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

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.