Anne Davin-Regli

Antibiotic Stress, Genetic Response and Altered Permeability of E. coli

Background Membrane permeability is the first step involved in resistance of bacteria to an antibiotic. The number and activity of efflux pumps and outer membrane proteins that constitute porins play major roles in the definition of intrinsic resistance in Gram-negative bacteria that is altered under antibiotic exposure. Methodology/Principal Findings Here we describe the genetic regulation of porins and efflux pumps of Escherichia coli during prolonged exposure to increasing concentrations of tetracycline and demonstrate, with the aid of quantitative real-time reverse transcriptase-polymerase chain reaction methodology and western blot detection, the sequence order of genetic expression of regulatory genes, their relationship to each other, and the ensuing increased activity of genes that code for transporter proteins of efflux pumps and down-regulation of porin expression. Conclusions/Significance This study demonstrates that, in addition to the transcriptional regulation of genes coding for membrane proteins, the post-translational regulation of proteins involved in the permeability of Gram-negative bacteria also plays a major role in the physiological adaptation to antibiotic exposure. A model is presented that summarizes events during the physiological adaptation of E. coli to tetracycline exposure.

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

Enterobacter aerogenes is among the five most frequently isolated nosocomial pathogens in France, and this bacterium also shows increasing multidrug resistance. In this study, various E. aerogenes strains isolated from hospital units were characterized for their outer-membrane proteins, antibiotic susceptibilities (inhibition diameters and MICs) and resistance mechanisms associated with modification of envelope permeability (porin alteration and active efflux). Diminished outer-membrane permeability due to porin alterations was found in conjunction with the expression of an enzymic barrier in resistant isolates. Interestingly, changes in the functional expression of porins appeared to play a special role in susceptibility to cefepime. An active efflux to quinolones was also identified. Simultaneous changes in envelope permeability, i.e. a porin deficiency (in) and an efflux mechanism (out), were clearly evident in two clinical strains.

Membrane Permeability and Regulation of Drug “Influx and Efflux” in Enterobacterial Pathogens

In Enterobacteriaceae, membrane permeability is a key in the level of susceptibility to antibiotics. Modification of the bacterial envelope by decreasing the porin production or increasing the expression of efflux pump systems has been reported. These phenomena are frequently associated with other resistance mechanisms such as alteration of antibiotics or modification of the drug targets, in various clinical isolates showing a Multi Drug Resistant phenotype (MDR). In Escherichia coli, Enterobacter aerogenes, Klebsiella pneumoniae and Salmonella enterica several genes and external factors are involved in the emergence of MDR isolates. These bacterial isolates exhibit a noticeable reduction of functional porins per cell due to a decrease, a complete shutdown of synthesis, or the expression of an altered porin and a high expression of efflux systems (e.g. overexpression of the pump). The combined action of these mechanisms during an infection confers a significant decrease in bacterial sensitivity to antibiotherapy ensuring dissemination and colonization of the patient and favours the acquisition of additional mechanisms of resistance. MarA and ramA are involved in a complex regulation cascade controlling membrane permeability and actively participate in the triggering of the MDR phenotype. Mutations in regulator genes have been shown to induce the overproduction of efflux and the down-regulation of porin synthesis. In addition, various compounds such as salicylate, imipenem or chloramphenicol are able to activate the MDR response. This phenomenon has been observed both in vitro during culture of bacteria in the presence of drugs and in vivo during antibiotic treatment of infected patients. These effectors activate the expression of specific global regulators, marA, ramA, or target other genes located downstream in the regulation cascade.

Quinoline Derivatives as Promising Inhibitors of Antibiotic Efflux Pump in Multidrug Resistant Enterobacter Aerogenes Isolates

Efflux pumps protect the bacterial cell by expelling toxic compounds before they reach intracellular targets. Because this mechanism actively contributes to the resistance of a given bacterium to more than one class of antibiotics, molecules that are able to block the relevant efflux pump are of potential significance to combat drug resistance caused by efflux pumps. Different quinoline derivatives including alkoxy, alkylamino, thioalkoxy and chloroquinolines have been previously reported to make Enterobacter aerogenes resistant isolates that over express the mechanism of efflux, noticeably more susceptible to structurally unrelated antibiotics. In addition, various quinoline derivatives significantly increase the intracellular concentration of chloramphenicol as reported with other inhibitors, thereby suggesting the inhibition of the drug transport by AcrAB-TolC pump, which is fully active in the clinicaly resistant isolates investigated. Here, we discuss the respective properties of this molecular family, taking into account the recent insights into the structural data of AcrB pump.

Enterobacter aerogenes and Enterobacter cloacae; versatile bacterial pathogens confronting antibiotic treatment

Enterobacter aerogenes and E. cloacae have been reported as important opportunistic and multiresistant bacterial pathogens for humans during the last three decades in hospital wards. These Gram-negative bacteria have been largely described during several outbreaks of hospital-acquired infections in Europe and particularly in France. The dissemination of Enterobacter sp. is associated with the presence of redundant regulatory cascades that efficiently control the membrane permeability ensuring the bacterial protection and the expression of detoxifying enzymes involved in antibiotic degradation/inactivation. In addition, these bacterial species are able to acquire numerous genetic mobile elements that strongly contribute to antibiotic resistance. Moreover, this particular fitness help them to colonize several environments and hosts and rapidly and efficiently adapt their metabolism and physiology to external conditions and environmental stresses. Enterobacter is a versatile bacterium able to promptly respond to the antibiotic treatment in the colonized patient. The balance of the prevalence, E. aerogenes versus E. cloacae, in the reported hospital infections during the last period, questions about the horizontal transmission of mobile elements containing antibiotic resistance genes, e.g., the efficacy of the exchange of resistance genes Klebsiella pneumoniae to Enterobacter sp. It is also important to mention the possible role of antibiotic use in the treatment of bacterial infectious diseases in this E. aerogenes/E. cloacae evolution.

RamA Is an Alternate Activator of the Multidrug Resistance Cascade in Enterobacter aerogenes

ABSTRACT Multidrug resistance (MDR) in Enterobacter aerogenes can be mediated by induction of MarA, which is triggered by certain antibiotics and phenolic compounds. In this study, we identified the gene encoding RamA, a 113-amino-acid regulatory protein belonging to the AraC-XylS transcriptional activator family, in the Enterobacter aerogenes ATCC 13048 type strain and in a clinical multiresistant isolate. Overexpression of RamA induced an MDR phenotype in drug-susceptible Escherichia coli JM109 and E. aerogenes ATCC 13048, as demonstrated by 2- to 16-fold-increased resistance to β-lactams, tetracycline, chloramphenicol, and quinolones, a decrease in porin production, and increased production of AcrA, a component of the AcrAB-TolC drug efflux pump. We show that RamA enhances the transcription of the marRAB operon but is also able to induce an MDR phenotype in a mar-deleted strain. We demonstrate here that RamA is a transcriptional activator of the Mar regulon and is also a self-governing activator of the MDR cascade.

Imipenem and expression of multidrug efflux pump in Enterobacter aerogenes

Imipenem is often used to treat intensive care unit patients infected by Enterobacter aerogenes, but it is leading to an increasing number of antibiotic resistant strains. Clinical isolates and imipenem resistant variants presented a high level of resistance to beta-lactam antibiotic group and to chemically unrelated drugs. We report here that imipenem selects strains which contain active efflux pumps ejecting various unrelated antibiotics including quinolones, tetracycline, and chloramphenicol. An increase of AcrA, an efflux pump component, was observed in the imipenem resistant variants. The overexpression of marA, involved in the genetic control of membrane permeability via porin and efflux pump expression, indicated the activation of the resistance genetic cascade in imipenem resistant variants.

mar Operon Involved in Multidrug Resistance of Enterobacter aerogenes

ABSTRACT We determined the sequence of the entire marRAB operon in Enterobacter aerogenes. It is functionally and structurally analogous to the Escherichia coli operon. The overexpression of E. aerogenes MarA induces a multidrug resistance phenotype in a susceptible strain, demonstrated by a noticeable resistance to various antibiotics, a decrease in immunodetected porins, and active efflux of norfloxacin.

Identification and Evolution of Drug Efflux Pump in Clinical Enterobacter aerogenes Strains Isolated in 1995 and 2003

Background The high mortality impact of infectious diseases will increase due to accelerated evolution of antibiotic resistance in important human pathogens. Development of antibiotic resistance is a evolutionary process inducing the erosion of the effectiveness of our arsenal of antibiotics. Resistance is not necessarily limited to a single class of antibacterial agents but may affect many unrelated compounds; this is termed ‘multidrug resistance’ (MDR). The major mechanism of MDR is the active expulsion of drugs by bacterial pumps; the treatment of Gram negative bacterial infections is compromised due to resistance mechanisms including the expression of efflux pumps that actively expel various usual antibiotics (ß-lactams, quinolones, …). Methodology/Principal Findings Enterobacter aerogenes has emerged among Enterobacteriaceae associated hospital infections during the last twenty years due to its faculty of adaptation to antibiotic stresses. Clinical isolates of E. aerogenes belonging to two strain collections isolated in 1995 and 2003 respectively, were screened to assess the involvement of efflux pumps in antibiotic resistance. Drug susceptibility assays were performed on all bacterial isolates and an efflux pump inhibitor (PAßN) previously characterized allowed to decipher the role of efflux in the resistance. Accumulation of labelled chloramphenicol was monitored in the presence of an energy poison to determine the involvement of active efflux on the antibiotic intracellular concentrations. The presence of the PAßN-susceptible efflux system was also identified in resistant E. aerogenes strains. Conclusions/Significance For the first time a noticeable increase in clinical isolates containing an efflux mechanism susceptible to pump inhibitor is report within an 8 year period. After the emergence of extended spectrum ß-lactamases in E. aerogenes and the recent characterisation of porin mutations in clinical isolates, this study describing an increase in inhibitor-susceptible efflux throws light on a new step in the evolution of mechanism in E. aerogenes.

Implication of Porins in β-Lactam Resistance of Providencia stuartii

An integrative approach combining biophysical and microbiological methods was used to characterize the antibiotic translocation through the outer membrane of Providencia stuartii. Two novel members of the General Bacterial Porin family of Enterobacteriaceae, named OmpPst1 and OmpPst2, were identified in P. stuartii. In the presence of ertapenem (ERT), cefepime (FEP), and cefoxitin (FOX) in growth media, several resistant derivatives of P. stuartii ATCC 29914 showed OmpPst1-deficiency. These porin-deficient strains showed significant decrease of susceptibility to β-lactam antibiotics. OmpPst1 and OmpPst2 were purified to homogeneity and reconstituted into planar lipid bilayers to study their biophysical characteristics and their interactions with β-lactam molecules. Determination of β-lactam translocation through OmpPst1 and OmpPst2 indicated that the strength of interaction decreased in the order of ertapenem ≫ cefepime > cefoxitin. Moreover, the translocation of these antibiotics through OmpPst1 was more efficient than through OmpPst2. Heterologous expression of OmpPst1 in the porin-deficient E. coli strain BL21(DE3)omp8 was associated with a higher antibiotic susceptibility of the E. coli cells to β-lactams compared with expression of OmpPst2. All our data enlighten the involvement of porins in the resistance of P. stuartii to β-lactam antibiotics.