MULTIDRUG-RESISTANCE IN KLEBSIELLA-PNEUMONIAE - A NOVEL GENE, RAMA, CONFERS A MULTIDRUG-RESISTANCE PHENOTYPE IN ESCHERICHIA-COLI

Spontaneous multidrug-resistant (Mdr) mutants of Klebsiella pneumoniae strain ECL8 arose at a frequency of 2.2 x 10(-8) and showed increased resistance to a range of unrelated antibiotics. including chloramphen icol, tetracycline, nalidixic acid, ampicillin, norfloxacin, trimethop rim and puromycin. A chromosomal fragment from one such mutant was clo ned, and found to confer an Mdr phenotype on Escherichia coli K12 cell s that was essentially identical to that of the K. pneumoniae mutant. Almost complete loss of the OmpF porin in the E. coli transformant, an d of the corresponding porin in the K. pneumoniae mutant, was observed . The presence of the Mdr mutation in K. pneumoniae or the cloned K. p neumoniae ramA (resistance antibiotic multiple) locus in E. coli Scien ces, Macquarie also resulted in active efflux of tetracycline, and inc reased active efflux of chloramphenicol. After transformation of a ram A plasmid into E. coli, expression of chloramphenicol resistance occur red later than expression of resistance to tetracycline, puromycin, tr imethoprim and nalidixic acid. The ramA gene was localized and sequenc ed. It encodes a putative positive transcriptional activator that is w eakly related to the E. coli MarA and SoxS proteins. A ramA gene was a lso found to be present in an Enterobacter cloacae fragment that has p reviously been shown to confer an Mdr phenotype, and it appears that r amA, rather than the romA gene identified in that study, is responsibl e for multidrug resistance. The ramA gene from the wild-type K. pneumo niae was identical to that of the mutant strain and also conferred an Mdr phenotype on E. coli, indicating that the mutation responsible for Mdr in K. pneumoniae had not been cloned.