Heavy Metal Susceptibility of Escherichia coli Isolated from Urine Samples from Sweden, Germany, and Spain

Bacterial heavy metal resistance related to environmental conditions

Contaminated water bodies such as rivers provide reservoirs for bacterial resistance. This field study tested the water quality and the bacterial resistance to heavy metals of Qishan River water pollution. Wastewater discharged to environmental surface waters is a major pathway of heavy metals and heavy metal-resistant bacteria. Contaminated water bodies such as rivers provide reservoirs for bacterial resistance. This field study tested the water quality and bacterial resistance to heavy metals of Qishan River water pollution. Guided by our research hypothesis that an overall increase in downstream heavy metal resistance levels was following an increase in human settlements were eight sites sampled along the Qishan River. These were situated upstream and downstream to the confluence of the Qishan River with the Kaoping River. In the laboratory bacterial heavy metal resistance was bio-assayed by disk diffusion and micro-dilution with six widely used heavy metals. The comparison of bacterial resistance was among Qishan River upstream sites (sites 1-6) and downstream sites (sites 7-9). Multi-drug-resistant bacteria and co-resistance against heavy metals and antibacterials appeared at site 8. This research discusses the correlation between environmental factors, and antibacterial and heavy metal resistance. The results provide stakeholders and authorities responsible for environmental pollution with a reference for risk assessment and management of bacterial resistance.

Limitations in predicting reduced susceptibility to third generation cephalosporins in Escherichia coli based on whole genome sequence data

Prediction of antibiotic resistance from whole genome sequence (WGS) data has been proposed. However, the performance of WGS data analysis for this matter may be influenced by the resistance mechanism's biology. This study compared traditional antimicrobial susceptibility testing with whole genome sequencing for identification of extended-spectrum beta-lactamases (ESBL) in a collection of 419 Escherichia coli isolates. BLASTn-based prediction and read mapping with srst2 gave matching results, and in 381/419 (91%) isolates WGS was congruent with phenotypic testing. Incongruent results were grouped by potential explanations into biological-related and sequence analysis-related results. Biological-related explanations included weak ESBL-enzyme activity (n = 4), inconclusive phenotypic ESBL-testing (n = 4), potential loss of plasmid during subculturing (n = 7), and other resistance mechanisms than ESBL-enzymes (n = 2). Sequence analysis-related explanations were cut-off dependency for read depth (n = 5), too stringent (n = 3) and too loose cut-off for nucleotide identity and coverage (n = 13), respectively. The results reveal limitations of both traditional antibiotic susceptibility testing and sequence-based resistance prediction and highlight the need for evidence-based standards in sequence analysis.

High-resolution temporal profiling of E. coli transcriptional response

Understanding how cells dynamically adapt to their environment is a primary focus of biology research. Temporal information about cellular behavior is often limited by both small numbers of data time-points and the methods used to analyze this data. Here, we apply unsupervised machine learning to a data set containing the activity of 1805 native promoters in E. coli measured every 10 minutes in a high-throughput microfluidic device via fluorescence time-lapse microscopy. Specifically, this data set reveals E. coli transcriptome dynamics when exposed to different heavy metal ions. We use a bioinformatics pipeline based on Independent Component Analysis (ICA) to generate insights and hypotheses from this data. We discovered three primary, time-dependent stages of promoter activation to heavy metal stress (fast, intermediate, and steady). Furthermore, we uncovered a global strategy E. coli uses to reallocate resources from stress-related promoters to growth-related promoters following exposure to heavy metal stress.

Oxidative stress induced by sub-lethal exposure to copper as a mediator in development of bacterial resistance to antibiotics

Limited information exists on how bacterial resistance to antibiotics is acquired and altered in response to short-term metal stress, and what the prevailing pathways are. Here the precursor mechanisms of development of bacterial antibiotic resistance mediated by oxidative stress induce under sub-lethal Cu²⁺ exposure were explored. The results showed that the overall level of antibiotic resistance in wild-type Escherichia coli and antibiotic-resistant E. coli was enhanced under 4 and 20 mg/L Cu²⁺ exposure, as demonstrated by the 2- to 8-fold increase in minimum inhibitory concentration (MIC). The MIC correlated with the increase of the cellular ROS generation and the enhancement of the antioxidant enzyme activity (p < 0.05), suggesting that changes in antibiotic resistance under sub-lethal Cu²⁺ exposure could be associated with oxidative stress. Likewise, enhanced cell membrane permeability and an increase in the number of bacteria entering the viable but non culturable (VBNC) state contributed to bacterial resistance to antibiotics. Moreover, the variance partitioning analysis demonstrated that the alterations of the antibiotic resistance phenotype of wild-type E. coli was mainly caused by oxidative stress-mediated increase in cell membrane permeability and entry into the VBNC state. The development of antibiotic resistance in resistant E. coli was primarily attributed to changes in the abundance and horizontal transfer ability of its antibiotic resistance genes, both of which contributed up to 20 %. Taken together the results allowed to propose a conseptual scheme on developing bacterial antibiotic resistance mediated by oxidative stress under sub-lethal Cu²⁺ exposure. This result provided a strong basis for reduction of early bacterial resistance.

Effects of chronic exposure to arsenic on the fecal carriage of antibiotic-resistant Escherichia coli among people in rural Bangladesh

Antibiotic resistance is a leading cause of hospitalization and death worldwide. Heavy metals such as arsenic have been shown to drive co-selection of antibiotic resistance, suggesting arsenic-contaminated drinking water is a risk factor for antibiotic resistance carriage. This study aimed to determine the prevalence and abundance of antibiotic-resistant Escherichia coli (AR-Ec) among people and drinking water in high (Hajiganj, >100 μg/L) and low arsenic-contaminated (Matlab, <20 μg/L) areas in Bangladesh. Drinking water and stool from mothers and their children (<1 year) were collected from 50 households per area. AR-Ec was detected via selective culture plating and isolates were tested for antibiotic resistance, arsenic resistance, and diarrheagenic genes by PCR. Whole-genome sequencing (WGS) analysis was done for 30 E. coli isolates from 10 households. Prevalence of AR-Ec was significantly higher in water in Hajiganj (48%) compared to water in Matlab (22%, p <0.05) and among children in Hajiganj (94%) compared to children in Matlab (76%, p <0.05), but not among mothers. A significantly higher proportion of E. coli isolates from Hajiganj were multidrug-resistant (83%) compared to isolates from Matlab (71%, p <0.05). Co-resistance to arsenic and multiple antibiotics (MAR index >0.2) was observed in a higher proportion of water (78%) and child stool (100%) isolates in Hajiganj than in water (57%) and children (89%) in Matlab (p <0.05). The odds of arsenic-resistant bacteria being resistant to third-generation cephalosporin antibiotics were higher compared to arsenic-sensitive bacteria (odds ratios, OR 1.2-7.0, p <0.01). WGS-based phylogenetic analysis of E. coli isolates did not reveal any clustering based on arsenic exposure and no significant difference in resistome was found among the isolates between the two areas. The positive association detected between arsenic exposure and antibiotic resistance carriage among children in arsenic-affected areas in Bangladesh is an important public health concern that warrants redoubling efforts to reduce arsenic exposure.

Beta-Lactam-Resistant Enterobacterales Isolated from Landfill Leachates

Antibiotic resistance is one of the main challenges worldwide due to the high morbidity and mortality caused by infections produced by resistant bacteria. In Colombia, this problem has been studied mainly from the clinical perspective; however, it is scarcely studied in the leachates produced in landfills. The objective of this study was to detect, identify and determine the antibiotic sensitivity profile of Enterobacterales isolated from a leachate treatment plant located in Cali, Colombia. Detection was performed using selective culture media, bacterial identification using Matrix-Assisted Laser Desorption/Ionization-Time-Of-Flight (MALDI-TOF, bioMérieux) and by sequencing the gene coding for the 16S ribosomal RNA subunit when discrepancies were observed between phenotypic characteristics and MALDI-TOF. Antibiotic sensitivity profiling was determined using the automated VITEK®2 system (bioMérieux). Twenty-one isolates were obtained, of which Klebsiella pneumoniae was the most frequent (23.8%), and 34% of the isolates showed decreased sensitivity to beta-lactam antibiotics such as cefoxitin, ampicillin/sulbactam and piperacillin/tazobactam. These findings suggest that leachates from landfills could be a reservoir of pathogenic bacteria carrying antibiotic resistance determinants, so periodic microbiological characterization of these effluents should be performed, promoting the One Health approach.

The Effect of Heavy Metals on Conjugation Efficiency of an F-Plasmid in Escherichia coli

Conjugation, the process by which conjugative plasmids are transferred between bacteria, is regarded as a major contributor to the spread of antibiotic resistance, in both environmental and clinical settings. Heavy metals are known to co-select for antibiotic resistance, but the impact of the presence of these metals on conjugation itself is not clear. Here, we systematically investigate the impact that five heavy metals (arsenic, cadmium, copper, manganese, and zinc) have on the transfer of an IncF conjugative plasmid in Escherichia coli. Our results show that two of the metals, cadmium and manganese, have no significant impact, while arsenic and zinc both reduce conjugation efficiency by approximately 2-fold. Copper showed the largest impact, with an almost 100-fold decrease in conjugation efficiency. This was not mediated by any change in transcription from the major Py promoter responsible for transcription of the conjugation machinery genes. Further, we show that in order to have this severe impact on the transfer of the plasmid, copper sulfate needs to be present during the mating process, and we suggest explanations for this.

Peptidoglycan compositional analysis of Mycobacterium smegmatis using high-resolution LC-MS

Peptidoglycan (PG) is the exoskeleton of bacterial cells and is required for their viability, growth, and cell division. Unlike most bacteria, mycobacteria possess an atypical PG characterized by a high degree of unique linkages and chemical modifications which most likely serve as important determinants of virulence and pathogenesis in mycobacterial diseases. Despite this important role, the chemical composition and molecular architecture of mycobacterial PG have yet to be fully determined. Here we determined the chemical composition of PG from Mycobacterium smegmatis using high-resolution liquid chromatography-mass spectrometry. Purified cell walls from the stationary phase were digested with mutanolysin and compositional analysis was performed on 130 muropeptide ions that were identified using an in silico PG library. The relative abundance for each muropeptide ion was measured by integrating the extracted-ion chromatogram. The percentage of crosslink per PG subunit was measured at 45%. While both 3→3 and 4→3 transpeptide cross-linkages were found in PG dimers, a high abundance of 3→3 linkages was found associated with the trimers. Approximately 43% of disaccharides in the PG of M. smegmatis showed modifications by acetylation or deacetylation. A significant number of PG trimers are found with a loss of 41.00 amu that is consistent with N-deacetylation, whereas the dimers show a gain of 42.01 amu corresponding to O-acetylation of the PG disaccharides. This suggests a possible role of PG acetylation in the regulation of cell wall homeostasis in M. smegmatis. Collectively, these data report important novel insights into the ultrastructure of mycobacterial PG.

Isolation, Identification, and Characterization of an Efficient Siderophore Producing Bacterium From Heavy Metal Contaminated Soil

An efficient siderophore producing strain, YQ9, was isolated from heavy metal contaminated soil and identified as Burkholderia vietnamiensis. To the best of our known, the strain owns the highest siderophore producing capacity among genus Burkholderia with 96.6% siderophore unit. Moreover, B. vietnamiensis YQ9 has good adaptability to different pH values, temperatures, NaCl, and Fe³⁺ concentrations. In addition, the minimum inhibitory concentration (MIC) of heavy metals and antibiotics were also tested. It was found that the MIC values of strain YQ9 to several major soil heavy metal pollutants, such as Pb²⁺, Zn²⁺, Cu²⁺, and Cd²⁺ reached 3000, 5000, 4500, and 1000 μmol·L^-1, respectively. And YQ9 was sensitive to 4 of 8 test antibiotics, including rifampicin, kanamycin, doxycycline hyclate, and gentamicin (25, 25, 30, and 30 μg·mL^-1, respectively). Strain YQ9 also owns the ability to produce indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and dissolve phosphorus. The IAA production capacity was 6.93 mg·L^-1, the ACC deaminase activity was 8.71 μmol α-KA·(h·mg)^-1, and the phosphorus dissolving capacity of YQ9 was 104.05 mg·L^-1. The traits were excellent, and the strain was qualified as a candidate for microbial reinforcement of phytoremediation in soil contaminated by heavy metals.

Heavy metal resistance of marine bacteria on the sediments of the Black Sea

The Black Sea is unfortunately globally established as a highly polluted sea, with contaminants from various sources polluting its marine sediments. This study aimed at analyzing heavy metal resistance levels by heterotrophic bacteria colonizing marine sediments across Black Sea shores within Turkey. Twenty-nine bacterial samples from marine sediments were investigated through exposure to sixteen heavy metal salts using the microdilution method. The minimum inhibitory concentration values for bacterial colonies within such marine sediment samples ranged from <0.97 mM/L to >1000 mM/L. Trough and peak minimum inhibitory concentration values were determined at <0.17 mg/mL and > 331 mg/mL. Peak tolerated and peak toxic heavy metals were identified as iron and cadmium, respectively. Resistance ratios were also obtained in this study. Bacillus wiedmannii was identified as the most resistant bacterial population when exposed to heavy metal salts. This study shows occurrence of heavy metal resistant bacteria within Black Sea sediments.

Characterization of Silver Resistance and Coexistence of sil Operon with Antibiotic Resistance Genes Among Gram-Negative Pathogens Isolated from Wound Samples by Using Whole-Genome Sequencing

Purpose

Methods

Results

Conclusion

Extraintestinal Pathogenic Escherichia coli: Beta-Lactam Antibiotic and Heavy Metal Resistance

Multiple-antibiotic-resistant (MAR) extra-intestinal pathogenic Escherichia coli (ExPEC) represents one of the most frequent causes of human nosocomial and community-acquired infections, whose eradication is of major concern for clinicians. ExPECs may inhabit indefinitely as commensal the gut of humans and other animals; from the intestine, they may move to colonize other tissues, where they are responsible for a number of diseases, including recurrent and uncomplicated UTIs, sepsis and neonatal meningitis. In the pre-antibiotic era, heavy metals were largely used as chemotherapeutics and/or as antimicrobials in human and animal healthcare. As with antibiotics, the global incidence of heavy metal tolerance in commensal, as well as in ExPEC, has increased following the ban in several countries of antibiotics as promoters of animal growth. Furthermore, it is believed that extensive bacterial exposure to heavy metals present in soil and water might have favored the increase in heavy-metal-tolerant microorganisms. The isolation of ExPEC strains with combined resistance to both antibiotics and heavy metals has become quite common and, remarkably, it has been recently shown that heavy metal resistance genes may co-select antibiotic-resistance genes. Despite their clinical relevance, the mechanisms underlining the development and spread of heavy metal tolerance have not been fully elucidated. The aim of this review is to present data regarding the development and spread of resistance to first-line antibiotics, such as beta-lactams, as well as tolerance to heavy metals in ExPEC strains.

Copper Homeostatic Mechanisms and Their Role in the Virulence of Escherichia coli and Salmonella enterica

Copper is an essential micronutrient that also exerts toxic effects at high concentrations. This review summarizes the current state of knowledge on copper handling and homeostasis systems in Escherichia coli and Salmonella enterica. We describe the mechanisms by which transcriptional regulators, efflux pumps, detoxification enzymes, metallochaperones, and ancillary copper response systems orchestrate cellular response to copper stress. E. coli and S. enterica are important pathogens of humans and animals. We discuss the critical role of copper during killing of these pathogens by macrophages and in nutritional immunity at the bacterial-pathogen-host interface. In closing, we identify opportunities to advance our understanding of the biological roles of copper in these model enteric bacterial pathogens.

Co-transfer of plasmid-encoded bla carbapenemases genes and mercury resistance operon in high-risk clones of Klebsiella pneumoniae

Carbapenemase-producing Klebsiella pneumoniae (CP-Kp) is a real global health threat. Environmental reservoirs of resistance gene determinats, such as effluents of hospital wastewaters, are acquiring increased relevance in the selection of plasmid-encoded carbapenemase genes. The presence of Hg in environmental reservoirs may exert a positive selective pressure on tolerant bacteria, favoring the co-transfer of carbapenemase genes and mer operons. In our study, 63 CP-Kp isolates were screened for mer operons by whole genome sequencing (MySeq). Conjugation assays were performed with 24 out of 63 CP-Kp isolates harboring the mer operon. Ten transconjugants (Tc-Kp) were selected with Hg. Plasmid DNA of Tc-Kp was extracted and sequenced using single-molecule real-time (SMRT) technology (PacBio, Sequel II system) with later annotation. Plasmid analysis revealed that Tc-Kp from bla_IMP-like (n = 3) showed a single plasmid belonging to IncC group with two complete mer operon next to bla_IMP-like. Tc-Kp from bla_VIM-1 (n = 2) harbored two plasmids, one with bla_VIM-1 in an IncL, and mer operon was in an IncFIB plasmid. Tc-Kp from bla_OXA-48-like (n = 5) showed 2 plasmids. bla_OXA-48-like was found in an IncL plasmid, whereas mer operon was (i) in an IncR plasmid associated with bla_CTX-M-15 in 3 Tc-Kp-OXA-48-like, (ii) in an IncC plasmid associated with bla_CMY-2 in 1 Tc-Kp-OXA-48-like, (iii) and in an IncFIB plasmid associated with bla_CTX-M-15 in 1 Tc-Kp-OXA-48-like. This is, to our knowledge, the first study to describe in K. pneumoniae producing plasmid-encoded carbapenemase, the potential impact of Hg in the co-transfer of mer operons and carbapenemase genes located in the same or different plasmids. KEY POINTS: • Environmental reservoirs are playing an important role in the selection of carbapenemase genes. • Conjugation assays, selecting with Hg, obtained 10 transconjugants with carbapenemase genes. • mer operons were located in the same or different plasmids than carbapenemase genes.

Staphylococcus saprophyticus Causing Infections in Humans Is Associated with High Resistance to Heavy Metals

Staphylococcus saprophyticus is a common pathogen of the urinary tract, a heavy metal-rich environment, but information regarding its heavy metal resistance is unknown. We investigated 422 S. saprophyticus isolates from human infection and colonization/contamination, animals, and environmental sources for resistance to copper, zinc, arsenic, and cadmium using the agar dilution method. To identify the genes associated with metal resistance and assess possible links to pathogenicity, we accessed the whole-genome sequence of all isolates and used in silico and pangenome-wide association approaches. The MIC values for copper and zinc were uniformly high (1,600 mg/liter). Genes encoding copper efflux pumps (copA, copB, copZ, mco, and csoR) and zinc transporters (zinT, czrAB, znuBC, and zur) were abundant in the population (20 to 100%). Arsenic and cadmium showed various susceptibility levels. Genes encoding the ars operon (arsRDABC), an ABC transporter and a two-component permease, were linked to resistance to arsenic (MICs ≥ 1,600 mg/liter; 14% [58/422]; P < 0.05). At least three cad genes (cadA or cadC and cadD-cadX or czrC) and genes encoding multidrug efflux pumps and hyperosmoregulation in acidified conditions were associated with resistance to cadmium (MICs ≥ 200 mg/liter; 20% [85/422]; P < 0.05). These resistance genes were frequently carried by mobile genetic elements. Resistance to arsenic and cadmium were linked to human infection and a clonal lineage originating in animals (P < 0.05). Altogether, S. saprophyticus was highly resistant to heavy metals and accumulated multiple metal resistance determinants. The highest arsenic and cadmium resistance levels were associated with infection, suggesting resistance to these metals is relevant for S. saprophyticus pathogenicity.

Distribution characteristics and potential risks of heavy metals and antimicrobial resistant Escherichia coli in dairy farm wastewater in Tai'an, China

Heavy metals and antimicrobial resistant bacteria in livestock and poultry environments can cause declines in production and significant economic losses, leading to potential environmental and public health issues. In this study, the heavy metal pollution status of livestock breeding water bodies in the Dawen river basin of Shandong Province in China was evaluated, and a total of 10 heavy metals were measured. In addition, antimicrobial susceptibility tests were conducted for Escherichia coli strains isolated from the water samples. The results showed that among all the metals, copper, zinc, and iron were detected at each sampling point, followed by nickel (detection rate of 95.74%), arsenic (detection rate of 89.36%), selenium (detection rate of 68.09%), lead (detection rate of 27.66%), and mercury (detection rate of 12.77%). Cadmium and hexavalent chromium were not detected. The contents of nine heavy metals were below the existing water standard values in China, whereas the iron pollution index in the water body in the study area was large and may pose a potential risk. A total of 17 E. coli isolates showed different resistance to β-lactams, aminoglycosides, tetracyclines, quinolone antibiotics and chloramphenicol, but were mainly resistant to β-lactams and tetracyclines. The detection rate of the tetA resistance gene was relatively high, indicating the overuse of cephalosporins and tetracyclines. The results of the present study might provide evidence of metal pollution and theoretical basis on the treatment of colibacillosis in the livestock industries.

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

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

Escherichia coli strains of chicken and human origin: Characterization of antibiotic and heavy-metal resistance profiles, phylogenetic grouping, and presence of virulence genetic markers

Multiple antibiotic-resistant extra-intestinal pathogenic Escherichia coli (ExPEC) strains represent a serious health care problem both for poultry and humans. Recently isolates with combined resistance to both antibiotics and heavy metals have been increased worldwide, with growing concern for possible co-selection of antimicrobial resistant genes. In the present study we characterized, at a phenotypic and genetic level, 80 E. coli isolates: forty independent isolates were collected from manure samples of healthy chickens and 40 from independent human extra-intestinal infections (ExPEC strains). The results obtained indicated that i) compared to chicken, human isolates presented a broader spectrum of antibiotic resistance and virulence potentials; ii) although at a lower extent, ExPEC-associated virulence genes were also present in chicken isolates, suggesting they may be potentially pathogens; iii) that arsenic (As) and zinc (Zn) tolerance genetic determinants were significantly more prevalent among chicken and human isolates respectively, while those responsible for tolerance to cadmium (Cd), silver (Ag) and copper (Cu) were equally distributed among the two groups of strains; iv) a very strong correlation was found between chicken gentamicin (GM) resistance and cadmium (Cd) tolerance. Elucidating the role of heavy metals in the selection and spread of highly pathogenic E. coli strains (co-selection) is of primary importance to lower the potential risk of infections in poultry and humans. The control of bacterial zoonotic agents, that commonly occur in livestock and that may be transmitted, directly or via the food chain, to human populations, could be of relevant interest.

Distribution of class 1 integrons in historic and contemporary collections of human pathogenic Escherichia coli

Integrons play a major role in the evolution and spread of antimicrobial resistance in human pathogens, including Escherichia coli. This study describes the occurrence of class 1 integrons in human pathogenic E. coli, in three isolate collections involving three periods from the last 100 years (i) the Murray collection (n = 58 bacteria isolated from the 1910s to 1940s); (ii) the E. coli reference (ECOR) collection (n = 37 isolates mainly from the 1980s); and (iii) a recently assembled collection (n = 88 isolates obtained in 2016). High-quality whole genome sequences (WGSs) were available for all isolates. Integrons were detected in the WGSs with the program IntegronFinder and the results compared with three established methods: (i) polymerase chain reaction detection of the integrase gene; (ii) BLAST searching using draft genomes; and (iii) mapping of short reads. No integrons were found in any of the Murray Collection isolates; however, integrons were present in 3% of the isolates from ECOR collection, assembled in the 1980s, and 26% of the isolates from the 2010s. Similarly, antimicrobial resistance determinants were not present in the Murray Collection isolates, whereas they were present in 19% of the ECOR Collection isolates and in 55% of the isolates obtained in during the 2010s.

Removal of Cu(II) from aqueous solutions imparted by a pectin-based film: Cytocompatibility, antimicrobial, kinetic, and equilibrium studies

To obtain pectin-based films is challenging due to the aqueous instability of polyelectrolyte mixtures. We overcome this issue by blending chitosan to pectin of high O-methoxylation degree (56%), followed by solvent evaporation. A durable film containing 74 wt% pectin content was produced and used as an adsorbent material toward Cu(II) ions. Kinetic and adsorption equilibrium studies showed that the pseudo-second-order and Sips isotherm models adjusted well to the experimental data, respectively. Langmuir isotherm indicated a maximum adsorption capacity (q_m) for Cu(II) removal of 29.20 mg g^-1. Differential scanning calorimetry, contact angle measurements, and X-ray photoelectron spectroscopy confirm the adsorption. The chemisorption plays an essential role in the process; thereby, the film reusability is low. After adsorption, the cytocompatible film/Cu(II) pair prevents the proliferation of Escherichia coli.

Novel partners with colistin to increase its in vivo therapeutic effectiveness and prevent the occurrence of colistin resistance in NDM- and MCR-co-producing Escherichia coli in a murine infection model

Objectives

The emergence of NDM- and MCR-1-co-producing Escherichia coli has compromised the use of carbapenems and colistin, which are critically important in clinical therapy, and represents a severe threat to public health worldwide. Here, we demonstrate synergism of colistin combined with existing antibiotics as a potential strategy to overcome XDR E. coli co-harbouring NDM and MCR-1 genes.

Methods

To comprehensively evaluate their combined activity, antibiotic combinations were tested against 34 different E. coli strains carrying both NDM and MCR-1 genes. Antibiotic resistance profiles and molecular characteristics were investigated by susceptibility testing, PCR, MLST, S1-PFGE and WGS. Antibiotic synergistic efficacy was evaluated through in vitro chequerboard experiments and dose-response assays. A mouse model was used to confirm active combination therapies. Additionally, combinations were tested for their ability to prevent high-level colistin-resistant mutants (HLCRMs).

Results

Combinations of colistin with rifampicin, rifabutin and minocycline showed synergistic activity against 34 XDR NDM- and MCR-1-co-producing E. coli strains, restoring, in part, susceptibility to both colistin and the partnering antibiotics. The therapeutic effectiveness of colistin combined with rifampicin or minocycline was demonstrated in a mouse model. Furthermore, colistin plus rifampicin showed significant activity in preventing the occurrence of HLCRMs.

Conclusions

The synergism of colistin in combinations with rifampicin, rifabutin or minocycline offers viable therapeutic alternatives against XDR NDM- and MCR-positive E. coli.

Cwp22, a novel peptidoglycan cross-linking enzyme, plays pleiotropic roles in Clostridioides difficile

Clostridioides difficile is a Gram-positive, spore-forming, toxin-producing anaerobe pathogen, and can induce nosocomial antibiotic-associated intestinal disease. While production of toxin A (TcdA) and toxin B (TcdB) contribute to the main pathogenesis of C. difficile, adhesion and colonization of C. difficile in the host gut are prerequisites for disease onset. Previous cell wall proteins (CWPs) were identified that were implicated in C. difficile adhesion and colonization. In this study, we predicted and characterized Cwp22 (CDR20291_2601) from C. difficile R20291 to be involved in bacterial adhesion based on the Vaxign reverse vaccinology tool. The ClosTron-generated cwp22 mutant showed decreased TcdA and TcdB production during early growth, and increased cell permeability and autolysis. Importantly, the cwp22 mutation impaired cellular adherence in vitro and decreased cytotoxicity and fitness over the parent strain in a mouse infection model. Furthermore, lactate dehydrogenase cytotoxicity assay, live-dead cell staining and transmission electron microscopy confirmed the decreased cell viability of the cwp22 mutant. Thus, Cwp22 is involved in cell wall integrity and cell viability, which could affect most phenotypes of R20291. Our data suggest that Cwp22 is an attractive target for C. difficile infection therapeutics and prophylactics.

Non-Hydrolytic β-Lactam Antibiotic Fragmentation by l,d-Transpeptidases and Serine β-Lactamase Cysteine Variants

Enzymes often use nucleophilic serine, threonine, and cysteine residues to achieve the same type of reaction; the underlying reasons for this are not understood. While bacterial d,d-transpeptidases (penicillin-binding proteins) employ a nucleophilic serine, l,d-transpeptidases use a nucleophilic cysteine. The covalent complexes formed by l,d-transpeptidases with some β-lactam antibiotics undergo non-hydrolytic fragmentation. This is not usually observed for penicillin-binding proteins, or for the related serine β-lactamases. Replacement of the nucleophilic serine of serine β-lactamases with cysteine yields enzymes which fragment β-lactams via a similar mechanism as the l,d-transpeptidases, implying the different reaction outcomes are principally due to the formation of thioester versus ester intermediates. The results highlight fundamental differences in the reactivity of nucleophilic serine and cysteine enzymes, and imply new possibilities for the inhibition of nucleophilic enzymes.