[A three-dimensional model for in vitro study of the association of three antibiotics. Application to the activity of piperacillin, tazobactam and amikacin against five strains of enterobacteria as a function of their phenotype of beta-lactam resistance]. / Modèle tridimensionnel pour l'étude in vitro de l'association de trois antibiotiques. Application à l'activité de pipéracilline, tazobactam et amikacine sur cinq souches d'entérobactéries en fonction de leur phénotype de résistance aux bêta-lactamines.

We described an in vitro 3-dimensional model to study the bactericidal activity of piperacillin (P), tazobactam (T) and amikacin (A) in combination against 5 strains of enterobacteria with different resistance patterns of beta-lactam antibiotics. A synergy was defined by calculation of sigma FBCP,T,A = BCp/MBCp + BCT/MBCT + BCA/MBCA and classic sigma FBCs for each double combination. The therapeutic value of each antibiotic was estimated by comparison of its bactericidal concentrations alone and in double or triple combination.

[In vitro antibacterial activity of piperacillin-tazobactam in combination with netilmicin or amikacin against Enterobacteriaceae resistant to amoxicillin]. / Activité antibactérienne in vitro de pipéracilline-tazobactam en association avec la nétilmicine ou l'amikacine sur des entérobactéries résistantes à l'amoxicilline.

The antibacterial in vitro activity of piperacillin and tazobactam (in a concentration ratio of 8/1) was studied in combination with netilmicin or amikacin by a microtiter checkerboard assay against 162 strains of Enterobacteriaceae. These strains were selected for their resistance pattern to beta-lactam antibiotics and their beta-lactamases were characterized by the mean of isoelectric focusing in comparison with reference strains. A comparison of the MICs of piperacillin, alone and in combination, assessed the efficacy of tazobactam as beta-lactamase inhibitor, particularly when a TEM-1 beta-lactamase was produced. When the strains were sensitive to the aminoglycosides (111 netilmicin-sensitive ones and 131 amikacin-sensitive ones), we observed 55% of synergistic effects and 45% of additions with the combinations piperacillin-tazobactam-netilmicin or amikacin. A synergistic effect was usually encountered with P. mirabilis, P. vulgaris, M. morganii and with the strains of E. coli, E. cloacae and S. marcescens which produced a cephalosporinase only. Among the 51 strains that were intermediate or resistant to netilmicin, 8 ones were inhibited by piperacillin-tazobactam-netilmicin at therapeutic levels (3 synergisms, 5 additions). Among the 31 strains that were intermediate or resistant to amikacin, 24 ones (18 synergisms, 6 additions) were inhibited by piperacillin-tazobactam-amikacin at therapeutic concentrations. In most of the cases, the combination of piperacillin-tazobactam with an aminoglycoside enhanced the antibacterial activity of these agents by decreasing the concentrations necessary to inhibit the strains.

[In vitro synergistic activity of piperacillin-tazobactam combination against beta-lactam antibiotics resistant strains of Enterobacteriaceae]. / Activité synergique in vitro de l'association pipéracilline-tazobactam vis-à-vis d'entérobactéries résistantes aux bêtalactamines.

The combination of piperacillin and tazobactam was studied in a microtiter checkerboard assay against 160 strains of Enterobacteriaceae selected for their resistance pattern to amoxicillin, ticarcillin, cephalothin and cefotaxime. Mean FIC indices were respectively 0.02, 0.17 and 0.01 for RRSS strains of E. coli, K. pneumoniae and P. mirabilis. Mean FIC indices were 0.03 for RRRI/R strains of K. pneumoniae producing a broad spectrum beta-lactamase, but the synergistic effect was out of therapeutic range for 16 strains of 20. Mean FIC indices were 0.53, 0.90, 0.55, 0.10 and 0.21 respectively against RSRS strains of E. coli, E. cloacae, S. marcescens, M. morganii and P. vulgaris. Mean FIC indices were 0.02, 0.07, 0.02 and 0.01 against RRRS/R strains of E. coli, E. cloacae, S. marcescens and M. morganii but they were in a therapeutical range (piperacillin less than or equal to 8 mg/l and tazobactam less than or equal to 4 mg/l) respectively for 7, 0, 4 and 10 strains of 10 in each species. Tazobactam restored the antibacterial activity of piperacillin against enterobacterial strains mainly producing a penicillinase or a cephalosporinase for M. morganii and P. vulgaris.

[Comparative study of the antibacterial activity of cefpodoxime against enterobacteria producing beta lactamases]. / Etude comparative de l'activité antibactérienne du cefpodoxime sur les entérobactéries productrices de bêta lactamases.

Cefpodoxime proxetil (RU 51 807) is the oral prodrug of cefpodoxime (RU 51 763), a third generation cephalosporin. The antibacterial activity of cefpodoxime was compared with the activities of amoxicillin in combination with clavulanic acid (AUG), cefaclor (CCl), cefuroxime (CXM) and cefotaxime (CTX), against species of Enterobacteriaceae showing a resistance pattern against ampicillin (AMP), ticarcillin (TIC), cefalothin (CFT) and cefotaxime (CTX) respectively. For strains AMP and TIC R, CFT and CTX S, MICs 90% of cefpodoxime were 1 mg/l (E. coli), 0.5 (K. pneumoniae), 0.06 (P. mirabilis), 0.5 (Shigella sp.) and 1 (Salmonella sp.); they were 4 to 16 times as high for AUG -CCL -CXM and 4 to 16 times as low for CTX. For K. pneumoniae AMP and TIC R, CFT I/R and CTX S, similar résults were obsereved for the 5 beta-lactam antibiotics, but with an activity 10 times as low. Among the species AMP R, TIC S, CFT R and CTX S, cefpodoxime was active against P. rettgeri, P. stuartii, C. diversus, E. aerogenes and Y. enterocolitica (MICs 90% ranging from 2 to 4 mg/l; from 0.12 to 1 mg/l for CTX) and less active or inactive against P. vulgaris, E. cloacae, S. marcescens, M. morganii and E. coli (MICs 90% ranged from 16 to 32 mg/l; from 1 to 4 mg/l for CTX).(ABSTRACT TRUNCATED AT 250 WORDS)

Differences between clavulanic acid and sulbactam in induction and inhibition of cephalosporinases in enterobacteria.

The ability of clavulanic acid and sulbactam to induce and inhibit cephalosporinases was evaluated in 16 clinical isolates of enterobacteria. Using the quantitative induction assay, the checkerboard method and the disc approximation test, clavulanic acid was shown to act as inducer for all species, whereas sulbactam only induced strains of Providencia stuartii. Antagonism was achieved using a combination of clavulanic acid and cefotaxime but a combination of sulbactam and cefotaxime was either synergistic or indifferent. This variation in effect was probably due to the fact that sulbactam, but not clavulanic acid could inhibit cephalosporinases. The data revealed a significant difference between sulbactam and clavulanic acid, which may have relevance to their relative usefulness in combination with beta-lactam antibiotics for the treatment of infections due to enterobacteria that produce inducible cephalosporinase.

Sulbactam: secondary mechanisms of action.

Light and scanning electron microscopy showed that 0.25, 0.5 and 1 times the minimum inhibitory concentrations (MICs) of sulbactam (SULB) caused filament formation in different species of Enterobacteriaceae, while 2 and 4 times the MICs caused spheroplast formation and subsequent lysis. By using a competitive assay with 125I-penicillin X, SULB showed a primary affinity for the PBP 1a and PBP3 of Escherichia coli, as well as for the PBP1a of Proteus mirabilis. The bactericidal interaction of human polymorphonuclear leukocytes (PMN) and SULB against E. coli K-1 resistant to the bactericidal activity of human serum was studied in vitro; however, SULB concentrations showed variations in the medium according to human kinetic data. Under these conditions, bacterial growth occurred in Hanks balanced salt solution containing SULB, PMN, or SULB-PMN in combination. In addition, bactericidal activity was observed in serum, with a killing rate of 90% for PMN or SULB, and 95% for SULB-PMN in combination. The postantibiotic enhancement of PMN bactericidal function was assessed against E. coli K1 pretreated with 0.5 the MIC of SULB (32 micrograms/ml) for 0.5 hr. The 90% bacterial killing rate of PMN occurred by 1.5 hr for pretreated bacteria and by 2.5 hr for untreated bacteria. Furthermore, the luminol-enhanced chemiluminescence (CL) assay using an E. coli stimulus showed that SULB does not modify PMN activity.

[Bactericidal activity of daptomycin and vancomycin alone or in combination with tobramycin, netilmicin or ampicillin against enterococcus]. / Activité bactéricide de la daptomycine et de la vancomycine seules ou en association avec la tobramycine, la nétilmicine ou l'ampicilline, sur les entérocoques.

The in vitro bactericidal activity of daptomycin and vancomycin alone or in combination was studied against enterococci in a microtiter checkerboard assay and by kill-kinetic experiments. Daptomycin was more active than vancomycin and was bactericidal. Better Fractional Bactericidal Concentration indices were observed with combinations of vancomycin with aminoglycosides, but in kill-kinetic studies, the combinations of 4 MICs of daptomycin with 4 mg/l of tobramycin or netilmicin produced the more lethal effect; these combinations were even more lethal than ampicillin and aminoglycosides in the same conditions. While vancomycin and ampicillin were antagonistic, synergistic FBC indices were observed with daptomycin and ampicillin in combination, but at 4 MICs of each antibiotic, the combination was less bactericidal than ampicillin alone. The bactericidal effect obtained with daptomycin in combination with aminoglycosides suggest that further evaluation of these combinations in enterococcal endocarditis could have a clinical interest if this bactericidal effect was confirmed by in vivo studies.