Stress by Antibiotics and Virulence of Enterococci
Enterococcus are human commensal bacteria which have emerged, in parallel with the use of antibiotics, as major nosocomial opportunistic pathogens. Understanding their virulence is as essential as uncovering the mechanisms behind their ability to survive to antibiotics and other stresses, if we want to find new ways to fight infections cause by multiresistant strains of enterococci.
Antibiotics are molecules used by microrganisms to communicate. Thus it is essential to understand the response of the bacterial cell to antibiotic concentrations below their bactericidal/bacteriostatic activity. We have found that vancomycin, a cell-wall active antibiotic, induces changes in the expression of genes which functions range from stress response, cell-wall integrity, cell-division, regulation, transport and those to which no function has been attributed, the hypothetical proteins. These studies constitute the basis for further analysis of each cathegory of genes involved in the response to vancomycin, which could be also involved in responses to other antibiotics with similar behaviour, i.e, cell-wall active and not entering the cell. A similar transcriptomic approach is being followed to study other stresses namely metal ions (often involved in regulation of virulent behaviours in other bacteria), molecules involved in cell-cell communication, both by quorum-sensing mechanisms and others, and biocides. We are trying to identify proteins involved in response and resistance to biocides and understand the potential for cross-resistance between biocide use and antibiotic resistance emergence.
Analysis of the results obtained from those studies provide us with possible targets for further studies on their role on virulence of enterococci. Often these studies involve mutant construction and testing in virulence models. In collaboration with groups from other Institutions we use insect models, mice and animal cell culture.
Another new area of work arising in the Lab deals with the hypothetical proteins. These proteins may be conserved among organisms or specific to enterococci and constitute nearly 30% of all sequenced genomes so far, of all organisms. This means that we are lacking at least 30% of information on the biological activity of those genes. In the Lab, we are foccusing on some of these genes and, in collaboration with the Membrane Chrystallography Lab, we plan on resolving the structures of those proteins and, together with othe molecular biology and biochemical approaches, attribute a role to those proteins.
In parallel with the more detailed studies mentined before, we maintain our involvement on research on environmental enterococcal isolates. These studies concern the dissemination of strain types and genes involved in antibiotic resistance and virulence.
- Frederic Gaspar, PhD Student
- Teresa Braga, PhD Student
- Marta Abrantes, PhD Student
- Renata Matos, PhD Student
- Neuza Teixeira, PhD Student
- Paulo Marujo, PhD
- Braga, TM, Marujo, PE, Pomba, C, Lopes, MFS. (2011), J Antimicrobial Chemother, 2011 66: 283-286.
- Gaspar, F, Teixeira, N, Rigottier-Gois, L, Marujo, P, Nielsen-LeRoux, Crespo, MTB, Lopes, MFS, Serror, P. (2009) Microbiology 155:3564-3571.
- Matos, R, Pinto, V, Ruivo, M, Lopes, MFS (2009) Int J Antimicrob Agents 34:142-147.
A resistência aos antibióticos é um tema actual e preocupante. Mais tarde ou mais cedo, as bactérias encontram sempre mecanismos de resistência aos antibióticos que vão sendo introduzidos no mercado. Este tema é ainda mais procupante quando se trata de bactérias que existem naturalmente e que são até benéficas tanto nos humanos e outros mamíferos, como em plantas, solos, águas e alimentos como o leite e os queijos. Os enterococos encaixam nesta categoria, mas são neste momento uma das principais causas de infecções hospitalares. Este facto deve-se à sua capacidade para facilmente resistirem aos antibióticos usados e por possuírem mecanismos de invasão do hospedeiro, os chamados mecanismos de virulência. O objectivo do nosso trabalho é, em última análise, compreender melhor os mecanismos de resistência aos antibióticos e de virulência destas bactérias para, no futuro, podermos encontrar novos alvos para terapia, sem prejuízo dos enterococos benéficos que existem no nosso organismo.