correlation in wastewater and significant differences between ARG abundance during warmer and colder seasons were determined, indicating a seasonal effect. Co-occurrence of mcr-1 and carbapenemase genes in a multi-drug resistant Enterobacter cloacae and Escherichia coli producing extended-spectrum beta-lactamase (ESBL) was determined. To the best of our knowledge, this is the first detection of mcr-1, bla_VIM and bla_OXA-48 in an ESBL-producing E. coli. Although wastewater treatment reduced the abundance of ARGs and resistant strains, a dissemination into the river might be possible because carbapenemase-, CTX-M- and mcr-1-gene harboring strains were still present in the effluent.

Genetic characterization of a novel sequence type of multidrug-resistant Citrobacter freundii strain recovered from wastewater treatment plant

A multidrug-resistant Citrobacter freundii strain R17 was isolated from a wastewater treatment plant in China. Whole-genome sequencing of strain R17 revealed a new sequence type (ST412) chromosome (length 5,124,258 bp) and an Inc FII (Yp) group plasmid pCFR17_1 (length 206,820 bp). A total of 13 antibiotic-resistance genes (ARGs) that confer resistance to eight different antibiotic groups were encoded by strain R17 and 12 of them were carried by plasmid pCFR17_1. These data and analysis suggest that the environment-derived C. freundii strains may serve as potential sources of ARGs and highlight the need of further surveillance of this bacteria in the future.