scholarly journals Molecular Genetic and Structural Modeling Studies of Staphylococcus aureus RNA Polymerase and the Fitness of Rifampin Resistance Genotypes in Relation to Clinical Prevalence

2006 ◽  
Vol 50 (1) ◽  
pp. 298-309 ◽  
Author(s):  
A. J. O'Neill ◽  
T. Huovinen ◽  
C. W. G. Fishwick ◽  
I. Chopra
Keyword(s):  
Staphylococcus Aureus ◽  
Rna Polymerase ◽  
Molecular Genetic ◽  
Fitness Costs ◽  
Novel Mutations ◽  
Resistant Strains ◽  
Rifampin Resistance ◽  
First Time ◽  
Selection Of

ABSTRACT The adaptive and further evolutionary responses of Staphylococcus aureus to selection pressure with the antibiotic rifampin have not been explored in detail. We now present a detailed analysis of these systems. The use of rifampin for the chemotherapy of infections caused by S. aureus has resulted in the selection of mutants with alterations within the β subunit of the target enzyme, RNA polymerase. Using a new collection of strains, we have identified numerous novel mutations in the β subunits of both clinical and in vitro-derived resistant strains and established that additional, undefined mechanisms contribute to expression of rifampin resistance in clinical isolates of S. aureus. The fitness costs associated with rifampin resistance genotypes were found to have a significant influence on their clinical prevalence, with the most common clinical genotype (H481N, S529L) exhibiting no fitness cost in vitro. Intragenic mutations which compensate for the fitness costs associated with rifampin resistance in clinical strains of S. aureus were identified for the first time. Structural explanations for rifampin resistance and the loss of fitness were obtained by molecular modeling of mutated RNA polymerase enzymes.

scholarly journals Strong In Vitro Activities of Two New Rifabutin Analogs against Multidrug-Resistant Mycobacterium tuberculosis

2010 ◽  
Vol 54 (12) ◽  
pp. 5363-5365 ◽  
Author(s):  
Ana-Belén García ◽  
Juan J. Palacios ◽  
María-Jesús Ruiz ◽  
José Barluenga ◽  
Fernando Aznar ◽  
...  
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Rna Polymerase ◽  
Molecular Dynamic ◽  
Multidrug Resistant ◽  
Dynamic Studies ◽  
Resistant Strains ◽  
Selection Of

ABSTRACT Two new rifabutin analogs, RFA-1 and RFA-2, show high in vitro antimycobacterial activities against Mycobacterium tuberculosis. MIC values of RFA-1 and RFA-2 were ≤0.02 μg/ml against rifamycin-susceptible strains and 0.5 μg/ml against a wide selection of multidrug-resistant strains, compared to ≥50 μg/ml for rifampin and 10 μg/ml for rifabutin. Molecular dynamic studies indicate that the compounds may exert tighter binding to mutants of RNA polymerase that have adapted to the rifamycins.

scholarly journals Rifamycin Resistance in Clostridium difficile Is Generally Associated with a Low Fitness Burden

2016 ◽  
Vol 60 (9) ◽  
pp. 5604-5607 ◽  
Author(s):  
Uyen T. Dang ◽  
Idalia Zamora ◽  
Kirk E. Hevener ◽  
Sudip Adhikari ◽  
Xiaoqian Wu ◽  
...  
Keyword(s):  
Clostridium Difficile ◽  
Rna Polymerase ◽  
Structural Modeling ◽  
Fitness Cost ◽  
Clinical Isolates ◽  
Β Subunit ◽  
Fitness Costs ◽  
Novel Mutations ◽  
Content Type

ABSTRACTWe characterized clinically occurring and novel mutations in the β subunit of RNA polymerase inClostridium difficile(CdRpoB), conferring rifamycin (including rifaximin) resistance. The Arg505Lys substitution did not impose anin vitrofitness cost, which may be one reason for its dominance among rifamycin-resistant clinical isolates. These observations were supported through the structural modeling ofCdRpoB. In general, most mutations lackedin vitrofitness costs, suggesting that rifamycin resistance may in some cases persist in the clinic.

scholarly journals Analysis of Mupirocin Resistance and Fitness in Staphylococcus aureus by Molecular Genetic and Structural Modeling Techniques

2004 ◽  
Vol 48 (11) ◽  
pp. 4366-4376 ◽  
Author(s):  
Julian Gregston Hurdle ◽  
Alexander John O'Neill ◽  
Eileen Ingham ◽  
Colin Fishwick ◽  
Ian Chopra
Keyword(s):  
Staphylococcus Aureus ◽  
Molecular Genetic ◽  
Trna Synthetase ◽  
Second Step ◽  
Fitness Costs ◽  
Before And After ◽  
Mupirocin Resistance ◽  
Resistant Mutants

ABSTRACT Chromosomal resistance to mupirocin in clinical isolates of Staphylococcus aureus arises from V588F or V631F mutations in isoleucyl-tRNA synthetase (IRS). Whether these are the only IRS mutations that confer mupirocin resistance or simply those that survive in the clinic is unknown. Mupirocin-resistant mutants of S. aureus 8325-4 were therefore generated to examine their ileS genotypes and the in vitro and in vivo fitness costs associated with them before and after compensatory evolution. Most spontaneous first-step mupirocin-resistant mutants carried V588F or V631F mutations in IRS, but a new mutation (G593V) was also identified. Second-step mutants carried combinations of previously identified IRS mutations (e.g., V588F/V631F and G593V/V631F), but additional combinations also occurred involving novel mutations (R816C, H67Q, and F563L). First-step mupirocin-resistant mutants were not associated with substantial fitness costs, a finding that is consistent with the occurrence of V588F or V631F mutations in the IRS of clinical strains. Second-step mutants were unfit, but fitness could be restored by subculture in the absence of mupirocin. In most cases, this was the result of compensatory mutations that also suppressed mupirocin resistance (e.g., A196V, E190K, and E195K), despite retention of the original mutations conferring resistance. Structural explanations for mupirocin resistance and loss of fitness were obtained by molecular modeling of mutated IRS enzymes, which provided data on mupirocin binding and interaction with the isoleucyl-AMP reactive intermediate.

The Effects of Shock Vancomycin Concentrations on the Formation of Heteroresistance in Staphylococcus aureus

2020 ◽  
Vol 65 (9-10) ◽  
pp. 3-7
Author(s):  
V. V. Gostev ◽  
Yu. V. Sopova ◽  
O. S. Kalinogorskaya ◽  
M. E. Velizhanina ◽  
I. V. Lazareva ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
In Vitro Selection ◽  
Methicillin Resistant Staphylococcus Aureus ◽  
High Concentration ◽  
Short Term ◽  
High Concentrations ◽  
Selection Of ◽  
Selection Of Resistance ◽  
Test Cultures

Glycopeptides are the basis of the treatment of infections caused by MRSA (Methicillin-Resistant Staphylococcus aureus). Previously, it was demonstrated that antibiotic tolerant phenotypes are formed during selection of resistance under the influence of high concentrations of antibiotics. The present study uses a similar in vitro selection model with vancomycin. Clinical isolates of MRSA belonging to genetic lines ST8 and ST239, as well as the MSSA (ATCC29213) strain, were included in the experiment. Test isolates were incubated for five hours in a medium with a high concentration of vancomycin (50 μg/ml). Test cultures were grown on the medium without antibiotic for 18 hours after each exposure. A total of ten exposure cycles were performed. Vancomycin was characterized by bacteriostatic action; the proportion of surviving cells after exposure was 70–100%. After selection, there was a slight increase in the MIC to vancomycin (MIC 2 μg/ml), teicoplanin (MIC 1.5–3 μg/ml) and daptomycin (MIC 0.25–2 μg/ml). According to the results of PAP analysis, all strains showed an increase in the area under curve depending on the concentration of vancomycin after selection, while a heteroresistant phenotype (with PAP/AUC 0.9) was detected in three isolates. All isolates showed walK mutations (T188S, D235N, E261V, V380I, and G223D). Exposure to short-term shock concentrations of vancomycin promotes the formation of heteroresistance in both MRSA and MSSA. Formation of VISA phenotypes is possible during therapy with vancomycin.

scholarly journals In VitroEfficacies and Resistance Profiles of Rifampin-Based Combination Regimens for Biofilm-Embedded Methicillin-Resistant Staphylococcus aureus

2013 ◽  
Vol 57 (11) ◽  
pp. 5717-5720 ◽  
Author(s):  
Hung-Jen Tang ◽  
Chi-Chung Chen ◽  
Kuo-Chen Cheng ◽  
Kuan-Ying Wu ◽  
Yi-Chung Lin ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Fusidic Acid ◽  
Antibacterial Activities ◽  
Methicillin Resistant ◽  
Content Type ◽  
Biofilm Model ◽  
Rifampin Resistance ◽  
Combination Regimens ◽  
Resistant Mutation

ABSTRACTTo compare thein vitroantibacterial efficacies and resistance profiles of rifampin-based combinations against methicillin-resistantStaphylococcus aureus(MRSA) in a biofilm model, the antibacterial activities of vancomycin, teicoplanin, daptomycin, minocycline, linezolid, fusidic acid, fosfomycin, and tigecycline alone or in combination with rifampin against biofilm-embedded MRSA were measured. The rifampin-resistant mutation frequencies were evaluated. Of the rifampin-based combinations, rifampin enhances the antibacterial activities of and even synergizes with fusidic acid, tigecycline, and, to a lesser extent, linezolid, fosfomycin, and minocycline against biofilm-embedded MRSA. Such combinations with weaker rifampin resistance induction activities may provide a therapeutic advantage in MRSA biofilm-related infections.

scholarly journals The Antimicrobial Peptide Temporin G: Anti-Biofilm, Anti-Persister Activities, and Potentiator Effect of Tobramycin Efficacy Against Staphylococcus aureus

2020 ◽  
Vol 21 (24) ◽  
pp. 9410
Author(s):  
Bruno Casciaro ◽  
Maria Rosa Loffredo ◽  
Floriana Cappiello ◽  
Guendalina Fabiano ◽  
Luisa Torrini ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Human Keratinocytes ◽  
Skin Infections ◽  
Positive Bacterium ◽  
Persister Cells ◽  
Dividing Cells ◽  
Adverse Environmental Conditions ◽  
Bacterial Skin Infections ◽  
First Time

Bacterial biofilms are a serious threat for human health, and the Gram-positive bacterium Staphylococcus aureus is one of the microorganisms that can easily switch from a planktonic to a sessile lifestyle, providing protection from a large variety of adverse environmental conditions. Dormant non-dividing cells with low metabolic activity, named persisters, are tolerant to antibiotic treatment and are the principal cause of recalcitrant and resistant infections, including skin infections. Antimicrobial peptides (AMPs) hold promise as new anti-infective agents to treat such infections. Here for the first time, we investigated the activity of the frog-skin AMP temporin G (TG) against preformed S. aureus biofilm including persisters, as well as its efficacy in combination with tobramycin, in inhibiting S. aureus growth. TG was found to provoke ~50 to 100% reduction of biofilm viability in the concentration range from 12.5 to 100 µM vs ATCC and clinical isolates and to be active against persister cells (about 70–80% killing at 50–100 µM). Notably, sub-inhibitory concentrations of TG in combination with tobramycin were able to significantly reduce S. aureus growth, potentiating the antibiotic power. No critical cytotoxicity was detected when TG was tested in vitro up to 100 µM against human keratinocytes, confirming its safety profile for the development of a new potential anti-infective drug, especially for treatment of bacterial skin infections.

scholarly journals Mercury resistance of Staphylococcus aureus

1970 ◽  
Vol 68 (1) ◽  
pp. 121-128 ◽  
Author(s):  
Barbara M. Hall
Keyword(s):  
Staphylococcus Aureus ◽  
Nasal Carriage ◽  
Mercury Resistance ◽  
Development Of Resistance ◽  
Mercury Salts ◽  
Local Endemic ◽  
Resistant Strains ◽  
Endemic Strain ◽  
Made In

SummaryReasons for the accumulation of mercury-resistant strains of Staphylococcus aureus in hospital have been studied. A collection of paired strains, that is staphylococci similar in every respect except sensitivity to mercury salts, was made. Tests were made in an attempt to demonstrate a link between mercury resistance and some other factor which might aid survival, viz. resistance to drying and heat, production of bound coagulase, growth in the presence of sublethal amounts of tetracycline, survival in human blood at 37°C. and uptake by polymorphs at 30°0. and 37°C., development of resistance to antibiotics and competition in mixed cultures. It was not possible to demonstrate any consistent link between mercury resistance and any of these properties. Paper strips impregnated with the mercurial diuretic, Mersalyl, were shown to differentiate between mercury-resistant and -sensitive strains in vitro. Furthermore, development of resistance to mercury by passage in mercuric chloride-broth was demonstrated.It is proposed that mercury resistance has developed as a result of exposure to the mercury ion. Mercurial diuretics have been frequently used in medical and geriatric patients and it is among these that the higher carrier rates of mercury-resistant strains are found even when the local endemic strain is disregarded. In obstetric patients, where mercurials are seldom used, mercury-resistant strains are rare.Nasal carriage of factory workers exposed to mercury products showed that this group is likely to carry resistant or partially resistant strains.

scholarly journals Characterization of a Putative Pathogenicity Island from Bovine Staphylococcus aureus Encoding Multiple Superantigens

2001 ◽  
Vol 183 (1) ◽  
pp. 63-70 ◽  
Author(s):  
J. Ross Fitzgerald ◽  
Steven R. Monday ◽  
Timothy J. Foster ◽  
Gregory A. Bohach ◽  
Patrick J. Hartigan ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
T Cells ◽  
Integration Site ◽  
Random Amplified Polymorphic Dna ◽  
Molecular Genetic ◽  
Pathogenicity Island ◽  
Molecular Genetic Analysis ◽  
Deletion Event ◽  
Allele Replacement

ABSTRACT Previous studies have demonstrated that a proportion ofStaphylococcus aureus isolates from bovine mastitis coproduce toxic shock syndrome toxin (TSST) and staphylococcal enterotoxin C (SEC). In this study, molecular genetic analysis of one such strain, RF122, revealed the presence of a 15,891-bp putative pathogenicity island (SaPIbov) encoding the genes for TSST (tst), the SEC bovine variant (sec-bovine), and a gene (sel) which encodes an enterotoxin-like protein. The island contains 21 open reading frames specifying hypothetical proteins longer than 60 amino acids including an integrase-like gene. The element is bordered by 74-bp direct repeats at the left and right junctions, and the integration site lies adjacent to the 3′ end of the GMP synthase gene (gmps) in the S. aureuschromosome. SaPIbov contains a central region of sequence identity with the previously characterized tst pathogenicity island SaPI1 (J. A. Lindsay et al., Mol. Microbiol. 29:527–543, 1998). A closely related strain, RF120, of the same multilocus enzyme electrophoretic type, random amplified polymorphic DNA type, and ribotype, does not contain the island, implying that the element is mobile and that a recent insertion/deletion event has taken place. TSST and TSST/SEC-deficient mutants of S. aureus strain RF122 were constructed by allele replacement. In vitro bovine Vβ-specific lymphocyte expansion analysis by culture supernatants of wild-type strains and of tst and sec-bovine allele replacement mutants revealed that TSST stimulates BTB13-specific T cells whereas SEC-bovine stimulates BTB93-specific T cells. This suggests that the presence of SaPIbov may contribute to modulation of the bovine immune response.

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