Multidrug resistance in Klebsiella pneumoniae: a novel gene, ramA, confers a multidrug resistance phenotype in Escherichia coli

Abstract

Spontaneous multidrug-resistant (Mdr) mutants of Klebsiella pneumniae strain ECL8 arose at a frequency of 2.2 x to a range of unrelated antibiotics, including chloramphenicol, tetracycline, nalidixic acid, ampicillin, norfloxacin, trimethoprim and puromycin. A chromosomal fragment from one such mutant was cloned, and found to confer an Mdr phenotype on Escherichia coli K12 cells that was essentially identical to that of the K. pneumoniae mutant. Almost complete loss of the OmpF porin in the E. coli transformant, and of the corresponding porin in the K. pneumniae mutant, was observed. The presence of the Mdr mutation in K. pneumoniae or the cloned K. pneumoniae ramA (msistance antibiotic multiple) locus in Em coli also resulted in active efflux of tetracycline, and increased active efflux of chloramphenicol. After transformation of a ramA plasmid into E. coli, expression of chloramphenicol resistance occurred later than expression of resistance to tetracycline, puromycin, trimethoprim and nalidixic acid. The ramA gene was localized and sequenced. It encodes a putative positive transcriptional activator that is weakly related to the Em coli MarA and SoxS proteins. A ramA gene was also found to be present in an Enferobacter cloacae fragment that has previously been shown to confer an Mdr phenotype, and it appears that ramA, rather than the m m A gene identified in that study, is responsible for multidrug resistance. The r0mA gene from the wild-type K. pneumoniae 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. and showed increased resistance 1

Porin alteration and active efflux: two in vivo drug resistance strategies used by Enterobacter aerogenes

“…The presence of Mdr or similar systems has been reported in Abbreviation: CCCP, carbonyl cyanide rn-chlorophenylhydrazone. (Ariza et al,-l995;Gambino et al, 1993;George et al, 1995;M a et al, 1995;Okusu et al, 1996). Drug efflux can be expressed conjointly to a reduction in drug uptake : examples of a drastic decrease in outer-membrane porins have been reported, pointing to a nodal site in the regulation cascade of the Mdr process (Cohen et al, 1988;Gambino et al, 1993;George et al, 1995).…”

“…(Ariza et al,-l995;Gambino et al, 1993;George et al, 1995;M a et al, 1995;Okusu et al, 1996). Drug efflux can be expressed conjointly to a reduction in drug uptake : examples of a drastic decrease in outer-membrane porins have been reported, pointing to a nodal site in the regulation cascade of the Mdr process (Cohen et al, 1988;Gambino et al, 1993;George et al, 1995). The spread of several resistance mechanisms and the modulation of the different bacterial responses to antibiotic therapy call for studies of multidrug resistance systems, their identification and their prevalence in strains isolated from hospital units.…”

Properties and Expression of a Multidrug Efflux Pump AcrAB-KocC from Klebsiella pneumoniae

“…36) It has been also reported that expression of acrA Kp was elevated in a strain of K. pneumoniae in which the expression of ramA was increased. 33) RamA is involved in the expression of acrAB in Enterobacter aerogenes and is closely related to K. pneumoniae.…”

“…37) Both RamA and MarA belong to the AraC-XylS transcriptional activator family. 36,38) It is not clear whether RamA is involved in the regulation of acrAB in K. pneumoniae. For these reasons, we also measured the expression level of ramA (Fig.…”

Stress responses, outer membrane permeability control and antimicrobial resistance in Enterobacteriaceae

“…In Enterobacteriaceae, the development of MDR is under positive regulation by global transcriptional activators that include members of the Ara/XylS superfamily such as MarA, RamA (absent in E. coli) and Rob, as well as the oxidative stress regulon SoxSR [10,[25][26][27][28][29]. Mutations in the corresponding genes are well documented and induce the overproduction of efflux pumps with concomitant repression of porin expression both directly and indirectly [10].…”