ABSTRACT
The rise of antibiotic resistance in pathogenic bacteria is endangering the efficacy of antibiotics, which consequently results in greater use of silver as a biocide. Chromosomal mapping of the Cus system or plasmid encoded Sil system and their relationship with silver resistance was studied for several gram-negative bacteria. However, only few reports investigated silver detoxification mediated by the Sil system integrated in Escherichia coli chromosome. Accordingly, this work aimed to study the Sil system in E. coli ATCC 8739 and to produce evidence for its role in silver resistance development. Silver resistance was induced in E. coli ATCC 8739 by stepwise passage in culture media containing increasing concentrations of AgNO3. The published genome of E. coli ATCC 8739 contains a region showing strong homology to the Sil system genes. The role of this region in E. coli ATCC 8739 was assessed by monitoring the expression of silC upon silver stress, which resulted in a 350-fold increased expression. De novo sequencing of the whole genome of a silver resistant strain derived from E. coli ATCC 8739 revealed mutations in ORFs putative for SilR and CusR. The silver resistant strain (E. coli AgNO3R) showed constitutive expression of silC which posed a cost of fitness resulting in retarded growth. Furthermore, E. coli AgNO3R exhibited cross-resistance to ciprofloxacin and a slightly increased tolerance to ampicillin. This study demonstrates that E. coli is able to develop resistance to silver, which may pose a threat towards an effective use of silver compounds as antiseptics.
Subject(s)
Anti-Bacterial Agents/pharmacology , Chromosomes/drug effects , Drug Resistance, Multiple, Bacterial/drug effects , Escherichia coli/drug effects , Metal Nanoparticles/chemistry , Silver/pharmacology , Chromosome Mapping , Microbial Sensitivity TestsABSTRACT
Com base em dados referentes aos candidatos de oito frabricas em duas capitais do Nordeste, este estudo tentou medir a contribuicao da educacao nao-formal na obtencao de emprego no nivel de operarios qualificados. Os resultados sugerem que ENF tem um papel positivo, embora limitado. ENF foi, dentre os fatores considerados, o unico que demonstrou um efeito significativo na 'Aquisicao de emprego' tendo tambem, junto com 'recomendacao' influenciado a variavel 'aptidao'. Uma versao mais completa do modelo em que obtencao de emprego foi vista como um processo constante de tres passos mostrou que educacao formal e experiencia de trabalho significativamente determinam o nivel da posicao aspirada pelo pretendente. Relacionando os resultados ao debate sobre a relacao educacao/mercado de trabalho, parece que certos dados do estudo estao coerentes com o modelo de socializacao, mas nao de acordo com as perspectivas teoricas credencialista e de capital humano.