The role of extracellular DNA in the maintenance of biofilms formed by gram-positive and gram-negative bacteria was studied. This study evaluated all the bacterial strains that were tested for the presence of extracellular DNA with an average size of 30 kb in the matrix. Our results indicate changes in community biomass, architecture, morphology, and the numbers of CFU in the presence of DNase. This effect seems to be common to biofilms established by various unrelated gram-positive and gram-negative bacteria. The cleavage of extracellular DNA leads to the formation of an altered biofilm that permits the increased penetration of antibiotics. Thus, the addition of DNase enhances the effect of antibiotics, resulting in decreased biofilm biomass and numbers of CFU.It is well known that bacteria form biofilms, in which they survive in the presence of high concentrations of antimicrobial agents (13,23,28,51,52,55). Antibiotics at concentrations of 10 2 to 10 4 times the MIC cause no killing effect on the bacteria in biofilm communities (2,7,14,22,24,32,54). Bacterial survival in biofilms may be determined by multiple different factors. Biofilms are covered by a surface film composed of lipid components similar to those in bacterial membranes, which are a barrier for the penetration of some antibiotics (57, 59). The roles of separate components of the biofilm matrix in the bacterial life have recently been studied (17,26,50,63). It is known that the matrix consists of proteins, polysaccharides, lipids, and nucleic acids, which form an extracellular polymeric substance (EPS) (21,34,56,64). Some suggest that EPS can interact with antibiotics in a manner that leads to a decline in antibacterial activity (5,8,29). It was also shown that bacterial survival in biofilms in the presence of antibiotics can be determined by special cells persisters, which are tolerant to various drugs (27,31,35,51). Recently, extracellular DNA has been found in the matrix of Pseudomonas aeruginosa and Neisseria gonorrhoeae biofilms (1,26,32,50,63). Previously, free circulating DNA was found in human blood plasma (3,45,61), and it is also present in marine sediments and soil (6,15,16,44,60). It was shown that the extracellular DNA in the biofilm matrix could take part in the development of bacterial communities (25,40,49,63). It can be released by live cells, possibly via membrane vesicles composed of bacterial lipids (65), or it may enter the matrix from lysed cells (10,18,19,48,58,65). We have recently found cell-free DNA as a component of EPS in biofilms formed by various unrelated gram-positive and gramnegative bacteria and fungi (G. Tetz and V. Tetz, unpublished data). It was previously shown that the destruction of the extracellular DNA of P. aeruginosa and Streptococcus pneumoniae could change the properties of the biofilms formed by these bacteria (30,40,63). At the same time, this phenomenon has not been studied with other microorganisms. The role of extracellular DNA in the interaction of bacterial biofilms with environmental factors i...

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Link to this article: http://journals.cambridge.org/abstract_S147905050400136X How to cite this article: V. V. Tetz, V. P. Korobov, N. K. Artemenko, L. M. Lemkina, N. V. Panjkova and G. V. Tetz (2004). Extracellular phospholipids of isolated bacterial communities. A B S T R A C TWe have made a comparative analysis of the extracellular phospholipid composition of biofilms of Gram-negative and Gram-positive bacteria. The surface film of a growing bacterial community contains small membrane vesicles and a bilipid layer covering the entire surface of that community. These supracommunity films containing the bilipid layer can cover the entire surface of a Petri dish and form a boundary between bacterial communities and the environment. A mixed bacterial lawn, formed by unrelated bacteria, also becomes covered with a single film containing a lipid bilayer. The phospholipid compositions of the bacterial cell and surface film bilipid layer reflect the nature of the bacterial strains forming the community, but have some specific differences.

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Drug penetration into bacterial biomembranes is one of the most important factors determining the efficiency of antibacterial therapy. Multicide, antibacterial drug, is a nanomolecule 1.3-2.0 nm in size, easily penetrating into staphylococcus biomembranes and causing rapid death of bacteria. The drug efficiency depends on its concentration and duration of exposure. Bacteria die as a result of cell wall perforation, which is associated with changes in its morphology and release of DNA from bacterial cell into the environment. Our results indicate the efficiency of primary damage to bacterial wall leading to elimination of biomembranes.