Crystallization and preliminary crystallographic studies of FoxE from Rhodobacter ferrooxidans SW2, an Fe(II) oxidoreductase involved in photoferrotrophy.

FoxE is a protein encoded by the foxEYZ operon of Rhodobacter ferrooxidans SW2 that is involved in Fe(II)-based anoxygenic photosynthesis (`photoferrotrophy'). It is thought to reside in the periplasm, where it stimulates light-dependent Fe(II) oxidation. It contains 259 residues, including two haem c-binding motifs. As no three-dimensional model is available and there is no structure with a similar sequence, crystals of FoxE were produced. They diffracted to 2.44 Å resolution using synchrotron radiation at the Fe edge. The phase problem was solved by SAD using SHELXC/D/E and the experimental maps confirmed the presence of two haems per molecule.

Avaliaçäo da sensibilidade a antimicrobianos de 87 amostras clínicas de enterococos resistentes à vancomicina / Evaluation of antimicrobial sensitivity of 87 clinical isolates of vancomycin-resistant enterococci

OBEJETIVOS. 1) Avaliar o padräo de sensibilidade in vitro de amostras clínicas de enterococos resitentes à vancomicina (ERV), aos antimicrobianos comumente utilizados no seu tratamento, bem como a antimicrobianos alternativos. 2) Avaliar a acurácia do E test, em comparaçäo aos outros testes de sensibilidade a antimicrobianos (microdiluiçäo em caldo e difusäo em disco). MATERIAL E MÉTODOS. Foram analisadas 87 amostras clínicas de ERVs selecionadas de 1.936 isolados de enterococos coletados em 97 hospitais norte-americanos, no último trimestre de 1992. A identificaçäo em nível de espécie foi feita pelos sistemas API 20S, Vitek e uma versäo modificada do método convencional proposto por Facklam e Collins. A avaliaçäo da sensibilidade in vitro aos antimicrobianos foi realizada pela técnica de microdiluiçäo em caldo, E test e métodos de difusäo em disco. As amostras foram testadas, tanto para antimicrobianos normalmente utilizados no tratamento de infecçöes enterocócicas (vancomicina, teicoplanina, ampicilina, penicilina, gentamicina e estreptomicina), como também para drogas alternativas potencialmente úteis (cloranfenicol, doxiciclina, esparfloxacina, ciprofloxacina, clinafloxacina, eritromicina, espectinomicina, trospectomicina, trimetoprim-sulfametoxazol e novobiocina). RESULTADOS. A avaliaçäo dos testes de sensibilidade das 87 amostras de ERV revelou resistência, a ampicilina em torno de 86 por cento, o mesmo sendo observado para penicilina. Em relaçäo aos aminoglicosídeos, obtivemos alto grau de resistência, em torno de 82 por cento e 85 por cento, para gentamicina e estreptomicina, respectivamente. Apesar de pertencer à mesma classe de vancomicina, a teicoplanina foi ativa contra 29 por cento das amostras de ERV. Entre os antimicrobianos alternativos testados, os que apresentaram maiores taxas de sensibilidade foram o cloranfenicol, a doxiciclina e a trospectomicina (82 por cento, 92 por cento e 94 por cento de isolados suscetíveis, respectivamente). CONCLUSÃO. O tratamento de infecçöes causadas por enterococos multirresistentes ainda é um desafio, e vários esquemas já vêm sendo propostos na literatura. Säo necessários, no entanto, mais trabalhos analisando a efetividade clínica dessas combinaçöes de antibióticos antes que recomendaçöes definitivas possam ser feitas.

[Evaluation of antimicrobial sensitivity of 87 clinical isolates of vancomycin-resistant enterococci]. / Avaliação da sensibilidade a antimicrobianos de 87 amostras clínicas de enterococos resistentes à vancomicina.

OBJECTIVES: 1) To evaluate the antimicrobial susceptibility pattern of vancomycin-resistant enterococci to the antimicrobial agents that are commonly used to treat enterococci infections and to some alternative drugs. 2) To evaluate the accuracy of E test for susceptibility testing enterococci. MATERIAL AND METHOD: We evaluated 87 clinical VRE isolates that were selected from a previous study which analyzed 1936 clinical isolates collected and processed in 97 US medical centers in the last quarter of 1992. The isolates were identified to the species level by using the API 20S System, the Vitek gram-positive identification cards and a modified version of the conventional method proposed by Facklam and Collins. The in vitro susceptibility testing was performed by broth microdilution, E test and disk diffusion methods, following the criteria described by the National Committee for Clinical Laboratory Standards (NCCLS). The VRE isolates were tested against antimicrobial agents commonly used to treat enterococci infections (vancomycin, teicoplanin, ampicillin, penicillin, gentamicin and streptomycin) and against ten potential alternative drugs (chloramphenicol, doxycycline, sparfloxacin, ciprofloxacin, clinafloxacin, erythromycin, spectinomycin, trospectomycin, trimetoprim-sulfametoxazol and novobiocin). RESULTS: Our results showed a high rate of resistance to ampicillin and penicillin (86%). High level resistance to gentamicin and streptomycin was demonstrated by 82% and 85% respectively. Although teicoplanin and vancomycin belong to the same antibiotic group (glycopeptide), 29% of VRE were susceptible to teicoplanin. Among the alternative drugs, trospectomycin, doxycyclin and chloramphenicol showed the highest in vitro activity, with 94%, 92% and 82% susceptibility respectively. In addition, erythromycin, trimetoprim-sulfametoxazol and ciprofloxacin showed the highest rates of resistance (98%, 83% and 69%, respectively). CONCLUSION: The treatment options for infections caused by vancomycin-resistant enterococci seem to be very narrow since a small percentage of those isolates were susceptible to the other antimicrobial agents commonly used to treat these infections and only a few of the alternative drugs tested showed good in vitro activity. Many regimens using various antibiotic combinations have been tested against VRE, most of them with fluoroquinolones. However further studies are necessary to evaluate the clinical role of these antibiotic combinations.