[Comparative antibacterial activity of ceftibuten (SH 39 720) against 150 K. pneumoniae strains producing different beta-lactamases].

Comparative antibacterial activity of ceftibuten (SH 39 720) on 150 K. pneumoniae strains producing different beta-lactamases. MICs of ceftibuten, cefotaxime + clavulanic acid (10 mg/l), ceftazidime and azthreonam were determined for 150 clinical isolates of K. pneumoniae: 15 "wild" type producing only the SHV-1 type beta-lactamase, 15 TEM-1 and 120 producing new "extended spectrum" beta-lactamases (48 CTX-1, 9 SHV-2, 4 SHV-3, 35 SHV-4, 24 SHV-5). Against SHV-1 and TEM-1 strains the bacteriostatic activity of ceftibuten was close to that of the other beta-lactams tested. This activity was preserved against strains producing CTX-1, SHV-2, SHV-3 beta-lactamases and MICs were comparable to those of cefotaxime + clavulanic acid. The MICs of ceftibuten against strains producing SHV-4 and SHV-5 beta-lactamases were higher (1 to 8 mg/l) but this level of antibacterial activity was superior to that of the other beta-lactam antibiotics. The bactericidal activity of ceftibuten was evaluated by kill kinetic studies: this activity was preserved against the CTX-A and SHV-2 strains--with concentrations equal to 2 or 4 x CMI a 4 log10 reduction of the bacterial inoculum was obtained at 24 h. A such reduction was not obtained with cefotaxime. This preserved antibacterial activity of ceftibuten against K. pneumoniae producing some new "extended spectrum" beta-lactamases need further studies to state the structure-activity relation-ships of this antibiotic.