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The penetration of /Mactam antibiotics through the outer membraneis a prerequisite for exhibiting the antibacterial activity against Gram-negative bacteria. The elucidation of penetration routes has been the subject of many papers, and our understanding of the functions of a variety of outer membraneproteins has increased in recent years. It is knownthat major outer membraneproteins which form porin channels, OmpFand OmpC,allow small hydrophilic molecules including /Mactam antibiotics to diffuse into the periplasmic space1*. On the other hand, catechol-substituted /?-lactam antibiotics, such as BO-12362), BO-13413'4), E-07025), M146596), and pirazmonam7) which all have potent antipseudomonal activity utilize a unique transport pathway, the to«i?-dependent iron transport pathway in Escherichia coli8). The uptake of iron in E. coli is known to require receptor proteins and the tonB gene product9) in conjunction with siderophores. Recently Curtis et al.10\ and Nikaido and Rosenberg 1 1 } identified the iron-regulated outer membrane receptor proteins, Fiu and Cir, specific to the catechol-substituted cephalosporins. In our paper, we report the diversity of the transport pathway as assessed from the characterization of spontaneous mutants of E. coli selected with BO-1236and BO-1341. Wealso note the influence of bacterial growth under anaerobic condition and in the presence of ascorbic acid as well as iron concentration in the medium, on the antibacterial activity of these catechol-substituted cephalosporins. BO-1236 and BO-1341, both of which were cephem antibiotics as shown in Fig. 1, were synthesized at the Okazaki Research Laboratories of Banyu Pharmaceutical Co., Ltd. (Okazaki,

Comparison of transport pathways of catechol-substituted cephalosporins, BO-1236 and BO-1341, through the outer membrane of Escherichia coli.