<I>Haemophilus influenzae</I> におけるペニシリン結合蛋白について

Abstract

The effects of β-lactam antibiotics on Haemophilus influenzae (H.inf.) were morphologically examined with light and phase-contrast microscopes. Furthermore, the penicillin binding proteins (PBPs) in the inner membrane of H. inf. were isolated and were compared with the PBPs of E. coll.The binding affinity of β-lactam antibiotics to these PBPs was determined by competition with benzyl-[14C]-penicillin G (14C-PCG) and the correlation between the affinity and the morphological changes of the bacteria was studied.(1) When H.inf.was exposed to penicillin G, ampicillin and sulbenicillin, the filament formation was observed at various concentrations lower than MIC and spheroplast was observed at concentrations higher than MIC.With piperacillin or apalcillin, filaments were formed at various concentrations both higher and lower than MIC. Thus the range of the effective concentration for filament formation was larger in these drugs than in the above-mentioned drugs. Of the three cephalosporius tested, the filament formation was observed with cefotiam and cefmetazole at concentrations lower than MIC.The range of the effective concentration was larger in the former than in the latter.(2) By comparing the PBPs of H.inf. with those of E.coli treated with temperature, it was inferred that the main components of the PBPs of H. inf. were IA, IB, 2, 3, 5 in the order of the molecular weight.The major difference from E.coli was that PBP-IB was found as a single band in a small quantity. On the other hand, PBP-3 made plural bands and no band corresponding to PBP-6 of E.coli was observed in H.inf.(3) There was no difference in the number of PBPs between the two strains, i.e., one sensitive and the other resistant to ampicillin.In the resistant strain, however, the image showing 14C-PCG binding to PBP-5 was faint.It was assumed that this is due to hydrolysis of 14C-PCG by, β-lactamase.(4) The affinity of β-lactam antibiotics to the individual PBPs was measured. It was revealed that sulbenicillin exhibited somewhat stronger affinity to PBP-IB, as compared with other drugs. Little difference, however, was observed between these drugs as regards the affinity to PBP-IB.Cephalosporin showed a stronger affinity to PBP-IA whereas mecillinam exhibited especially a strong affinity to PBP-2.Piperacillin and apalcillin formed filaments at various drug concentrations and exhibited the strongest affinity to PBP-3, followed by cefotiam, penicillin G, ampicillin, sulbenicillin and cefmetazole. On the other hand, cefazolin and mecillinam formed no filaments and showed little affinity to PBP-3. Cefmetazole, which strongly resisted the action of β-lactamase, exhibited a strong affinity to PBP-5.