Molecular Mechanisms and Epidemiology of Fosfomycin Resistance in Staphylococcus aureus Isolated From Patients at a Teaching Hospital in China. - Related Documents




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228401.0000Molecular Mechanisms and Epidemiology of Fosfomycin Resistance in Staphylococcus aureus Isolated From Patients at a Teaching Hospital in China. Staphylococcus aureus is a major cause of hospital- and community-acquired infections placing a significant burden on the healthcare system. With the widespread of multidrug-resistant bacteria and the lack of effective antibacterial drugs, fosfomycin has gradually attracted attention as an "old drug." Thus, investigating the resistance mechanisms and epidemiology of fosfomycin-resistant S. aureus is an urgent requirement. In order to investigate the mechanisms of resistance, 11 fosfomycin-resistant S. aureus isolates were analyzed by PCR and sequencing. The genes, including fosA, fosB, fosC, fosD, fosX, and tet38, as well as mutations in murA, glpT, and uhpT were identified. Quantitative real-time PCR (qRT-PCR) was conducted to evaluate the expression of the target enzyme gene murA and the efflux pump gene tet38 under the selection pressure of fosfomycin. Furthermore, multilocus sequence typing (MLST) identified a novel sequence type (ST 5708) of S. aureus strains. However, none of the resistant strains carried fosA, fosB, fosC, fosD, and fosX genes in the current study, and 12 distinct mutations were detected in the uhpT (3), glpT (4), and murA (5) genes. qRT-PCR revealed an elevated expression of the tet38 gene when exposed to increasing concentration of fosfomycin among 8 fosfomycin-resistant S. aureus strains and reference strain ATCC 29213. MLST analysis categorized the 11 strains into 9 STs. Thus, the mutations in the uhpT, glpT, and murA genes might be the primary mechanisms underlying fosfomycin resistance, and the overexpression of efflux pump gene tet38 may play a major role in the fosfomycin resistance in these isolates.202032670230
474610.9997Correlation of QRDR mutations and MIC levels in fluoroquinolone-resistant Staphylococcus aureus clinical isolates. Antimicrobial resistance is a global health problem. Among various antibiotic-resistant bacteria, Staphylococcus aureus, particularly methicillin-resistant S. aureus (MRSA), is a clinically important pathogen responsible for serious infections because of its multidrug resistance (MDR) and association with high mortality rates. The MDR nature of MRSA, including resistance to macrolides, aminoglycosides, fluoroquinolones, and tetracyclines, limits therapeutic choices and poses significant challenges in clinical management. This study aimed to analyze the correlation between mutations in the quinolone resistance-determining region (QRDR) and the minimum inhibitory concentration (MIC) of fluoroquinolone drugs, such as ciprofloxacin and levofloxacin, in MRSA and methicillin-sensitive S. aureus (MSSA). A total of 63 S. aureus clinical strains were isolated from blood samples of sepsis patients. DNA sequence analysis was performed using gDNA extracted from all S. aureus clinical isolates to identify mutations in the QRDR of gyrA, gyrB, parC, and parE. The MICs of antimicrobials were determined by the broth microdilution method. Among these genes, only mutations in parC showed a statistically significant positive correlation with elevated MIC levels, underscoring the primary role of parC in mediating resistance in our clinical isolates. Notably, all isolates exhibited a substitution at serine 80 (S80) in parC, and those harboring simultaneous substitutions at both S80 and glutamic acid 84 (E84) demonstrated markedly increased MIC values for both drugs. These findings reinforce previously reported associations between dual mutations and high-level fluoroquinolone resistance, while highlighting the distinct contribution of parC among the QRDR genes analyzed in this study. Furthermore, we found that the most frequent mutation in the QRDR was the cytosine-to-thymine mutation.IMPORTANCEAntimicrobial resistance is a growing global health crisis, making bacterial infections harder to treat. Staphylococcus aureus, especially MRSA, is a major concern due to its resistance to multiple antibiotics, including fluoroquinolones like ciprofloxacin and levofloxacin. Our study highlights how specific genetic mutations in the quinolone resistance-determining region (QRDR) influence fluoroquinolone resistance. We found that mutations in the parC gene, particularly substitutions at serine 80 (S80) and glutamic acid 84 (E84), significantly increase resistance. Understanding these mutations helps predict antibiotic resistance and may guide more effective treatment strategies. By identifying key genetic changes that drive fluoroquinolone resistance, our research contributes to developing improved diagnostic tools and targeted therapies to combat drug-resistant S. aureus infections. This knowledge is crucial for clinicians and researchers working to control the spread of antibiotic-resistant bacteria and improve patient outcomes.202541081515
229720.9995Efflux Pump Activity and Mutations Driving Multidrug Resistance in Acinetobacter baumannii at a Tertiary Hospital in Pretoria, South Africa. Acinetobacter baumannii (A. baumannii) has developed several resistance mechanisms. The bacteria have been reported as origin of multiple outbreaks. This study aims to investigate the use of efflux pumps and quinolone resistance-associated genotypic mutations as mechanisms of resistance in A. baumannii isolates at a tertiary hospital. A total number of 103 A. baumannii isolates were investigated after identification and antimicrobial susceptibility testing by VITEK2 followed by PCR amplification of bla (OXA-51) . Conventional PCR amplification of the AdeABC efflux pump (adeB, adeS, and adeR) and quinolone (parC and gyrA) resistance genes were performed, followed by quantitative real-time PCR of AdeABC efflux pump genes. Phenotypic evaluation of efflux pump expression was performed by determining the difference between the MIC of tigecycline before and after exposure to an efflux pump inhibitor. The Sanger sequencing method was used to sequence the parC and gyrA amplicons. A phylogenetic tree was drawn using MEGA 4.0 to evaluate evolutionary relatedness of the strains. All the collected isolates were bla (OXA-51) -positive. High resistance to almost all the tested antibiotics was observed. Efflux pump was found in 75% of isolates as a mechanism of resistance. The study detected parC gene mutation in 60% and gyrA gene mutation in 85%, while 37% of isolates had mutations on both genes. A minimal evolutionary distance between the isolates was reported. The use of the AdeABC efflux pump system as an active mechanism of resistance combined with point mutation mainly in gyrA was shown to contribute to broaden the resistance spectrum of A. baumannii isolates.202134659419
233130.9995Bacteriological and molecular study of fosfomycin resistance in uropathogenic Escherichia coli. The identification of genes associated with resistance has the potential to facilitate the development of novel diagnostic tests and treatment methods. The objective of this study was to examine the antibiotic resistance and Fosfomycin resistance genes in uropathogenic Escherichia coli (UPEC) in patients in Baghdad, Iraq. After analyzing 250 urine samples using various identification methods, including the examination of morphological characteristics, biochemical tests, and genetic detection, it was determined that E. coli was the most common bacteria present, accounting for 63.6% of the samples. Antibiotic susceptibility testing showed a significant prevalence of resistance to various antibiotics, with 99.3% of E. coli isolates exhibiting multiple drug resistance (MDR). Fosfomycin showed antibacterial properties against UPEC. The minimum inhibitory concentration (MIC) ranged from 512 to 1024 μg/mL, while the minimum bactericidal concentration (MBC) was 2048 μg/mL. In the time-kill assay, fosfomycin was effective against fosfomycin-resistant isolates within 8-12 h. The genetic determinants associated with fosfomycin resistance were examined through the utilization of polymerase chain reaction (PCR). The findings indicated that the genes murA, glpT, and cyaA were detected in all the isolates when genomic DNA was used as a template. However, all the tests yielded negative results when plasmid was used as a template. The genes fosA3 and fosA4 were detected in 8.6% and 5% of the isolates when genomic DNA was used as a template. When plasmid was used as a template, the genes fosA3 and fosA4 were found in 5.7% and 2.9% of the isolates, respectively. In conclusion, there is an increasing problem with antibiotic resistance in UPEC, with elevated rates of resistance to several antibiotics. The study also offers novel insights into the genetic foundation of fosfomycin resistance in UPEC.202438367167
228540.9995Efflux genes and active efflux activity detection in Malaysian clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). Efflux-mediated resistance has been recognized as an important contributor of antibiotic resistance in bacteria, especially in methicillin-resistant Staphylococcus aureus (MRSA) isolates. This study was carried out to detect and analyze efflux genes (norA and mdeA) and active efflux activity in a collection of Malaysian MRSA and methicillin-sensitive S. aureus (MSSA) clinical isolates. Nineteen isolates including three ATCC S. aureus reference strains were subjected to PCR detection and DNA sequence analysis for norA and mdeA and active efflux detection using modified minimum inhibitory concentration (MIC) assay. From the 19 isolates, 18 isolates harboured the mdeA gene while 16 isolates contained norA gene. DNA sequence analysis reveals 98-100% correlation between the PCR product and the published DNA sequences in GenBank. In addition, 16 isolates exhibited active efflux activity using the ethidium bromide (EtBr)-reserpine combination MIC assay. To our knowledge, this is the first report on the detection of efflux genes and active efflux activity amongst Malaysian clinical isolates of MRSA/MSSA. Detection of active efflux activity may explain the previous report on efflux-mediated drug resistance profile amongst the local clinical isolates.200818720500
550650.9995Genomic and phenotypic insight into antimicrobial resistance of Pseudomonas fluorescens from King George Island, Antarctica. The genus Pseudomonas includes metabolically versatile microorganisms occupying diverse niches, from environmental habitats to plant pathogens, and has clinically significant strains. For this reason, Pseudomonas spp. might act as a reservoir of antimicrobial resistance genes, which have been detected even in isolated environments. The aim of this study was to report the antimicrobial susceptibility profile of 25 Pseudomonas fluorescens isolates from soil samples collected on King George Island (Antarctic Peninsula), and to select non-clonal isolates with unusual phenotypes for whole genome sequencing (WGS). Six classes of antimicrobials were assessed with disk diffusion and colistin with minimum inhibitory concentration (MIC) by broth microdilution. In order to confirm the discrepant phenotypes, MIC by agar dilution was performed for the beta-lactams aztreonam, ceftazidime, cefepime and the aminoglycoside neomycin. The genus Pseudomonas was confirmed by matrix-assisted laser desorption/ionization - time of flight (MALDI-TOF) and the clonal relationships were examined using repetitive extragenic palindromic polymerase chain reaction (BOX-PCR), from which 14 strains were selected for WGS. Antimicrobial susceptibility testing revealed that all strains were susceptible to neomycin and exhibited varying degrees of intermediate or full resistance to aztreonam and colistin. Additionally, 11 strains demonstrated intermediate resistance to ceftazidime, and six were resistant to cefepime. The genomic analysis identified various efflux pumps, predominantly from the ABC transporter and resistance-nodulation-division families. Resistance genes were detected against eight classes of antimicrobials, listed by prevalence: beta-lactams, tetracyclines, polymyxins, aminoglycosides, fosmidomycin, fosfomycin, quinolones, and chloramphenicol. Genes associated with heavy-metal resistance, prophages, and adaptations to extreme environments were also investigated. One notable isolate exhibited not only the highest number of pathogenicity and resistance islands, but also presented a carbapenemase-encoding gene (bla (PFM-2)) in its genome. Overall, one plasmid was identified in a distinct isolate, which did not exhibit antimicrobial resistance determinants. The genotypic and phenotypic findings are consistent, suggesting that efflux pumps play a critical role in antimicrobial extrusion. This study offers valuable insight into the evolution of antimicrobial resistance in P. fluorescens, particularly in extreme environments, such as Antarctica. By exploring the antimicrobial resistance mechanisms in P. fluorescens, the study sheds light on how isolated ecosystems drive the natural evolution of resistance genes.202540099188
229660.9995Multi-drug resistance profiles and the genetic features of Acinetobacter baumannii isolates from Bolivia. INTRODUCTION: Acinetobacter baumannii is opportunistic in debilitated hospitalised patients. Because information from some South American countries was previously lacking, this study examined the emergence of multi-resistant A. baumannii in three hospitals in Cochabamba, Bolivia, from 2008 to 2009. METHODOLOGY: Multiplex PCR was used to identify the main resistance genes in 15 multi-resistant A. baumannii isolates. RT-PCR was used to measure gene expression. The genetic environment of these genes was also analysed by PCR amplification and sequencing. Minimum inhibitory concentrations were determined for key antibiotics and some were determined in the presence of an efflux pump inhibitor, 1-(1-napthylmethyl) piperazine. RESULTS: Fourteen strains were found to be multi-resistant. Each strain was found to have the blaOXA-58 gene with the ISAba3-like element upstream, responsible for over-expression of the latter and subsequent carbapenem resistance. Similarly, ISAba1, upstream of the blaADC gene caused over-expression of the latter and cephalosporin resistance; mutations in the gyrA(Ser83 to Leu) and parC (Ser-80 to Phe) genes were commensurate with fluoroquinolone resistance. In addition, the adeA, adeB efflux genes were over-expressed. All 15 isolates were positive for at least two aminoglycoside resistance genes. CONCLUSIONS: This is one of the first reports analyzing the multi-drug resistance profile of A. baumannii strains isolated in Bolivia and shows that the over-expression of theblaOXA-58, blaADC and efflux genes together with aminoglycoside modifying enzymes and mutations in DNA topoisomerases are responsible for the multi-resistance of the bacteria and the subsequent difficulty in treating infections caused by them.201323592642
578370.9995Molecular Investigation and Virulence Determination of Methicillin and Vancomycin Resistant Clinical Staphylococcus Aureus Isolates. Staphylococcus aureus is an opportunistic pathogen that provides conditions for host invasion due to various virulence factors and plays a role in causing various infections. The pathogenicity of these bacteria may vary depending on the host's susceptibility. This study investigates the sensitivity of S. aureus strains isolated from clinical samples to methicillin and vancomycin, and it evaluates the presence of resistance, virulence and toxin-producing genes, and their expression level in the methicillin-resistant S. aureus (MRSA), vancomycin-resistant S. aureus (VRSA), and vancomycin-intermediate S. aureus (VISA) isolates. A cross-sectional study was conducted, encompassing 502 S. aureus isolates obtained from diverse infections over the course of a year. The methicillin and vancomycin sensitivities of the isolates were ascertained by disk diffusion and microdilution broth methods, respectively. The presence of genes associated with resistance, adhesion, and toxin production was subsequently investigated through the implementation of multiplex polymerase chain reaction (PCR) methodology. The expression levels of virulence and resistance genes were detected in resistant and sensitive isolates using real-time quantitative PCR (qPCR). Among the 502 S. aureus isolates, 168 (33.6%) were identified as MRSA. Furthermore, a total of six isolates (1.2%) were identified as VRSA, and two isolates (0.4%) were identified as VISA. The distribution of virulence and resistance-related genes varied among the isolates. The results of the gene expression study demonstrated that the expression levels of the majority of the studied genes were significantly higher in resistant isolates (MRSA and VRSA) compared to sensitive isolates. It is imperative to acknowledge that VRSA and MRSA are regarded as grave hazards to human health. The present study underscores the necessity for enhanced sanitary measures to more effectively control this hospital pathogen, particularly in light of the presence and expression of genes encoding virulence factors in S. aureus isolates.202540980455
594580.9995Mechanisms of linezolid resistance among coagulase-negative staphylococci determined by whole-genome sequencing. Linezolid resistance is uncommon among staphylococci, but approximately 2% of clinical isolates of coagulase-negative staphylococci (CoNS) may exhibit resistance to linezolid (MIC, ≥8 µg/ml). We performed whole-genome sequencing (WGS) to characterize the resistance mechanisms and genetic backgrounds of 28 linezolid-resistant CoNS (21 Staphylococcus epidermidis isolates and 7 Staphylococcus haemolyticus isolates) obtained from blood cultures at a large teaching health system in California between 2007 and 2012. The following well-characterized mutations associated with linezolid resistance were identified in the 23S rRNA: G2576U, G2447U, and U2504A, along with the mutation C2534U. Mutations in the L3 and L4 riboproteins, at sites previously associated with linezolid resistance, were also identified in 20 isolates. The majority of isolates harbored more than one mutation in the 23S rRNA and L3 and L4 genes. In addition, the cfr methylase gene was found in almost half (48%) of S. epidermidis isolates. cfr had been only rarely identified in staphylococci in the United States prior to this study. Isolates of the same sequence type were identified with unique mutations associated with linezolid resistance, suggesting independent acquisition of linezolid resistance in each isolate. IMPORTANCE: Linezolid is one of a limited number of antimicrobials available to treat drug-resistant Gram-positive bacteria, but resistance has begun to emerge. We evaluated the genomes of 28 linezolid-resistant staphylococci isolated from patients. Multiple mutations in the rRNA and associated proteins previously associated with linezolid resistance were found in the isolates investigated, underscoring the multifocal nature of resistance to linezolid in Staphylococcus. Importantly, almost half the S. epidermidis isolates studied harbored a plasmid-borne cfr RNA methylase gene, suggesting that the incidence of cfr may be higher in the United States than previously documented. This finding has important implications for infection control practices in the United States. Further, cfr is commonly detected in bacteria isolated from livestock, where the use of phenicols, lincosamides, and pleuromutilins in veterinary medicine may provide selective pressure and lead to maintenance of this gene in animal bacteria.201424915435
550990.9995Exploring Virulence Characteristics of Clinical Escherichia coli Isolates from Greece. The aim of this study was to examine the genetic characteristics that could be associated with the virulence characteristics of Escherichia coli collected from clinical samples. A collection of 100 non-repetitive E. coli isolates was analyzed. All isolates were typed by MLST. String production, biofilm formation and serum resistance were examined for all isolates. Twenty E. coli isolates were completely sequenced Illumina platform. The results showed that the majority of E. coli isolates (87%) produced significant levels of biofilm, while none of the isolates were positive for string test and resistance to serum. Additionally, the presence of CRISPR/Cas systems (type I-E or I-F) was found in 18% of the isolates. Analysis of WGS data found that all sequenced isolates harbored a variety of virulence genes that could be implicated in adherence, invasion, iron uptake. Also, WGS data confirmed the presence of a wide variety of resistance genes, including ESBL- and carbapenemase-encoding genes. In conclusion, an important percentage (87%) of the E. coli isolates had a significant ability to form biofilm. Biofilms, due to their heterogeneous nature and ability to make microorganisms tolerant to multiple antimicrobials, complicate treatment strategies. Thus, in combination with the presence of multidrug resistance, expression of virulence factors could challenge antimicrobial therapy of infections caused by such bacteria.202540731998
5045100.9995Emergence of colistin-resistance in extremely drug-resistant Acinetobacter baumannii containing a novel pmrCAB operon during colistin therapy of wound infections. BACKGROUND: Colistin resistance is of concern since it is increasingly needed to treat infections caused by bacteria resistant to all other antibiotics and has been associated with poorer outcomes. Longitudinal data from in vivo series are sparse. METHODS: Under a quality-improvement directive to intensify infection-control measures, extremely drug-resistant (XDR) bacteria undergo phenotypic and molecular analysis. RESULTS: Twenty-eight XDR Acinetobacter baumannii isolates were longitudinally recovered during colistin therapy. Fourteen were susceptible to colistin, and 14 were resistant to colistin. Acquisition of colistin resistance did not alter resistance to other antibiotics. Isolates had low minimum inhibitory concentrations of an investigational aminoglycoside, belonged to multi-locus sequence type 94, were indistinguishable by pulsed-field gel electrophoresis and optical mapping, and harbored a novel pmrC1A1B allele. Colistin resistance was associated with point mutations in the pmrA1 and/or pmrB genes. Additional pmrC homologs, designated eptA-1 and eptA-2, were at distant locations from the operon. Compared with colistin-susceptible isolates, colistin-resistant isolates displayed significantly enhanced expression of pmrC1A1B, eptA-1, and eptA-2; lower growth rates; and lowered fitness. Phylogenetic analysis suggested that colistin resistance emerged from a single progenitor colistin-susceptible isolate. CONCLUSIONS: We provide insights into the in vivo evolution of colistin resistance in a series of XDR A. baumannii isolates recovered during therapy of infections and emphasize the importance of antibiotic stewardship and surveillance.201323812239
5930110.9995Clinical Resistant Strains of Enterococci and Their Correlation to Reduced Susceptibility to Biocides: Phenotypic and Genotypic Analysis of Macrolides, Lincosamides, and Streptogramins. Enterococci are troublesome nosocomial, opportunistic Gram-positive cocci bacteria showing enhanced resistance to many commonly used antibiotics. This study aims to investigate the prevalence and genetic basis of antibiotic resistance to macrolides, lincosamides, and streptogramins (MLS) in Enterococci, as well as the correlation between MLS resistance and biocide resistance. From 913 clinical isolates collected from King Khalid Hospital, Hail, Saudi Arabia, 131 isolates were identified as Enterococci spp. The susceptibility of the clinical enterococcal isolates to several MLS antibiotics was determined, and the resistance phenotype was detected by the triple disk method. The MLS-involved resistance genes were screened in the resistant isolates. The current results showed high resistance rates to MLS antibiotics, and the constitutive resistance to all MLS (cMLS) was the most prevalent phenotype, observed in 76.8% of resistant isolates. By screening the MLS resistance-encoding genes in the resistant isolates, the erythromycin ribosome methylase (erm) genes that are responsible for methylation of bacterial 23S rRNA were the most detected genes, in particular, ermB. The ereA esterase-encoding gene was the most detected MLS modifying-encoding genes, more than lnuA (adenylation) and mphC (phosphorylation). The minimum inhibitory concentrations (MICs) of commonly used biocides were detected in resistant isolates and correlated with the MICs of MLS antibiotics. The present findings showed a significant correlation between MLS resistance and reduced susceptibility to biocides. In compliance with the high incidence of the efflux-encoding genes, especially mefA and mefE genes in the tolerant isolates with higher MICs to both MLS antibiotics and biocides, the efflux of resistant isolates was quantified, and there was a significant increase in the efflux of resistant isolates with higher MICs as compared to those with lower MICs. This could explain the crucial role of efflux in developing cross-resistance to both MLS antibiotics and biocides.202336978327
2290120.9995Comprehensive study to investigate the role of various aminoglycoside resistance mechanisms in clinical isolates of Acinetobacter baumannii. Therapeutic resistance towards most of the current treatment regime by Acinetobacter baumannii has reduced the prescribing antibiotic pattern and option is being re-shifted towards more toxic agents including aminoglycosides. The present investigation aimed at to study various mechanisms towards aminoglycoside non-susceptibility in clinical isolates of A. baumannii. The bacteria were subjected to genetic basis assessment for the presence of aminoglycoside modifying enzymes (AME), 16S rRNA methylase encoding genes and relative expression of AdeABC and AbeM efflux pumps in relation to their susceptibility to five aminoglycosides. When isolates were subjected to typing by repetitive extragenic palindromic (REP) PCR, isolates could be separated into thirteen definite clones. The majority of isolates (94%) were positive for AME encoding genes. Possession of ant(2')-Ia correlated with non-susceptibility towards gentamicin, amikacin, kanamycin, tobramycin; while, presence of aph(3')-VIa attributed to resistance towards amikacin, kanamycin; possession of aac(3')-Ia allied with non-susceptibility to amikacin, tobramycin and presence of aac(3')IIa correlated with kanamycin non-susceptibility. Presence of armA was detected in 34.4%, 34.2%, 29.2%, 40.3%, and 64.2% of isolates showing non-susceptibility to gentamicin, amikacin, kanamycin, tobramycin and netilmicin, respectively. No isolates were found to carry rmtB or rmtC. Amikacin non-susceptibility in comparison to other aminoglycosides correlated with over production of adeB. Overall, the results represented a definitive correlation between presence of AME encoding genes as well as armA and resistance of A. baumannii towards aminoglycosides. On the other hand, the up-regulation of AdeABC and AbeM systems was found to have only the partial role in development of aminoglycoside resistance.201727889248
1582130.9995Integrated Genomic and Phenotypic Characterization of an Mcr-10.1-Harboring Multidrug Resistant Escherichia coli Strain From Migratory Birds in China. Background: The global rise in antibiotic resistance among multidrug resistant (MDR) Gram-negative (GN) bacteria has posed significant health challenges, leading to the resurgence of colistin as a key defense against these bacteria. However, the widespread use of colistin has resulted in the rapid emergence of colistin resistance on a global scale. Ten members of the (mobile colistin resistance) mcr gene family, mcr-1 through mcr-10, have been reported and documented. Currently, bacteria reported to carry the mcr-10.1 gene are sensitive to colistin, but the mechanism underlying the low-level resistance phenomenon mediated by mcr-10.1 remains unclear. Methods: In this study, antimicrobial susceptibility testing (AST) was conducted on Escherichia coli (E.coli) isolated from Chinese migratory birds, resulting in the selection of 87 strains exhibiting MDR phenotypes. Whole-genome sequencing (draft) was performed on these 87 MDR E. coli strains, and for one of the E. coli strains carrying the mcr-10.1 gene, whole-genome sequencing, phenotypic characterization, AST and conjugation experiments were conducted to identify its resistance phenotypes and genetic characteristics. Results: Whole-genome sequencing (draft) of 87 MDR E. coli isolates revealed a diverse array of resistance genes, predominantly including aminoglycoside, β-lactam, tetracycline, and sulfonamide resistance genes. Remarkably, one isolate, despite being sensitive to colistin, harbored the mcr-10.1 gene. Further sequencing showed that mcr-10.1 was located in the conserved region of xerC-mcr-10.1, a hotspot for movable elements with various insertion sequences (ISs) or transposons nearby. Phenotypic characterization indicated that the MDR plasmid pGN25-mcr10.1 had no significant effect on the growth of GN25 and its derivatives but reduced the number of bacterial flagella. Conclusions: It is particularly important to note that bacteria harboring the mcr-10.1 gene may exhibit low minimum inhibitory concentration (MIC) values, but that the MIC values under colistin selective pressure can become progressively higher and exacerbate the difficulty of treating infections caused by mcr-10.1-associated bacteria. Therefore, vigilance for such "silent transmission" is warranted, and continuous monitoring of the spread of mcr-10.1 is necessary in the future.202540343190
5499140.9995Antibiotic Resistance/Susceptibility Profiles of Staphylococcus equorum Strains from Cheese, and Genome Analysis for Antibiotic Resistance Genes. In food, bacteria carrying antibiotic resistance genes could play a prominent role in the spread of resistance. Staphylococcus equorum populations can become large in a number of fermented foods, yet the antibiotic resistance properties of this species have been little studied. In this work, the resistance/susceptibility (R/S) profile of S. equorum strains (n = 30) from cheese to 16 antibiotics was determined by broth microdilution. The minimum inhibitory concentration (MIC) for all antibiotics was low in most strains, although higher MICs compatible with acquired genes were also noted. Genome analysis of 13 strains showed the S. equorum resistome to be composed of intrinsic mechanisms, acquired mutations, and acquired genes. As such, a plasmidic cat gene providing resistance to chloramphenicol was found in one strain; this was able to provide resistance to Staphylococcus aureus after electroporation. An msr(A) polymorphic gene was identified in five strains. The Mrs(A) variants were associated with variable resistance to erythromycin. However, the genetic data did not always correlate with the phenotype. As such, all strains harbored a polymorphic fosB/fosD gene, although only one acquired copy was associated with strong resistance to fosfomycin. Similarly, a plasmid-associated blaR1-blaZI operon encoding a penicillinase system was identified in five ampicillin- and penicillin G-susceptible strains. Identified genes not associated with phenotypic resistance further included mph(C) in two strains and norA in all strains. The antibiotic R/S status and gene content of S. equorum strains intended to be employed in food systems should be carefully determined.202337511416
5766150.9995Ceftazidime resistance in Pseudomonas aeruginosa is multigenic and complex. Pseudomonas aeruginosa causes a wide range of severe infections. Ceftazidime, a cephalosporin, is a key antibiotic for treating infections but a significant proportion of isolates are ceftazidime-resistant. The aim of this research was to identify mutations that contribute to resistance, and to quantify the impacts of individual mutations and mutation combinations. Thirty-five mutants with reduced susceptibility to ceftazidime were evolved from two antibiotic-sensitive P. aeruginosa reference strains PAO1 and PA14. Mutations were identified by whole genome sequencing. The evolved mutants tolerated ceftazidime at concentrations between 4 and 1000 times that of the parental bacteria, with most mutants being ceftazidime resistant (minimum inhibitory concentration [MIC] ≥ 32 mg/L). Many mutants were also resistant to meropenem, a carbapenem antibiotic. Twenty-eight genes were mutated in multiple mutants, with dacB and mpl being the most frequently mutated. Mutations in six key genes were engineered into the genome of strain PAO1 individually and in combinations. A dacB mutation by itself increased the ceftazidime MIC by 16-fold although the mutant bacteria remained ceftazidime sensitive (MIC < 32 mg/L). Mutations in ampC, mexR, nalC or nalD increased the MIC by 2- to 4-fold. The MIC of a dacB mutant was increased when combined with a mutation in ampC, rendering the bacteria resistant, whereas other mutation combinations did not increase the MIC above those of single mutants. To determine the clinical relevance of mutations identified through experimental evolution, 173 ceftazidime-resistant and 166 sensitive clinical isolates were analysed for the presence of sequence variants that likely alter function of resistance-associated genes. dacB and ampC sequence variants occur most frequently in both resistant and sensitive clinical isolates. Our findings quantify the individual and combinatorial effects of mutations in different genes on ceftazidime susceptibility and demonstrate that the genetic basis of ceftazidime resistance is complex and multifactorial.202337192202
2295160.9995The drug resistance profile of Mycobacterium abscessus group strains from Korea. BACKGROUND: Bacteria of the Mycobacterium abscessus group are the second most common pathogens responsible for lung disease caused by nontuberculous mycobacteria in Korea. There is still a lack of studies investigating the genetic mechanisms involved in M. abscessus resistance to antibiotics other than clarithromycin. This study investigated the characteristics of drug resistance exhibited by M. abscessus clinical isolates from Korea. METHODS: We performed drug susceptibility testing for a total of 404 M. abscessus clinical strains. Subspecies were differentiated by molecular biological methods and examined for mutations in drug resistance-related genes. RESULTS: Of the 404 strains examined, 202 (50.00%), 199 (49.26%), and 3 (0.74%) strains were identified as M. abscessus, M. massiliense, and M. bolletii, respectively. Of the 152 clarithromycin-resistant strains, 6 possessed rrl mutations, while 4 of the 30 amikacin-resistant strains contained rrs mutations, and 5 of the 114 quinolone-resistant strains had gyr mutations. All mutant strains had high minimal inhibitory concentration values for the antibiotics. CONCLUSIONS: Our results showed the distribution of the strains with mutations in drug resistance-related genes was low in the M. abscessus group. Furthermore, we performed drug susceptibility testing and sequence analyses to determine the characteristics of these genes in the M. abscessus group.201424422193
5768170.9994The resistance mechanism of Escherichia coli induced by ampicillin in laboratory. BACKGROUND: Multi-drug-resistant Escherichia coli poses a great threat to human health, especially resistant to ampicillin (AMP), but the mechanism of drug resistance is not very clear. PURPOSE: To understand the mechanism of resistance of E. coli to beta-lactam antibiotics by inducing drug resistance of sensitive bacteria in laboratory. METHODS: Clinical sensitive E. coli strain was induced into resistance strain by 1/2 minimum inhibitive concentration (MIC) induced trails of AMP. The drug resistance spectrum was measured by modified K-B susceptibility test. Whole-genome sequencing analysis was used to analyze primary sensitive strain, and resequencing was used to analyze induced strains. Protein tertiary structure encoded by the gene containing single nucleotide polymorphism (SNP) was analyzed by bioinformatics. RESULTS: After 315 hrs induced, the MIC value of E. coli 15743 reached to 256 µg/mL, 64 times higher than that of the sensitive bacteria. During the induction process, the bacterial resistance process is divided into two stages. The rate of drug resistance occurs rapidly before reaching the critical concentration of 32 µg/mL, and then the resistance rate slows down. Sequencing of the genome of resistant strain showed that E. coli 15743 drug-resistant strain with the MIC values of 32 and 256 µg/mL contained four and eight non-synonymous SNPs, respectively. These non-synonymous SNPs were distributed in the genes of frdD, ftsI, acrB, OmpD, marR, VgrG, and envZ. CONCLUSION: These studies will improve our understanding of the molecular mechanism of AMP resistance of E. coli, and may provide the basis for prevention and control of multi-drug-resistant bacteria and generation of new antibiotics to treat E. coli infection.201931571941
5938180.9994Characterization of Mechanisms Lowering Susceptibility to Flumequine among Bacteria Isolated from Chilean Salmonid Farms. Despite their great importance for human therapy, quinolones are still used in Chilean salmon farming, with flumequine and oxolinic acid currently approved for use in this industry. The aim of this study was to improve our knowledge of the mechanisms conferring low susceptibility or resistance to quinolones among bacteria recovered from Chilean salmon farms. Sixty-five isolates exhibiting resistance, reduced susceptibility, or susceptibility to flumequine recovered from salmon farms were identified by their 16S rRNA genes, detecting a high predominance of species belonging to the Pseudomonas genus (52%). The minimum inhibitory concentrations (MIC) of flumequine in the absence and presence of the efflux pump inhibitor (EPI) Phe-Arg-β-naphthylamide and resistance patterns of isolates were determined by a microdilution broth and disk diffusion assays, respectively, observing MIC values ranging from 0.25 to >64 µg/mL and a high level of multi-resistance (96%), mostly showing resistance to florfenicol and oxytetracycline. Furthermore, mechanisms conferring low susceptibility to quinolones mediated by efflux pump activity, quinolone target mutations, or horizontally acquired resistance genes (qepA, oqxA, aac(6')-lb-cr, qnr) were investigated. Among isolates exhibiting resistance to flumequine (≥16 µg/mL), the occurrence of chromosomal mutations in target protein GyrA appears to be unusual (three out of 15), contrasting with the high incidence of mutations in GyrB (14 out of 17). Bacterial isolates showing resistance or reduced susceptibility to quinolones mediated by efflux pumps appear to be highly prevalent (49 isolates, 75%), thus suggesting a major role of intrinsic resistance mediated by active efflux.201931847389
1584190.9994Molecular mechanisms and genomic basis of tigecycline-resistant Enterobacterales from swine slaughterhouses. The continuous emergence of tigecycline-resistant bacteria is undermining the effectiveness of clinical tigecycline. Environmental tigecycline-resistant bacteria have the potential to infect humans through human-environment interactions. Furthermore, the mechanisms of tigecycline resistance in Enterobacterales are complicated. In this study, we aimed to investigate the additional pathways of tigecycline resistance in environmental Enterobacterales besides tet(X) and tmexCD-toprJ. During the years 2019-2020, tigecycline-resistant Enterobacterales (n = 45) negative for tet(X) and tmexCD-toprJ were recovered from 328 different samples from two slaughterhouses. Five distinct bacteria species were identified, of which Klebsiella pneumoniae (n = 37) was the most common, with K. pneumoniae ST45 and ST35 being the predominant clones. Tigecycline resistance determinants analysis showed that tet(A) mutations and ramR inactivation were the most prevalent mechanisms for tigecycline resistance in the 45 strains. Two known tet(A) variants (type 1 and tet(A)-v) and one novel tet(A) variant (type 3) were identified. Cloning experiments confirmed that the novel type 3 tet(A) could enhance the 4-fold MIC for tigecycline. Inactivation of ramR was induced by either point mutations or indels of sequences, which could result in the overexpression of AcrAB pump genes leading to tigecycline resistance. In addition, all isolates were resistant to a wide range of antimicrobials and carried various resistance genes. These findings enriched the epidemiological and genomic characterizations of tigecycline-resistant Enterobacterales from slaughterhouses and contributed to a better understanding of the complex mechanisms of tigecycline resistance in environmental bacteria.202235985220