# | Rank | Similarity | Title + Abs. | Year | PMID |
|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 |
| 6317 | 0 | 1.0000 | O-specific polysaccharide confers lysozyme resistance to extraintestinal pathogenic Escherichia coli. Extraintestinal pathogenic Escherichia coli (ExPEC) is the leading cause of bloodstream and other extraintestinal infections in human and animals. The greatest challenge encountered by ExPEC during an infection is posed by the host defense mechanisms, including lysozyme. ExPEC have developed diverse strategies to overcome this challenge. The aim of this study was to characterize the molecular mechanism of ExPEC resistance to lysozyme. For this, 15,000 transposon mutants of a lysozyme-resistant ExPEC strain NMEC38 were screened; 20 genes were identified as involved in ExPEC resistance to lysozyme-of which five were located in the gene cluster between galF and gnd, and were further confirmed to be involved in O-specific polysaccharide biosynthesis. The O-specific polysaccharide was able to inhibit the hydrolytic activity of lysozyme; it was also required by the complete lipopolysaccharide (LPS)-mediated protection of ExPEC against the bactericidal activity of lysozyme. The O-specific polysaccharide was further shown to be able to directly interact with lysozyme. Furthermore, LPS from ExPEC strains of different O serotypes was also able to inhibit the hydrolytic activity of lysozyme. Because of their cell surface localization and wide distribution in Gram-negative bacteria, O-specific polysaccharides appear to play a long-overlooked role in protecting bacteria against exogenous lysozyme. | 2018 | 29405825 |
| 6318 | 1 | 0.9998 | Phenotypic differences between Salmonella and Escherichia coli resulting from the disparate regulation of homologous genes. Phenotypic differences among closely related bacteria have been largely ascribed to species-specific genes, such as those residing in pathogenicity islands. However, we now report that the differential regulation of homologous genes is the mechanism responsible for the divergence of the enteric bacteria Salmonella enterica and Escherichia coli in their ability to make LPS modifications mediating resistance to the antibiotic polymyxin B. In S. enterica serovar Typhimurium, the PmrA/PmrB two-component system governing polymyxin B resistance is induced in low Mg(2+) in a process that requires the PmrD protein and by Fe(3+) in a PmrD-independent fashion. We establish that E. coli K-12 induces PmrA-activated gene transcription and polymyxin B resistance in response to Fe(3+), but that it is blind to the low Mg(2+) signal. The highly divergent PmrD protein is responsible for this phenotype as replacement of the E. coli pmrD gene by its Salmonella counterpart resulted in an E. coli strain that transcribed PmrA-activated genes and displayed polymyxin B resistance under the same conditions as Salmonella. Molecular analysis of natural isolates of E. coli and Salmonella revealed that the PmrD proteins are conserved within each genus and that selection might have driven the divergence between the Salmonella and E. coli PmrD proteins. Investigation of PmrD function demonstrated statistically different distributions for the Salmonella and E. coli isolates in PmrD-dependent transcription occurring in low Mg(2+). Our results suggest that the differential regulation of conserved genes may have ecological consequences, determining the range of niches a microorganism can occupy. | 2004 | 15569938 |
| 6314 | 2 | 0.9998 | Identification of genes involved in the resistance of mycobacteria to killing by macrophages. The survival of M. leprae and M. tuberculosis in the human host is dependent upon their ability to produce gene products that counteract the bactericidal activities of macrophages. To identify such mycobacterial genes and gene products, recombinant DNA libraries of mycobacterial DNA in E. coli were passed through macrophages to enrich for clones carrying genes that endow the normally susceptible E. coli bacteria with an enhanced ability to survive within macrophages. Following three cycles of enrichment, 15 independent clones were isolated. Three recombinants were characterized in detail, and each confers significantly enhanced survival on E. coli cells carrying them. Two of the cloned genetic elements also confer enhanced survival onto M. smegmatis cells. Further characterization of these genes and gene products should provide insights into the survival of mycobacteria within macrophages and may identify new approaches of targets for combatting these important pathogens. | 1994 | 8080180 |
| 8892 | 3 | 0.9998 | Fur is the master regulator of the extraintestinal pathogenic Escherichia coli response to serum. Drug-resistant extraintestinal pathogenic Escherichia coli (ExPEC) strains are the major cause of colisepticemia (colibacillosis), a condition that has become an increasing public health problem in recent years. ExPEC strains are characterized by high resistance to serum, which is otherwise highly toxic to most bacteria. To understand how these bacteria survive and grow in serum, we performed system-wide analyses of their response to serum, making a clear distinction between the responses to nutritional immunity and innate immunity. Thus, mild heat inactivation of serum destroys the immune complement and abolishes the bactericidal effect of serum (inactive serum), making it possible to examine nutritional immunity. We used a combination of deep RNA sequencing and proteomics in order to characterize ExPEC genes whose expression is affected by the nutritional stress of serum and by the immune complement. The major change in gene expression induced by serum-active and inactive-involved metabolic genes. In particular, the serum metabolic response is coordinated by three transcriptional regulators, Fur, BasR, and CysB. Fur alone was responsible for more than 80% of the serum-induced transcriptional response. Consistent with its role as a major serum response regulator, deletion of Fur renders the bacteria completely serum sensitive. These results highlight the role of metabolic adaptation in colisepticemia and virulence. IMPORTANCE: Drug-resistant extraintestinal pathogenic Escherichia coli (ExPEC) strains have emerged as major pathogens, especially in community- and hospital-acquired infections. These bacteria cause a large spectrum of syndromes, the most serious of which is septicemia, a condition with a high mortality rate. These bacterial strains are characterized by high resistance to serum, otherwise highly toxic to most bacteria. To understand the basis of this resistance, we carried out system-wide analyses of the response of ExPEC strains to serum by using proteomics and deep RNA sequencing. The major changes in gene expression induced by exposure to serum involved metabolic genes, not necessarily implicated in relation to virulence. One metabolic regulator-Fur-involved in iron metabolism was responsible for more than 80% of the serum-induced response, and its deletion renders the bacteria completely serum sensitive. These results highlight the role of metabolic adaptation in virulence. | 2014 | 25118243 |
| 6331 | 4 | 0.9998 | Epistatic control of intrinsic resistance by virulence genes in Listeria. Elucidating the relationships between antimicrobial resistance and virulence is key to understanding the evolution and population dynamics of resistant pathogens. Here, we show that the susceptibility of the gram-positive bacterium Listeria monocytogenes to the antibiotic fosfomycin is a complex trait involving interactions between resistance and virulence genes and the environment. We found that a FosX enzyme encoded in the listerial core genome confers intrinsic fosfomycin resistance to both pathogenic and non-pathogenic Listeria spp. However, in the genomic context of the pathogenic L. monocytogenes, FosX-mediated resistance is epistatically suppressed by two members of the PrfA virulence regulon, hpt and prfA, which upon activation by host signals induce increased fosfomycin influx into the bacterial cell. Consequently, in infection conditions, most L. monocytogenes isolates become susceptible to fosfomycin despite possessing a gene that confers high-level resistance to the drug. Our study establishes the molecular basis of an epistatic interaction between virulence and resistance genes controlling bacterial susceptibility to an antibiotic. The reported findings provide the rationale for the introduction of fosfomycin in the treatment of Listeria infections even though these bacteria are intrinsically resistant to the antibiotic in vitro. | 2018 | 30180166 |
| 6333 | 5 | 0.9998 | Outer Membrane Proteins form Specific Patterns in Antibiotic-Resistant Edwardsiella tarda. Outer membrane proteins of Gram-negative bacteria play key roles in antibiotic resistance. However, it is unknown whether outer membrane proteins that respond to antibiotics behave in a specific manner. The present study specifically investigated the differentially expressed outer membrane proteins of an antibiotic-resistant bacterium, Edwardsiella tarda, a Gram-negative pathogen that can lead to unnecessary mass medication of antimicrobials and consequently resistance development in aquaculture and a spectrum of intestinal and extraintestinal diseases in humans. The comparison of a clinically isolated strain to the laboratory derived kanamycin-, tetracycline-, or chloramphenicol-resistant strains identified their respective outer membrane proteins expression patterns, which are distinct to each other. Similarly, the same approach was utilized to profile the patterns in double antibiotic-resistant bacteria. Surprisingly, one pattern is always dominant over the other as to these three antibiotics; the pattern of chloramphenicol is over tetracycline, which is over kanamycin. This type of pattern was also confirmed in clinically relevant multidrug-resistant bacteria. In addition, the presence of plasmid encoding antibiotic-resistant genes also alters the outer membrane protein profile in a similar manner. Our results demonstrate that bacteria adapt the antibiotic stress through the regulation of outer membrane proteins expression. And more importantly, different outer membrane protein profiles were required to cope with different antibiotics. This type of specific pattern provides the rationale for the development of novel strategy to design outer membrane protein arrays to identify diverse multidrug resistance profiles as biomarkers for clinical medication. | 2017 | 28210241 |
| 4381 | 6 | 0.9998 | Specific Gene Loci of Clinical Pseudomonas putida Isolates. Pseudomonas putida are ubiquitous inhabitants of soils and clinical isolates of this species have been seldom described. Clinical isolates show significant variability in their ability to cause damage to hosts because some of them are able to modulate the host's immune response. In the current study, comparisons between the genomes of different clinical and environmental strains of P. putida were done to identify genetic clusters shared by clinical isolates that are not present in environmental isolates. We show that in clinical strains specific genes are mostly present on transposons, and that this set of genes exhibit high identity with genes found in pathogens and opportunistic pathogens. The set of genes prevalent in P. putida clinical isolates, and absent in environmental isolates, are related with survival under oxidative stress conditions, resistance against biocides, amino acid metabolism and toxin/antitoxin (TA) systems. This set of functions have influence in colonization and survival within human tissues, since they avoid host immune response or enhance stress resistance. An in depth bioinformatic analysis was also carried out to identify genetic clusters that are exclusive to each of the clinical isolates and that correlate with phenotypical differences between them, a secretion system type III-like was found in one of these clinical strains, a determinant of pathogenicity in Gram-negative bacteria. | 2016 | 26820467 |
| 6328 | 7 | 0.9997 | Inactivation of MarR gene homologs increases susceptibility to antimicrobials in Bacteroides fragilis. Bacteroides fragilis is the strict anaerobic bacteria most commonly found in human infections, and has a high mortality rate. Among other virulence factors, the remarkable ability to acquire resistance to a variety of antimicrobial agents and to tolerate nanomolar concentrations of oxygen explains in part their success in causing infection and colonizing the mucosa. Much attention has been given to genes related to multiple drug resistance derived from plasmids, integrons or transposon, but such genes are also detected in chromosomal systems, like the mar (multiple antibiotic resistance) locus, that confer resistance to a range of drugs. Regulators like MarR, that control expression of the locus mar, also regulate resistance to organic solvents, disinfectants and oxygen reactive species are important players in these events. Strains derived from the parental strain 638R, with mutations in the genes hereby known as marRI (BF638R_3159) and marRII (BF638R_3706) were constructed by gene disruption using a suicide plasmid. Phenotypic response of the mutant strains to hydrogen peroxide, cell survival assay against exposure to oxygen, biofilm formation, resistance to bile salts and resistance to antibiotics was evaluated. The results showed that the mutant strains exhibit statistically significant differences in their response to oxygen stress, but no changes were observed in survival when exposed to bile salts. Biofilm formation was not affected by either gene disruption. Both mutant strains however, became more sensitive to multiple antimicrobial drugs tested. This indicates that as observed in other bacterial species, MarR are an important resistance mechanism in B. fragilis. | 2018 | 28847541 |
| 6320 | 8 | 0.9997 | Identification of the Extracytoplasmic Function σ Factor σ(P) Regulon in Bacillus thuringiensis. Bacillus thuringiensis and other members of the Bacillus cereus family are resistant to many β-lactams. Resistance is dependent upon the extracytoplasmic function sigma factor σ(P). We used label-free quantitative proteomics to identify proteins whose expression was dependent upon σ(P). We compared the protein profiles of strains which either lacked σ(P) or overexpressed σ(P). We identified 8 members of the σ(P) regulon which included four β-lactamases as well as three penicillin-binding proteins (PBPs). Using transcriptional reporters, we confirmed that these genes are induced by β-lactams in a σ(P)-dependent manner. These genes were deleted individually or in various combinations to determine their role in resistance to a subset of β-lactams, including ampicillin, methicillin, cephalexin, and cephalothin. We found that different combinations of β-lactamases and PBPs are involved in resistance to different β-lactams. Our data show that B. thuringiensis utilizes a suite of enzymes to protect itself from β-lactam antibiotics. IMPORTANCE Antimicrobial resistance is major concern for public health. β-Lactams remain an important treatment option for many diseases. However, the spread of β-lactam resistance continues to rise. Many pathogens acquire antibiotic resistance from environmental bacteria. Thus, understanding β-lactam resistance in environmental strains may provide insights into additional mechanisms of antibiotic resistance. Here, we describe how a single regulatory system, σ(P), in B. thuringiensis controls expression of multiple genes involved in resistance to β-lactams. Our findings indicate that some of these genes are partially redundant. Our data also suggest that the large number of genes controlled by σ(P) results in increased resistance to a wider range of β-lactam classes than any single gene could provide. | 2022 | 35080471 |
| 6332 | 9 | 0.9997 | Search and analysis of genes involved in antibiotic resistance in Chilean strains of Piscirickettsia salmonis. Piscirickettsia salmonis is the pathogen causing Piscirickettsiosis. For treatment, the industry mainly uses oxytetracycline and florfenicol, so it is essential to understand the degree of susceptibility of this pathogen to these drugs. But this is still unknown for a large number of P. salmonis strains, as are the molecular mechanisms responsible for greater or lesser susceptibility. However, genes that confer resistance to these antimicrobials have been reported and characterized for this and other bacterial species, among which are membrane proteins that take out the drug. Our results identified differences in the degree of susceptibility to both antibiotics among different Chilean isolated of these bacteria. We analysed 10 available genomes in our laboratory and identified ~140 genes likely to be involved in antibiotic resistance. We analysed six specific genes, which suggests that some of them would eventually be relevant in conferring resistance to both antibiotics, as they encode for specific transporter proteins, which increase the number of transcripts when grown in media with these antibiotics. Our results were corroborated with EtBr permeability analysis, which revealed that the LF-89 strain accumulates this compound and has a reduced capacity to expulse it compared with the field strains. | 2017 | 27982445 |
| 8928 | 10 | 0.9997 | Increased survival of antibiotic-resistant Escherichia coli inside macrophages. Mutations causing antibiotic resistance usually incur a fitness cost in the absence of antibiotics. The magnitude of such costs is known to vary with the environment. Little is known about the fitness effects of antibiotic resistance mutations when bacteria confront the host's immune system. Here, we study the fitness effects of mutations in the rpoB, rpsL, and gyrA genes, which confer resistance to rifampin, streptomycin, and nalidixic acid, respectively. These antibiotics are frequently used in the treatment of bacterial infections. We measured two important fitness traits-growth rate and survival ability-of 12 Escherichia coli K-12 strains, each carrying a single resistance mutation, in the presence of macrophages. Strikingly, we found that 67% of the mutants survived better than the susceptible bacteria in the intracellular niche of the phagocytic cells. In particular, all E. coli streptomycin-resistant mutants exhibited an intracellular advantage. On the other hand, 42% of the mutants incurred a high fitness cost when the bacteria were allowed to divide outside of macrophages. This study shows that single nonsynonymous changes affecting fundamental processes in the cell can contribute to prolonged survival of E. coli in the context of an infection. | 2013 | 23089747 |
| 6335 | 11 | 0.9997 | Gene Amplification Uncovers Large Previously Unrecognized Cryptic Antibiotic Resistance Potential in E. coli. The activation of unrecognized antibiotic resistance genes in the bacterial cell can give rise to antibiotic resistance without the need for major mutations or horizontal gene transfer. We hypothesize that bacteria harbor an extensive array of diverse cryptic genes that can be activated in response to antibiotics via adaptive resistance. To test this hypothesis, we developed a plasmid assay to randomly manipulate gene copy numbers in Escherichia coli cells and identify genes that conferred resistance when amplified. We then tested for cryptic resistance to 18 antibiotics and identified genes conferring resistance. E. coli could become resistant to 50% of the antibiotics tested, including chloramphenicol, d-cycloserine, polymyxin B, and 6 beta-lactam antibiotics, following this manipulation. Known antibiotic resistance genes comprised 13% of the total identified genes, where 87% were unclassified (cryptic) antibiotic resistance genes. These unclassified genes encoded cell membrane proteins, stress response/DNA repair proteins, transporters, and miscellaneous or hypothetical proteins. Stress response/DNA repair genes have a broad antibiotic resistance potential, as this gene class, in aggregate, conferred cryptic resistance to nearly all resistance-positive antibiotics. We found that antibiotics that are hydrophilic, those that are amphipathic, and those that inhibit the cytoplasmic membrane or cell wall biosynthesis were more likely to induce cryptic resistance in E. coli. This study reveals a diversity of cryptic genes that confer an antibiotic resistance phenotype when present in high copy number. Thus, our assay can identify potential novel resistance genes while also describing which antibiotics are prone to induce cryptic antibiotic resistance in E. coli. IMPORTANCE Predicting where new antibiotic resistance genes will rise is a challenge and is especially important when new antibiotics are developed. Adaptive resistance allows sensitive bacterial cells to become transiently resistant to antibiotics. This provides an opportune time for cells to develop more efficient resistance mechanisms, such as tolerance and permanent resistance to higher antibiotic concentrations. The biochemical diversity harbored within bacterial genomes may lead to the presence of genes that could confer resistance when timely activated. Therefore, it is crucial to understand adaptive resistance to identify potential resistance genes and prolong antibiotics. Here, we investigate cryptic resistance, an adaptive resistance mechanism, and identify unknown (cryptic) antibiotic resistance genes that confer resistance when amplified in a laboratory strain of E. coli. We also pinpoint antibiotic characteristics that are likely to induce cryptic resistance. This study may help detect novel antibiotic resistance genes and provide the foundation to help develop more effective antibiotics. | 2021 | 34756069 |
| 4827 | 12 | 0.9997 | A multidrug resistance plasmid contains the molecular switch for type VI secretion in Acinetobacter baumannii. Infections with Acinetobacter baumannii, one of the most troublesome and least studied multidrug-resistant superbugs, are increasing at alarming rates. A. baumannii encodes a type VI secretion system (T6SS), an antibacterial apparatus of Gram-negative bacteria used to kill competitors. Expression of the T6SS varies among different strains of A. baumannii, for which the regulatory mechanisms are unknown. Here, we show that several multidrug-resistant strains of A. baumannii harbor a large, self-transmissible resistance plasmid that carries the negative regulators for T6SS. T6SS activity is silenced in plasmid-containing, antibiotic-resistant cells, while part of the population undergoes frequent plasmid loss and activation of the T6SS. This activation results in T6SS-mediated killing of competing bacteria but renders A. baumannii susceptible to antibiotics. Our data show that a plasmid that has evolved to harbor antibiotic resistance genes plays a role in the differentiation of cells specialized in the elimination of competing bacteria. | 2015 | 26170289 |
| 6321 | 13 | 0.9997 | An active β-lactamase is a part of an orchestrated cell wall stress resistance network of Bacillus subtilis and related rhizosphere species. A hallmark of the Gram-positive bacteria, such as the soil-dwelling bacterium Bacillus subtilis, is their cell wall. Here, we report that d-leucine and flavomycin, biofilm inhibitors targeting the cell wall, activate the β-lactamase PenP. This β-lactamase contributes to ampicillin resistance in B. subtilis under all conditions tested. In contrast, both Spo0A, a master regulator of nutritional stress, and the general cell wall stress response, differentially contribute to β-lactam resistance under different conditions. To test whether β-lactam resistance and β-lactamase genes are widespread in other Bacilli, we isolated Bacillus species from undisturbed soils, and found that their genomes can encode up to five β-lactamases with differentiated activity spectra. Surprisingly, the activity of environmental β-lactamases and PenP, as well as the general stress response, resulted in a similarly reduced lag phase of the culture in the presence of β-lactam antibiotics, with little or no impact on the logarithmic growth rate. The length of the lag phase may determine the outcome of the competition between β-lactams and β-lactamases producers. Overall, our work suggests that antibiotic resistance genes in B. subtilis and related species are ancient and widespread, and could be selected by interspecies competition in undisturbed soils. | 2019 | 30637927 |
| 6319 | 14 | 0.9997 | Unstable tandem gene amplification generates heteroresistance (variation in resistance within a population) to colistin in Salmonella enterica. Heteroresistance, a phenomenon where subpopulations of a bacterial isolate exhibit different susceptibilities to an antibiotic, is a growing clinical problem where the underlying genetic mechanisms in most cases remain unknown. We isolated colistin resistant mutants in Escherichia coli and Salmonella enterica serovar Typhimurium at different concentrations of colistin. Genetic analysis showed that genetically stable pmrAB point mutations were responsible for colistin resistance during selection at high drug concentrations for both species and at low concentrations for E. coli. In contrast, for S. Typhimurium mutants selected at low colistin concentrations, amplification of different large chromosomal regions conferred a heteroresistant phenotype. All amplifications included the pmrD gene, which encodes a positive regulator that up-regulates proteins that modify lipid A, and as a result increase colistin resistance. Inactivation and over-expression of the pmrD gene prevented and conferred resistance, respectively, demonstrating that the PmrD protein is required and sufficient to confer resistance. The heteroresistance phenotype is explained by the variable gene dosage of pmrD in a population, where sub-populations with different copy number of the pmrD gene show different levels of colistin resistance. We propose that variability in gene copy number of resistance genes can explain the heteroresistance observed in clinically isolated pathogenic bacteria. | 2016 | 27381382 |
| 8893 | 15 | 0.9997 | Transcriptome of uropathogenic Escherichia coli during urinary tract infection. A uropathogenic Escherichia coli strain CFT073-specific DNA microarray that includes each open reading frame was used to analyze the transcriptome of CFT073 bacteria isolated directly from the urine of infected CBA/J mice. The in vivo expression profiles were compared to that of E. coli CFT073 grown statically to exponential phase in rich medium, revealing the strategies this pathogen uses in vivo for colonization, growth, and survival in the urinary tract environment. The most highly expressed genes overall in vivo encoded translational machinery, indicating that the bacteria were in a rapid growth state despite specific nutrient limitations. Expression of type 1 fimbriae, a virulence factor involved in adherence, was highly upregulated in vivo. Five iron acquisition systems were all highly upregulated during urinary tract infection, as were genes responsible for capsular polysaccharide and lipopolysaccharide synthesis, drug resistance, and microcin secretion. Surprisingly, other fimbrial genes, such as pap and foc/sfa, and genes involved in motility and chemotaxis were downregulated in vivo. E. coli CFT073 grown in human urine resulted in the upregulation of iron acquisition, capsule, and microcin secretion genes, thus partially mimicking growth in vivo. On the basis of gene expression levels, the urinary tract appears to be nitrogen and iron limiting, of high osmolarity, and of moderate oxygenation. This study represents the first assessment of any E. coli pathotype's transcriptome in vivo and provides specific insights into the mechanisms necessary for urinary tract pathogenesis. | 2004 | 15501767 |
| 6171 | 16 | 0.9997 | Host response to infection with a temperature-sensitive mutant of Salmonella typhimurium in a susceptible and a resistant strain of mice. The inoculation of a temperature-sensitive mutant of Salmonella typhimurium induced a long-lasting infection in susceptible (C57BL/6) and resistant (A/J) mice. During week 1 of infection, the number of bacteria in the spleens was similar in both mouse strains. Then, the decrease of bacteria was more rapid in the resistant strain. Splenomegaly and granulomatous hepatitis were more severe in the susceptible strain. The immune response induced by this infection was studied. In both mouse strains delayed-type hypersensitivity to Salmonella antigens was present, and resistance to reinfection with a virulent strain of S. typhimurium or with Listeria monocytogenes appeared with the same kinetics. Thus, it does not seem that the gene(s) controlling natural resistance to S. typhimurium act(s) on acquired immunity. | 1985 | 3897053 |
| 4383 | 17 | 0.9997 | Importance of Core Genome Functions for an Extreme Antibiotic Resistance Trait. Extreme antibiotic resistance in bacteria is associated with the expression of powerful inactivating enzymes and other functions encoded in accessory genomic elements. The contribution of core genome processes to high-level resistance in such bacteria has been unclear. In the work reported here, we evaluated the relative importance of core and accessory functions for high-level resistance to the aminoglycoside tobramycin in the nosocomial pathogen Acinetobacter baumannii Three lines of evidence establish the primacy of core functions in this resistance. First, in a genome scale mutant analysis using transposon sequencing and validation with 594 individual mutants, nearly all mutations reducing tobramycin resistance inactivated core genes, some with stronger phenotypes than those caused by the elimination of aminoglycoside-inactivating enzymes. Second, the core functions mediating resistance were nearly identical in the wild type and a deletion mutant lacking a genome resistance island that encodes the inactivating enzymes. Thus, most or all of the core resistance determinants important in the absence of the enzymes are also important in their presence. Third, reductions in tobramycin resistance caused by different core mutations were additive, and highly sensitive double and triple mutants (with 250-fold reductions in the MIC) that retained accessory resistance genes could be constructed. Core processes that contribute most strongly to intrinsic tobramycin resistance include phospholipid biosynthesis, phosphate regulation, and envelope homeostasis.IMPORTANCE The inexorable increase in bacterial antibiotic resistance threatens to undermine many of the procedures that transformed medicine in the last century. One strategy to meet the challenge antibiotic resistance poses is the development of drugs that undermine resistance. To identify potential targets for such adjuvants, we identified the functions underlying resistance to an important class of antibiotics for one of the most highly resistant pathogens known. | 2017 | 29233894 |
| 4708 | 18 | 0.9997 | Proteomic analysis of nalidixic acid resistance in Escherichia coli: identification and functional characterization of OM proteins. The worldwide emergence of antibiotic-resistant bacteria poses a serious threat to human health. To understand the mechanisms of the resistance is extremely important to the control of these bacteria. In the current study, proteomic methodologies were utilized to characterize OM proteome of Escherichia coli with nalidixic acid (NA) resistance. The OM proteins TolC, OmpT, OmpC and OmpW were found to be up-regulated, and FadL was down-regulated in the NA-resistant E. coli strains. The changes at the level of protein expression were validated using Western blotting. Furthermore, the possible roles these altered proteins played in regulation of NA resistance were investigated using genetically modified strains with the deletion of these genes. The results obtained from functional characterization of these genetically modified strains suggest that TolC and OmpC may play more important roles in the control of NA resistance than other OM proteins identified. To gain better understanding of the mechanisms of NA resistance, we also characterized the role of the two-component system EnvZ/OmpR which is responsible for the regulation of OmpC and OmpF expression in response to NA resistance using their genetically modified strains. Our results suggest that OmpF and the EnvZ/OmpR are also important participants of the pathways regulating the NA resistance of E. coli. | 2008 | 18438992 |
| 4386 | 19 | 0.9997 | Large-scale screening of a targeted Enterococcus faecalis mutant library identifies envelope fitness factors. Spread of antibiotic resistance among bacteria responsible for nosocomial and community-acquired infections urges for novel therapeutic or prophylactic targets and for innovative pathogen-specific antibacterial compounds. Major challenges are posed by opportunistic pathogens belonging to the low GC% gram-positive bacteria. Among those, Enterococcus faecalis is a leading cause of hospital-acquired infections associated with life-threatening issues and increased hospital costs. To better understand the molecular properties of enterococci that may be required for virulence, and that may explain the emergence of these bacteria in nosocomial infections, we performed the first large-scale functional analysis of E. faecalis V583, the first vancomycin-resistant isolate from a human bloodstream infection. E. faecalis V583 is within the high-risk clonal complex 2 group, which comprises mostly isolates derived from hospital infections worldwide. We conducted broad-range screenings of candidate genes likely involved in host adaptation (e.g., colonization and/or virulence). For this purpose, a library was constructed of targeted insertion mutations in 177 genes encoding putative surface or stress-response factors. Individual mutants were subsequently tested for their i) resistance to oxidative stress, ii) antibiotic resistance, iii) resistance to opsonophagocytosis, iv) adherence to the human colon carcinoma Caco-2 epithelial cells and v) virulence in a surrogate insect model. Our results identified a number of factors that are involved in the interaction between enterococci and their host environments. Their predicted functions highlight the importance of cell envelope glycopolymers in E. faecalis host adaptation. This study provides a valuable genetic database for understanding the steps leading E. faecalis to opportunistic virulence. | 2011 | 22194979 |