A ROB-LIKE GENE OF ENTEROBACTER-CLOACAE AFFECTING PORIN SYNTHESIS ANDSUSCEPTIBILITY TO MULTIPLE ANTIBIOTICS

A chromosomal gene of Enterobacter cloacae affecting the synthesis of major outer membrane proteins in E. cloacae and Escherichia coli was c loned by using selection for resistance to cefoxitin in E, coli, The p resence of the gene, when plasmid-borne, led to a decrease in the amou nt of porin F in E, cloacae and the amount of OmpF in E, coli and caus ed 2- to 32-fold increases in the MICs of chloramphenicol, tetracyclin e, quinolones, and p-lactam antibiotics, The gene encoded a 33-kDa pro tein, similar (83% identity) to the protein Rob involved in the initia tion of DNA replication in E. coli, which was called RobA(EC1) by anal ogy. RobA from E, cloacae was found to inhibit ompF expression at the posttranscriptional level via activation of micF, a gene also apparent ly present in E, cloacae, as detected by PCR. As with its homolog from E, coli, RobA(EC1) is related to the XylS-AraC class of positive tran scriptional regulators, along with MarA and SoxS, which also cause a m icF-mediated decrease in the level of ompF expression.