Molecular characterisation of trimethoprim resistance in Escherichia coli and Klebsiella pneumoniae during a two year intervention on trimethoprim use

Resistome Signature and Antibiotic Resistance Mechanisms in Rhizospheric Soil Bacteriomes of Mecca Region, Saudi Arabia: Insights into Impact on Human Health

The objective of this investigation is to ascertain the distinctive profile of the rhizospheric soil resistome within the Mecca region, while also evaluating the potential risks associated with the horizontal transfer of resistome determinants to the open environment and human clinical isolates. We have made metagenomic whole-genome shotgun sequencing for rhizospheric microbiomes of two endemic plants, namely Moringa oleifera and Abutilon fruticosum. The rhizospheric resistomes of the two plants and the abundance of antibiotic resistance genes (ARGs) were identified by cross-referencing encoded proteins with the comprehensive antibiotic resistance database (CARD). The identified ARGs were then analyzed for their antimicrobial resistance (AMR) mechanisms. Predominantly within this soil are the two bacterial species Pseudomonas aeruginosa and Mycobacterium tuberculosis. These opportunistic human pathogens are implicated in respiratory infections and are correlated with heightened mortality rates. The most prevalent array of ARGs existing in this soil comprises mexA, mexC, mexE, and cpxR, associated with mechanisms of antibiotic active efflux, along with ACC(2), ACC(3), AAC(6), and APH(6), in addition to arr1, arr3, arr4, iri, rphA, and rphB, implicated in antibiotic inactivation. Furthermore, vanS, vanR, and vanJ are identified for antibiotic target alteration, while rpoB2 and RbpA are noted for antibiotic target replacement and protection, respectively. These mechanisms confer resistance against a diverse spectrum of drug classes encompassing fluoroquinolones, aminoglycosides, glycopeptides, and rifampicins. This study underscores the potential hazards posed to human health by the presence of these pathogenic bacteria within the rhizospheric soil of the Mecca region, particularly in scenarios where novel ARGs prevalent in human populations are harbored and subsequently transmitted through the food chain to human clinical isolates. Consequently, stringent adherence to good agricultural and food transportation practices is imperative, particularly with regard to edible plant parts and those utilized in folkloric medicine.

Whole genome sequencing of uropathogenic E. coli from Ireland reveals diverse resistance mechanisms and strong correlation with phenotypic (EUCAST) susceptibility testing

Urinary tract infections (UTI) caused by uropathogenic Escherichia coli (UPEC) pose a global health concern. Resistance mechanisms, including genetic mutations in antimicrobial target genes, efflux pumps, and drug deactivating enzymes, hinder clinical treatment. These resistance factors often spread through mobile genetic elements. Molecular techniques like whole genome sequencing (WGS), multilocus sequence typing (MLST), and phylotyping help decode bacterial genomes and categorise resistance genes. In this study, we analysed 57 UPEC isolates from different UTI patients following EUCAST guidelines. A selection of 17 representative strains underwent WGS, phylotyping, MLST, and comparative analysis to connect laboratory susceptibility data with predictive genomics based on key resistance genes and chromosomal mutations in antimicrobial targets. Trimethoprim resistance consistently correlated with dfr genes, with six different alleles detected among the isolates. These dfr genes often coexisted with class 1 integrons, with the most common gene cassette combining dfr and aadA. Furthermore, 52.9% of isolates harboured the blaTem-1 gene, rendering resistance to ampicillin and amoxicillin. Ciprofloxacin-resistant strains exhibited mutations in GyrA, GyrB and ParC, plasmid-mediated quinolone resistance genes (qnrb10), and aac(6')-Ib-cr5. Nitrofurantoin resistance in one isolate stemmed from a four amino acid deletion in NfsB. These findings illustrate the varied strategies employed by UPEC to resist antibiotics and the correlation between clinical susceptibility testing and molecular determinants. As molecular testing gains prominence in clinical applications, understanding key resistance determinants becomes crucial for accurate susceptibility testing and guiding effective antimicrobial therapy.

Deep mutational scanning of Pneumocystis jirovecii dihydrofolate reductase reveals allosteric mechanism of resistance to an antifolate

Pneumocystis jirovecii is a fungal pathogen that causes pneumocystis pneumonia, a disease that mainly affects immunocompromised individuals. This fungus has historically been hard to study because of our inability to grow it in vitro. One of the main drug targets in P. jirovecii is its dihydrofolate reductase (PjDHFR). Here, by using functional complementation of the baker's yeast ortholog, we show that PjDHFR can be inhibited by the antifolate methotrexate in a dose-dependent manner. Using deep mutational scanning of PjDHFR, we identify mutations conferring resistance to methotrexate. Thirty-one sites spanning the protein have at least one mutation that leads to resistance, for a total of 355 high-confidence resistance mutations. Most resistance-inducing mutations are found inside the active site, and many are structurally equivalent to mutations known to lead to resistance to different antifolates in other organisms. Some sites show specific resistance mutations, where only a single substitution confers resistance, whereas others are more permissive, as several substitutions at these sites confer resistance. Surprisingly, one of the permissive sites (F199) is without direct contact to either ligand or cofactor, suggesting that it acts through an allosteric mechanism. Modeling changes in binding energy between F199 mutants and drug shows that most mutations destabilize interactions between the protein and the drug. This evidence points towards a more important role of this position in resistance than previously estimated and highlights potential unknown allosteric mechanisms of resistance to antifolate in DHFRs. Our results offer unprecedented resources for the interpretation of mutation effects in the main drug target of an uncultivable fungal pathogen.

Modulation of multidrug-resistant clone success in Escherichia coli populations: a longitudinal, multi-country, genomic and antibiotic usage cohort study

BACKGROUND

The effect of antibiotic usage on the success of multidrug-resistant (MDR) clones in a population remains unclear. With this genomics-based molecular epidemiology study, we aimed to investigate the contribution of antibiotic use to Escherichia coli clone success, relative to intra-strain competition for colonisation and infection.

METHODS

We sequenced all the available E coli bloodstream infection isolates provided by the British Society for Antimicrobial Chemotherapy (BSAC) from 2012 to 2017 (n=718) and combined these with published data from the UK (2001-11; n=1090) and Norway (2002-17; n=3254). Defined daily dose (DDD) data from the European Centre for Disease Prevention and Control (retrieved on Sept 21, 2021) for major antibiotic classes (β-lactam, tetracycline, macrolide, sulfonamide, quinolone, and non-penicillin β-lactam) were used together with sequence typing, resistance profiling, regression analysis, and non-neutral Wright-Fisher simulation-based modelling to enable systematic comparison of resistance levels, clone success, and antibiotic usage between the UK and Norway.

FINDINGS

Sequence type (ST)73, ST131, ST95, and ST69 accounted for 892 (49·3%) of 1808 isolates in the BSAC collection. In the UK, the proportion of ST69 increased between 2001-10 and 2011-17 (p=0·0004), whereas the proportions of ST73 and ST95 did not vary between periods. ST131 expanded quickly after its emergence in 2003 and its prevalence remained consistent throughout the study period (apart from a brief decrease in 2009-10). The extended-spectrum β-lactamase (ESBL)-carrying, globally disseminated MDR clone ST131-C2 showed overall greater success in the UK (154 [56·8%] of 271 isolates in 2003-17) compared with Norway (51 [18·3%] of 278 isolates in 2002-17; p<0·0001). DDD data indicated higher total use of antimicrobials in the UK, driven mainly by the class of non-penicillin β-lactams, which were used between 2·7-times and 5·1-times more in the UK per annum (ratio mean 3·7 [SD 0·8]). This difference was associated with the higher success of the MDR clone ST131-C2 (pseudo-R2 69·1%). A non-neutral Wright-Fisher model replicated the observed expansion of non-MDR and MDR sequence types under higher DDD regimes.

INTERPRETATION

Our study indicates that resistance profiles of contemporaneously successful clones can vary substantially, warranting caution in the interpretation of correlations between aggregate measures of resistance and antibiotic usage. Our study further suggests that in countries with low-to-moderate use of antibiotics, such as the UK and Norway, the extent of non-penicillin β-lactam use modulates rather than determines the success of widely disseminated MDR ESBL-carrying E coli clones. Detailed understanding of underlying causal drivers of success is important for improved control of resistant pathogens.

FUNDING

Trond Mohn Foundation, Marie Skłodowska-Curie Actions, European Research Council, Royal Society, and Wellcome Trust.

Antimicrobial resistance patterns of Acinetobacter baumannii and Klebsiella pneumoniae isolated from dogs presented at a veterinary academic hospital in South Africa

Background

Acinetobacter baumannii and Klebsiella pneumoniae are opportunistic bacterial pathogens responsible for hospital-acquired infections in veterinary medicine. Infection with these bacteria always requires urgent antimicrobial therapy. However, there is no evidence of studies that have investigated the antimicrobial drug resistance profile of these organisms in a veterinary setting in South Africa. This study investigated the antimicrobial resistance (AMR) patterns of A. baumannii and K. pneumoniae from clinical specimens obtained from dogs presented at a veterinary academic hospital. The findings of this study contribute to an improved understanding of the AMR profile of these bacteria in veterinary medicine.

Materials and Methods

Retrospective data of clinical samples from dogs that were positive for A. baumannii and K. pneumoniae between 2007 and 2013 were used in this study. The antimicrobial susceptibility of the isolates was determined using the disk diffusion method following the Clinical and Laboratory Standards Institute guidelines. The A. baumannii isolates were subjected to a panel of 20 antibiotics, while K. pneumoniae isolates were subjected to a panel of 22 antibiotics. Data were analyzed using descriptive statistics and presented using tables and figures.

Results

Twenty (n = 20) A. baumannii isolates were isolated from bronchoalveolar lavage, foreign objects, bone, urine, skin, blood, ear, nasal, and oral cavity. Almost all A. baumannii (95%, 19/20) isolates were resistant to at least one antibiotic, and 60% (12/20) were multidrug-resistant (MDR). Klebsiella pneumoniae (n = 56) was isolated from urine, foreign objects, abscesses, ears, eyes, tracheal aspirations, bronchoalveolar lavages, eyes, abdominal aspirates, anal glands, bones, and intestinal and lung biopsies. All K. pneumoniae (100%, 56/56) isolates were resistant to at least one antibiotic, and 98% (55/56) were MDR.

Conclusion

Both A. baumannii and K. pneumoniae were isolated in various clinical tissue samples and exhibited a high prevalence of resistance to multiple antibiotics. In addition, these bacteria exhibited a high prevalence of resistance to β-lactam compared to other classes of antibiotics, which is likely to impact treatment options and patient prognosis.

Uropathogenic Escherichia coli (UPEC)-Associated Urinary Tract Infections: The Molecular Basis for Challenges to Effective Treatment

Urinary tract infections (UTIs) are among the most common bacterial infections, especially among women and older adults, leading to a significant global healthcare cost burden. Uropathogenic Escherichia coli (UPEC) are the most common cause and accounts for the majority of community-acquired UTIs. Infection by UPEC can cause discomfort, polyuria, and fever. More serious clinical consequences can result in urosepsis, kidney damage, and death. UPEC is a highly adaptive pathogen which presents significant treatment challenges rooted in a complex interplay of molecular factors that allow UPEC to evade host defences, persist within the urinary tract, and resist antibiotic therapy. This review discusses these factors, which include the key genes responsible for adhesion, toxin production, and iron acquisition. Additionally, it addresses antibiotic resistance mechanisms, including chromosomal gene mutations, antibiotic deactivating enzymes, drug efflux, and the role of mobile genetic elements in their dissemination. Furthermore, we provide a forward-looking analysis of emerging alternative therapies, such as phage therapy, nano-formulations, and interventions based on nanomaterials, as well as vaccines and strategies for immunomodulation. This review underscores the continued need for research into the molecular basis of pathogenesis and antimicrobial resistance in the treatment of UPEC, as well as the need for clinically guided treatment of UTIs, particularly in light of the rapid spread of multidrug resistance.

Diversity of virulence and antibiotic resistance genes expressed in Class A biosolids and biosolids-amended soil as revealed by metatranscriptomic analysis

Class A biosolids is a treated sewage sludge, commonly applied to agricultural fields, home lawns/gardens, golf courses, forests, and remediation sites around the world. This practice is of public and agricultural concern due to the possibility that biosolids contain antibiotic-resistant bacteria and fungal pathogens that could persist for extended periods in soil. This possibility was determined by metatranscriptomic analysis of virulence, antibiotic resistance, and plasmid conjugation genes, a Class A biosolids, organically managed soil, and biosolids-amended soil under realistic conditions. Biosolids harbored numerous transcriptionally active pathogens, antibiotic resistance genes, and conjugative genes that annotated mostly to Gram-positive pathogens of animal hosts. Biosolids amendment to soil significantly increased the expression of virulence genes by numerous pathogens and antibiotic-resistant genes that were strongly associated with biosolids. Biosolids amendment also significantly increased the expression of virulence genes by native soil fungal pathogens of plant hosts, which suggests higher risks of crop damage by soil fungal pathogens in biosolids-amended soil. Although results are likely to be different in other soils, biosolids, and microbial growth conditions, they provide a more holistic, accurate view of potential health risks associated with biosolids and biosolids-amended soils than has been achievable with more selective cultivation and PCR-based techniques.

Antibiotic use in infants within the first year of life is associated with the appearance of antibiotic-resistant genes in their feces

Background

Antibiotic resistance, an increasing challenge, is not only a national threat but also a global threat. Carriage of resistance genes is not limited to adults alone, various microbiota niches present in the body system of children have been found to harbor bacteria carrying resistant genes, especially, their gut microbiota. This study aims to identify selected antibiotic-resistant genes from the fecal samples of infants and the association of antibiotics use with the occurrence of resistant genes in the infant's gut.

Methods

A total number of 172 metagenomic DNA samples previously extracted from stool samples of 28 Nigerian babies longitudinally within their first year of life were screened for the presence of ESBL genes (blaSHV, blaTEM, and blaCTX-M), PMQR genes (qnrA, qnrB, qnrS, qepA), ribosomal protection protein tetracycline resistance gene, (RPP) β-lactamase (blaZ), macrolide (ermA, ermB, mefA/E), aminoglycoside modifying enzymes gent^R (aac(6')/aph(2″)) and dfrA genes by PCR. Nineteen (19) of the 28 babies used antibiotics during the study. The association between antibiotic use by the babies within the first year of life and occurrence of resistant genes were analyzed by Spearman rank correlation.

Results

One hundred and twenty-two (122) samples (71%) out of the 172 isolates had antibiotic-resistance genes. PMQR genes were absent in all the samples. Three isolates had blaTEM gene, nine isolates had blaSHV gene, six isolates had blaCTX-M gene and 19 isolates had dfrA gene, 31 samples had tet gene, 29 samples had mef gene, 27 samples had ermB gene, four samples had ermA gene, 13 samples had blaZ gene and 16 samples had aac gene. The babies whose samples had resistant genes used antibiotics in the same months the samples were collected. Interestingly, the 11 babies whose samples had the dfrA gene all used antibiotics in the same months their samples were collected but none of them used trimethoprim/sulfamethoxazole antibiotic. The overall correlation matrix of the babies showed a strong association between antibiotic use (AU) and antibiotic use presence of resistance genes (AUPRG) with a coefficient of 0.89. Antibiotic-resistant genes are present in the gut of infants and their occurrence is strongly connected with antibiotic use by infants.

An Improvement in the Antimicrobial Resistance Patterns of Urinary Isolates in the Out-Of-Hospital Setting following Decreased Community Use of Antibiotics during the COVID-19 Pandemic

After the onset of COVID-19 pandemic, a decrease in antibiotic consumption in the out-of-hospital setting was observed. However, data about the impact of this reduction on antimicrobial resistance are lacking. The aim of this study was to assess antibiotic consumption and antibiotic resistance at the community level in an Italian province before and after the beginning of the COVID-19 pandemic. We carried out an observational study, comparing antibiotic consumption in the community during 2019 and 2020 and the antibiotic resistance patterns of Enterobacterales cultured from urine samples from the out-of-hospital setting during the first semester of 2020 and 2021. Overall, antibiotic consumption decreased by 28% from 2019 to 2020 (from 13.9 to 9.97 DDD/1000 inhabitants/day). The main reductions involved penicillins (ATC J01C, from 6.9 to 4.8 DDD/1000 inhabitants/day, −31%), particularly amoxicillin/clavulanate (ATC J01CR02, −30%) and amoxicillin (J01CA04, −35.2%). Overall, 6445 strains of Enterobacterales were analyzed; in 2020, the susceptibility rate of amoxicillin/clavulanate increased from 57.5% to 87% among isolates from the primary care setting (p < 0.001) and from 39% to 72% (p < 0.001) among isolates from LTCF. The reduction in the community use of antibiotics observed in 2020 was followed by a change in the antimicrobial resistance patterns of urinary isolates.

Multi-year antimicrobial-resistance trends in urine Escherichia coli isolates from both community-based and hospital-based laboratories of an Australian local health district

OBJECTIVES

Efforts to monitor and combat antimicrobial resistance (AMR) are typically focused on the hospital-based laboratory setting. The aim of this study was to longitudinally examine and compare trends in AMR among urine Escherichia coli isolates from a private community-based laboratory and a public hospital-based laboratory in an Australian local health district.

METHODS

A total of 108 262 urine E. coli isolates from a public hospital-based laboratory (N = 34 103) and a private community-based laboratory (N = 74 159) in a single health district between 2007-2019 were analysed. Linear regression was used to identify significance of change in AMR rates in both laboratories independently and detect any significant interaction of each setting in proportional change over the study period.

RESULTS

Similar AMR trends were detected among urinary E. coli isolates in private community-based laboratory and public hospital-based laboratory settings over 12 y. AMR rates were consistently higher in the public hospital-based setting. Ampicillin was the only antibiotic for which the E. coli resistance trend did not significantly change over the time period in either laboratory setting. All other antibiotics showed a significant increase in AMR rates over time in both settings.

CONCLUSIONS

AMR rates in both the private community-based laboratory and public hospital-based laboratory settings increased over time and were consistently higher in the public hospital-based laboratory setting. Since private laboratories handle the vast majority of pathology volumes in community outpatient settings in Australia, interventions incorporating the community-based laboratory setting are critical to addressing AMR in the community.

Investigating and Modeling the Regulation of Extracellular Antibiotic Resistance Gene Bioavailability by Naturally Occurring Nanoparticles

Extracellular antibiotic resistance genes (eARGs) are widespread in the environment and can genetically transform bacteria. This work examined the role of environmentally relevant nanoparticles (NPs) in regulating eARG bioavailability. eARGs extracted from antibiotic-resistant B. subtilis were incubated with nonresistant recipient B. subtilis cells. In the mixture, particle type (either humic acid coated nanoparticles (HASNPs) or their micron-sized counterpart (HASPs)), DNase I concentration, and eARG type were systematically varied. Transformants were counted on selective media. Particles decreased bacterial growth and eARG bioavailability in systems without nuclease. When DNase I was present (≥5 μg/mL), particles increased transformation via chromosomal (but not plasmid-borne) eARGs. HASNPs increased transformation more than HASPs, indicating that the smaller nanoparticle with greater surface area per volume is more effective in increasing eARG bioavailability. These results were also modeled via particle aggregation theory, which represented eARG-bacteria interactions as transport leading to collision, followed by attachment. Using attachment efficiency as a fitting factor, the model predicted transformant concentrations within 35% of experimental data. These results confirm the ability of NPs to increase eARG bioavailability and suggest that particle aggregation theory may be a simplified and suitable framework to broadly predict eARG uptake.

E. coli bacteraemia and antimicrobial resistance following antimicrobial prescribing for urinary tract infection in the community

Background

Urinary tract infections are one of the most common infections in primary and secondary care, with the majority of antimicrobial therapy initiated empirically before culture results are available. In some cases, however, over 40% of the bacteria that cause UTIs are resistant to some of the antimicrobials used, yet we do not know how the patient outcome is affected in terms of relapse, treatment failure, progression to more serious illness (bacteraemia) requiring hospitalization, and ultimately death. This study analyzed the current patterns of antimicrobial use for UTI in the community in Scotland, and factors for poor outcomes.

Objectives

To explore antimicrobial use for UTI in the community in Scotland, and the relationship with patient characteristics and antimicrobial resistance in E. coli bloodstream infections and subsequent mortality.

Methods

We included all adult patients in Scotland with a positive blood culture with E. coli growth, receiving at least one UTI-related antimicrobial (amoxicillin, amoxicillin/clavulanic acid, ciprofloxacin, trimethoprim, and nitrofurantoin) between 1st January 2009 and 31st December 2012. Univariate and multivariate logistic regression analysis was performed to understand the impact of age, gender, socioeconomic status, previous community antimicrobial exposure (including long-term use), prior treatment failure, and multi-morbidity, on the occurrence of E. coli bacteraemia, trimethoprim and nitrofurantoin resistance, and mortality.

Results

There were 1,093,227 patients aged 16 to 100 years old identified as receiving at least one prescription for the 5 UTI-related antimicrobials during the study period. Antimicrobial use was particularly prevalent in the female elderly population, and 10% study population was on long-term antimicrobials. The greatest predictor for trimethoprim resistance in E. coli bacteraemia was increasing age (OR 7.18, 95% CI 5.70 to 9.04 for the 65 years old and over group), followed by multi-morbidity (OR 5.42, 95% CI 4.82 to 6.09 for Charlson Index 3+). Prior antimicrobial use, along with prior treatment failure, male gender, and higher deprivation were also associated with a greater likelihood of a resistant E. coli bacteraemia. Mortality was significantly associated with both having an E. coli bloodstream infection, and those with resistant growth.

Conclusion

Increasing age, increasing co-morbidity, lower socioeconomic status, and prior community antibiotic exposure were significantly associated with a resistant E. coli bacteraemia, which leads to increased mortality.

Identification and validation of potent inhibitor of Escherichia coli DHFR from MMV pathogen box

The present study is conducted to find the solution of rising antimicrobial resistance (AMR) in Escherichia coli which is a pathogen responsible for fatal systemic infections in human and animals. The enzyme dihydrofolate reductase (DHFR) is found in all organisms. In this study DHFR of E. coli (ec-DHFR) and human DHFR (h-DHFR) is targeted by novel chemical entities (NCE) from the Pathogen box of Medicines for Malaria Venture, Switzerland (MMV) using molecular modelling. The in-silico studies were further validated by in-vitro assays. The virtual screening of 400 MMV compounds was conducted using PyRx standard tool followed by manual docking of selected compounds by Autodock vina and Ligplot program. The in-silico studies showed good binding energy and strong hydrogen bond in docking of MMV675968 with ec-DHFR and no hydrogen bond with h-DHFR. This was further validated by the Molecular dynamic studies that revealed high binding free energy in ec-DHFR and in-vitro assays that produced good synergy in combination study of MMV675968 with last line (meropenem) and last resort (colistin) antibiotics. The extensive MD simulation and energetic analysis thus concludes that MMV675968 targets ec-DHFR. The combination studies were conducted with MMV675968 and FDA approved drugs against a panel of multidrug resistant Escherichia coli isolates. The synergistic results obtained in combination studies concluded that in-vitro data is consistent with in-silico data and that MMV675968 is a potential lead for future process of antimicrobial drug development against the multidrug resistance E. coli.Communicated by Ramaswamy H. Sarma.

Antimicrobial resistance in urinary pathogens and culture-independent detection of trimethoprim resistance in urine from patients with urinary tract infection

Background

Although urinary tract infections (UTIs) are extremely common, isolation of causative uropathogens is not always routinely performed, with antibiotics frequently prescribed empirically. This study determined the susceptibility of urinary isolates from two Health and Social Care Trusts (HSCTs) in Northern Ireland to a range of antibiotics commonly used in the treatment of UTIs. Furthermore, we determined if detection of trimethoprim resistance genes (dfrA) could be used as a potential biomarker for rapid detection of phenotypic trimethoprim resistance in urinary pathogens and from urine without culture.

Methods

Susceptibility of E. coli and Klebsiella spp. isolates (n = 124) to trimethoprim, amoxicillin, ceftazidime, ciprofloxacin, co-amoxiclav and nitrofurantoin in addition to susceptibility of Proteus mirabilis (n = 61) and Staphylococcus saprophyticus (n = 17) to trimethoprim was determined by ETEST® and interpreted according to EUCAST breakpoints. PCR was used to detect dfrA genes in bacterial isolates (n = 202) and urine samples(n = 94).

Results

Resistance to trimethoprim was observed in 37/124 (29.8%) E. coli and Klebsiella spp. isolates with an MIC₉₀ > 32 mg/L. DfrA genes were detected in 29/37 (78.4%) trimethoprim-resistant isolates. Detection of dfrA was highly sensitive (93.6%) and specific (91.4%) in predicting phenotypic trimethoprim resistance among E. coli and Klebsiella spp. isolates. The dfrA genes analysed were detected using a culture-independent PCR method in 16/94 (17%) urine samples. Phenotypic trimethoprim resistance was apparent in isolates cultured from 15/16 (94%) dfrA-positive urine samples. There was a significant association (P < 0.0001) between the presence of dfrA and trimethoprim resistance in urine samples containing Gram-negative bacteria (Sensitivity = 75%; Specificity = 96.9%; PPV = 93.8%; NPV = 86.1%).

Conclusions

This study demonstrates that molecular detection of dfrA genes is a good indicator of trimethoprim resistance without the need for culture and susceptibility testing.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02551-9.

Structure-guided functional studies of plasmid-encoded dihydrofolate reductases reveal a common mechanism of trimethoprim resistance in Gram-negative pathogens

Two plasmid-encoded dihydrofolate reductase (DHFR) isoforms, DfrA1 and DfrA5, that give rise to high levels of resistance in Gram-negative bacteria were structurally and biochemically characterized to reveal the mechanism of TMP resistance and to support phylogenic groupings for drug development against antibiotic resistant pathogens. Preliminary screening of novel antifolates revealed related chemotypes that showed high levels of inhibitory potency against Escherichia coli chromosomal DHFR (EcDHFR), DfrA1, and DfrA5. Kinetics and biophysical analysis, coupled with crystal structures of trimethoprim bound to EcDHFR, DfrA1 and DfrA5, and two propargyl-linked antifolates (PLA) complexed with EcDHFR, DfrA1 and DfrA5, were determined to define structural features of the substrate binding pocket and guide synthesis of pan-DHFR inhibitors.

Critical residue variations in two of the most clinically prevalent DHFR isoforms are identified as a common structural element in trimethoprim-resistant DHFR which impose changes on enzyme catalysis and ligand-cofactor cooperativity.

Multidrug Resistance Genes Carried by a Novel Transposon Tn7376 and a Genomic Island Named MMGI-4 in a Pathogenic Morganella morganii Isolate

Antimicrobial resistance in Morganella morganii is increasing in recent years, which is mainly introduced via extra genetic and mobile elements. The aim of our study is to analyze the multidrug resistance (MDR) and characterize the mobile genetic elements (MGEs) in M. morganii isolates. Here, we report the characteristic of a pathogenic M. morganii isolate containing multidrug resistance genes that are mainly carried by a novel transposon Tn7376 and a genomic island. Sequence analysis suggested that the Tn7376 could be generated through homologous recombination between two different IS26-bounded translocatable units (TUs), namely, module A (IS26-Hp-IS26-mph(A)-mrx(A)-mphR-IS6100-chrA-sul1-qacEΔ1) and module B (ISCR1-sul1-qacEΔ1-cmlA1-aadA1-aadB-intI1-IS26), and the genomic island named MMGI-4 might derive from a partial structure of different original genomic islands that also carried IS26-mediated TUs. Notably, a 2,518-bp sequence linked to the module A and B contains a 570-bp dfrA24 gene. To the best of our knowledge, this is the first report of the novel Tn7376 possessing a complex class 1 integron that carried an infrequent gene dfrA24 in M. morganii.

IMPORTANCE Mobile genetic elements (MGEs), especially for IS26-bounded translocatable units, may act as a reservoir for a variety of antimicrobial resistance genes in clinically important pathogenic bacteria. We expounded this significant genetic characteristic by investigating a representative M. morganii isolate containing multidrug resistance genes, including the infrequent dfrA24. Our study suggested that these acquired resistance genes were mainly driven by IS26-flanked important MGEs, such as the novel Tn7376 and the MMGI-4. We demonstrated that IS26-related MGEs contributed to the emergence of the extra gene dfrA24 in M. morganii through some potential genetic events like recombination, transposition, and integration. Therefore, it is of importance to investigate persistently the prevalence these MEGs in the clinical pathogens to provide risk assessment of emergence and development of novel resistance genes.

Rapid decline of ceftazidime resistance in antibiotic-free and sub-lethal environments is contingent on genetic background

Trade-offs of antibiotic resistance evolution, such as fitness cost and collateral sensitivity (CS), could be exploited to drive evolution toward antibiotic susceptibility. Decline of resistance may occur when resistance to other drug leads to CS to the first one and when compensatory mutations, or genetic reversion of the original ones, reduce fitness cost. Here we describe the impact of antibiotic-free and sublethal environments on declining ceftazidime resistance in different Pseudomonas aeruginosa resistant mutants. We determined that decline of ceftazidime resistance occurs within 450 generations, which is caused by newly acquired mutations and not by reversion of the original ones, and that the original CS of these mutants is preserved. In addition, we observed that the frequency and degree of this decline is contingent on genetic background. Our results are relevant to implement evolution-based therapeutic approaches, as well as to redefine global policies of antibiotic use, such as drug cycling.

Longitudinal Monitoring Reveals Persistence of Colistin-Resistant Escherichia coli on a Pig Farm Following Cessation of Colistin Use

Colistin-resistant bacteria harboring plasmid-mediated mcr genes are of concern as they may be a cause of serious nosocomial infections. It is hypothesized that cessation of colistin use as a feed additive for pigs will reduce the occurrence and distribution of mcr genes in farms. The aim of this study was to investigate this hypothesis by longitudinal monitoring and characterizing of mcr positive Escherichia coli (MCRPE) isolates after colistin was withdrawn on a central Thailand pig farm that previously had a high frequency of MCRPE. Colistin use ceased at the beginning of 2017, and subsequently 170 samples were collected from farrowing sows and suckling piglets (n = 70), wastewater (n = 50) and farm workers (n = 50) over a 3.5-year period. Bacteria were identified by MALDI-TOF mass spectrometry and minimal inhibitory concentrations were determined by broth microdilution. The antibiogram of mcr positive E. coli isolates was determined using the Vitek2 automated susceptibility machine, and multiplex and simplex PCRs were performed for mcr-1-8 genes. MCRPE containing either mcr-1 or mcr-3 were isolated from pigs throughout the investigation period, but with a declining trend, whereas MCRPE isolates were recovered from humans only in 2017. MCRPE were still being recovered from wastewater in 2020. Most MCRPE isolates possessed the virulence genes Stap, Stb, or Stx2e, reflecting pathogenic potential in pigs, and showed high rates of resistance to ampicillin, gentamicin and tetracycline. Pulsed-field gel electrophoresis and multi-locus sequence typing showed that diverse MCRPE clones were distributed on the farm. The study identified a decline of pathogenic MCRPE following withdrawal of colistin, with pigs being the primary source, followed by wastewater. However, short-term therapeutic usage of other antibiotics could enhance the re-occurrence of mcr-carrying bacteria. Factors including the environment, management, and gene adaptations that allow maintenance of colistin resistance require further investigation, and longer-term studies are needed.

Prevalence, antimicrobial resistance and virulence genes of Salmonella serovars isolated from humans and animals

We investigated the prevalence, antimicrobial susceptibility, antimicrobial resistance and virulence genes of Salmonella isolates recovered from humans and different species of animals. Out of 1231 samples, 88 (7.15%) Salmonella isolates were obtained, among which 21 (23.86%) belonged to Salmonella enterica subsp. enterica sero var. Weltevreden, 22 (25%) to S. Enteritidis, 16 (18.2%) to S. Typhi and 14 (15.9%) to S. Newport; 7 (7.95%) isolates were untypable. Among the 88 isolates, 65.90% showed resistance to gentamicin, 61.36% to tetracycline, 61.18% to cefotaxime, 48.86% to trimethoprim, 45.45% to ampicillin, 11.36% to ceftriaxone, 10.22% to chloramphenicol and 7.95% each to ciprofloxacin and cefepime. Most of the isolates were susceptible, with a low MIC (≤ 0.25 μg/ml) value, to cefepime, cefotaxime, ciprofloxacin, ceftriaxone and co-trimoxazole and with a moderate MIC (0.5-4 μg/ml) to ampicillin, tetracycline, gentamicin and chloramphenicol. The resistance genes bla_TEM, tetA and dfrA12 were most prevalent, irrespective of the host of origin of the isolates. While invA was used for molecular detection of Salmonella, other virulence genes, viz. sipA, sipB, sipC, stn and pagN, were also detected in all Salmonella isolates. A total of 38.64% isolates were multidrug-resistant (MDR), and various virulence genes were present among the isolated serovars. This study highlights the importance of continuous monitoring and surveillance for pathogenic Salmonella and their potential risks to both humans and animals.

Distribution, Phylogeny and Evolution of Clinical and Environmental Vibrio vulnificus Antibiotic-Resistant Genes

Vibrio vulnificus is an emergent marine pathogen and is the cause of a deadly septicemia. However, the evolution mechanism of antibiotic-resistant genes (ARGs) is still unclear. Twenty-two high-quality complete genomes of V. vulnificus were obtained and grouped into 16 clinical isolates and 6 environmental isolates. Genomic annotations found 23 ARG orthologous genes, among which 14 ARGs were shared by V. vulnificus and other Vibrio members. Furthermore, those ARGs were located in their chromosomes, rather than in the plasmids. Phylogenomic reconstruction based on single-copy orthologous protein sequences and ARG protein sequences revealed that clinical and environmental V. vulnificus isolates were in a scattered distribution. The calculation of non-synonymous and synonymous substitutions indicated that most of ARGs evolved under purifying selection with the Ka/Ks ratios lower than one, while h-ns, rsmA, and soxR in several clinical isolates evolved under the positive selection with Ka/Ks ratios >1. Our result indicated that V. vulnificus antibiotic-resistant armory was not only confined to clinical isolates, but to environmental ones as well and clinical isolates inclined to accumulate beneficial non-synonymous substitutions that could be retained to improve competitiveness.

Genotyping of Escherichia coli Causing Vaginal Infection in Dysplastic Patients with Similar Genetic Backgrounds Between Commensal and Virulent Strains

Background: Escherichia coli in the vagina includes several virulence factors in its genome mobile genetic elements and can facilitate colonization, mainly in immunosuppressed patients. Objectives: This work aimed to demonstrate that E. coli strains of vaginal origin isolated from dysplastic patients possess virulence and resistance genes Methods: This study included one hundred and five E. coli strains isolated from women with cervical dysplasia and vaginal infection. The strains were characterized by antimicrobial susceptibility. The Clermont algorithm performed the phylogenetic assignment. The structure of class 1 integrons was performed by identifying integrase (int1), the variable region, and qacEΔ1-sul1 genes. The variable region was amplified, sequenced, and analyzed. Enterobacterial repetitive intergenic consensus (ERIC) PCR and virus typing typed strains with identical genetic arrangements by detecting virulence genes related to cytotoxicity, adherence, and iron uptake. Results: Escherichia coli strains showed great resistance to β-lactams and quinolones, and phylogenetic assignment showed that the group A/C was highly predominant. Sixteen integrons were identified, with monogenic arrays represented by aadA1, dfrB4dfrA7, dfr2D, and dfrA17 cassettes. The prevalence of the biogenic arrays aadA1/dfrA1 and aadA5/dfrA17 was lower than that of blaOXA-1/aadA1. Concerning virulence genes, fimH, traT, and iutA were the most predominant. Conclusions: The high incidence of virulence and resistance factors in commensal and virulent strains of E. coli revealed potential tools in the pathogenesis of vaginal infection.

Impact of spent engine oil contamination on the antibiotic resistome of a tropical agricultural soil

Profiling of hydrocarbon-contaminated soils for antibiotic resistance genes (ARGs) is becoming increasingly important due to emerging realities of their preponderance in hydrocarbon-inundated matrices. In this study, the antibiotic resistome of an agricultural soil (1S) and agricultural soil contaminated with spent engine oil (AB1) were evaluated via functional annotation of the open reading frames (ORFs) of their metagenomes using the comprehensive antibiotic database (CARD) and KEGG KofamKOALA. CARD analysis of AB1 metagenome revealed the detection of 24 AMR (antimicrobial resistance) gene families, 66 ARGs, and the preponderance (69.7%) of ARGs responsible for antibiotic efflux in AB1 metagenome. CARD analysis of 1S metagenome revealed four AMR gene families and five ARGs. Functional annotation of the two metagenomes using KofamKOALA showed 171 ARGs in AB1 and 29 ARGs in 1S, respectively. Majority of the detected ARGs in AB1 (121; 70.8%) and 1S (16; 55.2%) using KofamKOALA are responsible for antibiotic efflux while ARGs for other resistance mechanisms were also detected. All the five major antibiotic efflux pump systems were detected in AB1 metagenome, though majority of the ARGs for antibiotic efflux belong to the RND (resistance-nodulation-cell division) and MFS (major facilitator superfamily) efflux systems. Significant differences observed in the ARGs recovered from 1S and AB1 metagenomes were statistically validated (P < 0.05). SEO contamination is believed to be responsible for ARGs increase in AB1 metagenome via mechanisms of cross-resistance especially with efflux pumps. The detection of these ARGs is of great public health concern in this era of multidrug resistant isolates resurgence.

Mechanism of Resistance Development in E. coli against TCAT, a Trimethoprim-Based Photoswitchable Antibiotic

During the last decades, a continuous rise of multi-drug resistant pathogens has threatened antibiotic efficacy. To tackle this key challenge, novel antimicrobial therapies are needed with increased specificity for the site of infection. Photopharmacology could enable such specificity by allowing for the control of antibiotic activity with light, as exemplified by trans/cis-tetra-ortho-chloroazobenzene-trimethoprim (TCAT) conjugates. Resistance development against the on (irradiated, TCATa) and off (thermally adapted, TCATd) states of TCAT were compared to that of trimethoprim (TMP) in Escherichia coli mutant strain CS1562. Genomics and transcriptomics were used to explore the acquired resistance. Although TCAT shows TMP-like dihydrofolate reductase (DHFR) inhibition in vitro, transcriptome analyses show different responses in acquired resistance. Resistance against TCATa (on) relies on the production of exopolysaccharides and overexpression of TolC. While resistance against TCATd (off) follows a slightly different gene expression profile, both indicate hampering the entrance of the molecule into the cell. Conversely, resistance against TMP is based on alterations in cell metabolism towards a more persister-like phenotype, as well as alteration of expression levels of enzymes involved in the folate biosynthesis. This study provides a deeper understanding of the development of new therapeutic strategies and the consequences on resistance development against photopharmacological drugs.

Diarrhea in an infant due to Shigella flexneri 1 carrying multiple cephalosporinase-encoding genes

Background

Infections caused by multidrug-resistant shigellae resistant to broad-spectrum cephalosporins are becoming more prevalent in the Middle East. We report a case of severe diarrhea due to a multiresistant Shigella flexneri 1 strain carrying four different ß-lactamase genes.

Case presentation

A one-year-old Syrian infant presented with severe acute diarrhea, vomiting and dehydration. She did not respond to empirical treatment with amoxicillin-clavulanic acid followed by cefotaxime. Later, stool culture revealed S. flexneri 1 resistant to both these drugs. The patient was successfully treated with meropenem to which S. flexneri 1 was susceptible. The isolate was resistant to eight classes of antibiotics, and the whole genome sequence (WGS) identified four ß-lactamase genes (bla_CTX-M-15, bla_EC-8, bla_OXA-1, and bla_TEM-1) along with genes mediating resistance to seven other antibiotic classes. The WGS also identified several virulence genes including senA that encodes ShET-2 which induces watery diarrhea. Phylogenetically, the isolate was closely related to isolates from South Asia.

Conclusions

This report highlights the emergence of extremely resistant Shigella that has acquired multiple resistance genes to cephalosporins rendering these drugs ineffective.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13099-021-00413-9.

Genomic analysis revealing the resistance mechanisms of extended-spectrum β-lactamase-producing Klebsiella pneumoniae isolated from pig and humans in Malaysia

Extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae has been associated with a wide range of infections in humans and animals. The objective of this study was to determine the genomic characteristics of two multiple drug resistant, ESBLs-producing K. pneumoniae strains isolated from a swine in 2013 (KP2013Z28) and a hospitalized patient in 2014 (KP2014C46) in Malaysia. Genomic analyses of the two K. pneumoniae strains indicated the presence of various antimicrobial resistance genes associated with resistance to β-lactams, aminoglycosides, colistin, fluoroquinolones, phenicols, tetracycline, sulfonamides, and trimethoprim, corresponding to the antimicrobial susceptibility profiles of the strains. KP2013Z28 (ST25) and KP2014C46 (ST929) harbored 5 and 2 genomic plasmids, respectively. The phylogenomics of these two Malaysian K. pneumoniae, with other 19 strains around the world was determined based on SNPs analysis. Overall, the strains were resolved into five clusters that comprised of strains with different resistance determinants. This study provided a better understanding of the resistance mechanisms and phylogenetic relatedness of the Malaysian strains with 19 strains isolated worldwide. This study also highlighted the needs to monitor the usage of antibiotics in hospital settings, animal husbandry, and agricultural practices due to the increase of β-lactam, aminoglycosides, tetracycline, and colistin resistance among pathogenic bacteria for better infection control.

Occurrence of Antibiotic-Resistant Bacteria and Genes in Two Drinking Water Treatment and Distribution Systems in the North-West Province of South Africa

With the increasing spread of antimicrobial resistance, there is growing attention to the contribution made by drinking water systems. The potential health impact of two drinking water treatment and distribution systems (A and B) in the North-West Province of South Africa was determined by investigating the water quality and occurrence of antimicrobial-resistant heterotrophic bacteria and genes in the raw and treated water over four seasons. Most of the physicochemical parameters except for electrical conductivity were within permissible limits. Coliform bacteria reduced from raw to potable water except for counts higher than the threshold recorded in Summer and Winter. A total of 203 heterotrophic bacterial isolates were recovered on chromogenic R2A medium and subjected to susceptibility testing to twelve antibiotics. Most of the isolates were resistant to β-lactam antibiotics and Trimethoprim, whereas they were susceptible to Ciprofloxacin, Erythromycin, and Neomycin. The proportions of Cephalothin and Kanamycin-resistant isolates were significantly higher (p < 0.05) after treatment for site A, compared to significantly lower β-lactam, Oxytetracycline, and Trimethoprim-resistant isolates for B. Over 50% of isolates were of high risk, indicating their origin from high antibiotic-use sources. Seventy-one (35%) isolates were multidrug-resistant, out of which the majority (53.5%, n = 38) possessed the strA gene, followed by strB 21 (29.6%), dfrB 13 (18.3%), aadA 11 (15.5%), bla_CTX-M 5 (7.0%), and tetA 3 (4.2%). The 16S rRNA gene sequences of the isolates revealed strains belonging to eight bacterial families, some of which are clinically important.

Evaluation of multiplex tandem PCR (MT-PCR) assays for the detection of bacterial resistance genes among Enterobacteriaceae in clinical urines

Background

Increasing resistance drives empirical use of less potent and previously reserved antibiotics, including for urinary tract infections (UTIs). Molecular profiling, without culture, might better guide early therapy.

Objectives

To explore the potential of AusDiagnostics multiplex tandem (MT) PCR UTI assays.

Methods

Two MT-PCR assays were developed successively, seeking 8 or 16 resistance genes. Amplification was tracked in real time, with melting temperatures used to confirm product identity. Assays were variously performed on: (i) extracted DNA; (ii) cultured bacteria; (iii) urine spiked with reference strains; and (iv) bacteria harvested from clinical urines. Results were compared with those from sequencing, real-time SybrGreen PCR or phenotypic susceptibility.

Results

Performance was similar irrespective of whether DNA, cultures or urines were used, with >90% sensitivity and specificity with respect to common β-lactamases, dfr genes and aminoglycoside resistance determinants except aadA1/A2/A3, for which carriage correlated poorly with streptomycin resistance. Fluoroquinolone-susceptible and -resistant Escherichia coli (but not other species) were distinguished by the melting temperatures of their gyrA PCR products. The time from urine to results was <3 h.

Conclusions

The MT-PCR assays rapidly identified resistance genes from Gram-negative bacteria in urines as well as from cultivated bacteria. Used directly on urines, this assay has the potential to guide early therapy.

Highly Contingent Phenotypes of Lon Protease Deficiency in Escherichia coli upon Antibiotic Challenge

Evolutionary trajectories and mutational landscapes of drug-resistant bacteria are influenced by cell-intrinsic and extrinsic factors. In this study, I demonstrated that loss of the Lon protease altered susceptibility of Escherichia coli to trimethoprim and that these effects were strongly contingent on the drug concentration and genetic background. Lon, an AAA⁺ ATPase, is a bacterial master regulator protease involved in cytokinesis, suppression of transposition events, and clearance of misfolded proteins. I show that Lon deficiency enhances intrinsic drug tolerance at sub-MIC levels of trimethoprim. As a result, loss of Lon, though disadvantageous under drug-free conditions, has a selective advantage at low concentrations of trimethoprim. At high drug concentrations, however, Lon deficiency is detrimental for E. coli I show that the former is explained by suppression of drug efflux by Lon, while the latter can be attributed to SulA-dependent hyperfilamentation. On the other hand, deletion of lon in a trimethoprim-resistant mutant E. coli strain (harboring the Trp30Gly dihydrofolate reductase [DHFR] allele) directly potentiates resistance by enhancing the in vivo stability of mutant DHFR. Using extensive mutational analysis at 3 hot spots of resistance, I show that many resistance-conferring mutations render DHFR prone to proteolysis. This trade-off between gaining resistance and losing in vivo stability limits the number of mutations in DHFR that can confer trimethoprim resistance. Loss of Lon expands the mutational capacity for acquisition of trimethoprim resistance. This paper identifies the multipronged action of Lon in trimethoprim resistance in E. coli and provides mechanistic insight into how genetic backgrounds and drug concentrations may alter the potential for antimicrobial resistance evolution.IMPORTANCE Understanding the evolutionary dynamics of antimicrobial resistance is vital to curb its emergence and spread. Being fundamentally similar to natural selection, the fitness of resistant mutants is a key parameter to consider in the evolutionary dynamics of antimicrobial resistance (AMR). Various intrinsic and extrinsic factors modulate the fitness of resistant bacteria. This study demonstrated that Lon, a bacterial master regulator protease, influences drug tolerance and resistance. Lon is a key regulator of several fundamental processes in bacteria, including cytokinesis. I demonstrated that Lon deficiency produces highly contingent phenotypes in E. coli challenged with trimethoprim and can expand the mutational repertoire available to E. coli to evolve resistance. This multipronged influence of Lon on drug resistance provides an illustrative instance of how master regulators shape the response of bacteria to antibiotics.

Antibiotic resistance in fecal sludge and soil in Ho Chi Minh City, Vietnam

This study investigated the prevalence of antibiotic-resistant bacteria and genes in fecal sludge and soil in Ho Chi Minh City, Vietnam, and identified the factors contributing to the survival of antibiotic-resistant bacteria in soil. Sludge and soil samples (n = 24 and 55, respectively) were collected from residential septic systems and environmental reservoirs (i.e., canals, rivers, and parks) in twelve districts of Ho Chi Minh City and tested against a library of 12 antibiotic-resistant genes and 1 integron gene. The susceptibility of isolated Escherichia coli from sludge and soil (n = 104 and 129, respectively) was tested against nine antibiotics. Over 60% of sludge and soil samples harbored sul1, ere(A), intI1, cmIA, and tet(A) genes. The three most common phenotypic resistances found in E. coli isolated from sludge and soil were to ampicillin, tetracycline, and sulfamethoxazole/trimethoprim. In a temporal microcosm study of antibiotic-susceptible and multi-drug-resistant E. coli inoculated in soil, temperature (21.4 vs. 30 °C), resistance phenotype, and soil background microbial community were associated with E. coli decay rates over 73 days. This is the first study that provides insights into the high prevalence of antibiotic resistance in septic systems and environmental reservoirs in Ho Chi Minh City, Vietnam. Findings highlight that the fecal sludge and soil environments in Vietnam are likely reservoirs for dissemination of and human exposure to antibiotic resistance.

Rapid decline of bacterial drug-resistance in an antibiotic-free environment through phenotypic reversion

Antibiotic resistance typically induces a fitness cost that shapes the fate of antibiotic-resistant bacterial populations. However, the cost of resistance can be mitigated by compensatory mutations elsewhere in the genome, and therefore the loss of resistance may proceed too slowly to be of practical importance. We present our study on the efficacy and phenotypic impact of compensatory evolution in Escherichia coli strains carrying multiple resistance mutations. We have demonstrated that drug-resistance frequently declines within 480 generations during exposure to an antibiotic-free environment. The extent of resistance loss was found to be generally antibiotic-specific, driven by mutations that reduce both resistance level and fitness costs of antibiotic-resistance mutations. We conclude that phenotypic reversion to the antibiotic-sensitive state can be mediated by the acquisition of additional mutations, while maintaining the original resistance mutations. Our study indicates that restricting antimicrobial usage could be a useful policy, but for certain antibiotics only.

Antibiotic Resistance and Characteristics of Integrons in Escherichia coli Isolated from Penaeus vannamei at a Freshwater Shrimp Farm in Zhejiang Province, China

Our study was conducted to investigate the antibiotic susceptibility profiles, integrons and their associated gene cassettes (GCs), and insertion sequence common regions of Escherichia coli isolates from Penaeus vannamei collected at a large-scale freshwater shrimp farm in Zhejiang Province, People's Republic of China. A total of 182 E. coli isolates were identified from 200 samples. With the exception of imipenem, isolates were most commonly resistant to β-lactams, followed by tetracylines and sulfonamides. Fifty-two (28.6%) E. coli isolates were classified as multidrug resistant, and the patterns were highly diverse, with 29 types represented. The multiple-antibiotic resistance indices of the isolates were 0.17 to 0.56; 9.3% (17) of the 182 isolates were positive for class 1 integrons, 0.5% (1 isolate) was positive for class 2 integrons, and an insertion sequence common region 1 element was found upstream of the intI1 (integrase) gene in one of the intI1-positive isolates. Four GC arrays were detected in class 1 integrons, and one GC array was detected in class 2 integrons. Although the overall prevalence of antimicrobial-resistant bacteria in P. vannamei was lower than that previously reported for poultry and livestock farms in China, concerns about the inappropriate use of antibiotics and the transmission of antimicrobial-resistant bacteria in aquaculture were raised. Alternative approaches to reducing or replacing the use of antibiotics should be further studied.

Trimethoprim susceptibility in E. coli community-acquired urinary tract infections in France

OBJECTIVES

Trimethoprim has been recently included in the French guidelines for the treatment of urinary tract infections, but no epidemiological data supports its use. We aimed to determine the trimethoprim susceptibility of Escherichia coli isolates responsible for community-acquired urinary tract infections in women of childbearing age.

MATERIALS AND METHODS

We conducted a national prospective survey. A total of 350 strains of E. coli isolated from urines in 35 laboratories were included. Antibiotic susceptibility testing was performed in each laboratory.

RESULTS

We reported a susceptibility rate of 78%, and a similar clinical categorization between trimethoprim and cotrimoxazole for 97.4% of isolates. We pointed out an association between resistance to trimethoprim and other antibiotic classes.

CONCLUSION

The results support trimethoprim as a second-line therapy based on antibiotic susceptibility testing results. We confirm that trimethoprim and cotrimoxazole susceptibility rates are very close.

A Comparison of Genotypic and Phenotypic Methods for Analyzing the Susceptibility to Sulfamethoxazole and Trimethoprim in Edwardsiella piscicida

In a study of 39 isolates of Edwardsiella piscicida made from Korean aquaculture sites, sul genes were detected in 16 isolates and dfr genes in 19. Ten isolates were shown to contain both sul and dfr genes. MIC and disc diffusion zones assays were performed to measure the phenotypic susceptibilities of the 39 isolates. Normalized resistance interpretation was applied to these data to categorize isolates as either fully susceptible or as manifesting reduced susceptibility. The standard CLSI protocols specify the use of a mixture of sulfamethoxazole/trimethoprim (20:1) in both MIC and disc diffusion tests. Using the CLSI MIC protocol, 100% of the isolates containing dfr genes, but only 75% of the isolates containing sul genes, were categorized as manifesting reduced susceptibility. Using the CLSI disc diffusion protocol, only 58% of the isolates containing dfr genes and 69% of those containing sul genes were categorized as manifesting reduced susceptibility. When the single agent trimethoprim was substituted for the combined mixture in both the MIC and disc diffusion protocols, 100% of the dfr-positive isolates were categorized as NWT. When the single-agent sulfamethoxazole was substituted, the analysis of the MIC characterized 100% and the disc zone data 94% of the sul-positive isolates as manifesting reduced susceptibility. It is argued that the use of trimethoprim and sulfamethoxazole as single agents in phenotypic susceptibility tests would provide more meaningful data than the currently recommended use of these two agents combined.

Diversity of CTX-M Extended-Spectrum β-Lactamases in Escherichia coli Isolates from Retail Raw Ground Beef: First Report of CTX-M-24 and CTX-M-32 in Algeria

The aim of this study was to investigate the prevalence and molecular features of extended-spectrum cephalosporin resistance in Escherichia coli isolates contaminating ground beef at retail in Algeria. Of 371 ground beef samples, 27.5% were found to contain cefotaxime-resistant E. coli isolates distributed into A (24.5%), B1 (60.8%), and D (14.7%) phylogroups. A rate of 88.2% of isolates had a multidrug-resistance phenotype. All strains were producers of CTX-M type extended-spectrum β-lactamases (ESBLs): CTX-M-1, CTX-M-3, CTX-M-14, CTX-M-15, CTX-M-24, or CTX-M-32. Conjugation assays allowed the transfer of bla_CTX-M-1 in association with IncI1 plasmids, bla_CTX-M-15 with IncI1 and IncK+B/O plasmids, bla_CTX-M-3 with IncK plasmids, and bla_CTX-M-14 with IncF1B or IncK plasmids. Sequence analysis of gyrA and parC genes showed mutations in 98.6% of ciprofloxacin-resistant isolates. The patterns "GyrA: S83L+D87N, ParC: S80I" (46.5%) and "ParC: S80I" (42.3%) were predominant. qnrS1, qnrB, and aac(6')-Ib-cr were detected in 18.7% of isolates. The tet genes, tetA, tetB, and tetA+tetB, were present in 95.7% of tetracycline-resistant isolates. The sul genes (sul1, sul2, sul3, sul1+sul2, sul2+sul3, and sul1+sul3) and the dfr gene clusters (dfrA1, dfrA5, dfrA7, dfrA8, dfrA12, dfrA5+dfrA12, dfrA1+dfrA5, dfrA7+dfrA12, dfrA5+dfrA7, and dfrA1+dfrA5+dfrA7) were found in 96.4% and 85.5% of sulfamethoxazole/trimethoprim-resistant isolates, respectively. Classes 1 and 2 integrons were detected in 67.6% and 9.8% of isolates, respectively. This study highlighted the significant presence of resistance genes, in particular those of CTXM ESBLs, in the beef meat, with the risk of their transmission to humans through food chain.

Class 1 integrons are low-cost structures in Escherichia coli

Resistance integrons are bacterial genetic platforms that can capture and express antibiotic resistance genes embedded within gene cassettes. The capture and shuffling of gene cassettes are mediated by the integrase IntI, the expression of which is regulated by the SOS response in Escherichia coli. Gene cassettes are expressed from a common Pc promoter. Despite the clinical and environmental relevance of integrons, the selective forces responsible for their evolution and maintenance are poorly understood. Here, we conducted pairwise competition experiments in order to assess the fitness cost of class 1 integrons in E. coli. We found that integrons are low-cost structures and that their cost is further reduced by their tight regulation. We show that the SOS response prevents the expression of costly integrases whose cost is activity dependent. Thus, when an integron is repressed, its cost depends mostly on the expression of its gene cassettes array and increases with Pc strength and the number of cassettes in the array. Furthermore, different cassettes have different costs. Lastly, we showed that subinhibitory antibiotic concentrations promoted the selection of integron-carrying bacteria, especially those with a strong Pc promoter. These results provide new insights into the evolutionary dynamics of integron-carrying bacterial populations.

Bacterial clonal diagnostics as a tool for evidence-based empiric antibiotic selection

Despite the known clonal distribution of antibiotic resistance in many bacteria, empiric (pre-culture) antibiotic selection still relies heavily on species-level cumulative antibiograms, resulting in overuse of broad-spectrum agents and excessive antibiotic/pathogen mismatch. Urinary tract infections (UTIs), which account for a large share of antibiotic use, are caused predominantly by Escherichia coli, a highly clonal pathogen. In an observational clinical cohort study of urgent care patients with suspected UTI, we assessed the potential for E. coli clonal-level antibiograms to improve empiric antibiotic selection. A novel PCR-based clonotyping assay was applied to fresh urine samples to rapidly detect E. coli and the urine strain's clonotype. Based on a database of clonotype-specific antibiograms, the acceptability of various antibiotics for empiric therapy was inferred using a 20%, 10%, and 30% allowed resistance threshold. The test's performance characteristics and possible effects on prescribing were assessed. The rapid test identified E. coli clonotypes directly in patients' urine within 25-35 minutes, with high specificity and sensitivity compared to culture. Antibiotic selection based on a clonotype-specific antibiogram could reduce the relative likelihood of antibiotic/pathogen mismatch by ≥ 60%. Compared to observed prescribing patterns, clonal diagnostics-guided antibiotic selection could safely double the use of trimethoprim/sulfamethoxazole and minimize fluoroquinolone use. In summary, a rapid clonotyping test showed promise for improving empiric antibiotic prescribing for E. coli UTI, including reversing preferential use of fluoroquinolones over trimethoprim/sulfamethoxazole. The clonal diagnostics approach merges epidemiologic surveillance, antimicrobial stewardship, and molecular diagnostics to bring evidence-based medicine directly to the point of care.

Prevalence, serotyping and antimicrobials resistance mechanism of Salmonella enterica isolated from clinical and environmental samples in Saudi Arabia

Salmonella is recognized as a common foodborne pathogen, causing major health problems in Saudi Arabia. Herein, we report epidemiology, antimicrobial susceptibility and the genetic basis of resistance among S. enterica strains isolated in Saudi Arabia. Isolation of Salmonella spp. from clinical and environmental samples resulted in isolation of 33 strains identified as S. enterica based on their biochemical characteristics and 16S-rDNA sequences. S. enterica serovar Enteritidis showed highest prevalence (39.4%), followed by S. Paratyphi (21.2%), S. Typhimurium (15.2%), S. Typhi and S. Arizona (12.1%), respectively. Most isolates were resistant to 1st and 2nd generation cephalosporin; and aminoglycosides. Moreover, several S. enterica isolates exhibited resistance to the first-line antibiotics used for Salmonellosis treatment including ampicillin, trimethoprim–sulfamethoxazole and chloramphenicol. In addition, the results revealed the emergence of two S. enterica isolates showing resistance to third-generation cephalosporin. Analysis of resistance determinants in S. enterica strains (n = 33) revealed that the resistance to β-lactam antibiotics, trimethoprim–sulfamethoxazole, chloramphenicol, and tetracycline, was attributed to the presence of carb-like, dfrA1, floR, tetA gene, respectively. On the other hand, fluoroquinolone resistance was related to the presence of mutations in gyrA and parC genes. These findings improve the information about foodborne Salmonella in Saudi Arabia, alarming the emergence of multi-drug resistant S. enterica strains, and provide useful data about the resistance mechanisms.

Genetic redundancy and persistence of plasmid-mediated trimethoprim/sulfamethoxazole resistant effluent and stream water Escherichia coli

Antibiotic resistant bacteria may persist in effluent receiving surface water in the presence of low (sub-inhibitory) antibiotic concentrations if the bacteria possess multiple genes encoding resistance to the same antibiotic. This redundancy of antibiotic resistance genes may occur in plasmids harboring conjugation and mobilization (mob) and integrase (intI) genes. Plasmids extracted from 76 sulfamethoxazole-trimethoprim resistant Escherichia coli originally isolated from effluent and an effluent-receiving stream were used as DNA template to identify sulfamethoxazole (sul) and trimethoprim (dfr) resistances genes plus detect the presence of intI and mob genes using PCR. Sulfamethoxazole and trimethoprim resistance was plasmid-mediated with three sul (sul1, sul2 and sul3 genes) and four dfr genes (dfrA12, dfrA8, dfrA17, and dfrA1 gene) the most prevalently detected. Approximately half of the plasmids carried class 1 and/or 2 integron and, although unrelated, half were also transmissible. Sampling site in relationship to effluent input significantly affected the number of intI and mob but not the number of sul and dfr genes. In the presence of low (sub-inhibitory) sulfamethoxazole concentration, isolates persisted regardless of integron and mobilization gene designation, whereas in the presence of trimethoprim, the presence of both integron and mobilization genes made isolates less persistent than in the absence of both or the presence of a gene from either group individually. Regardless, isolates persisted in large concentrations throughout the experiment. Treated effluent containing antibiotic resistant bacteria may be an important source of integrase and mobilization genes into the stream environment. Sulfamethoxazole-trimethoprim resistant bacteria may have a high degree of genetic redundancy and diversity carrying resistance to each antibiotic, although the role of integrase and mobilization genes towards persistence is unclear.

Molecular Characterization of Cotrimoxazole Resistance Genes and Their Associated Integrons in Clinical Isolates of Gram-Negative Bacteria from Tanzania

Cotrimoxazole is widely used, particularly as a prophylactic drug in HIV patients. We assessed resistance mechanisms among cotrimoxazole resistant-Gram negative bacterial isolates (n = 123) obtained from blood (n = 69) and urine (n = 54) from Tanzanian patients. sul genes were detected in 98% (121/123) of the isolates. Coexistence of sul1 and sul2 was common (49/123). The dfr genes were found in 63% (77/123) of all isolates. sul1, dfrA15, and dfrA5 genes predominated among Klebsiella pneumoniae, while sul2 and dfrA1 genes were frequent in Escherichia coli isolates. Two isolates, both K. pneumoniae, carried sul3. Integrons were detected in 81.3% (100/123) of all isolates. Class 1 integrons were found in 95% (42/44), 53% (23/43), and 80.6% (25/31) of K. pneumoniae, E. coli, and other Enterobacteriaceae isolates, respectively. Class 2 integrons were found in 14% of E. coli, but not in K. pneumoniae. All sul1 genes in K. pneumoniae were carried in class 1 integrons. Gene cassette arrays dfrA5 and dfrA15-aadA1 were most frequently associated with class 1 integrons, while class 2 integrons contained only dfrA1-sat2-aadA1 gene cassettes. This is the first report of sul3 gene in K. pneumoniae from human sources. The finding that mechanisms differ between E. coli and K. pneumoniae may broaden our understanding of cotrimoxazole resistance.

Antibacterial Antifolates: From Development through Resistance to the Next Generation

The folate cycle is one of the key metabolic pathways used by bacteria to synthesize vital building blocks required for proliferation. Therapeutic agents targeting enzymes in this cycle, such as trimethoprim and sulfamethoxazole, are among some of the most important and continually used antibacterials to treat both Gram-positive and Gram-negative pathogens. As with all antibacterial agents, the emergence of resistance threatens the continued clinical use of these life-saving drugs. In this article, we describe and analyze resistance mechanisms that have been clinically observed and review newer generations of preclinical compounds designed to overcome the molecular basis of the resistance.

Breaking the Spell: Combating Multidrug Resistant 'Superbugs'

Multidrug-resistant (MDR) bacteria have become a severe threat to community wellbeing. Conventional antibiotics are getting progressively more ineffective as a consequence of resistance, making it imperative to realize improved antimicrobial options. In this review we emphasized the microorganisms primarily reported of being resistance, referred as ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa, and Enterobacteriaceae) accentuating their capacity to "escape" from routine antimicrobial regimes. The upcoming antimicrobial agents showing great potential and can serve as alternative therapeutic options are discussed. We also provided succinct overview of two evolving technologies; specifically network pharmacology and functional genomics profiling. Furthermore, In vivo imaging techniques can provide novel targets and a real time tool for potential lead molecule assessment. The employment of such approaches at prelude of a drug development process, will enables more informed decisions on candidate drug selection and will maximize or predict therapeutic potential before clinical testing.

Crystal Structures of Trimethoprim-Resistant DfrA1 Rationalize Potent Inhibition by Propargyl-Linked Antifolates

Multidrug-resistant Enterobacteriaceae, notably Escherichia coli and Klebsiella pneumoniae, have become major health concerns worldwide. Resistance to effective therapeutics is often carried by class I and II integrons that can confer insensitivity to carbapenems, extended spectrum β-lactamases, the antifolate trimethoprim, fluoroquinolones, and aminoglycosides. Specifically of interest to the study here, a prevalent gene (dfrA1) coding for an insensitive dihydrofolate reductase (DHFR) confers 190- or 1000-fold resistance to trimethoprim for K. pneumoniae and E. coli, respectively. Attaining inhibition of both the wild-type and resistant forms of the enzyme is critical for new antifolates. For several years, we have been developing the propargyl-linked antifolates (PLAs) as effective inhibitors against trimethoprim-resistant DHFR enzymes. Here, we show that the PLAs are active against both the wild-type and DfrA1 DHFR proteins. We report two high-resolution crystal structures of DfrA1 bound to potent PLAs. The structure-activity relationships and crystal structures will be critical in driving the design of broadly active inhibitors against wild-type and resistant DHFR.

Sulfonamide Resistance Genes (sul) M in Extended Spectrum Beta Lactamase (ESBL) and Non-ESBL Producing Escherichia coli Isolated From Iranian Hospitals

Background:

Extensive use of cotrimoxazole has been associated with increasing level of Escherichia coli resistance.

Objectives:

In the current study, we focused on assessing the prevalence of E. coli resistance to cotrimoxazole and frequency of its associated genes.

Materials and Methods:

One-hundred and forty-four E. coli isolates were identified during March 2007 to April 2012 at Ilam hospitals and Milad (Tehran) hospital. Antibiotic susceptibility for screening of resistance isolates was done by the Kirby-Bauer method. The sul1, sul2, sul3, dfrA1, dfrA5, int1, blaTEM, blaSHV and CTX-M genes were detected by polymerase chain reaction (PCR) amplification. Plasmid curing was done for identifying correlations between resistance genes and plasmids.

Results:

Amongst the 144 E. coli isolates, seventy-two (50%) Extended Spectrum Beta Lactamase (ESBL)-producing and seventy-two (50%) non-ESBL-producing E. coli isolates were identified; eighty-seven isolates (60.41%) were resistant to cotrimoxazole. Frequencies of sul1, sul2 and sul3, were 81% (116 isolates), 67% (96 isolates) and 2.29% (three isolates), respectively. Furthermore, 50.57% (72 isolates) had sul1 and sul2, 2.29% (3 isolates) contained sul2 and sul3, and 2.29% (three isolates) contained sul1, sul2 and sul3 genes, simultaneously. Thirty-four (39.1%) of the isolates had the dfrA1 gene. Five (5.7%) of the isolates had the dfrA5 gene. Sixty-eight (78.2%) strains contained the int1 gene. Furthermore, dfrA1 and dfrA5 were present in three (3.4%) of the isolates. The results showed that of the ESBL-producing isolates, 85.2% (n = 122), 53.2% (n = 76) and 26.1% (n = 37) were blaTEM, blaSHV and CTX-M harboring isolates, respectively.

Conclusions:

Our study indicated a high frequency of cotrimoxazole resistance gene in E. coli isolates from Ilam and Tehran (Milad) hospitals, and sul genes had a major role in cotrimoxazole resistance of these isolates.

Antimicrobial resistance in commensal Escherichia coli from pigs during metaphylactic trimethoprim and sulfamethoxazole treatment and in the post-exposure period

The prevalence of trimethoprim (TMP) and sulfamethoxazole (SMX) resistance in commensal E. coli from pigs was tested in this study. E. coli was derived from three groups of piglets in successive stages of metaphylactic therapy and from two groups of sows 10 and 18 weeks after the treatment. MIC values of TMP and SMX were determined for a total of 352 strains. The presence of resistance genes (dfrA1, dfrA5, dfrA7, dfrA12, dfrA17, sul1, sul2, sul3) and class 1 and 2 integron-associated dfrA gene cassettes was tested. Resistance to TMP was very high during the administration of the antimicrobial (from 97 to 100%) and amounted to 86% and 69% in the post-exposure period; MIC > 32 mg/L. The isolates from all groups of pigs were resistant to sulfamethoxazole, with MIC > 1028 mg/L. The dfrA1 and sul1 genes (as part of integrons) dominated in E. coli from piglets, but the dfrA12 and sul1 genes were prevalent in E. coli from sows. Coexistence of the different dfrA genes was detected in 71 isolates from all groups of swine. Transcription analysis revealed that most of these genes were not transcribed, particularly gene cassettes of class 1 integrons. The research revealed a high level of resistance associated with the metaphylactic treatment, persistence and circulation of resistance in bacterial populations. Diverse genetic background with multiple and not transcribed resistance genes was observed.