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Previous issue date: 2014-03-31 / Persistence is an antimicrobial tolerance phenotype with an unclear molecular background. Such tolerant cells (called persisters) correspond to small portions of the bacterial population and are capable of surviving excessive concentrations of the drug, even though they do not possess any specific resistance mechanism. The clinical impact of persisters lies on their capacity to resume multiplication and reestablish the infection after the concentration of the drug diminishes in the infection site, possibly being responsible for the re-incidence and for the chronic aspect of certain infectious diseases. This survival phenotype has been observed in several species; however reports involving A. baumannii are scarce. Therefore, this work aimed to evaluate the persistence phenotype to antimicrobial drugs in nosocomial isolates of A. baumannii, as well as verifying the possible contribution of the sodB gene, which is involved in the control of oxidative stress, and the pmrC gene, a determinant of polymyxins resistance, in persister cells formed upon polymyxin B exposure. In order to do so, clinical isolates of A. baumannii were exposed to high concentration of tobramycin and polymyxin B for 6 h and the number of surviving cells were estimated every 1.5 h. In addition, the gene expressions at transcription level of two isolates were evaluated after the exposure to polymyxin B for 5 h. A high heterogeneity in the ability to form persister cells was observed among the isolates, presenting no correlation between the fractions of persisters after tobramycin and polymyxin B treatments. These data may indicate genetic or epigenetic variations that are determinant to the development of this characteristic, and that are not related among drugs of different classes. Moreover, the preliminary results of the gene expression assays may suggest that the mechanism involved in the polymyxin B resistance phenotype does not directly participate in persistence to polymyxin B, nor indicate the participation of sodB in this phenotype. In conclusion, the molecular mechanisms for persistence are still to be determined, and this characterization is highly important to assist in the development of new therapeutic options. / A persist?ncia ? um fen?tipo de toler?ncia a f?rmacos antimicrobianos com bases moleculares pouco entendidas. Tais c?lulas tolerantes (chamadas de persisters) correspondem a pequenas parcelas da popula??o bacteriana e s?o capazes de sobreviver a concentra??es elevadas do f?rmaco, mesmo sem possuir mecanismos de resist?ncia espec?ficos. O impacto cl?nico das c?lulas persisters se d? pela capacidade destas c?lulas de retomar seu crescimento e restabelecer a infec??o ap?s os n?veis do f?rmaco diminu?rem no s?tio da infec??o, podendo ser respons?veis pela reincid?ncia e pelo aspecto cr?nico de certas doen?as infecciosas. Este fen?tipo de sobreviv?ncia j? foi observado em in?meras esp?cies, por?m relatos envolvendo o A. baumannii s?o escassos. Portanto, este trabalho teve por objetivo avaliar o fen?tipo de persist?ncia a drogas antimicrobianas em isolados nosocomiais de A. baumannii, bem como verificar a poss?vel participa??o do gene sodB envolvido no controle do estresse oxidativo e do gene pmrC, determinante de resist?ncia ?s polimixinas, em c?lulas persisters formadas a partir da exposi??o ? polimixina B. Para tal, isolados cl?nicos de A. baumannii foram expostos a concentra??es elevadas de tobramicina e polimixina B por 6 h e o n?mero de c?lulas sobreviventes foi averiguado em intervalos de 1,5 h. Al?m disso, as express?es g?nicas a n?vel de transcri??o de dois isolados foram avaliadas ap?s a exposi??o ? polimixina B por 5 h. Uma grande heterogeneidade na capacidade de forma??o de c?lulas persisters foi observada dentre os isolados, n?o havendo correla??o entre a fra??o de persisters ap?s o tratamento com tobramicina e polimixina B. Estes dados podem indicar varia??es gen?ticas ou epigen?ticas determinantes para o desenvolvimento desta caracter?stica, as quais n?o s?o relacionadas entre drogas de diferentes classes. Al?m disso, os resultados preliminares dos ensaios de express?o g?nica podem sugerir que o mecanismo de resist?ncia ?s polimixinas n?o participa diretamente na persist?ncia ? polimixina B, e que n?o h? a participa??o de sodB no desenvolvimento e manuten??o deste fen?tipo nas condi??es testadas. O estudo desta caracter?stica e de seus determinantes moleculares s?o de suma import?ncia para o desenvolvimento de novas op??es terap?uticas.
| Identifer | oai:union.ndltd.org:IBICT/oai:tede2.pucrs.br:tede/5488 |
| Date | 31 March 2014 |
| Creators | Barth Junior, Valdir Crist?v?o |
| Contributors | Oliveira, Silvia Dias de |
| Publisher | Pontif?cia Universidade Cat?lica do Rio Grande do Sul, Programa de P?s-Gradua??o em Biologia Celular e Molecular, PUCRS, BR, Faculdade de Bioci?ncias |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Format | application/pdf |
| Source | reponame:Biblioteca Digital de Teses e Dissertações da PUC_RS, instname:Pontifícia Universidade Católica do Rio Grande do Sul, instacron:PUC_RS |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | 8198246930096637360, 600, 600, 36528317262667714 |
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