REGULATION OF BETA-LACTAMASE SYNTHESIS AS A NOVEL SITE OF ACTION FOR SUPPRESSION OF METHICILLIN RESISTANCE IN STAPHYLOCOCCUS-AUREUS

Nearly all clinical isolates of methicillin resistant Staphylococcus a ureus (MRSA) produce beta-lactamase as well as an additional low-affin ity penicillin-binding protein called PBP2a or PBP2', the main factor for mediating methicillin resistance. Polidocanol (PDO), a dodecyl pol yethyleneoxide ether, resensitizes clinical isolates of MRSA to methic illin; in addition, their resistance to benzylpenicillin (BP) is reduc ed. The action of PDO is based on the inhibition of the induced synthe ses of PBP2a and beta-lactamase. Induction in our study was performed with 2-(2'-carboxyphenyl)benzoyl-6-aminopenicillanic acid (CBAP). Indu cible PBP2a production in MRSA strains is under the control of the sam e regulatory system which is responsible for the induction of beta-lac tamase synthesis. BlaR1, a membrane-spanning protein with a penicillin sensor and a signal transducer domain represents the starting point o f this induction cascade. Based on its amphiphilic properties, it is l ikely that the action of PDO is located in the bacterial membrane. The refore we investigated the possibility that BlaR1 might be the main ta rget for PDO action. We were able to detect the BlaR1 sensor domain in resistant staphylococcal cells even in the noninduced state by fluoro graphy. In a competition assay, CBAP was bound specifically, with a hi gh affinity to the penicillin sensor. Moreover, the binding of CBAP wa s very stable. As concerns PDO, no significant interaction with the pe nicillin binding site of BlaR1 was detectable. This is why the BlaR1 t ransducer domain is thought to be the actual target area of PDO. In th is case, PDO would interfere with the transmission of the signal, gene rated by the receptor binding of CBAP, through the membrane via BlaR1 into the staphylococcal cell. This assumption could be confirmed by th e analysis of the concentration-effect relationship, whereafter PDO do es not work as a competitive, but as a noncompetitive antagonist of CB AP. Our results demonstrate that BlaR1 could be an attractive new targ et for the development of new drugs to overcome methicillin resistance .