Biofilm of Salmonella

Advances in the study of the salmonella bacteria, being undertaken at the Pamplona Institute of Agrobiotechnology and Natural Resources and led by professor Iñigo Lasa Uzcudun of the Public University of Navarre, have been recognised in the principal international magazine in the field of Microbiology, Molecular Microbiology, at a congress held recently in the German city of Heidelberg.

The Navarre researchers are analysing the role that a new family of Salmonella typhimurium proteins play in the biosynthesis of cellulose and in the formation of the biofilm of the salmonella bacteria.

Biofilms

The presence of biofilms is commonplace in nature. Who has not seen the mucous material on the inside of a vase after we have had flowers there some time, the slimy substance covering stones on riverbeds … these are biofilms. The capacity for biofilm formation does not appear to be restricted to any one specific group of micro-organisms and, nowadays, it is believed that, if the environmental conditions are right, all micro-organisms are able to form biofilms.

Although the composition of biofilm is variable depending on the system under study, in general the main component of biofilm is water – as much as 97% of the total content. Apart from water and the bacterian cells, the biofilm matrix is a complex formed principally by exopolysacharrides.

Bacterian and infectious biofilms

Currently, with chronic infections such as those related to medical implants or other chronic conditions such as otitis media, pneumonia or chronic urinary infections, amongst others, direct analysis of the infected implants and tissues clearly show that the bacteria responsible for the infection grows adhering to the tissue or implant, producing biofilms.

The bacteria are protected, inside the biofilm, from the action of antibodies from attack by phagocytic cells and from antimicrobian treatment. Thus, they do not respond suitably to antibiotic treatament and produce recurrent episodes with the result that, in most cases, the only solution is the substitution of an implant. This is because the bacterias in the biofilm can be up to 1000 times more resistant to antibiotics than these same bacteria grown in a liquid medium.

In the last five years, many research groups have directed their efforts to identifying the genes responsible for the formation of the biofilms and those genes required to maintain the structure of the biofilm. In order to identify these genes, there has been a recent development in genomics and proteomics that has resulted in many of these groups are using microarrays or proteomic techniques for identifying the genes that express themselves in a different way in biofilm conditions or planktonic conditions, even though we are dealing with the same bacteria. Amongst these genes, a great proportion of genes are repeatedly found the function of which is unknown, which points to the existence of genes specific to the biofilm lifestyle and the phenotype of which has not been possible to visualise to date.

It is precisely on the Salmonella and Staphylococcus bacteria that Professor Lasa Uzkudun’s research group has been carrying studies. They have discovered a new family of proteins related to the formation of biofilms and which have been unidentified to date. This group of proteins may well explain the mechanism of the biofilm when colonising new surfaces, the method of adhering to different media, the regulation of the process of biofilm formation, etc., given that some of the discovered proteins have a precursor function in the formation of the biofilm.

Finally, it would appear logical that the formation of the biofilm be produced in response to the ambient conditions and so exist systems that transmit the signal for the surrounding environment to the interior of the bacteria in order to suit the expression of the genes to the new environment. Even so, despite all that has been learned in recent years about bacterian biofilms, what is the “Biofilm” phenotype still remains to be defined exactly. Only then can it be determined what are the physiological changes which take place therein and what are the genetic requirements and regulation mechanisms of such a process.