Efflux Pump, the Masked Side of ß-Lactam Resistance in Klebsiella pneumoniae Clinical Isolates

International audienceBACKGROUND: Beta-lactamase production and porin decrease are the well-recognized mechanisms of acquired beta-lactam resistance in Klebsiella pneumoniae isolates. However, such mechanisms proved to be absent in K. pneumoniae isolates that are non susceptible to cefoxitin (FOX) and susceptible to amoxicillin+clavulanic acid in our hospital. Assessing the role of efflux pumps in this beta-lactam phenotype was the aim of this study. METHODOLOGY/FINDINGS: MICs of 9 beta-lactams, including cloxacillin (CLX), and other antibiotic families were tested alone and with an efflux pump inhibitor (EPI), then with both CLX (subinhibitory concentrations) and EPI against 11 unique bacteremia K. pneumoniae isolates displaying the unusual phenotype, and 2 ATCC strains. CLX and EPI-dose dependent effects were studied on 4 representatives strains. CLX MICs significantly decreased when tested with EPI. A similar phenomenon was observed with piperacillin+tazobactam whereas MICs of the other beta-lactams significantly decreased only in the presence of both EPI and CLX. Thus, FOX MICs decreased 128 fold in the K. pneumoniae isolates but also 16 fold in ATCC strain. Restoration of FOX activity was CLX dose-dependent suggesting a competitive relationship between CLX and the other beta-lactams with regard to their efflux. For chloramphenicol, erythromycin and nalidixic acid whose resistance was also due to efflux, adding CLX to EPI did not increase their activity suggesting differences between the efflux process of these molecules and that of beta-lactams. CONCLUSION: This is the first study demonstrating that efflux mechanism plays a key role in the beta-lactam susceptibility of clinical isolates of K. pneumoniae. Such data clearly evidence that the involvement of efflux pumps in beta-lactam resistance is specially underestimated in clinical isolates

TRY plant trait database – enhanced coverage and open access

Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

Detection of bacterial DNA in serum and ascitic fluid of asymptomatic outpatients with cirrhosis and non-neutrocytic ascites

Background and aims: Bacterial DNA (bactDNA) has been found in serum and ascitic fluid (AF) of 30-40% of hospitalized patients with cirrhosis and non-neutrocytic ascites, but its prevalence in outpatients is unknown. The aim of this prospective study was to investigate the presence of bactDNA in AF and serum among cirrhotic outpatients with non-neutrocytic ascites. Methods: Thirty-one consecutive patients with cirrhosis and non-neutrocytic ascites, who underwent therapeutic paracentesis in our outpatient clinic, were enrolled over a 13-week period. Of these patients, 13 had a single paracentesis and 18 patients had several consecutive paracenteses (2-10) over the study period. Overall, 98 serum and non-neutrocytic AF specimens were obtained and tested for the presence of bactDNA by polymerase chain reaction amplification of the 16S ribosomal RNA gene. Results: The main causes of cirrhosis were alcohol (53.5%) and hepatitis C (30%). The median MELD score was 16 and there were 54.8% Child-Pugh C patients. BactDNA was negative in all samples from 28 of the 31 patients, including 15 patients with several paracentesis. One patient had a single AF sample culture positive and bactDNA positive for Streptococcus mitis, whereas the simultaneous blood sample was negative. For each of the last two patients, DNA from Lactococcus lactis was detected in a single blood sample but not in the simultaneous AF sample. Conclusions: In contrast to that reported previously in hospitalized patients, bactDNA is rarely detected in serum and AF of outpatients with cirrhosis and non-neutrocytic ascites. © 2011 John Wiley & Sons A/S.SCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe

MICs of cefoxitin and nalidixic acid tested alone and with inhibitor efflux (PAβN) and sub-inhibitory concentrations of cloxacillin towards 4 representative <i>K. pneumoniae</i> strains.

<p>FOX: cefoxitin, NAL: nalidixic acid, CLX: cloxacillin, *: 0.096 mM (50 mg/L), ^♦: 1/20 CLX MIC.</p

MICs of various antibiotics tested alone and with efflux inhibitor PAβN* towards 11 <i>K. pneumoniae</i> clinical isolates and ATCC strains.

<p>*: 0.096 mM (50 mg/L), CMP: chloramphenicol, NAL: nalidixic acid, OFX: ofloxacin, AMX: amoxicillin, AMC: amoxicillin+clavulanic acid, PIP: piperacillin, TZP: piperacillin+tazobactam, FOX: cefoxitin, CAZ: ceftazidime, FEP: cefepime, ERT: ertapenem, CLX: cloxacillin, ERY: erythromicin, +: with PAβN, −: without PAβN, nd: not determined.</p

MICs of cefoxitin for two <i>K. pneumoniae</i> isolates (KpBj 7 and 9) and strain ATCC 11296 measured in the presence of efflux inhibitor PAβN (0.096 mM) and increased concentrations of cloxacillin (CLX).

<p>MIC percent (MIC%) represents the decrease in cefoxitin MIC in the presence of different CLX concentrations (plotted as CLX (mM)) compared with MIC measured without PAßN and CLX.</p

Detection of AcrA and TolC in <i>Klebsiella pneumoniae</i> isolates.

<p>Top part, immunodetection was carried out with antiserum directed against denatured AcrA; bottom part, immunodetection was carried out with antiserum directed against denatured TolC porin. WT, <i>E. aerogenes</i> wild type strain producing normal level of AcrA and TolC; <i>acrA</i>, <i>acrA</i> deleted strain; <i>tolC</i>, <i>tolC</i> deleted strain <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0004817#pone.0004817-Pradel1" target="_blank">[16]</a>. a and b indicate the migration of the molecular weight marker 30 kD and 43 kD, respectively. ATCC, ATCC11296, lanes 1 to 11, strain KPBj 1 to strain KPBj 11.</p