The PhD, entitled Identification and characterisation of new factors involved in the processes of formation of biofilm from Gram-positive bacteria.
Biofilms are communities of microorganisms in a matrix that joins them together and to living or inert substrates, points out Alejandro Toledo. Although they are widely found in nature, and in many cases have beneficial effects, their study has been boosted on discovering their relation to chronic infections associated to medical implants such as those tissues involving infections of the middle ear, of the prostate gland, pneumonia in patients with cystic fibrosis, osteomyelitis, etc.
In the interior of the biofilm, bacteria present greater resistance to antibiotics, to the opsonisation by antibodies and to phagocytosis, which explains the chronic character of these infections, states the author of the PhD.
The aim of the PhD was the characterisation of the process of formation of the Staphylococcus aureus biofilm.
Regulating mechanisms unknown to date
The starting point for the research was the Bap protein (Biofilm associated protein). Bap, according to the thesis, presents a structural organisation similar to other surface proteins of unknown function in a number of species of bacteria such as: Esp de Enterococcus faecalis, mus20 of Pseudomonas putida, and sty2875 of Salmonella typhi.
Thus, taking into account the structural homology between Bap and Esp, it was decided to analyse for a possiblerelationship between the presence of the esp gene and the ability to produce biofilm by E. faecalis. The results showed that the presence of the esp gene was involved in the formation processes of these biofilms.
Two new genes
The results obtained to date intuitively suggest the existence of various mechanisms for forming biofilm as a function of the origin of the bacteria strains, as a consequence of which it was decided to widen the scope of the research, using a strain of Staphylococcus aureus from otitis media.
For the identification of the genes involved in the formation of the biofilm of this strain, two different strategies were followed. The first, following the usual methods, involved identifying mutants that had lost the capacity to form biofilm, thus enabling identification of the essential genes and positive regulators of the process. The results showed that a positive regulator known as Pnp (Polynucleotide phosphorylase) exists and which regulates the accumulation of the main exopolysaccharide involved in the formation of the biofilm for this bacteria.
Moreover, the second strategy arose during the development of a medium chemically defined in order to study how environmental signals affect the process of formation of the biofilm. Unexpectedly, most of the clinical strains of Staphylococcus aureus were unable to form biofilm in the synthetic medium, which suggested to us that the process was, perhaps, repressed in this medium.