Antibiotic-Induced, Increased Conjugative Transfer Is Common to Diverse Naturally Occurring ESBL Plasmids in Escherichia coli

Prospective One-Health investigation into low-abundant extended-spectrum β-lactamase producing Enterobacterales enables detection of potential dissemination events and persistence

BACKGROUND

Following a one-health approach, we sought to determine reservoirs of extended-spectrum β-lactamase (ESBL)-producing Enterobacterales (ESBL-PE), other than Escherichia coli or Klebsiella pneumoniae complex species (i.e., low-abundant species), and their associated ESBL genes and plasmid-replicon profiles.

METHODS

From 06/2017-05/2019, ESBL-PE isolates were recovered from clinical samples routinely collected at the University Hospital Basel (Basel, Switzerland), as well as from wastewater and foodstuffs collected monthly at predefined locations throughout the city of Basel. Whole-genome sequencing was performed for characterization of ESBL-PE isolates.

RESULTS

Among 1634 isolates recovered, 114 (7%) belonged to 17 low-abundant ESBL-PE species. Seven species originated from more than one compartment, mainly from clinical and wastewater samples (6/17). Sixteen different ESBL genes were identified, with blaCTX-M-15 (27%), blaFONA-6 (23%) and blaSHV-12 (16%) being most frequent. The blaCTX-M-1 gene was the only ESBL gene recovered from all three compartments. Putative plasmids constituted 60% of ESBL gene-containing contigs, while chromosomes comprised 40%. Foodstuff isolates showed the highest proportion (91%, 41/45) of ESBL genes located on chromosomes, whereas wastewater isolates had the highest proportion (95%, 37/39) of putative plasmids. Multi-replicon combinations were identified in 81% of the isolates. Epidemiological links were found among some clinical and wastewater isolates.

CONCLUSIONS

The dominance of blaCTX-M-15 among low-abundant ESBL-PE species supports its species-independent transmission potential beyond the E. coli and K. pneumoniae complex, and blaCTX-M-1 may be transmitted between strains recovered from different compartments. The substantial overlap between low-abundant ESBL-PE present in wastewater and clinical samples supports the utility of wastewater surveillance for antibiotic resistance monitoring.

Resolved genomes of wastewater ESBL-producing Escherichia coli and metagenomic analysis of source wastewater samples

Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli pose a serious threat to human health because of their resistance to the most commonly prescribed antibiotics: penicillins and cephalosporins. In this study, we provide a genomic and metagenomic context for the determinant beta-lactam resistance genes of ESBL-positive E. coli isolated from various wastewater treatment utilities in Oregon, USA. Class A beta-lactamase genes on chromosomes (blaCTX-M, blaTEM) were clustered with antibiotic resistance genes associated with other classes of antibiotics (sulfonamides and aminoglycosides) along with insertional elements. ESBL genes such as blaCTX-M, blaTEM, and blaSHV were also detected on conjugable plasmids of IncF and IncI incompatibility types. One novel IncF plasmid (pSHV2A_ESBLF) was identified, which carried a multidrug resistance genotype (blaSHV-2A, aadA22, aac3, aph6, tetA, and sul1) in addition to a mer (mercury resistance) operon, colicin, and aerobactin genes. Shotgun metagenomic analysis of the ESBL-producing E. coli-originating wastewater samples showed the presence of class A beta-lactamases; however, the ESBL genes identified in the E. coli genomes were below the detection limits. Other ESBL-associated genes (i.e., blaOXA.11, blaFOX.7, and blaGES.17) were identified in the wastewater samples, and their occurrences were correlated with the core microbial genera (e.g., Paraprevotella). In the E. coli genomes and wastewater samples, tetracycline, aminoglycoside, and beta-lactam resistance determinants frequently co-occurred. The combination of whole-genome and metagenomic analysis provides a holistic description of ESBL-producing organisms and genes in wastewater systems.IMPORTANCEUsing a hybrid sequencing and assembly strategy (short- and long-read sequencing), we identified the distribution of ARGs and virulence factors harbored on plasmids and chromosomes. We further characterized plasmids' incompatibility types and the co-occurrences of ARGs and virulence factors on plasmids and chromosomes. We investigated the transferability of plasmid-mediated beta-lactams via conjugation. Finally, using shotgun metagenomic analysis of the ESBL-producing Escherichia coli-originated wastewater samples, we described the microbial community, the resistome composition, and the potential associations with plasmid-mediated beta-lactam genes and other ARGs.

Non-Canonical Aspects of Antibiotics and Antibiotic Resistance

The understanding of antibiotic resistance, one of the major health threats of our time, is mostly based on dated and incomplete notions, especially in clinical contexts. The "canonical" mechanisms of action and pharmacodynamics of antibiotics, as well as the methods used to assess their activity upon bacteria, have not changed in decades; the same applies to the definition, acquisition, selective pressures, and drivers of resistance. As a consequence, the strategies to improve antibiotic usage and overcome resistance have ultimately failed. This review gathers most of the "non-canonical" notions on antibiotics and resistance: from the alternative mechanisms of action of antibiotics and the limitations of susceptibility testing to the wide variety of selective pressures, lateral gene transfer mechanisms, ubiquity, and societal factors maintaining resistance. Only by having a "big picture" view of the problem can adequate strategies to harness resistance be devised. These strategies must be global, addressing the many aspects that drive the increasing prevalence of resistant bacteria aside from the clinical use of antibiotics.

Interplay Between Antimicrobial Resistance and Global Environmental Change

Antibiotic resistance genes predate the therapeutic uses of antibiotics. However, the current antimicrobial resistance crisis stems from our extensive use of antibiotics and the generation of environmental stressors that impose new selective pressure on microbes and drive the evolution of resistant pathogens that now threaten human health. Similar to climate change, this global threat results from human activities that change habitats and natural microbiomes, which in turn interact with human-associated ecosystems and lead to adverse impacts on human health. Human activities that alter our planet at global scales exacerbate the current resistance crisis and exemplify our central role in large-scale changes in which we are both protagonists and architects of our success but also casualties of unanticipated collateral outcomes. As cognizant participants in this ongoing planetary experiment, we are driven to understand and find strategies to curb the ongoing crises of resistance and climate change.

Dissemination of IncI plasmid encoding bla CTX-M-1 is not hampered by its fitness cost in the pig's gut

Multiresistance plasmids belonging to the IncI incompatibility group have become one of the most pervasive plasmid types in extended-spectrum beta-lactamase-producing Escherichia coli of animal origin. The extent of the burden imposed on the bacterial cell by these plasmids seems to modulate the emergence of "epidemic" plasmids. However, in vivo data in the natural environment of the strains are scarce. Here, we investigated the cost of a bla CTX-M-1-IncI1 epidemic plasmid in a commensal E. coli animal strain, UB12-RC, before and after oral inoculation of 15 6- to 8-week- old specific-pathogen-free pigs. Growth rate in rich medium was determined on (i) UB12-RC and derivatives, with or without plasmid, in vivo and/or in vitro evolved, and (ii) strains that acquired the plasmid in the gut during the experiment. Although bla CTX-M-1-IncI1 plasmid imposed no measurable burden on the recipient strain after conjugation and during the longitudinal carriage in the pig's gut, we observed a significant difference in the bacterial growth rate between IncI1 plasmid-carrying and plasmid-free isolates collected during in vivo carriage. Only a few mutations on the chromosome of the UB12-RC derivatives were detected by whole-genome sequencing. RNA-Seq analysis of a selected set of these strains showed that transcriptional responses to the bla CTX-M-1-IncI1 acquisition were limited, affecting metabolism, stress response, and motility functions. Our data suggest that the effect of IncI plasmid on host cells is limited, fitness cost being insufficient to act as a barrier to IncI plasmid spread among natural population of E. coli in the gut niche.

Evaluation and validation of laboratory procedures for the surveillance of ESBL-, AmpC-, and carbapenemase-producing Escherichia coli from fresh meat and caecal samples

Introduction

Extended-spectrum β-lactamase- (ESBL) and AmpC- β-lactamase-producing Enterobacterales are widely distributed and emerging in both human and animal reservoirs worldwide. A growing concern has emerged in Europe following the appearance of carbapenemase-producing Escherichia coli (E. coli) in the primary production of food animals. In 2013, the European Commission (EC) issued the Implementing Decision on the monitoring and reporting of antimicrobial resistance in zoonotic and commensal bacteria. The European Union Reference Laboratory for Antimicrobial Resistance (EURL-AR) was tasked with providing two laboratory protocols for samples derived from meat and caecal content, respectively, for the isolation of ESBL- and AmpC-producing E. coli (part 1) and carbapenemase-producing (CP) E. coli (part 2). In this study, we describe the current protocols, including the preparatory work for the development.

Methods

Up to nine laboratory procedures were tested using minced meat as the matrix from beef, pork, and chicken as well as six procedures for the caecal content of cattle, pigs, and chicken. Variables included sample volume, pre-enrichment volume, pre-enrichment broth with and without antimicrobial supplementation, and incubation time/temperature. The procedures were evaluated against up to nine E. coli strains harboring different AMR genes and belonging to the three β-lactamase groups.

Results and discussion

The laboratory procedures tested revealed that the most sensitive and specific methodologies were based on a Buffered Peptone Water pre-enrichment of 225 ml to 25 g or 9 ml to 1 g for minced meat and caecal content, respectively, incubated at 37°C overnight, followed by inoculation onto MacConkey agar supplemented with 1 mg/L cefotaxime for detecting ESBL- and AmpC-producing E. coli and Chrom ID SMART (Chrom ID CARBA and OXA) for CP E. coli, incubated overnight at 37 and 44°C, respectively. We provided two isolation protocols for the EU-specific monitoring of ESBL- and AmpC- producing E. coli (part 1) and CP E. coli (part 2) from fresh meat (protocol 1) and caecal (protocol 2) samples, which have been successfully implemented by all EU Member States for the monitoring period 2014-2027 (EU 2020/1729).

Whole strains vs MGEs in short and longterm transmission of ESBL genes between healthcare and community settings in Uganda

Multidrug-resistant ESBL-producing Escherichia coli are a leading cause of infections in hospital and community settings. Based on samples from two hospitals in Uganda and households of inpatients we tested the hypothesis that ESBL E. coli and/or their resistance determinants could spread within the healthcare and community settings through discharged patients that were still colonized. We used bacterial culture, susceptibility testing whole genome sequencing and detailed bioinformatics analysis to test the above hypothesis. Genome analysis revealed presence of predominantly blaCTX-M-15 and blaOXA-1 genes with a total resistome with genes belonging to 14 different classes of antimicrobials. Short-term cases of strain sharing were reported within each setting and strains from the two settings were found to cluster together based on their overall resistome. Long-term horizontal transfer of ESBL genes by various IncF and IncY types of plasmids shared between healthcare and community settings was demonstrated. Based on hybrid assembly, plasmid reconstruction and phylogenetic analyses, our study suggests that while the dissemination of AMR between healthcare and community settings in the short-term is possible at whole strain level, the long-term transmission between healthcare and communities is sustained by the transfer of plasmids circulating across niches and disseminating related resistomes.

The Behavior of Some Bacterial Strains Isolated from Fallow Deer Compared to Antimicrobial Substances in Western Romania

(1) Background: The resistance levels of Escherichia coli, Salmonella spp., Pseudomonas spp., Staphylococcus spp., etc., isolated from the nasal cavity and the rectum of Dama dama deer from three hunting grounds in Western Romania were assessed. (2) Methods: The analysis was completed using the diffusimetric method, compliant with CLSI reference standards, and with Vitek-2 (BioMérieux, France), on 240 samples. (3) Results: The results were statistically analyzed (by one-way ANOVA) revealing that in four of the ten E. coli strains isolated from animals, 87.5% (p < 0.001) resistance was found. E. coli strains were resistant to cephalexin (100%); seven strains were resistant to cephalothin and ampicillin; six were resistant to cefquinome and cefoperazone; five were resistant to amoxicillin/clavulanic acid; and four were resistant to ceftiofur. However, E. coli was sensitive to amikacin (100%). The most efficient structures were beta-lactams, amikacin, and imipenem, to which all 47 strains studied (100%) were sensitive, followed by nitrofurantoin, to which 45 strains (95.7%) were sensitive, neomycin, to which 44 strains (93.6%) were sensitive, ceftiofur, to which 43 strains (91.5%) were sensitive, and trimethoprim/sulfamethoxazole and marbofloxacin, to which 42 strains (89.4%) were sensitive. (4) Conclusions: In wild animal populations, where a human presence is frequently reported, including a constant presence of domestic animals, despite the perceived low risk of emerging resistance to antimicrobials, resistance is likely to develop frequently.

Stimulants and donors promote megaplasmid pND6-2 horizontal gene transfer in activated sludge

The activated sludge process is characterized by high microbial density and diversity, both of which facilitate antibiotic resistance gene transfer. Many studies have suggested that antibiotic and non-antibiotic drugs at sub-inhibitory concentrations are major inducers of conjugative gene transfer. The self-transmissible plasmid pND6-2 is one of the endogenous plasmids harbored in Pseudomonas putida ND6, which can trigger the transfer of another co-occurring naphthalene-degrading plasmid pND6-1. Therefore, to illustrate the potential influence of stimulants on conjugative transfer of pND6-2, we evaluated the effects of four antibiotics (ampicillin, gentamycin, kanamycin, and tetracycline) and naphthalene, on the conjugal transfer efficiency of pND6-2 by filter-mating experiment. Our findings demonstrated that all stimulants within an optimal dose promoted conjugative transfer of pND6-2 from Pseudomonas putida GKND6 to P. putida KT2440, with tetracycline being the most effective (100 µg/L and 10 µg/L), as it enhanced pND6-2-mediated intra-genera transfer by approximately one hundred-fold. Subsequently, seven AS reactors were constructed with the addition of donors and different stimulants to further elucidate the conjugative behavior of pND6-2 in natural environment. The stimulants positively affected the conjugal process of pND6-2, while donors reshaped the host abundance in the sludge. This was likely because stimulant addition enhanced the expression levels of conjugation transfer-related genes. Furthermore, Blastocatella and Chitinimonas were identified as the potential receptors of plasmid pND6-2, which was not affected by donor types. These findings demonstrate the positive role of sub-inhibitory stimulant treatment on pND6-2 conjugal transfer and the function of donors in re-shaping the host spectrum of pND6-2.

A Streamlined Approach for Fluorescence Labelling of Low-Copy-Number Plasmids for Determination of Conjugation Frequency by Flow Cytometry

Bacterial conjugation plays a major role in the dissemination of antibiotic resistance and virulence traits through horizontal transfer of plasmids. Robust measurement of conjugation frequency of plasmids between bacterial strains and species is therefore important for understanding the transfer dynamics and epidemiology of conjugative plasmids. In this study, we present a streamlined experimental approach for fluorescence labelling of low-copy-number conjugative plasmids that allows plasmid transfer frequency during filter mating to be measured by flow cytometry. A blue fluorescent protein gene is inserted into a conjugative plasmid of interest using a simple homologous recombineering procedure. A small non-conjugative plasmid, which carries a red fluorescent protein gene with a toxin–antitoxin system that functions as a plasmid stability module, is used to label the recipient bacterial strain. This offers the dual advantage of circumventing chromosomal modifications of recipient strains and ensuring that the red fluorescent protein gene-bearing plasmid can be stably maintained in recipient cells in an antibiotic-free environment during conjugation. A strong constitutive promoter allows the two fluorescent protein genes to be strongly and constitutively expressed from the plasmids, thus allowing flow cytometers to clearly distinguish between donor, recipient, and transconjugant populations in a conjugation mix for monitoring conjugation frequencies more precisely over time.

Hormetic Effect of Pyroligneous Acids on Conjugative Transfer of Plasmid-mediated Multi-antibiotic Resistance Genes within Bacterial Genus

Spread of antibiotic resistance genes (ARGs) by conjugation poses great challenges to public health. Application of pyroligneous acids (PA) as soil amendments has been evidenced as a practical strategy to remediate pollution of ARGs in soils. However, little is known about PA effects on horizontal gene transfer (HGT) of ARGs by conjugation. This study investigated the effects of a woody waste-derived PA prepared at 450°C and its three distillation components (F1, F2, and F3) at different temperatures (98, 130, and 220°C) on conjugative transfer of plasmid RP4 within Escherichia coli. PA at relatively high amount (40-100 μL) in a 30-mL mating system inhibited conjugation by 74-85%, following an order of PA > F3 ≈ F2 ≈ F1, proving the hypothesis that PA amendments may mitigate soil ARG pollution by inhibiting HGT. The bacteriostasis caused by antibacterial components of PA, including acids, phenols, and alcohols, as well as its acidity (pH 2.81) contributed to the inhibited conjugation. However, a relatively low amount (10-20 μL) of PA in the same mating system enhanced ARG transfer by 26-47%, following an order of PA > F3 ≈ F2 > F1. The opposite effect at low amount is mainly attributed to the increased intracellular reactive oxygen species production, enhanced cell membrane permeability, increased extracellular polymeric substance contents, and reduced cell surface charge. Our findings highlight the hormesis (low-amount promotion and high-amount inhibition) of PA amendments on ARG conjugation and provide evidence for selecting an appropriate amount of PA amendment to control the dissemination of soil ARGs. Moreover, the promoted conjugation also triggers questions regarding the potential risks of soil amendments (e.g., PA) in the spread of ARGs via HGT.

Plant production of a virus-like particle-based vaccine candidate against porcine reproductive and respiratory syndrome

Porcine reproductive and respiratory syndrome (PRRS) is a disease leading to spontaneous abortions and stillbirths in sows and lowered life quality and expectancy in growing pigs. PRRS is prevalent worldwide and has significant economic impacts to swine industries around the globe. Co-expression of the two most abundant proteins in the viral envelope, the matrix protein (M) and glycosylated protein 5 (GP5), can produce a neutralizing immune response for the virus providing a potentially effective subunit vaccine against the disease, but these proteins are difficult to express. The goal of this research was to display antigenic portions of the M and GP5 proteins on the surface of tobacco mosaic virus-like particles. A modified tobacco mosaic virus coat protein (TMVc) was transiently expressed in Nicotiana benthamiana leaves and targeted to three subcellular compartments along the secretory pathway to introduce glycosylation patterns important for M-GP5 epitope immunogenicity. We found that accumulation levels in the apoplast were similar to the ER and the vacuole. Because glycans present on plant apoplastic proteins are closest to those present on PRRSV proteins, a TMVc-M-GP5 fusion construct was targeted to the apoplast and accumulated at over 0.5 mg/g of plant fresh weight. TMVc virus-like particles self-assembled in plant cells and surface-displayed the M-GP5 epitope, as visualized by transmission electron microscopy and immunogold localization. These promising findings lay the foundation for immunogenicity and protective-immunity studies in animals to examine the efficacy of this vaccine candidate as a measure to control PRRS.

A Glimpse at the Anti-Phage Defenses Landscape in the Foodborne Pathogen Salmonella enterica subsp. enterica serovar Typhimurium

Bacteriophages, which specifically infect and kill bacteria, are currently used as additives to control pathogens such as Salmonella in human food (PhageGuard S^®) or animal feed (SalmoFREE^®, Bafasal^®). Indeed, salmonellosis is among the most important zoonotic foodborne illnesses. The presence of anti-phage defenses protecting bacteria against phage infection could impair phage applications aiming at reducing the burden of foodborne pathogens such as Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium) to the food industry. In this study, the landscape of S. Typhimurium anti-phage defenses was bioinformatically investigated in publicly available genomes using the webserver PADLOC. The primary anti-phage systems identified in S. Typhimurium use nucleic acid degradation and abortive infection mechanisms. Reference systems were identified on an integrative and conjugative element, a transposon, a putative integrative and mobilizable element, and prophages. Additionally, the mobile genetic elements (MGEs) containing a subset of anti-phage systems were found in the Salmonella enterica species. Lastly, the MGEs alone were also identified in the Enterobacteriaceae family. The presented diversity assessment of the anti-phage defenses and investigation of their dissemination through MGEs in S. Typhimurium constitute a first step towards the design of preventive measures against the spread of phage resistance that may hinder phage applications.

Non-caloric artificial sweeteners modulate conjugative transfer of multi-drug resistance plasmid in the gut microbiota

Non-caloric artificial sweeteners have been widely permitted as table sugar substitutes with high intensities of sweetness. They can pass through the intestinal tract without significant metabolization and frequently encounter the gut microbiome, which is composed of diverse bacterial species and is a pool of antibiotic resistance genes (ARGs). However, little is known about whether these sweeteners could accelerate the spread of ARGs in the gut microbiome. Here, we established an in vitro conjugation model by using Escherichia coli that carries chromosome-inserted Tn7 lacI^q-pLpp-mCherry and plasmid-encoded gfpmut3b gene as the donor and murine fecal bacteria as the recipient. We found that four commonly used artificial sweeteners (saccharin, sucralose, aspartame, and acesulfame potassium) can increase reactive oxygen species (ROS) production and promote plasmid-mediated conjugative transfer to the gut microbiome. Cell sorting and 16S rRNA gene amplicon sequencing analysis of fecal samples reveal that the tested sweeteners can promote the broad-host-range plasmid permissiveness to both Gram-negative and Gram-positive gut bacteria. The increased plasmid permissiveness was also validated with a human pathogen Klebsiella pneumoniae. Collectively, our study demonstrates that non-caloric artificial sweeteners can induce oxidative stress and boost the plasmid-mediated conjugative transfer of ARGs among the gut microbiota and a human pathogen. Considering the soaring consumption of these sweeteners and the abundance of mobile ARGs in the human gut, our results highlight the necessity of performing a thorough risk assessment of antibiotic resistance associated with the usage of artificial sweeteners as food additives.

Assessment of a plasmid conjugation procedure to monitor horizontal transfer of an extended-spectrum β-lactamase resistance gene under food chain scenarios

Plasmids are relevant reservoirs of antimicrobial resistance genes (ARGs) which confer adaptive advantages to their host and can be horizontally transferred. The aims of this study were to develop a conjugation procedure to monitor the horizontal transfer of a 193 kb plasmid containing the extended-spectrum β-lactamase production gene bla _CTX-M-14 between two Escherichia coli strains under a range of food chain-related scenarios, including temperature (20-37 °C), pH (5.0-9.0) or the presence of some biocidal agents (benzalkonium chloride, sodium hypochlorite or peracetic acid). The average conjugation rate in LB broth after 18 h at 37 °C was 2.09e-04 and similar rates were observed in a food matrix (cow's milk). The conjugation was reduced at temperatures below 37 °C, at alkaline pH (especially at pH 9.0) or in the presence of benzalkonium chloride. Peracetic acid and sodium hypochlorite slightly increased conjugation rates, which reached 5.59e-04 and 6.77e-03, respectively. The conjugation procedure described can be used to identify risk scenarios leading to an enhanced ARGs transmission via plasmid conjugation, as well as to identify novel intervention strategies impairing plasmid conjugation and tackling antimicrobial resistance.

Examining the impact of zinc on horizontal gene transfer in Enterobacterales

Antimicrobial resistance is one of the main international health concerns for humans, animals, and the environment, and substantial efforts have focused on reducing its development and spread. While there is evidence for correlations between antimicrobial usage and antimicrobial resistance development, specific information on the effect of heavy metal/antimicrobial usage on bacterial conjugation is more limited. The aim of this study was to investigate the effects of zinc and antimicrobials in different concentrations on horizontal gene transfer of an ampicillin resistance gene, using a multi-drug resistant Escherichia coli donor strain and three different Salmonella enterica serovars as recipient strains. Differences in conjugation frequencies for the different Salmonella recipients were observed, independent of the presence of zinc or the antimicrobials. Selective pressure on the recipient strains, in the form of ampicillin, resulted in a decrease in conjugation frequencies, while, the presence of rifampicin resulted in increases. Zinc exposure affected conjugation frequencies of only one of the three recipient strains, thus the effect of zinc on conjugation frequencies seemed to be concentration and strain dependent. Furthermore, differences in growth rates due to plasmid carriage were observed for one of the Salmonella strains.

Target-enriched long-read sequencing (TELSeq) contextualizes antimicrobial resistance genes in metagenomes

BACKGROUND

Metagenomic data can be used to profile high-importance genes within microbiomes. However, current metagenomic workflows produce data that suffer from low sensitivity and an inability to accurately reconstruct partial or full genomes, particularly those in low abundance. These limitations preclude colocalization analysis, i.e., characterizing the genomic context of genes and functions within a metagenomic sample. Genomic context is especially crucial for functions associated with horizontal gene transfer (HGT) via mobile genetic elements (MGEs), for example antimicrobial resistance (AMR). To overcome this current limitation of metagenomics, we present a method for comprehensive and accurate reconstruction of antimicrobial resistance genes (ARGs) and MGEs from metagenomic DNA, termed target-enriched long-read sequencing (TELSeq).

RESULTS

Using technical replicates of diverse sample types, we compared TELSeq performance to that of non-enriched PacBio and short-read Illumina sequencing. TELSeq achieved much higher ARG recovery (>1,000-fold) and sensitivity than the other methods across diverse metagenomes, revealing an extensive resistome profile comprising many low-abundance ARGs, including some with public health importance. Using the long reads generated by TELSeq, we identified numerous MGEs and cargo genes flanking the low-abundance ARGs, indicating that these ARGs could be transferred across bacterial taxa via HGT.

CONCLUSIONS

TELSeq can provide a nuanced view of the genomic context of microbial resistomes and thus has wide-ranging applications in public, animal, and human health, as well as environmental surveillance and monitoring of AMR. Thus, this technique represents a fundamental advancement for microbiome research and application. Video abstract.

Effects of Nutrient Level and Growth Rate on the Conjugation Process That Transfers Mobile Antibiotic Resistance Genes in Continuous Cultures

Bacteria in the effluent of wastewater treatment plants (WWTPs) can transfer antibiotic resistance genes (ARGs) to the bacteria in receiving water through conjugation; however, there is a lack of quantitative assessment of this phenomenon in continuous cultures. Our objective was to determine the effects of background nutrient levels in river water column and growth rates of bacteria on the conjugation frequency of ARGs from effluent bacteria to river bacteria, as well as on the resulting resistance level (i.e., MICs) of the river bacteria. Chemostats were employed to simulate the discharge points of WWTPs into rivers, where effluent bacteria (donor cells) meet river bacteria (recipient cells). Both donor and recipient cells were Escherichia coli cells, and the donor cells were constructed by filter mating with bacteria in the effluent of a local WWTP. Results showed that higher bacterial growth rate (0.45 h^-1 versus 0.15 h^-1) led to higher conjugation frequencies (10^-4 versus 10^-6 transconjugant per recipient). The nutrient level also significantly affected the conjugation frequency, albeit to a lesser extent than the growth rate. The MIC against tetracycline increased from 2 mg/L in the recipient to 64 to 128 mg/L in transconjugants. In comparison, the MIC only increased to as high as 8 mg/L in mutants. Whole-genome sequencing showed that the tet-containing plasmid in both the donor and the transconjugant cells also occur in other fecal bacterial genera. The quantitative information obtained from this study can inform hazard identification related to the proliferation of wastewater-associated ARGs in surface water. IMPORTANCE WWTPs have been regarded as an important hot spot of ARGs. The discharge point of WWTP effluent, where ARGs may be horizontally transferred from bacteria of treated wastewater to bacteria of receiving water, is an important interface between the human-dominated ecosystem and the natural environment. The use of batch cultures in previous studies cannot adequately simulate the nutrient conditions and growth rates in receiving water. In this study, chemostats were employed to simulate the continuous growth of bacteria in receiving water. Furthermore, the experimental setup allowed for separate investigations on the effects of nutrient levels (i.e., simulating background nutrients in river water) and bacterial growth rates on conjugation frequencies and resulting resistance levels. The study generates statistically sound ecological data that can be used to estimate the risk of wastewater-originated ARGs as part of the One Health framework.

Insights into the impact of manure on the environmental antibiotic residues and resistance pool

The intensive use of antibiotics in the veterinary sector, linked to the application of manure-derived amendments in agriculture, translates into increased environmental levels of chemical residues, AR bacteria (ARB) and antibiotic resistance genes (ARG). The aim of this review was to evaluate the current evidence regarding the impact of animal farming and manure application on the antibiotic resistance pool in the environment. Several studies reported correlations between the prevalence of clinically relevant ARB and the amount and classes of antibiotics used in animal farming (high resistance rates being reported for medically important antibiotics such as penicillins, tetracyclines, sulfonamides and fluoroquinolones). However, the results are difficult to compare, due to the diversity of the used antimicrobials quantification techniques and to the different amounts and types of antibiotics, exhibiting various degradation times, given in animal feed in different countries. The soils fertilized with manure-derived products harbor a higher and chronic abundance of ARB, multiple ARG and an enriched associated mobilome, which is also sometimes seen in the crops grown on the amended soils. Different manure processing techniques have various efficiencies in the removal of antibiotic residues, ARB and ARGs, but there is only a small amount of data from commercial farms. The efficiency of sludge anaerobic digestion appears to be dependent on the microbial communities composition, the ARB/ARG and operating temperature (mesophilic vs. thermophilic conditions). Composting seems to reduce or eliminate most of antibiotics residues, enteric bacteria, ARB and different representative ARG in manure more rapidly and effectively than lagoon storage. Our review highlights that despite the body of research accumulated in the last years, there are still important knowledge gaps regarding the contribution of manure to the AMR emergence, accumulation, spread and risk of human exposure in countries with high clinical resistance rates. Land microbiome before and after manure application, efficiency of different manure treatment techniques in decreasing the AMR levels in the natural environments and along the food chain must be investigated in depth, covering different geographical regions and countries and using harmonized methodologies. The support of stakeholders is required for the development of specific best practices for prudent – cautious use of antibiotics on farm animals. The use of human reserve antibiotics in veterinary medicine and of unprescribed animal antimicrobials should be stopped and the use of antibiotics on farms must be limited. This integrated approach is needed to determine the optimal conditions for the removal of antibiotic residues, ARB and ARG, to formulate specific recommendations for livestock manure treatment, storage and handling procedures and to translate them into practical on-farm management decisions, to ultimately prevent exposure of human population.

Biocides used as material preservatives modify rates of de novo mutation and horizontal gene transfer in bacteria

Antimicrobial resistance (AMR) is a global health problem with the environment being an important compartment for the evolution and transmission of AMR. Previous studies showed that de-novo mutagenesis and horizontal gene transfer (HGT) by conjugation or transformation - important processes underlying resistance evolution and spread - are affected by antibiotics, metals and pesticides. However, natural microbial communities are also frequently exposed to biocides used as material preservatives, but it is unknown if these substances induce mutagenesis and HGT. Here, we show that active substances used in material preservatives can increase rates of mutation and conjugation in a species- and substance-dependent manner, while rates of transformation are not increased. The bisbiguanide chlorhexidine digluconate, the quaternary ammonium compound didecyldimethylammonium chloride, the metal copper, the pyrethroid-insecticide permethrin, and the azole-fungicide propiconazole increase mutation rates in Escherichia coli, whereas no increases were identified for Bacillus subtilis and Acinetobacter baylyi. Benzalkonium chloride, chlorhexidine and permethrin increased conjugation in E. coli. Moreover, our results show a connection between the RpoS-mediated general stress and the RecA-linked SOS response with increased rates of mutation and conjugation, but not for all biocides. Taken together, our data show the importance of assessing the contribution of material preservatives on AMR evolution and spread.

Sub-lethal photocatalysis promotes horizontal transfer of antibiotic resistance genes by conjugation and transformability

The spread of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in water is increasingly becoming a worldwide problem due to frequent recent major public health events. Herein, the horizontal ARG transfer mechanisms were studied under sub-lethal photocatalysis. The results show that ARGs had at most a 3- to 6-fold increase in the conjugative transfer frequency when only donor bacteria were induced with sub-lethal photocatalysis, while the frequency exhibited a trend toward inhibition when only the recipient bacteria were induced. However, when the donor or recipient bacteria were induced beforehand for a specific time, the frequency increased by a maximum of 10- to 22-fold. Moreover, the horizontal transfer frequency and its mechanism were related to the oxidative stress systems, ATP systems and the expression of related genes. Furthermore, the transformability of extracellular plasmids of the ARB and the contribution in horizontal transfer were also studied. Results show that the transformation frequency accounted for up to 50% of the total number of transconjugants, indicating that transformation might be a primary mode of horizontal ARG transfer by ARB in water. All of the above results demonstrate that sub-lethal photocatalysis will increase the frequency of horizontal gene transfer of ARGs through both conjugative transfer and the transformation pathway, which increases the risk of ARB in aquatic environments.

Link Between Antibiotic Persistence and Antibiotic Resistance in Bacterial Pathogens

Both, antibiotic persistence and antibiotic resistance characterize phenotypes of survival in which a bacterial cell becomes insensitive to one (or even) more antibiotic(s). However, the molecular basis for these two antibiotic-tolerant phenotypes is fundamentally different. Whereas antibiotic resistance is genetically determined and hence represents a rather stable phenotype, antibiotic persistence marks a transient physiological state triggered by various stress-inducing conditions that switches back to the original antibiotic sensitive state once the environmental situation improves. The molecular basics of antibiotic resistance are in principle well understood. This is not the case for antibiotic persistence. Under all culture conditions, there is a stochastically formed, subpopulation of persister cells in bacterial populations, the size of which depends on the culture conditions. The proportion of persisters in a bacterial population increases under different stress conditions, including treatment with bactericidal antibiotics (BCAs). Various models have been proposed to explain the formation of persistence in bacteria. We recently hypothesized that all physiological culture conditions leading to persistence converge in the inability of the bacteria to re-initiate a new round of DNA replication caused by an insufficient level of the initiator complex ATP-DnaA and hence by the lack of formation of a functional orisome. Here, we extend this hypothesis by proposing that in this persistence state the bacteria become more susceptible to mutation-based antibiotic resistance provided they are equipped with error-prone DNA repair functions. This is - in our opinion - in particular the case when such bacterial populations are exposed to BCAs.

Evolution of horizontal transmission in antimicrobial resistance plasmids

Mobile genetic elements (MGEs) are one of the main vectors for the spread of antimicrobial resistance (AMR) across bacteria, due to their ability to move horizontally between bacterial lineages. Horizontal transmission of AMR can increase AMR prevalence at multiple scales, from increasing the prevalence of infections by resistant bacteria to pathogen epidemics and worldwide spread of AMR across species. Among MGEs, conjugative plasmids are the main contributors to the spread of AMR. This review discusses the selective pressures acting on MGEs and their hosts to promote or limit the horizontal transmission of MGEs, the mechanisms by which transmission rates can evolve, and their implications for limiting the spread of AMR, with a focus on AMR plasmids.

Models for Gut-Mediated Horizontal Gene Transfer by Bacterial Plasmid Conjugation

The emergence of new antimicrobial resistant and virulent bacterial strains may pose a threat to human and animal health. Bacterial plasmid conjugation is a significant contributor to rapid microbial evolutions that results in the emergence and spread of antimicrobial resistance (AR). The gut of animals is believed to be a potent reservoir for the spread of AR and virulence genes through the horizontal exchange of mobile genetic elements such as plasmids. The study of the plasmid transfer process in the complex gut environment is limited due to the confounding factors that affect colonization, persistence, and plasmid conjugation. Furthermore, study of plasmid transfer in the gut of humans is limited to observational studies, leading to the need to identify alternate models that provide insight into the factors regulating conjugation in the gut. This review discusses key studies on the current models for in silico, in vitro, and in vivo modeling of bacterial conjugation, and their ability to reflect the gut of animals. We particularly emphasize the use of computational and in vitro models that may approximate aspects of the gut, as well as animal models that represent in vivo conditions to a greater extent. Directions on future research studies in the field are provided.

Chicken Skin Decontamination of Thermotolerant Campylobacter spp. and Hygiene Indicator Escherichia coli Assessed by Viability Real-Time PCR

Thermotolerant Campylobacter spp. are fecal contaminants of chicken meat with serious implications for human health. E. coli is considered as hygiene indicator since, in contrast to Campylobacter. spp., the bacterium is generally present in the avian gut. Stress exposure may transiently cease bacterial division. Therefore, colony forming units (CFU) may underestimate the infection risk of pathogens. We developed a viability real-time PCR (v-qPCR) for the quantification of viable E. coli targeting the uidA gene, encoding β-glucuronidase, which is usually detected for phenotypic species identification. The short- and long-term effects of decontaminating chicken skin on the survival of both C. jejuni and an ESBL-producing E. coli were evaluated by CFU and v-qPCR. The results showed that freezing and storage in cool conditions are potentially underestimated by CFU but not by v-qPCR. The effect of treatment with peroxyacetic acid on survival was consistently detected by CFU and v-qPCR. v-qPCR analysis detected bacterial survival upon the application of lactic acid, which awaits further analysis. Interestingly, both bacteria showed similar kinetics of inactivation upon the application of reduction strategies, suggesting that E. coli might be a complementary hygiene indicator. We conclude that v-qPCR can improve food safety under the consideration of some limitations.

The Dynamics of the Antimicrobial Resistance Mobilome of Salmonella enterica and Related Enteric Bacteria

The foodborne pathogen Salmonella enterica is considered a global public health risk. Salmonella enterica isolates can develop resistance to several antimicrobial drugs due to the rapid spread of antimicrobial resistance (AMR) genes, thus increasing the impact on hospitalization and treatment costs, as well as the healthcare system. Mobile genetic elements (MGEs) play key roles in the dissemination of AMR genes in S. enterica isolates. Multiple phenotypic and molecular techniques have been utilized to better understand the biology and epidemiology of plasmids including DNA sequence analyses, whole genome sequencing (WGS), incompatibility typing, and conjugation studies of plasmids from S. enterica and related species. Focusing on the dynamics of AMR genes is critical for identification and verification of emerging multidrug resistance. The aim of this review is to highlight the updated knowledge of AMR genes in the mobilome of Salmonella and related enteric bacteria. The mobilome is a term defined as all MGEs, including plasmids, transposons, insertion sequences (ISs), gene cassettes, integrons, and resistance islands, that contribute to the potential spread of genes in an organism, including S. enterica isolates and related species, which are the focus of this review.

Clinically healthy household dogs and cats as carriers of multidrug-resistant Salmonella enterica with variable R plasmids

Introduction. Antimicrobial resistance (AMR) is a One Health issue concerning humans, animals and the environment and a unified One Health approach is required to contain this problematic issue. Dogs and cats are popular pet animals and are known to carry many bacterial pathogens that are of public health importance, including Salmonella . However, data on AMR in companion animals is limited.

Gap statement. Scant AMR data from bacteria originating from companion animals limits an accurate assessment of the impacts of pet-animal-related AMR on public health.

Purpose. This study aimed to phenotypically and genetically investigate AMR in Salmonella isolated from pet dogs and cats in Thailand.

Methodology. Salmonella enterica were isolated from pet dogs (n=159) and cats (n=19) in Thailand between 2016 and 2019. All isolates were serotyped. Phenotypic and genotypic antimicrobial resistance was examined. PCR-based replicon typing, replicon sequence typing and plasmid multilocus sequence typing were conducted to characterize plasmids.

Results. Seventy-seven serovars were identified, with serovars Weltevreden (9.6%) and Stockholm (9.0%) the most common. Most of the isolates (34.3%) were multidrug-resistant. The serovar Stockholm was an ESBL-producer and carried the β-lactamase genes bla TEM-1 and bla CTX-M-55. The plasmid-mediated quinolone resistance (PMQR) gene, qnrS, was also detected (10.1%). Class 1 integrons carrying the dfrA12-aadA2 cassette array were most frequent (45.9%). Five plasmid replicon types as IncA/C (0.6%), N (1.1%), IncFIIA (28.7%), IncHI1 (2.2%), and IncI1 (3.4%) were identified. Based on the pMLST typing scheme (n=9), plasmids were assigned into five different STs including IncA/C-ST6 (n=1), IncH1-ST16 (n=4), IncI1-ST3 (n=1), IncI1-ST60 (n=1) and IncI1-ST136 (n=1). The ST 16 of IncHI1 plasmid was a novel plasmid ST. Subtyping F-type plasmids using the RST scheme (n=9) revealed four different combinations of replicons including S1:A-:B- (n=4), S1:A-:B22 (n=2), S3:A-:B- (n=1) and S-:A-:B47 (n=1).

Conclusions. Our findings highlight the role of clinically healthy household dogs and cats as carriers of AMR Salmonella strains with different R plasmid. The implementation of AMR phenotypes instigation and genotypic monitoring and surveillance programmes in companion animals are imperative as integral components of the One Health framework.

Plasmid co-infection: linking biological mechanisms to ecological and evolutionary dynamics

As infectious agents of bacteria and vehicles of horizontal gene transfer, plasmids play a key role in bacterial ecology and evolution. Plasmid dynamics are shaped not only by plasmid-host interactions but also by ecological interactions between plasmid variants. These interactions are complex: plasmids can co-infect the same cell and the consequences for the co-resident plasmid can be either beneficial or detrimental. Many of the biological processes that govern plasmid co-infection-from systems that exclude infection by other plasmids to interactions in the regulation of plasmid copy number-are well characterized at a mechanistic level. Modelling plays a central role in translating such mechanistic insights into predictions about plasmid dynamics and the impact of these dynamics on bacterial evolution. Theoretical work in evolutionary epidemiology has shown that formulating models of co-infection is not trivial, as some modelling choices can introduce unintended ecological assumptions. Here, we review how the biological processes that govern co-infection can be represented in a mathematical model, discuss potential modelling pitfalls, and analyse this model to provide general insights into how co-infection impacts ecological and evolutionary outcomes. In particular, we demonstrate how beneficial and detrimental effects of co-infection give rise to frequency-dependent selection on plasmid variants. This article is part of the theme issue 'The secret lives of microbial mobile genetic elements'.

Global protein responses of multi-drug resistant plasmid containing Escherichia coli to ampicillin, cefotaxime, imipenem and ciprofloxacin

OBJECTIVES

This study compared the proteomics of Escherichia coli containing the multi-drug resistance pEK499 plasmid under antimicrobial stress and no antimicrobial.

METHODS

We utilised mass spectrometry-based proteomics to compare the proteomes of the bacteria and plasmid under antimicrobial stress and no antimicrobial.

RESULTS

Our analysis identified statistically significant differentially abundant proteins common to groups exposed to the β-lactam antimicrobials but not ciprofloxacin, indicating a β-lactam stress response to exposure from this class of drugs, irrespective of β-lactam resistance or susceptibility. Data arising from comparisons of the proteomes of ciprofloxacin-treated E. coli and controls detected an increase in the relative abundance of proteins associated with ribosomes, translation, the TCA-cycle and several proteins associated with detoxification and a decrease in the relative abundances of proteins associated with stress response, including oxidative stress. We identified changes in proteins associated with persister formation in the presence of ciprofloxacin but not the β-lactams. The plasmid proteome differed across each treatment and did not follow the pattern of antimicrobial - AMR protein associations: a relative increase in the amount of bla_CTX-M-15 in the presence of cefotaxime and ciprofloxacin but not the other β-lactams, suggesting regulation of the bla_CTX-M-15 protein production.

CONCLUSIONS

The proteomic data from the this study provided novel insights into the proteins produced from the chromosome and plasmid under different antimicrobial stresses. These data also identified novel proteins not previously associated with AMR or antimicrobials responses in pathogens, which may well represent potential targets of AMR inhibition.

Antimicrobial-induced horizontal transfer of antimicrobial resistance genes in bacteria: a mini-review

The emergence and spread of antimicrobial resistance (AMR) among pathogenic bacteria constitute an accelerating crisis for public health. The selective pressures caused by increased use and misuse of antimicrobials in medicine and livestock production have accelerated the overall selection of resistant bacteria. In addition, horizontal gene transfer (HGT) plays an important role in the spread of resistance genes, for example mobilizing reservoirs of AMR from commensal bacteria into pathogenic ones. Antimicrobials, besides antibacterial function, also result in undesirable effects in the microbial populations, including the stimulation of HGT. The main aim of this narrative review was to present an overview of the current knowledge of the impact of antimicrobials on HGT in bacteria, including the effects of transformation, transduction and conjugation, as well as other less well-studied mechanisms of HGT. It is widely accepted that conjugation plays a major role in the spread of AMR in bacteria, and the focus of this review is therefore mainly on the evidence provided that antimicrobial treatment affects this process. Other mechanisms of HGT have so far been deemed less important in this respect; however, recent discoveries suggest their role may be larger than previously thought, and the review provides an update on the rather limited knowledge currently available regarding the impact of antimicrobial treatment on these processes as well. A conclusion from the review is that there is an urgent need to investigate the mechanisms of antimicrobial-induced HGT, since this will be critical for developing new strategies to combat the spread of AMR.

Molecular detection of blaCTX-M gene to predict phenotypic cephalosporin resistance and clinical outcome of Escherichia coli bloodstream infections in Vietnam

BACKGROUND

Blood stream infections (BSI) caused by Extended Spectrum Beta-Lactamases (ESBLs) producing Enterobacteriaceae is a clinical challenge leading to high mortality, especially in developing countries. In this study, we sought to describe the epidemiology of ESBL-producing Escherichia coli strains isolated from Vietnamese individuals with BSI, to investigate the concordance of genotypic-phenotypic resistance, and clinical outcome of ESBL E. coli BSI.

METHODS

A total of 459 hospitalized patients with BSI were screened between October 2014 and May 2016. 115 E. coli strains from 115 BSI patients were isolated and tested for antibiotic resistance using the VITEK®2 system. The ESBL phenotype was determined by double disk diffusion method following the guideline of Clinical and Laboratory Standards Institute. Screening for beta-lactamase (ESBL and carbapenemase) genes was performed using a multiplex-PCR assay.

RESULTS

58% (67/115) of the E. coli strains were ESBL-producers and all were susceptible to both imipenem and meropenem. Resistance to third-generation cephalosporin was common, 70% (81/115) were cefotaxime-resistant and 45% (52/115) were ceftazidime-resistant. blaCTX-M was the most common ESBL gene detected (70%; 80/115) The sensitivity and specificity of blaCTX-M-detection to predict the ESBL phenotype was 87% (76-93% 95% CI) and 54% (39-48% 95% CI), respectively. 28%% (22/80) of blaCTX-M were classified as non-ESBL producers by phenotypic testing for ESBL production. The detection of blaCTX-M in ESBL-negative E. coli BSI was associated with fatal clinical outcome (27%; 6/22 versus 8%; 2/26, p = 0.07).

CONCLUSION

A high prevalence of ESBL-producing E. coli isolates harbouring blaCTX-M was observed in BSI patients in Vietnam. The genotypic detection of blaCTX-M may have added benefit in optimizing and guiding empirical antibiotic therapy of E. coli BSI to improve clinical outcome.

Mobilization of the nonconjugative virulence plasmid from hypervirulent Klebsiella pneumoniae

Background

Klebsiella pneumoniae, as a global priority pathogen, is well known for its capability of acquiring mobile genetic elements that carry resistance and/or virulence genes. Its virulence plasmid, previously deemed nonconjugative and restricted within hypervirulent K. pneumoniae (hvKP), has disseminated into classic K. pneumoniae (cKP), particularly carbapenem-resistant K. pneumoniae (CRKP), which poses alarming challenges to public health. However, the mechanism underlying its transfer from hvKP to CRKP is unclear.

Methods

A total of 28 sequence type (ST) 11 bloodstream infection-causing CRKP strains were collected from Ruijin Hospital in Shanghai, China, and used as recipients in conjugation assays. Transconjugants obtained from conjugation assays were confirmed by XbaI and S1 nuclease pulsed-field gel electrophoresis, PCR detection and/or whole-genome sequencing. The plasmid stability of the transconjugants was evaluated by serial culture. Genetically modified strains and constructed mimic virulence plasmids were employed to investigate the mechanisms underlying mobilization. The level of extracellular polysaccharides was measured by mucoviscosity assays and uronic acid quantification. An in silico analysis of 2608 plasmids derived from 814 completely sequenced K. pneumoniae strains available in GenBank was performed to investigate the distribution of putative helper plasmids and mobilizable virulence plasmids.

Results

A nonconjugative virulence plasmid was mobilized by the conjugative plasmid belonging to incompatibility group F (IncF) from the hvKP strain into ST11 CRKP strains under low extracellular polysaccharide-producing conditions or by employing intermediate E. coli strains. The virulence plasmid was mobilized via four modes: transfer alone, cotransfer with the conjugative IncF plasmid, hybrid plasmid formation due to two rounds of single-strand exchanges at specific 28-bp fusion sites or homologous recombination. According to the in silico analysis, 31.8% (242) of the putative helper plasmids and 98.8% (84/85) of the virulence plasmids carry the 28-bp fusion site. All virulence plasmids carry the origin of the transfer site.

Conclusions

The nonconjugative virulence plasmid in ST11 CRKP strains is putatively mobilized from hvKP or E. coli intermediates with the help of conjugative IncF plasmids. Our findings emphasize the importance of raising public awareness of the rapid dissemination of virulence plasmids and the consistent emergence of hypervirulent carbapenem-resistant K. pneumoniae (hv-CRKP) strains.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13073-021-00936-5.

Antibiotic resistance and plasmid analysis of Enterobacteriaceae isolated from retail meat in Lagos Nigeria

BACKGROUND

The presence of antibiotic resistant microorganisms in food is of great concern globally. This research was carried out to detect and characterize plasmid carriage and profiles among members of Enterobacteriaceae from different meat types in Nigeria.

METHOD

From a total of 80 meat samples comprising of mutton,pork, beef and chicken, organisms belonging to the family Enterobacteriaceae wereisolated by standard procedures and identified by API 20E system. Antibiotics susceptibilities testing (AST) againstselected classes of antimicrobial agents and plasmid extraction was carried outby disc diffusion and alkaline lysis methods respectively.

RESULTS

One-hundred and ten Enterobacteriaceae were isolated,species identification revealed isolates belonging to 7 genera comprising of Escherichia, Enterobacter, Klebsiella,Citrobacter, Proteus, Salmonella and Serratia. Overall resistance of theorganisms to amoxycillin/clavulanic acid was 91 (82.7%), streptomycin 85(75.7%) and perfloxacin 74 (67.2%) while ofloxacin had the highestsusceptibility rate (91.8%). Plasmids profiling revealed ranges of plasmids from1 to 3 copies with estimated sizes range of 700bp to 1.1kb among E. coli, K. pneumoniae, E. aerogenesand Proteus mirabilis. All theisolates with plasmids were multidrug resistant and were isolated from chicken excepta strain of E. coli from pork whichharboured a single plasmid copy suggesting these meat as reservoirs forantibiotic resistant bacteria.

CONCLUSION

Our findings revealed high level of meat contamination with antibioticresistant Enterobacteriaceae harbouring resistant plasmids. An integratedsurveillance system and safety practice must be ensured among the processorsand retailers.

Antioxidant Molecules as a Source of Mitigation of Antibiotic Resistance Gene Dissemination

Escherichia coli is the most commonly identified human pathogen and a prominent microorganism of the gut microbiota. Acquired resistance to antibiotics in this species is driven mainly by horizontal gene transfer and plasmid acquisition. Currently, the main concern is the acquisition of extended-spectrum β-lactamases of the CTX-M type in E. coli, a worldwide-observed phenomenon. Plasmids encoding CTX-M enzymes have different scaffolds and conjugate at different frequencies. Here, we show that the conjugation rates of several plasmid types encoding broad-spectrum β-lactamases are increased when the E. coli donor strain is exposed to subinhibitory concentrations of diverse orally given antibiotics, including fluoroquinolones, such as ciprofloxacin and levofloxacin, but also trimethoprim and nitrofurantoin. This study provides insights into underlying mechanisms leading to increased plasmid conjugation frequency in relation to DNA synthesis inhibitor-type antibiotics, involving reactive oxygen species (ROS) production and probably increased expression of genes involved in the SOS response. Furthermore, we show that some antioxidant molecules currently approved for unrelated clinical uses, such as edaravone, p-coumaric acid, and N-acetylcysteine, may antagonize the ability of antibiotics to increase plasmid conjugation rates. These results suggest that several antioxidative molecules might be used in combination with these "inducer" antibiotics to mitigate the unwanted increased resistance plasmid dissemination.

Genomic Diversity and Virulence Potential of ESBL- and AmpC-β-Lactamase-Producing Escherichia coli Strains From Healthy Food Animals Across Europe

The role of livestock animals as a putative source of ESBL/pAmpC E. coli for humans is a central issue of research. In a large-scale pan-European surveillance, 2,993 commensal Escherichia spp. isolates were recovered from randomly collected fecal samples of healthy cattle, pigs and chickens in various abattoirs. One-hundred Escherichia spp. isolates (0.5% from cattle, 1.3% pigs, 8.0% chickens) fulfilled the criteria for cefotaxime and ceftazidime non-wildtype (EUCAST). In silico screening of WGS data of 99 isolates (98 E. coli and 1 E. fergusonii) revealed bla_SHV–12 (32.3%), bla_CTX–M–1 (24.2%), and bla_CMY–2 (22.2%) as predominant ESBL/pAmpC types. Other types were bla_SHV–2 (1.0%), bla_{CTX–M–2/–14/–15} (1.0/6.1/1.0%), and bla_TEM–52 (5.1%). Six isolates revealed AmpC-promoter mutations (position −42 (C > T) and one carried mcr-1. The majority (91.3%) of ESBL/pAmpC genes were located on plasmids. SHV-12 was mainly (50%) encoded on IncI1α plasmids (pST-3/-26/-95), followed by IncX3 (12.5%) and IncK2 (3.1%). The bla_TEM–52 genes were located on IncI1α-pST-36 (60%) and IncX1 plasmids (20%). The dominant plasmid lineage among CTX-M-1 isolates was IncI1α (pST-3/-295/-317) (87.5%), followed by IncN-pST-1 (8.3%). CMY-2 was mostly identified on IncI1α (pST-12/-2) (54.5%) and IncK2 (31.8%) plasmids. Several plasmids revealed high similarity to published plasmids from human and animal Enterobacteriaceae. The isolates were assigned to phylogroups A/C (34.7/7.1%), B1 (27.6%), B2 (3.1%), D/F (9.2/10.2%), E (5.1%), and to E. clades (3.0%). With 51 known and 2 novel MLST types, a wide variety of STs was found, including STs previously observed in human isolates (ST10/38/117/131/648). ESBL/AmpC types or STs were rarely correlated with the geographic origin of the isolates or animal species. Virulence gene typing identified extraintestinal pathogenic E. coli (ExPEC; 2.0%), avian pathogenic E. coli (APEC; 51.5%), and atypical enteropathogenic E. coli (EPEC; 6.1%). In conclusion, the high diversity of STs and phylogenetic groups provides hardly any hint for clonal spread of single lineages but hints toward the dissemination of cephalosporin resistance genes in livestock via distinct, globally successful plasmid lineages. Even though a number of isolates could not be assigned to a distinct pathotype, our finding of combined multidrug-resistance and virulence in this facultative pathogen should be considered an additional threat to public health.

Selection of ESBL-producing Escherichia coli in the gut of calves experimentally fed with milk containing antibiotic residues

In the bovine sector, the spread of Enterobacterales producing extended-spectrum and AmpC β-lactamases (ESBL/AmpC) mostly concerns veal calves, and the use of waste milk containing antibiotic residues has been recurrently incriminated. In this study, calves were experimentally fed with milk containing either 2,000 μg/L or 20,000 μg/L of the critically important antibiotic cefquinome. The total counts of enterobacterales and ESBL-producing E. coli were monitored using non-selective and selective media. Our data highlighted the important combination of two main factors (cefquinome exposure and initial ESBL colonization level) in the ESBL selection and amplification process in the gut of calves. Results also proved the dose-independent effect of cefquinome administration on the selection and amplification of ESBL-producing E. coli. Finally, the bla_CTX-M-1/IncI1 ST3 plasmid was systematically recovered after cefquinome exposure, highlighting its epidemic success. Altogether, this work is one of the rare experimental studies providing quantitative information on the impact of waste milk containing antimicrobials on the ESBL load in calves' microbiota, and the first one using cefquinome. These data emphasise the need for global guidelines on the use of waste milk on dairy farms in order to decrease the antimicrobial resistance burden in this sector.

ESBL and AmpC β-Lactamase Encoding Genes in E. coli From Pig and Pig Farm Workers in Vietnam and Their Association With Mobile Genetic Elements

Animals are considered important sources of ESBL/AmpC-producing bacteria in humans. We analyzed indications of transfer of ESBL/AmpC genes between pigs and pig farmers in Vietnam by analyzing whole genome sequences of 114 ESBL/AmpC-producing E. coli isolated from the two hosts, and performed conjugation experiments and plasmid profiling to confirm that such transfer could have happened. ESBL-encoding genes detected in pigs and pig farmers included bla _CTX-M-55, bla _CTX-M-27, bla _CTX-M-65, bla _CTX-M-15, bla _CTX-M-14, bla _CTX-M-3, bla _CTX-M-24, and bla _CARB-2, and AmpC β-lactamases included bla _CMY-2, bla _DHA-1, and bla _CMY-42. The most frequent ESBL gene, bla _CTX-M-55, was carried on plasmid with replicons types IncF, IncX, IncH, IncN, IncR, and IncP. The insertion transposases downstream of the bla _CTX-M-55 gene were different in plasmids carried by different strains. The second most detected gene, bla _CTX-M-27, is found in a stable genetic arrangement with the same flanking transposons seen across strains, and the gene was located on similar conjugal IncF plasmid types, suggesting a horizontal spread of these plasmids. In three strains, we observed a novel bla _CTX-M-27 harboring IncF type of plasmid which had not been reported before. Its closest reference in NCBI was the non-ESBL Salmonella Typhimurium plasmid pB71 that might have experienced an insertion of bla _CTX-M-27. Our data also point to an emergence of plasmids co-carrying ESBL genes, mcr genes, quinolones and other antimicrobials resistance determinants, and such plasmids require special attention. Plasmids phylogeny confirmed that the bla _CTX-M-55 encoding plasmids varied considerably, while those encoding bla _CTX-M-27 were closely related. Plasmids harboring both ESBL genes were confirmed to be conjugative and not to differ in transfer efficacy. The isolates carrying the plasmids, even those with plasmids of similar types, showed wide genetic variation with high number of SNPs, suggesting horizontal spread of plasmids into different clonal lines. Their virulence profiles did not confirm to known pathotypes, suggesting that unrelated commensals are a main reservoir for ESBL and AmpC β-lactamases in both humans and pigs. Overall, despite evidence of transferability of plasmids in the analyzed strains, our findings do not support that ESBL-producing E. coli from pigs or their ESBL/AmpC encoding plasmids are commonly spread to workers in close contact with the animals.

Isolation and characterization of human pathogenic multidrug resistant bacteria associated with plastic litter collected in Zanzibar

Plastic pollution is a growing problem, not at least in areas where poor waste management results in direct pollution of coastal zones, such as South Asia and regions in Africa. In addition to the effect on ecosystems and their related services, plastic pollution may also affect human health indirectly as vectors for infectious disease. As plastic offers a suitable surface for the attachment of biofilm forming bacteria, it may contribute to disease outbreaks and antimicrobial resistance. To investigate the role of plastic litter as potential vectors for pathogenic bacteria, we collected plastic litter from four rural sites in Zanzibar, and isolated adhered bacteria. Isolates were short-read sequenced for further molecular analysis. This revealed that collected plastic litter was associated with diverse bacterial species, including human pathogens Citrobacter freundii, Klebsiella pneumoniae and Vibrio cholerae. Furthermore, most isolates were found to be multidrug resistant. Our findings confirm that plastic litter, serve as novel reservoir for human multidrug resistant pathogenic bacteria that combined with poor sanitation and waste handling, may lead to transmission of infectious diseases and antimicrobial resistance. These findings add a new level to the environmental challenges with plastic pollution; the potential health risk associated with exposure to plastic litter.

New strategies to prevent and control avian pathogenic Escherichia coli (APEC)

Avian pathogenic Escherichia coli (APEC) infections are associated with major economical losses and decreased animal welfare. In broiler production, APEC infections have traditionally been controlled by antibiotics, resulting in an increased prevalence of antibiotic-resistant E. coli. Concerns have been raised that transfer of antibiotic-resistant APEC via the food chain may result in risks for extra-intestinal infection of humans related to zoonotic transfer and increased difficulties in the treatment of human infections caused APEC-related E. coli types. In this review, the risks associated with APEC are presented based on new knowledge on transmission, virulence and antibiotic resistance of APEC. A major new change in our understanding of APEC is the high degree of genuine vertical transfer of APEC from parents to offspring. A new strategy for controlling APEC, including control of antibiotic-resistant APEC, has to focus on limiting vertical transfer from parents to offspring, and subsequent horizontal transmission within and between flocks and farms, by using all-in-all-out production systems and implementing a high level of biosecurity. Vaccination and the use of competitive exclusion are important tools to be considered. A specific reduction of antibiotic-resistant APEC can be obtained by implementing culling strategies, only allowing the use of antibiotics in cases where animal welfare is threatened. Strategies to reduce APEC, including antibiotic-resistant APEC, need to be implemented in the whole production pyramid, but it has to start at the very top of the production pyramid.

Global evolutionary epidemiology and resistome dynamics of Citrobacter species, Enterobacter hormaechei, Klebsiella variicola, and Proteeae clones

Citrobacter spp., Enterobacter hormaechei subsp., Klebsiella variicola and Proteae tribe members are rarely isolated Enterobacterales increasingly implicated in nosocomial infections. Herein, we show that these species contain multiple genes encoding resistance to important antibiotics and are widely and globally distributed, being isolated from human, animal, plant, and environmental sources in 67 countries. Certain clones and clades of these species were internationally disseminated, serving as reservoirs and mediums for the global dissemination of antibiotic resistance genes. As they can easily transmit these genes to more pathogenic species, additional molecular surveillance studies should be undertaken to identify and contain these antibiotic-resistant species.

Plasmid Transfer by Conjugation in Gram-Negative Bacteria: From the Cellular to the Community Level

Bacterial conjugation, also referred to as bacterial sex, is a major horizontal gene transfer mechanism through which DNA is transferred from a donor to a recipient bacterium by direct contact. Conjugation is universally conserved among bacteria and occurs in a wide range of environments (soil, plant surfaces, water, sewage, biofilms, and host-associated bacterial communities). Within these habitats, conjugation drives the rapid evolution and adaptation of bacterial strains by mediating the propagation of various metabolic properties, including symbiotic lifestyle, virulence, biofilm formation, resistance to heavy metals, and, most importantly, resistance to antibiotics. These properties make conjugation a fundamentally important process, and it is thus the focus of extensive study. Here, we review the key steps of plasmid transfer by conjugation in Gram-negative bacteria, by following the life cycle of the F factor during its transfer from the donor to the recipient cell. We also discuss our current knowledge of the extent and impact of conjugation within an environmentally and clinically relevant bacterial habitat, bacterial biofilms.

Secondary Effects of Antibiotics on Microbial Biofilms

Biofilms are assemblages of microorganisms attached to each other, or to a surface, and encased in a protective, self-produced matrix. Such associations are now recognized as the predominant microbial growth mode. The physiology of cells in biofilms differs from that of the planktonic cells on which most research has been conducted. Consequently, there are significant gaps in our knowledge of the biofilm lifestyle. Filling this gap is particularly important, given that biofilm cells may respond differently to antibiotics than do planktonic cells of the same species. Understanding the effects of antibiotics on biofilms is of paramount importance for clinical practice due to the increased levels of antibiotic resistance and resistance dissemination in biofilms. From a wider environmental perspective antibiotic exposure can alter the ecology of biofilms in nature, and hence disrupt ecosystems. Biofilm cells display increased resilience toward antibiotics. This resilience is often explained by mechanisms and traits such as decreased antibiotic penetration, metabolically inactive persister cells, and intrinsic resistance by members of the biofilm community. Together, these factors suggest that cells in biofilms are often exposed to subinhibitory concentrations of antimicrobial agents. Here we discuss how cells in biofilms are affected by the presence of antibiotics at subinhibitory concentrations, and the possible ramifications of such secondary effects for healthcare and the environment.