Construction Of The Homologous Recombination Plasmid Of SigB In Staphylococcus Aureus

Staphylococcus aureus (S. aureus), one of the most frequently isolated bacterial pathogens in hospital infections, is also a common pathogen producing biofilm. Data obtained recently from intensive-care units in Germany indicated that S. aureus is the second most frequent cause of catheter-related septicemia (15.4%). S. aureus producing the biofilm could be high resistant to antimicrobial agents and avoid the immune killing and clearance. Moreover biofilm could act as"niduses"of acute infection if the mobilized host defenses can not eliminate the planktonic cells, which can be released at any time during the infection,leading to underlying chronic infections and even more severe consequences. Therefore, to know how biofilm comes into being in S. aureus and other pathogens has presently become a hot topic.Despite the great efforts have made, the mechanism of biofilm forming by S. aureus had not still been known much about. The studies so far in biofilm forming showed that the attachment of the bacterial cells to the polymer surface was the first step,which may occur very rapidly. And thereafter multilayered cell clusters formed by the growth dependent accumulation of bacteria were surrounded by a slimy matrix induced by polysaccharide intercellular adhesion(PIA)whose synthesization was catalyzed by products encoded by ica operon. This process was regulated by multiple factors and in multiple levels. Among them sigB, theσfactor code gene was thought to be the key factor since it had been demonstrated could regulate directly not only the expression of ica but also control the expression of sarA and/or agr. However recent studies found that the S. aureus whose sigB was deleted by homologous recombination is still able to form biofilm. Since all the experimental bacteriia in the literature were limited to study on some specified strains, the strains isolated from clinic during July 2004 to December 2004 in our hospital had been used as the target in this study. The resistance to antibiotics and the presence of biofilm of these strains were identified and the genes related to the forming of biofilm were amplified by PCR. Then the homologous recombination plasmid of sigB gene was constructed from Staphylococcus aureus.