Occurrence of tetracycline resistance genes among Escherichia coli isolates from the phase 3 clinical trials for tigecycline

Multi-drug-resistant Escherichia coli in adult male patients with enlarged prostate attending general hospitals in Benue state

The aim of this study was to investigate multi-drug-resistant (MDR) Escherichia coli in urine of adult male patients with enlarged prostate. Three hundred and sixty-eight samples of urine and blood were collected. Escherichia coli was isolated, purified, and identified and prostate-specific antigen (PSA) was determined. Multi-drug resistance test and specific drug resistance genes were assessed. Prevalence of Escherichia coli was high (38.5%) in patients with PSA of 60-79 ng ml-1 and 60% were MDR. The isolates showed highest resistance to tetracycline (53.3.0%) and least to cephalosporins (5%). They had intL and gyrA genes, which are integron, and quinolone resistance genes and sul1 and sul2 which are sulphonamide resistance-associated genes. Levofloxacin, ertapenem, and Augmentin (100% susceptibilities) were considered choice drugs for treatment of Escherichia coli infection in patients with elevated PSA.

D-Ring Modifications of Tetracyclines Determine Their Ability to Induce Resistance Genes in the Environment

The widespread utilization of tetracyclines (TCs) in agriculture and medicine has led to the borderless spread of tetracycline resistance in humans, animals, and the environment, posing huge risks to both the ecosystem and human society. Changes in the functional group modifications resulted in a higher bacteriostatic efficacy of the new generation of TCs, but their effect on the emergence and evolution of antibiotic resistance genes (ARGs) is not yet known. To this end, four TCs from three generations were chosen to compare their structural effects on influencing the evolution of ARGs in soil microbial communities. The findings revealed that low-generation TCs, such as tetracycline and oxytetracycline, exhibited a greater propensity to stimulate the production and proliferation of ARGs than did high-generation tigecycline. Molecular docking analysis demonstrated that modifications of the D-ring functional group determined the binding capacity of TCs to the substrate-binding pocket of transcriptional regulators and efflux pumps mainly involved in drug resistance. This can be further evidenced by reverse transcription-quantitative polymerase chain reaction quantification and intracellular antibiotic accumulation assessment. This study sheds light on the mechanism of the structural effect of antibiotic-induced ARG production from the perspective of compound-protein binding, therefore providing theoretical support for controlling the dissemination of antibiotic resistance.

Alteration of the migration trajectory of antibiotic resistance genes by microplastics in a leachate activated sludge system

The environmental behavior of emerging contaminants of microplastics (MPs), antibiotics and antibiotic resistance genes (ARGs) in the leachate activated sludge system has been monitored and analyzed comprehensively. The results suggested that MPs could effectively alter the migration trajectory of tetracycline resistance genes (tet genes) in the leachate activated sludge system under intermittent and continuous influent conditions. After adding MPs, the total average abundance of tet genes in leachate increased from 0.74 ± 0.07 to 0.78 ± 0.07 (log10tet genes/log10 16S rRNA) and that in sludge increased from 0.65 ± 0.08 to 0.70 ± 0.06 (log10tet genes/log10 16S rRNA). Except for tetA, the abundance of tetB, tetO, tetM and tetQ on MPs increased with increasing TC concentration under both aerobic and anaerobic conditions. MPs not only significantly affect the abundance level and migration trajectory of ARGs in the leachate activated sludge system, but also remarkably improve the level of heavy metals in the ambient environment, indirectly promoting the selective effect of antibiotic-resistant bacteria (ARB) and promoting the development of antibiotic resistance (AR). In addition, MPs changed their physicochemical properties and released hazardous substances with aging to force tet genes to migrate from the leachate activated sludge system to the MPs, making AR more difficult to eliminate and persisted in wastewater treatment plants. Meanwhile, microorganisms played a driving role, making MPs serve as a niche for ARGs and ARB colonization. The co-occurrence network analysis indicated the specific distribution pattern of tet genes and microorganisms in different media, and the potential host was speculated. This study improves the understanding of the environmental behavior of emerging contaminants in leachate activated sludge system and lays a theoretical for protecting the ecological environment.

MALDI-TOF MS for rapid detection and differentiation between Tet(X)-producers and non-Tet(X)-producing tetracycline-resistant Gram-negative bacteria

The extensive use of tetracycline antibiotics has led to the widespread presence of tetracycline-resistance genes in Gram-negative bacteria and this poses serious threats to human and animal health. In our previous study, we reported a method for rapid detection of Tet(X)-producers using MALDI-TOF MS. However, there have been multiple machineries involved in tetracycline resistance including efflux pump, and ribosomal protection protein. Our previous demonstrated the limitation in probing the non-Tet(X)-producing tetracycline-resistant strains. In this regard, we further developed a MALDI-TOF MS method to detect and differentiate Tet(X)-producers and non-Tet(X)-producing tetracycline-resistant strains. Test strains were incubated with tigecycline and oxytetracycline in separate tubes for 3 h and then analyzed spectral peaks of tigecycline, oxytetracycline, and their metabolite. Strains were distinguished using MS ratio for [metabolite/(metabolite+ tigecycline or oxytetracycline)]. Four control strains and 319 test strains were analyzed and the sensitivity was 98.90% and specificity was 98.34%. This was consistent with the results obtained from LC-MS/MS analysis. Interestingly, we also found that the reactive oxygen species (ROS) produced by tetracycline-susceptible strains were able to promote the degradation of oxytetracycline. Overall, the MALDI^Tet(X)-plus test represents a rapid and reliable method to detect Tet(X)-producers, non-Tet(X)-producing tetracycline-resistant strains, and tetracycline-susceptible strains.

Low levels of tetracyclines select for a mutation that prevents the evolution of high-level resistance to tigecycline

In a collection of Escherichia coli isolates, we discovered a new mechanism leading to frequent and high-level tigecycline resistance involving tandem gene amplifications of an efflux pump encoded by the tet(A) determinant. Some isolates, despite carrying a functional tet(A), could not evolve high-level tigecycline resistance by amplification due to the presence of a deletion in the TetR(A) repressor. This mutation impaired induction of tetA(A) (encoding the TetA(A) efflux pump) in presence of tetracyclines, with the strongest effect observed for tigecycline, subsequently preventing the development of tet(A) amplification-dependent high-level tigecycline resistance. We found that this mutated tet(A) determinant was common among tet(A)-carrying E. coli isolates and analysed possible explanations for this high frequency. First, while the mutated tet(A) was found in several ST-groups, we found evidence of clonal spread among ST131 isolates, which increases its frequency within E. coli databases. Second, evolution and competition experiments revealed that the mutation in tetR(A) could be positively selected over the wild-type allele at sub-inhibitory concentrations of tetracyclines. Our work demonstrates how low concentrations of tetracyclines, such as those found in contaminated environments, can enrich and select for a mutation that generates an evolutionary dead-end that precludes the evolution towards high-level, clinically relevant tigecycline resistance.

A study on evolution of antimicrobial resistance reveals how sub-inhibitory concentrations of antibiotics enrich and select for a mutated allele that prevents evolution towards clinically significant levels of antibiotic resistance.

Occurrence of antibiotics and bacterial resistance genes in wastewater: resistance mechanisms and antimicrobial resistance control approaches

Antimicrobial pharmaceuticals are classified as emergent micropollutants of concern, implying that even at low concentrations, long-term exposure to the environment can have significant eco-toxicological effects. There is a lack of a standardized regulatory framework governing the permissible antibiotic content for monitoring environmental water quality standards. Therefore, indiscriminate discharge of antimicrobials at potentially active concentrations into urban wastewater treatment facilities is rampant. Antimicrobials may exert selective pressure on bacteria, leading to resistance development and eventual health consequences. The emergence of clinically important multiple antibiotic-resistant bacteria in untreated hospital effluents and wastewater treatment plants (WWTPs) has been linked to the continuous exposure of bacteria to antimicrobials. The levels of environmental exposure to antibiotics and their correlation to the evolution and spread of resistant bacteria need to be elucidated to help in the formulation of mitigation measures. This review explores frequently detected antimicrobials in wastewater and gives a comprehensive coverage of bacterial resistance mechanisms to different antibiotic classes through the expression of a wide variety of antibiotic resistance genes either inherent and/or exchanged among bacteria or acquired from the reservoir of antibiotic resistance genes (ARGs) in wastewater systems. To complement the removal of antibiotics and ARGs from WWTPs, upscaling the implementation of prospective interventions such as vaccines, phage therapy, and natural compounds as alternatives to widespread antibiotic use provides a multifaceted approach to minimize the spread of antimicrobial resistance.

Antibiotics Resistance in Escherichia coli Isolated from Livestock in the Emirate of Abu Dhabi, UAE, 2014–2019

Escherichia coli (E. coli) is a zoonotic pathogen that showed growing resistance to antibiotics. No descriptive analysis highlights the threat of antimicrobial-resistant (AMR) of E. coli among livestock in the United Arab Emirates (UAE). Herein, we conducted phenotypic and genotypic resistance studies on E. coli isolates from livestock samples in the Emirate of Abu Dhabi based on routine diagnosis between the periods 2014–2019. Bacterial culture and disk diffusion methods were used for bacterial isolation and phenotypic resistance analysis. Resistance mechanism was studied by PCR targeting the most commonly resistance genes: ampicillin (blaSHV, blaCMY, and blaTEM-1B), tetracyclines (tetA and tetB), co-trimoxazole [sulfamethoxazole (sul1, sul2, and sul3) + trimethoprim (dfrA1 and dfrA17)], aminoglycosides [aph(3'')-Ia, aph(6)-Id, and aac(3)-IV], and fluoroquinolones (qnrA and aac(6’)-Ib-cr). Analysis of 165 E. coli isolates showed resistant to ampicillin, tetracycline, co-trimoxazole, gentamicin, and enrofloxacin by 157/165 (95.4%), 154/165 (93.6%), 141/165 (86%), 139/165 (85%), and 135/165 (82.7%), respectively. Predominant resistance gene/s detected by PCR were blaCMY (119/160, 72%) and blaTEM-1B (154/160, 96.3%) for ampicillin; tetA (162/164, 98.8%) and tetB (112/164, 68.3%) for tetracyclines; sul2 (156/164, 95%), sul3 (138/164, 84%), and dfra17 (74/164, 44.5%) for co-trimoxazole; aph(3'')-Ia (134/164, 82.1%) and aph(6)-Id (161/164, 98.2%) for aminoglycosides; and aac(6’)-Ib-cr (61/61, 100%) for enrofloxacin. Both phenotypic and genotypic analyses revealed that all E. coli isolates were multidrug-resistant (resistance to 3, 4, and 5 antibiotics classes by 3.6%, 57.6%, and 38.8%, respectively) carrying one or more resistance gene/s for the same antibiotic. PCR profiling confirmed the presence of resistance genes corresponding to their antibiotic profile. Results of the study will highlight the knowledge based on E. coli AMR related to livestock in UAE that may call for interventions.

Changes in antibiotic resistance genotypes and phenotypes after two typical sewage disposal processes

Antibiotic resistome is a growing concern around the world. Wastewater treatment plants (WWTPs) have been identified as hotspots for antibiotic resistance gene (ARG) research. However, the distribution of antibiotic resistance genotypes and phenotypes in biofilm wastewater treatment system is poorly understood. In this study, the abundance and fate of antibiotic resistance genotypes and phenotypes in two typical wastewater treatment processes [biological aerated filter (BAF), anaerobic-oxic (A/O)] were quantitatively studied. The average removal rate of total ARGs was greater than 90%. In the biological treatment unit, the abundance of ARGs increased in the A/O unit and decreased in the biofilm unit. In addition, the resistance of tetracycline resistant bacteria changed after sewage disposal, which was closely related to the evolution of bacterial community. In total, the removal rate of resistance bacteria in A/O system was lower than that in BAF system. Genotypes were the basis of determining the phenotypes of microbial resistance. But it is necessary to pay close attention to antibiotic resistance phenotype due to its high variability. More specifically, antibiotic resistance mitigation in WWTPs should focus more on removing bacterial hosts to reduce the release of ARGs into the environment.

Impacts of antibiotics on biofilm bacterial community and disinfection performance on simulated drinking water supply pipe wall

Overuse of antibiotics is accelerating the spread of resistance risk in the environment. In drinking water supply systems, the effect of antibiotics on the resistance of biofilm is unclear, and there have been few studies in disinfectant-containing systems. Here, we designed a series of drinking water supply reactors to investigate the effects of antibiotics on biofilm and bacteria in the water. At low concentrations, antibiotics could promote the growth of bacteria in biofilm; among the tested antibiotics (tetracycline, sulfadiazine and chloramphenicol), tetracycline had the strongest ability to promote this. And the antibiotic resistant bacteria (ARB) could inhibit the growth of bacteria in drinking water. Results have shown that antibiotics enhanced the bacterial chlorine resistance in the effluent, but reduced that in the biofilm. Furthermore, metagenomic analysis showed that antibiotics reduced the richness of biofilm communities. The dominant phyla in the biofilm were Proteobacteria, Planctomycetes, and Firmicutes. In tetracycline-treated biofilm, the dominant phylum was Planctomycetes. In sulfadiazine- and chloramphenicol-treated groups, bacteria with complex cell structures preferentially accumulated. The dominant class in biofilm in the ARB-added group was Gammaproteobacteria. The abundance of antibiotic resistant genes (ARGs) was correlated with biofilm community structure. This study shows that antibiotics make the biofilm community structure of drinking water more resistant to chlorine. ARGs may be selective for certain bacteria in the process, and there may ultimately be enhanced chlorine and antibiotic resistance of effluent bacteria in drinking water.

Correlation of minimum inhibitory concentrations between human and animal antimicrobials against Escherichia coli isolated from livestock

We analyzed the correlation between minimum inhibitory concentrations (MICs) of antimicrobials used in humans and those used in animals to enable comparison of antimicrobial susceptibility between Escherichia coli isolated from humans and those from animals. We compared the following pairs of MIC data: piperacillin (PIPC) to ampicillin (ABPC), amikacin (AMK) to kanamycin (KM), minocycline (MINO) to oxytetracycline (OTC), and levofloxacin (LVFX) to enrofloxacin (ERFX) using 103 isolates of E. coli from healthy livestock (cattle, pigs, broiler chickens, and layer chickens). Kappa analysis of the agreement for resistance and susceptibility between PIPC and ABPC, AMK and KM, MINO and OTC, and LVFX and ERFX showed almost perfect (κ = 0.81), slight (κ = 0.12), fair (κ = 0.37), and moderate (κ = 0.46) agreement, respectively. Within the antimicrobial pairs, all isolates resistant to the human antimicrobial were also resistant to the veterinary antimicrobial. However, there was less agreement within the pairs for those isolates that were sensitive to the human antimicrobial. The percentage agreement for susceptibility, defined as the percentage of isolates sensitive to both antimicrobials compared with isolates sensitive to both antimicrobials, as well as those sensitive only to the human antimicrobial, was 89.9%, 87.3%, 64.0%, and 89.9% for PIPC and ABPC, AMK and KM, MINO and OTC, and LVFX and ERFX, respectively. Our results suggest that the possibility of missing the resistance for antimicrobials used in human medicine by examining MICs for the equivalent antimicrobials used in veterinary medicine is low.

Rapid detection of plasmid-mediated high-level tigecycline resistance in Escherichia coli and Acinetobacter spp

OBJECTIVES

The emergence and spread of plasmid-encoded tet(X3/X4) genes that confer high-level tigecycline and eravacycline resistance in Escherichia coli and Acinetobacter spp. pose serious threats to human and animal health. We developed a rapid and robust assay to detect Tet(X3/X4) in Gram-negative bacteria based on eravacycline degradation by the presence of the Tet(X) enzyme in the test strain.

METHODS

This tetracycline inactivation method (TIM) is based on the degradation of eravacycline by the Tet(X3/X4)-producing strain, which results in reduced eravacycline activity against an acid-producing thermophile Bacillus stearothermophilus indicator strain. For Tet(X)-negative strains, eravacycline retains its antimicrobial activity. Coupled with a pH-sensitive dye (bromocresol purple), the reduced colorimetric inhibition zone can be measured to determine the production of Tet(X3/X4). One hundred and eighteen isolates, including 30 tet(X4)-positive E. coli, 30 tet(X3)-positive Acinetobacter spp. and 58 tet(X)-negative E. coli and Acinetobacter spp., were examined to evaluate the performance of this TIM.

RESULTS

The sensitivity and specificity for E. coli carrying tet(X4) was 96.7% and 100%, respectively, and for Acinetobacter spp. carrying tet(X3) both were 100%. The TIM assay can be completed within 6.5 h.

CONCLUSIONS

The TIM is a simple, rapid and cost-effective method for the detection of plasmid-mediated high-level tigecycline resistance in E. coli and Acinetobacter spp.

Phenotypic and genetic barriers to establishment of horizontally transferred genes encoding ribosomal protection proteins

Background

Ribosomal protection proteins (RPPs) interact with bacterial ribosomes to prevent inhibition of protein synthesis by tetracycline. RPP genes have evolved from a common ancestor into at least 12 distinct classes and spread by horizontal genetic transfer into a wide range of bacteria. Many bacterial genera host RPP genes from multiple classes but tet(M) is the predominant RPP gene found in Escherichia coli.

Objectives

We asked whether phenotypic barriers (low-level resistance, high fitness cost) might constrain the fixation of other RPP genes in E. coli.

Methods

We expressed a diverse set of six different RPP genes in E. coli, including tet(M), and quantified tetracycline susceptibility and growth phenotypes as a function of expression level, and evolvability to overcome identified phenotypic barriers.

Results

The genes tet(M) and tet(Q) conferred high-level tetracycline resistance without reducing fitness; tet(O) and tet(W) conferred high-level resistance but significantly reduced growth fitness; tetB(P) conferred low-level resistance and while mutants conferring high-level resistance were selectable these had reduced growth fitness; otr(A) did not confer resistance and resistant mutants could not be selected. Evolution experiments suggested that codon usage patterns in tet(O) and tet(W), and transcriptional silencing associated with nucleotide composition in tetB(P), accounted for the observed phenotypic barriers.

Conclusions

With the exception of tet(Q), the data reveal significant phenotypic and genetic barriers to the fixation of additional RPP genes in E. coli.

Detection of Phylogenetic Groups and Drug Resistance Genes of Escherichia coli Causing Urinary Tract Infection in Southwest Iran

Background: Many bacteria can cause urinary tract infections (UTIs), among which Escherichia coli is the most common causative agent. Escherichia coli strains are divided into eight phylogenetic groups based on the new Quadroplex-PCR method, which are different in terms of patterns of resistance to antibiotics, virulence, and environmental characteristics. Objectives: This study aimed to determine the phylogenetic groups and the prevalence of drug resistance genes in E. coli strains causing UTIs. Methods: In this descriptive cross-sectional study, 129 E. coli isolates obtained from the culture of patients with UTIs were evaluated for phylogenetic groups using the new method of Clermont et al. The identification of phylogenetic groups and antibiotic resistance genes was performed using the multiplex polymerase chain reaction (PCR) method. Results: In this study, concerning the distribution of phylogenetic groups among E. coli isolates, the phylogenetic group B2 (36.4%) was the most common phylogenetic group, followed by phylogroups C (13.2%), clade I (10.1%), D (9.3%), and A (3.1%) while groups B1 and F were not observed in any of the isolates, and 20.2% had an unknown state. Also, out of 129 E. coli isolates, the total frequency of tetA, tetB, sul1, sul2, CITM, DfrA, and qnr resistance genes was 59.7%, 66.7, 69, 62, 30.2, 23.3, and 20.2%, respectively. In this study, there was a significant relationship between antibiotics (P = 0.026), cefotaxime (P = 0.003), and nalidixic acid (P = 0.044) and E. coli phylogenetic groups. No significant relationship was observed between E. coli phylogenetic groups and antibiotic resistance genes. Conclusions: The results of this study showed that strains belonging to group B2 had the highest prevalence among other phylogroups, and also, the frequency of antibiotic resistance genes and drug-resistant isolates had a higher prevalence in this phylogroup. These results show that phylogroup B2 has a more effective role in causing urinary tract infections compared to other phylogroups, and this phylogroup can be considered a genetic reservoir of antibiotic resistance.

The Antibiotic Resistome: A Guide for the Discovery of Natural Products as Antimicrobial Agents

The use of life-saving antibiotics has long been plagued by the ability of pathogenic bacteria to acquire and develop an array of antibiotic resistance mechanisms. The sum of these resistance mechanisms, the antibiotic resistome, is a formidable threat to antibiotic discovery, development, and use. The study and understanding of the molecular mechanisms in the resistome provide the basis for traditional approaches to combat resistance, including semisynthetic modification of naturally occurring antibiotic scaffolds, the development of adjuvant therapies that overcome resistance mechanisms, and the total synthesis of new antibiotics and their analogues. Using two major classes of antibiotics, the aminoglycosides and tetracyclines as case studies, we review the success and limitations of these strategies when used to combat the many forms of resistance that have emerged toward natural product-based antibiotics specifically. Furthermore, we discuss the use of the resistome as a guide for the genomics-driven discovery of novel antimicrobials, which are essential to combat the growing number of emerging pathogens that are resistant to even the newest approved therapies.

Emergence of a Novel tet(L) Variant in Campylobacter spp. of Chicken Origin in China

Tetracyclines are widely used in veterinary medicine and food animal production. Campylobacter members are major foodborne pathogens, and their resistance to tetracycline has been widely reported in different countries. To date, Tet(O), a ribosomal protection protein, is the only confirmed Tet resistance determinant in Campylobacter spp. Here, we reported the detection and characterization of a novel Tet resistance element in Campylobacter spp. of chicken origin. This gene is identified to be a variant of tet(L), which encodes an efflux pump for Tet resistance. The variant was detected in 14 of the 82 tetracycline-resistant Campylobacter isolates collected from chickens in Henan, China. Cloning of the tet(L) variant into tetracycline-susceptible Campylobacter jejuni NCTC 11168 confirmed its function in conferring resistance to tetracycline and doxycycline. In addition, this tet(L) variant elevated the MIC (4-fold increase) of tigecycline in the heterologous Escherichia coli host. Sequencing analysis indicated the tet(L) variant was located within a multidrug-resistance genomic island (MDRGI) containing tet(L) variant IS1216E-ORF1-fexA-Δtnp-IS1216E-tet(O)-tnpV-repA This MDRGI is inserted into conserved gene potB on the chromosome. Multilocus sequence type (MLST) analysis revealed that both clonal expansion and horizontal transfer were involved in the dissemination of the tet(L) variant. These findings reveal the emergence of a new Tet resistance determinant in Campylobacter spp., which may facilitate their adaptation to the antimicrobial selection pressure in chickens.

Rapid Detection of High-Level Tigecycline Resistance in Tet(X)-Producing Escherichia coli and Acinetobacter spp. Based on MALDI-TOF MS

The emergence and spread of the novel mobile Tet(X) tetracycline destructases confer high-level tigecycline and eravacycline resistance in Escherichia coli and Acinetobacter spp. and pose serious threats to human and animal health. Therefore, a rapid and robust Tet(X) detection assay was urgently needed to monitor the dissemination of tigecycline resistance. We developed a rapid and simple assay to detect Tet(X) producers in Gram-negative bacteria based on matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). This MALDI^Tet(X) test was based on the inactivation of tigecycline by a Tet(X)-producing strain after a 3-h incubation of bacterial cultures with tigecycline. Culture supernatants were analyzed using MALDI-TOF MS to identify peaks corresponding to tigecycline (586 ± 0.2 m/z) and a tigecycline metabolite (602 ± 0.2 m/z). The results were calculated using the MS ratio [metabolite/(metabolite + tigecycline)]. The sensitivity of the MALDI^Tet(X) test with all 216 test strains was 99.19%, and specificity was 100%. The test can be completed within 3 h. Overall, the MALDI^Tet(X) test is an accurate, rapid, cost-effective method for the detection of Tet(X)-producing E. coli and Acinetobacter spp. by determining the unique peak of an oxygen-modified derivative of tigecycline.

Antimicrobial resistance and prevalence of tetracycline resistance genes in Escherichia coli isolated from lesions of colibacillosis in broiler chickens in Sistan, Iran

BACKGROUND

Antibiotics have long been the first line of defense to prevent Escherichia coli infections, but they have lost their potency since bacteria have grown increasingly resistant to treatment. The present research aimed to study the drug resistance and the prevalence of tetracycline resistance genes in E. coli isolated from broilers with colibacillosis.

RESULTS

The results showed that the most prevalent type of drug resistance was to tetracycline at 95.0%, and the least was to gentamicin at 21.7%. The prevalences of antimicrobial resistance among the tested antibiotics were significantly different (p < 0.001). A statistically significant difference was observed between the prevalence of the tet genes (p < 0.001). The tetD positive isolates and antibiotic sensitivity to tetracycline showed statistical significant differences (p = 0.017).

CONCLUSIONS

Considering the results, tetA is the most common tetracycline resistance gene, and the presence of tetD and antibiotic sensitivity to tetracycline had a significant relationship in E. coli isolated from colibacillosis infections.

Characterization of pTS14, an IncF2:A1:B1 Plasmid Carrying tet(M) in a Salmonella enterica Isolate

The objective of this study was to explore the genetic and biological features of the tet(M)-harboring plasmid pTS14 in Salmonella enterica strain S14 isolated from a chicken fecal sample. Plasmid pTS14 was identified by conjugation, S1-pulsed-field gel electrophoresis (PFGE), Southern hybridization, and plasmid sequencing. The biological characteristics of pTS14 were assessed via stability, growth kinetics, and starvation survival experiments. Strain S14, belonging to ST3007, harbored a 119-kb tet(M)-bearing IncF2:A1:B1 conjugative plasmid pTS14. The plasmid pTS14 contained a novel transposon Tn6709 with the genetic structure IS26-tnpA1-tnpA2-Δorf13-LP-tet(M)-tnpX-ΔtnpR-IS26, and the resistance genes tet(B), tet(D), strAB, sul2, and bla_TEM–1b. In addition, pTS14 was found to be highly stable in the recipient strain E. coli J53. The transconjugant TS14 exhibited a higher survival ratio than E. coli J53 under permanent starvation-induced stress. The tet(M)-bearing IncF2 epidemic plasmid lineage may accelerate the dissemination of tet(M) and other genes by coselection, which could constitute a potentially serious threat to clinical treatment regimens.

Identification of Selected Antibiotic Resistance Genes in Two Different Wastewater Treatment Plant Systems in Poland: A Preliminary Study

Antibiotic resistance is a growing problem worldwide. The emergence and rapid spread of antibiotic resistance determinants have led to an increasing concern about the potential environmental and public health endangering. Wastewater treatment plants (WWTPs) play an important role in this phenomenon since antibacterial drugs introduced into wastewater can exert a selection pressure on antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs). Therefore, WWTPs are perceived as the main sources of antibiotics, ARB and ARG spread in various environmental components. Furthermore, technological processes used in WWTPs and its exploitation conditions may influence the effectiveness of antibiotic resistance determinants’ elimination. The main aim of the present study was to compare the occurrence of selected tetracycline and sulfonamide resistance genes in raw influent and final effluent samples from two WWTPs different in terms of size and applied biological wastewater treatment processes (conventional activated sludge (AS)-based and combining a conventional AS-based method with constructed wetlands (CWs)). All 13 selected ARGs were detected in raw influent and final effluent samples from both WWTPs. Significant ARG enrichment, especially for tet(B, K, L, O) and sulIII genes, was observed in conventional WWTP. The obtained data did not show a clear trend in seasonal fluctuations in the abundance of selected resistance genes in wastewaters.

Characterization of the IncHI2 plasmid pTW4 harboring tet(M) from an isolate of Escherichia coli ST162

To investigate the genetic features and biological costs of the plasmid pTW4 harboring tet(M) in an isolate of Escherichia coli ST162 from a duck. The complete nucleotide sequence of plasmid pTW4 was determined. The characteristics of plasmid pTW4 in E. coli were investigated by stability and direct competition assays. pTW4 is an IncHI₂-type plasmid that contained the resistant genes tet(M), floR, strAB, sul2, rmtB, and bla_CMY-2. Tet(M) is located in the composite transposon Tn6539 within the multidrug resistant (MDR) region on this plasmid. Furthermore, the resistance gene rmtB and bla_CMY-2 were found outside the MDR region. The plasmid pTW4 remained stable in the host strain E. coli J53 after passage under an antibiotic-free environment for 7 days. However, the strain E. coli J53/pTW4 showed a fitness disadvantage of 6% per ten generations in the process of growth competition with E. coli J53. In conclusion, the plasmid pTW4, a mobile MDR vehicle, may promote the dissemination of tet(M), floR, rmtB, strAB, sul2, and bla_CMY-2 among bacteria and then, but it appears to confer growth disadvantage to the host.

Biogenic Synthesis of ZnO Nanoparticles and Its Potential Use as Antimicrobial Agent Against Multidrug-Resistant Pathogens

In case of Escherichia coli and Klebsiella pneumoniae infection, the increased prominence of multidrug-resistance strains has become the greatest challenge in the urinary tract disease treatment. Therefore, the 16S rRNA sequencing of multidrug-resistant strains was performed, in addition to those of plasmids and genes responsible for multidrug resistance. These strains showed containing responsible genes Sulfonamides sul1, Tetracycline Tet(A), Tetracycline Tet(B), chloramphenicol catA1, β-lactams blaSHV, and cmlA. Also, the strains demonstrated resistance to at least 10 types of antibiotics or more due to carrying various plasmids. For increasing the level of public health in daily life and treatment of multidrug-resistant bacteria, the nanomedicine was employed. Consequently, ZnO nanoparticles (ZnONPs-E) were synthesized by employing supernatant of Escherichia hermannii strain isolated from raw milk source. The E. hermannii strain produces high concentration of ZnONPs-E compared to other strains so we used it in this study. This ZnONPs-E has a minimal inhibitory concentration (MIC) ranged from the concentration 10 μg/ml to 40 μg/ml against E. coli and K. pneumoniae, respectively. The antimicrobial efficiency of ZnONPs-E was 40 µg/ml and it was superior to the reported values in literature. Moreover, SEM results evident for distorted membrane morphology, blebbing of membrane, cell elongation, and leakage of cellular contents due to ZnONPs-E activity against tested bacteria. These results indicated that the ZnONPs-E exhibited interesting antimicrobial activity against pathogenic extended-spectrum β-lactamases (ESBLs) strains. The present study revealed that the active components entered in biosynthesis of ZnONPs-E pave the way to lead its effective nano-medical and drug delivery applications.

Antibiotic resistance genes identified in wastewater treatment plant systems - A review

The intensive use of antibiotics for human, veterinary and agricultural purposes, results in their continuous release into the environment. Together with antibiotics, antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) are introduced into wastewater. Wastewater treatment plants (WWTPs) are believed to be probable hotspots for antibiotic resistance dissemination in the environment as they offer convenient conditions for ARB proliferation as well as for horizontal transfer of ARGs among different microorganisms. In fact, genes conferring resistance to all classes of antibiotics together with mobile genetic elements (MGEs) like plasmids, transposons, bacteriophages, integrons are detected in WWTPs in different countries. It seems that WWTPs with conventional treatment processes are capable of significant reduction of ARB but are not efficient in ARG removal. Implementation of advanced wastewater cleaning processes in addition to a conventional wastewater treatment is an important step to protect the aquatic environment. Growing interest in presence and fate of ARB and ARGs in WWTP systems resulted in the fact that knowledge in this area has increased staggeringly in the past few years. The main aim of the article is to collect and organize available data on ARGs, that are commonly detected in raw sewage, treated wastewater or activated sludge. Resistance to the antibiotics usually used in antibacterial therapy belonging to main classes like beta-lactams, macrolides, quinolones, sulfonamides, trimethoprim and tetracyclines was taken into account. The presence of multidrug efflux genes is also included in this paper. The occurrence of antibiotics may promote the selection of ARB and ARGs. As it is important to discuss the problem considering all aspects that influence it, the levels of antibiotics detected in influent and effluent of WWTPs were also presented.

Bats as a reservoir of resistant Escherichia coli: A methodical view. Can we fully estimate the scale of resistance in the reservoirs of free-living animals?

Bats are a poorly understood reservoir of pathogenic and multi-drug resistant microorganisms; therefore, the aim of the study was to analyze the presence of drug resistance among E. coli isolated from the species of bats occurring naturally in Poland. The strategy of isolation and identification of resistant strains from pooled and single-animal samples was based on selective media with cefotaxime, chloramphenicol, kanamycin and tetracycline, the use of the ADSRRS-fingerprinting method for genomic differentiation of isolates, and the classical methods of evaluation of phenotypic and genotypic resistance. Of the 78 isolated isolates confirmed as E. coli, there were 38 genetically distinct strains resistant at least to one antimicrobial. 71% of these strains met the multi-drug resistance criterion. Moreover, two different multidrug resistant strains were isolated from three single samples. The highest resistance was observed in the case of ampicillin (66%), kanamycin (84%), sulfamethoxazole/trimetoprim (61%/55% respectively), and streptomycin (50%), which in most cases was confirmed by the presence of an adequate gene. Two isolates from single hosts produced extended-spectrum beta-lactamases (bla_CTX-M-3, bla_CTX-M-15, bla_TEM-1). With the exception of tetracycline resistance, which was dominant among isolates from single animals, no significant differences in the resistance of the strains from both groups of samples were observed. Bats should not be neglected as another environmental reservoir and as an unpredictable source of potential pathogenic and multidrug resistant bacteria and should be extensively studied to predict the direction of the development and range of spreading resistance.

IS26-Flanked Composite Transposon Tn6539 Carrying the tet(M) Gene in IncHI2-Type Conjugative Plasmids From Escherichia coli Isolated From Ducks in China

Tet(M)-type proteins confer resistance to tetracycline and related antibiotics by interacting with the ribosome. Genes encoding Tet(M) have been found in a range of bacteria, including Escherichia coli. In the current study, conjugation experiments were performed between seven different tetracycline-resistant, azide-susceptible E. coli strains isolated from ducks and tetracycline-sensitive, azide-resistant E.coli J53. Transconjugants were obtained from two of the strains at a frequency of 1.2 × 10^-8. PCR, southern blotting and sequencing demonstrated that tet(M) in the transconjugants was located on a ~50 kb IncHI2-type plasmid and was part of a composite transposon, designated Tn6539. This transposon is flanked by two IS26 elements in opposite orientation and contains the Tn3ΔtnpA+Δorf13-lp-tet(M)+gamma delta+tnpX+ΔtnpR sequences. The Δorf13-lp-tet(M) sequence was a highly conserved genetic fragment in E. coli harboring tet(M) and mainly located in the composite transposons flanked by IS6-family elements. In summary, Tn6539 is a new composite transposon capable of horizontal transfer of tet(M) among E. coli isolates.

Occurrence of virulent and antibiotic-resistant Shiga toxin-producing Escherichia coli in some food products and human stool in Egypt

AIM

Shiga toxin-producing Escherichia coli (STEC) represent a severe public health issue worldwide, causing life-threatening diseases in the human gastrointestinal tract. This study aimed to determine the occurrence of virulent and antibiotic-resistant STEC in retail meat and milk products and human stool samples and to characterize the genes encoding for virulence and antibiotic resistance among the identified STEC isolates.

MATERIALS AND METHODS

A total of 260 food samples were randomly collected from retail markets in different localities of El Giza Governorate, Egypt. 50 stool specimens were obtained from children that had diarrhea at Embaba Fever Hospital. All collected samples were initially subjected to bacteriological examination and serotyping, and then subsequently, the isolates were exposed to polymerase chain reaction application and sequencing for the identification of the virulence-related genes. Finally, the virulent STEC isolates were tested for antibiotic susceptibility.

RESULTS

Serotyping of the 76 biochemically identified isolates showed that 18 were STEC with a predominance of non-O157 (16) while 2 O157:K-serotype was detected only in one food and one human isolate. Molecular identification of the virulence genes illustrated that the minced meat showed the highest prevalence of STEC (8%) as compared to the other food products. In the humans, the O157 was the only serotype that expresses the Shiga toxin-associated gene (eaeA). Antibiotic susceptibility test displayed that 13 of the 17 food and human isolates (76.47%) were resistant to cephalothin (KF30). 9 of the 13 cephalothin-resistant isolates harbor the β lactamase (blaTEM )-resistant gene. All isolates were sensitive to chloramphenicol, ciprofloxacin, amikacin, and gentamicin. DNA sequencing and phylogenetic analysis of the stx2-positive minced meat isolate revealed a high genetic relatedness with beef minced meat from the USA and Australia.

CONCLUSION

This study showed the predominance of non-O157 among the identified isolates. Minced meat showed the highest prevalence of STEC as compared to the other food products, and this work illustrates the necessity to consider the food products as a potential source of the non-O157 STEC serotypes. DNA sequencing and phylogenetic analysis revealed a high genetic relatedness with beef minced meat from the USA and Australia. This highlights the high probability of worldwide spread of such serotypes, signifying the importance of the one world concept.

Whole-Genome Analysis of Antimicrobial-Resistant and Extraintestinal Pathogenic Escherichia coli in River Water

Contamination of surface waters by antimicrobial-resistant bacteria and pathogenic bacteria is a great concern. In this study, 531 Escherichia coli isolates obtained from the Yamato River in Japan were evaluated phenotypically for resistance to 25 antimicrobials. Seventy-six isolates (14.3%) were multidrug resistant (MDR), 66 (12.4%) were nonsusceptible to one or two classes of agents, and 389 (73.3%) were susceptible. We performed whole-genome sequencing of selected strains by using Illumina technology. In total, the genome sequences of 155 strains were analyzed for antibiotic resistance determinants and phylogenetic characteristics. More than 50 different resistance determinants, including acquired resistance genes and chromosomal resistance mutations, were detected. Among the sequenced MDR strains (n = 66), sequence type 155 (ST155) complex (n = 9), ST10 complex (n = 9), and ST69 complex (n = 7) were prevalent. Among extraintestinal pathogenic E. coli (ExPEC) strains (n = 58), clinically important clonal groups, namely, ST95 complex (n = 18), ST127 complex (n = 8), ST12 complex (n = 6), ST14 complex (n = 6), and ST131 complex (n = 6), were prevalent, demonstrating the clonal distribution of environmental ExPEC strains. Typing of the fimH (type 1 fimbrial adhesin) gene revealed that ST131 complex strains carried fimH22 or fimH41, and no strains belonging to the fimH30 subgroup were detected. Fine-scale phylogenetic analysis and virulence gene content analysis of strains belonging to the ST95 complex (one of the major clonal ExPEC groups causing community-onset infections) revealed no significant differences between environmental and clinical strains. The results indicate contamination of surface waters by E. coli strains belonging to clinically important clonal groups.IMPORTANCE The prevalence of antimicrobial-resistant and pathogenic E. coli strains in surface waters is a concern because surface waters are used as sources for drinking water, irrigation, and recreational purposes. In this study, MDR and ExPEC strains in river water were characterized by genomic sequencing and analysis. We detected more than 50 resistance determinants and identified clonal groups specific to MDR and ExPEC strains. This study showed contamination of surface waters by E. coli strains belonging to clinically important clonal groups. Overall, this study advances our understanding of environmental MDR and ExPEC strains.

Modelling of tetracycline resistance gene transfer by commensal Escherichia coli food isolates that survived in gastric fluid conditions

Antimicrobial resistance (AR) is a major public health concern and a food safety issue worldwide. Escherichia coli strains, indicators of antibiotic resistance, are a source of horizontal gene transfer to other bacteria in the human intestinal system. A probabilistic exposure model was used to estimate the transfer of the AR gene tet(A). The acid resistance and kinetic behaviour of E. coli was analysed as a function of pH to describe the inactivation of E. coli in simulated gastric fluid (SGF), the major host barrier against exogenous micro-organisms. The kinetic parameters of microbial inactivation in SGF were estimated using GInaFiT, and log-linear + tail and Weibull models were found to be suitable for commensal and enterohaemorrhagic E. coli (EHEC), respectively. A probabilistic exposure model was developed to estimate E. coli survival in gastric pH conditions as well as gene transfer from resistant to susceptible cells in humans. E. coli-contaminated retail foods for consumption without further cooking and gastric pH data in South Korea were considered as an example. The model predicts that 22-33% of commensal E. coli can survive under gastric pH conditions of Koreans. The estimated total mean tet(A) transfer level by commensal E. coli was 1.68 × 10^-4-8.15 × 10^-4 log CFU/mL/h. The inactivation kinetic parameters of E. coli in SGF and the quantitative exposure model can provide useful information regarding risk management options to control the spread of AR.

Colistin and tigecycline resistance in carbapenemase-producing Gram-negative bacteria: emerging resistance mechanisms and detection methods

A literature review was undertaken to ascertain the molecular basis for tigecycline and colistin resistance mechanisms and the experimental basis for the detection and delineation of this resistance particularly in carbapenemase-producing Gram-negative bacteria. Pubmed, Google Scholar and Science Direct were searched with the keywords colistin, tigecycline, resistance mechanisms and detection methods. Trans-complementation and comparative MIC studies, mass spectrometry, chromatography, spectrofluorometry, PCR, qRT-PCR and whole genome sequencing (WGS) were commonly used to determine tigecycline and colistin resistance mechanisms, specifically modifications in the structural and regulatory efflux (acrAB, OqxAB, kpgABC adeABC-FGH-IJK, mexAB-XY-oprJM and soxS, rarA robA, ramRAB marRABC, adeLRS, mexRZ and nfxb) and lipid A (pmrHFIJFKLM, lpxA, lpxC lpxD and mgrB, pmrAB, phoPQ,) genes respectively. Mutations in the ribosomal 16S rRNA operon rrnBC, also yielded resistance to tigecycline through target site modifications. The mcr-1 gene conferring resistance to colistin was identified via WGS, trans-complementation and a murine thigh infection model studies. Common detection methods are mainly antibiotic sensitivity testing with broth microdilution while molecular identification tools are mostly PCR and WGS. Spectrofluorometry, MALDI-TOF MS, micro-array and real-time multiplex PCR hold much promise for the future as new detection tools.

Antimicrobial resistance and integron profiles in multidrug-resistant Escherichia coli isolates from pigs

From July 2006 to June 2008, a total of 3876 Escherichia coli strains were collected from 1014 porcine intestinal contents to investigate antimicrobial resistance and related gene patterns. Average resistance rates of porcine E. coli isolates were 93.2% for tetracycline, 65.3% for ampicillin, 60.4% for chloramphenicol, 57.7% for streptomycin, 35.8% for nalidixic acid, 23.6% for gentamicin, 10.8% for ciprofloxacin, 10.0% for norfloxacin, 4.5% for cephalothin, 1.0% for cefoxitin, and 0.4% for cefazolin. The number of isolates resistant to more than 3 different classes of antimicrobials was 2537. Among these, 92 isolates were resistant to 5 or more classes of antimicrobials, and 69 isolates among 92 multidrug-resistant (MDR) isolates were integrase positive. Among 69 integrase-positive MDR isolates, only class I integron was detected in 19 isolates (20.7%). The class-1-integron-positive isolates had different sizes and gene contents (i.e., 1.0 kb containing aadA1 and 1.5 kb containing aadA1-dfrA1 and aadA1-aadB), and showed 15 distinct types by pulsed-field gel electrophoresis (PFGE) analysis, with 80% cut-off band pattern similarity. PFGE typing of four groups of isolates with identical antimicrobial resistance gene profiles showed two heterogeneous groups, while one group had very similar PFGE patterns; the fourth group was not typeable due to DNA degradation. In conjugation experiments, class I integron-harboring isolates transferred resistance to ampicillin, norfloxacin, gentamicin, and chloramphenicol to the recipient strain. This study showed that antimicrobial resistance rates and corresponding genes in porcine E. coli isolates are different from those in human isolates described by previous studies, and that transfer of antimicrobial-resistant genes from animal to human occurred. These data can be used as a baseline to evaluate the effect of antimicrobial use after implementation of the animal antimicrobial ban for prophylactic and growth promotion except for therapeutic use in 2012 in Korea.

Prevalence of tetracycline resistance genes among multi-drug resistant bacteria from selected water distribution systems in southwestern Nigeria

Background

Antibiotic resistance genes [ARGs] in aquatic systems have drawn increasing attention they could be transferred horizontally to pathogenic bacteria. Water treatment plants (WTPs) are intended to provide quality and widely available water to the local populace they serve. However, WTPs in developing countries may not be dependable for clean water and they could serve as points of dissemination for antibiotic resistant bacteria. Only a few studies have investigated the occurrence of ARGs among these bacteria including tetracycline resistance genes in water distribution systems in Nigeria.

Methodology

Multi-drug resistant (MDR) bacteria, including resistance to tetracycline, were isolated from treated and untreated water distribution systems in southwest Nigeria. MDR bacteria were resistant to >3 classes of antibiotics based on break-point assays. Isolates were characterized using partial 16S rDNA sequencing and PCR assays for six tetracycline-resistance genes. Plasmid conjugation was evaluated using E. coli strain DH5α as the recipient strain.

Results

Out of the 105 bacteria, 85 (81 %) and 20 (19 %) were Gram- negative or Gram- positive, respectively. Twenty-nine isolates carried at least one of the targeted tetracycline resistance genes including strains of Aeromonas, Alcaligenes, Bacillus, Klebsiella, Leucobacter, Morganella, Proteus and a sequence matching a previously uncultured bacteria. Tet(A) was the most prevalent (16/29) followed by tet(E) (4/29) and tet30 (2/29). Tet(O) was not detected in any of the isolates. Tet(A) was mostly found with Alcaligenes strains (9/10) and a combination of more than one resistance gene was observed only amongst Alcaligenes strains [tet(A) + tet30 (2/10), tet(A) + tet(E) (3/10), tet(E) + tet(M) (1/10), tet(E) + tet30 (1/10)]. Tet(A) was transferred by conjugation for five Alcaligenes and two E. coli isolates.

Conclusions

This study found a high prevalence of plasmid-encoded tet(A) among Alcaligenes isolates, raising the possibility that this strain could shuttle resistance plasmids to pathogenic bacteria.

Prevalence of Antimicrobial Resistance and Transfer of Tetracycline Resistance Genes in Escherichia coli Isolates from Beef Cattle

The aim of this study was to investigate the prevalence and transferability of resistance in tetracycline-resistant Escherichia coli isolates recovered from beef cattle in South Korea. A total of 155 E. coli isolates were collected from feces in South Korea, and 146 were confirmed to be resistant to tetracycline. The tetracycline resistance gene tet(A) (46.5%) was the most prevalent, followed by tet(B) (45.1%) and tet(C) (5.8%). Strains carrying tet(A) plus tet(B) and tet(B) plus tet(C) were detected in two isolates each. In terms of phylogenetic grouping, 101 (65.2%) isolates were classified as phylogenetic group B1, followed in decreasing order by D (17.4%), A (14.2%), and B2 (3.2%). Ninety-one (62.3%) isolates were determined to be multidrug resistant by the disk diffusion method. MIC testing using the principal tetracyclines, namely, tetracycline, chlortetracycline, oxytetracycline, doxycycline, and minocycline, revealed that isolates carrying tet(B) had higher MIC values than isolates carrying tet(A). Conjugation assays showed that 121 (82.9%) isolates could transfer a tetracycline resistance gene to a recipient via the IncFIB replicon (65.1%). This study suggests that the high prevalence of tetracycline-resistant E. coli isolates in beef cattle is due to the transferability of tetracycline resistance genes between E. coli populations which have survived the selective pressure caused by the use of antimicrobial agents.

tet genes as indicators of changes in the water environment: relationships between culture-dependent and culture-independent approaches

The aim of this study was to identify tetracycline resistance determinants that could be used as molecular indicators of anthropogenic changes in aquatic environments. Two parallel approaches were used to examine the prevalence of tet genes: a culture-based method involving standard PCR and a method relying on quantitative PCR. The studied site was the Łyna River in Olsztyn (Poland). The culture-dependent method revealed that the concentrations of doxycycline-resistant bacteria harboring the tet(B) gene were higher in wastewater and downstream river samples than in upstream water samples. The tet(B) gene was transferred from environmental bacteria to Escherichia coli. The results generated by the culture-independent method validated statistically significant differences in tet(B) concentrations between upstream and downstream river sections, and revealed that tet(B) levels were correlated with the presence of other tetracycline resistance genes, dissolved oxygen concentrations, temperature and doxycycline concentrations in water. Our findings indicate that doxycycline-resistant bacteria, in particular E. coli harboring tet(B) or increased concentrations of tet(B), are potentially robust indicators of changes in water environments.

Characterization of antibiotic-resistance genes in antibiotic resistance Escherichia coli isolates from a lake

The spread of antibiotic-resistance bacteria and antibiotic-resistance genes (ARGs) has been of concern worldwide. In this study, 114 Escherichia coli isolates were isolated from surface water samples of a lake to identify their susceptibility to antibiotics, including tetracycline (TC), gentamicin (GN), ampicillin (AMP), streptomycin (ST), oxytetracycline (OC), levofloxacin (LEV), nalidixic acid (NA), and sulfamethoxazole/trimethoprim (SFT). Isolates showing resistance to TC, GN, AMP, ST, OC, LEV, NA, and SFT occurred in 50, 76, 68, 71, 55, 32, 82, and 85 % of the total isolates, respectively. Thirty-seven different resistance patterns were identified, and the most abundant resistance profile (28 of 104) was TC/GN/AMP/ST/OC/LEV/NA/SFT. The occurrence of 29 ARGs were detected in their corresponding resistance clones, and 88 % of TC-resistance, 94 % of SFT-resistance, 90 % of AMP-resistance, 78 % of ST-resistance, and 72 % of quinolone-resistance clones can be described by their corresponding ARGs. It should be noted that most of these antibiotic-resistance clones harbored at least two corresponding ARGs, indicating that high frequencies of combined ARGs occurred in these isolates. In addition, 9 new types of DNA sequence of qnr(B) gene were obtained and were clustered into the same group as showed by phylogenetic trees analysis. These results suggest that the development of antibiotic resistance can be ascribed to the high frequency in the recombination of ARGs through horizontal gene transfer.

Genotypic and phenotypic characterization of antimicrobial-resistant Escherichia coli from farm-raised diarrheic sika deer in Northeastern China

In China, overuse and/or abuse of antimicrobials are common in stockbreeding, which possess high risks of antimicrobial-resistant contaminations. The serogroups, major virulence genes, and antimicrobial resistant patterns of the antimicrobial-resistant Escherichia coli (E. coli) were investigated in the feces of diarrheic farm-raised sika deer from 50 farms in three Northeastern provinces of China. A total of 220 E. coli isolates were obtained and characterized. Twenty-eight O serogroups were identified from the obtained E. coli isolates with O2, O26, O128, O142 and O154 being dominant. Nearly all the isolates were resistant to at least four of the tested antimicrobials. More than 90% of the E. coli isolates carried at least one of the tested virulence genes. About 85% of the E. coli isolates carried one or more antimicrobial-resistant genes responsible for resistant phenotypes of sulfonamides, streptomycin/spectionomycin or tetracycline. The antimicrobial resistant level and pathogenic group occurrences of the obtained E. coli isolates were higher than that of livestock and wild animals reported in some developed countries. Thus, the fecal-carrying antimicrobial-resistant E. coli from the farm-raised sika deer is potentially a significant contamination source for freshwater systems and food chain, and may pose great health risks for human and animals in Northeastern China.

Prevalence of tet genes mediating tetracycline resistance in Escherichia coli clinical isolates in Osun State, Nigeria

The occurrence of tetracycline resistance determinants in 203 Escherichia coli isolates recovered from clinical samples at three different hospitals in Nigeria between June 2009 and May 2010 was investigated. The isolates were subjected to standard procedures. Antibiotic susceptibility to a panel of eight antibiotics was also performed, and resistance genes were detected with the polymerase chain reaction (PCR) technique. One hundred and six E. coli isolates (52.2%) were obtained at LAUTECH Teaching Hospital Osogbo, 85 (41.9%) from OAUTHC Ile Ife and 12 (5.9%) from Osun State Hospital Asubiaro Osogbo. Result of the disk diffusion antibiotic susceptibility test showed 96.1% isolates to be resistant to ampicillin, 77.8% to tetracycline, 37.9% to cotrimoxazole, 38.4% to nalidixic acid, 20.7% to ofloxacin, 17.7% to ceftriaxone, 11.8% to gentamycin, and 2% to nitrofurantoin. One hundred and sixty two (79.9%) isolates had minimum inhibitory concentration (MIC) of tetracycline ≥ 128 μg/ml. The polymerase chain reaction (PCR) detected tetA gene in 89 (43.8%) isolates, tetB gene in 65 (32.0%), and both tetA and tetB genes in 9 (4.4%) isolates. The study demonstrated a relatively high level of gene mediated antibiotic resistance to tetracycline and other antibiotics in E. coli clinical isolates in Southwest region of Nigeria.

Prevalence of tetracycline resistance genes and identification of tet(M) in clinical isolates of Escherichia coli from sick ducks in China

Tetracycline resistance is one of the most frequently encountered resistance properties in bacteria of animal origin. The aim of the present study was to investigate the prevalence and diversity of tetracycline resistance (tet) genes among Escherichia coli clinical isolates from diseased ducks in China and to report the identification and sequencing of the tet(M) gene. The susceptibility of 85 Escherichia coli strains to tetracyclines was determined by broth microdilution, and the presence of tet genes was investigated by multiplex PCR. All of the 85 isolates were fully resistant to both oxytetracycline and tetracycline, and 76.5 % were resistant to doxycycline. Seventy-seven of the isolates (90.6 %) encoded multiple tet genes, with 17.6, 38.8 and 34.1 % encoding two, three and four tet genes, respectively, and only 7.1 % encoded a single tet(A) gene. The MICs of oxytetracycline and tetracycline for all isolates ranged from 16 to ≥128 µg ml−1 with a MIC90 of >128 µg ml−1, regardless of the type or number of tet genes encoded. Isolates containing tet(M) commonly had more than one tet gene per strain. The doxycycline resistance rate in the tet(M)-positive isolates was significantly higher than in the tet(M)-negative isolates (P<0.05). A full-length tet(M) gene, including the promoter region, was obtained by PCR in seven of the 41 tet(M)-positive isolates and was sequenced and cloned. The cloned tet(M) gene conferred resistance to tetracyclines in the recombinant Escherichia coli host strain. These results revealed that, in these isolates, the prevalence of multiple tet genes was strikingly high and that tet(M) played a role in doxycycline resistance.

Multidrug-resistant gram-negative bacteria colonization of healthy US military personnel in the US and Afghanistan

Background

The US military has seen steady increases in multidrug-resistant (MDR) gram-negative bacteria (GNB) infections in casualties from Iraq and Afghanistan. This study evaluates the prevalence of MDR GNB colonization in US military personnel.

Methods

GNB colonization surveillance of healthy, asymptomatic military personnel (101 in the US and 100 in Afghanistan) was performed by swabbing 7 anatomical sites. US-based personnel had received no antibiotics within 30 days of specimen collection, and Afghanistan-based personnel were receiving doxycycline for malaria chemoprophylaxis at time of specimen collection. Isolates underwent genotypic and phenotypic characterization.

Results

The only colonizing MDR GNB recovered in both populations was Escherichia coli (p=0.01), which was seen in 2% of US-based personnel (all perirectal) and 11% of Afghanistan-based personnel (10 perirectal, 1 foot+groin). Individuals with higher off-base exposures in Afghanistan did not show a difference in overall GNB colonization or MDR E. coli colonization, compared with those with limited off-base exposures.

Conclusion

Healthy US- and Afghanistan-based military personnel have community onset-MDR E. coli colonization, with Afghanistan-based personnel showing a 5.5-fold higher prevalence. The association of doxycycline prophylaxis or other exposures with antimicrobial resistance and increased rates of MDR E. coli colonization needs further evaluation.

Efflux: how bacteria use pumps to control their microenvironment

Efflux pumps are a potent and clinically important cause of antibiotic resistance. The particular focus of this chapter is on the efflux pump as a target for antimicrobial therapy and the development of new antibacterials to address the efflux problem.Tigecycline is an example of how old antibiotics, in this case tetracyclines, which have become substrates for efflux pumps, can be extensively modified to restore antimicrobial activity and clinical efficacy.

The prevalence of antimicrobial-resistant Escherichia coli in two species of invasive alien mammals in Japan

The prevalence of antimicrobial resistance in 128 Escherichia coli isolates was investigated in two species of invasive alien mammals (IAMs): the small Asian mongoose (SAM) and Japanese weasel (JW). The SAM is found on the main island of Okinawa, Japan, where a large number of livestock is available, and the JW is present on a small island, where is isolated from the main island, and have a small number of livestock. We focused on the two IAMs, inhabiting under the different environments, and compared their prevalence of antimicrobial-resistant E. coli. In the comparison of the frequencies of antimicrobial-resistant E. coli isolates between the SAM and JW, JW showed significantly higher prevalence of resistance against three drugs, ampicillin, chlortetracycline and nalidixic acid, compared with SAM's test results (P<0.05). The bla(TEM) gene and the aph1 gene were detected in 35 subjects (91%) of ampicillin-resistant isolates and 6 subjects (100%) of kanamycin-resistant isolates, respectively. The tet (A) gene was detected in 62 subjects (46%) of CTC-resistant isolates, and the tet (B) gene was detected in 25 subjects (8%) of those in IAM. The present results suggest that some IAMs were the carrier of antimicrobial-resistant bacteria and their genes, and the frequencies of these resistances were different between two IAM species.

The impact of environmental contamination with antibiotics on levels of resistance in soil bacteria

This study examined the effects of tetracycline and streptomycin on microorganisms in three different soil habitats: forest soil, agricultural soil, and compost. These antibiotics are commonly used in both medical and veterinary therapy as well as in the production of plant biomass and until quite recently, the production of animal biomass. Microcosms were used as model systems in which the number of microorganisms in environments containing different amounts of antibiotics was analyzed. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of tetracycline and streptomycin were determined. The MIC and MBC values of tetracycline against the tested strains were 20 to 180 microg/ mL and 30 to 300 microg/mL, respectively, and of streptomycin, 360 to 500 microg/mL and > or =500 microg/mL, respectively. Resistant bacterial strains were identified and their physiological profiles assessed. Streptomycin and tetracycline were found to reduce the number of bacteria in the studied soils by between 50 and 80%. Soil bacteria were found to be more resistant to streptomycin than to tetracycline. The bacterial species showing the highest resistance to tetracycline were Rhizobium radiobacter, Burkholderia cepacia, Brevundimonas vesicularis, and Pasteurella multocida. Most soils with high concentrations of streptomycin (5 mg/kg) contained Rhizobium radiobacter, Burkholderia cepacia, and Sphingomonas multivorum, among others. The strains most resistant to tetracycline were isolated from agricultural soil that is constantly subjected to tetracycline pressure from animal manures and biosolids. Among resistant strains, opportunistic pathogens were identified.

In vitro activity of tigecycline against patient isolates collected during phase 3 clinical trials for hospital acquired pneumonia

The in vitro activity of tigecycline was evaluated against 819 baseline pathogens isolated from 383 patients enrolled in the phase 3 clinical trial investigating the efficacy of tigecycline in hospital acquired pneumonia (HAP). The trials were global, enrolling patients in 27 countries. Tigecycline was active against the most prevalent pathogens in HAP, including gram-positive and gram-negative strains (90% of MICs ≤2 µg/mL for the entire collection). The spectrum of activity of tigecycline included important pathogens such as Staphylococcus aureus (including methicillin-resistant S. aureus), Enterococcus faecalis, Streptococcus pneumoniae, Acinetobacter baumannii/calcoaceticus complex, Escherichia coli, Klebsiella pneumonia, and Enterobacter cloacae. As reported previously, a few genera, such as Pseudomonas aeruginosa and the Proteeae, were generally less susceptible to tigecycline by comparison to other gram-negative pathogens. The excellent in vitro, expanded, broad-spectrum activity of tigecycline in the clinical isolates confirmed the potential utility of tigecycline for pathogens associated with with hospital acquired pneumonia infections.