TICARCILLIN IS BACTERICIDAL AND HAS A MODE OF ACTION AND RANGE OF ACTIVITY SIMILAR TO CARBENICILLIN BUT IT IS 2 TO 4 TIMES MORE ACTIVE AGAINST PSEUDOMONAS AERUGINOSA AND INDOLE POSITIVE WHICH ARE NOT INHIBITED BY ANTIBIOTICS OTHER THEN GENTAMICIN AND POLYMYXIN B. CARBENICILLIN IS NEITHER PENICILLIN RESISTANT NOR ACID RESISTANT. TICARCILLIN IS A Β£-LACTAM ANTIBACTERIAL ANTIBIOTIC. IT IS MAINLY BACTERICIDAL. IT INHIBITS THE THIRD AND FINAL STAGE OF BACTERIAL CELL WALL SYNTHESIS BY PREFERENTIALLY BINDING TO SPECIFIC PENICILLIN-BINDING PROTEINS (PBPS) THAT ARE LOCATED INSIDE THE BACTERIAL CELL WALL. PENICILLIN-BINDING PROTEINS ARE RESPONSIBLE FOR SEVERAL STEPS IN THE SYNTHESIS OF THE CELL WALL AND ARE FOUND IN QUANTITIES OF SEVERAL HUNDRED TO SEVERAL THOUSAND MOLECULES PER BACTERIAL CELL. PENICILLIN-BINDING PROTEINS VARY AMONG DIFFERENT BACTERIAL SPECIES. THUS, THE INTRINISIC ACTIVITY OF TICARCILLIN, AS WELL AS THE OTHER PENICILLINS, AGAINST A PARTICULAR ORGANISM DEPENDS ON ITS ABILITY TO GAIN ACCESS TO AND BIND WITH THE NECESSARY PBP. LIKE ALL Β£-LACTAM ANTIBIOTICS, TICARCILLIN'S ABILITY TO INTERFERE WITH PBP-MEDIATED CELL WALL SYNTHESIS ULTIMATELY LEADS TO CELL LYSIS. LYSIS IS MEDIATED BY BACTERIAL CELL WALL AUTOLYTIC ENZYMES (I.E., AUTOLYSINS). THE RELATIONSHIP BETWEEN PBPS AND AUTOLYSINS IS UNCLEAR, BUT IT IS POSSIBLE THAT THE Β£-LACTAM ANTIBIOTIC INTERFERES WITH AN AUTOLYSIN INHIBITOR.