Showing papers by "Paul M. Tulkens published in 2013"

Antibiotic activity against small-colony variants of Staphylococcus aureus: review of in vitro, animal and clinical data

Abstract: The pathogen Staphylococcus aureus uses various strategies for persisting in the host, among which switching to a small-colony variant (SCV) phenotype is of particular biological and therapeutic significance. Phenotypically, SCVs are characterized by a slow growth rate, atypical colony morphology and unusual biochemical features, constituting a real challenge for identification by the clinical microbiology laboratory. Their metabolic defects also alter their susceptibility to antibiotics, which, combined with the ability to survive intracellularly and, for some strains, to form biofilms, largely contributes to therapeutic failures. This paper reviews the available literature on antibiotic activity against SCVs of S. aureus in vitro, in animal models and in clinics. In vitro, aminoglycosides and antifolate agents show high MICs for electron-transport-defective and thymidine-dependent SCVs, respectively. The other antibiotic classes usually show MICs comparable to those measured for the parental strains, but they are less bactericidal. Intracellularly, auxotrophs for thymidine, haemin or menadione show contrasting behaviours with respect to their response to antibiotics, resulting from differences in their intracellular fate. In animal models, SCVs often persist in various locations, including metastatic ones, in spite of the administration of active antibiotics. In healthcare, several case reports mention the selection of SCVs after prolonged administration of not only aminoglycosides and antifolate agents, but also several other antibiotic classes. Apparent eradication requires several weeks or even months of aggressive polytherapy combined, whenever possible, with surgical intervention. Further research is thus warranted for optimizing the treatment of infections caused by SCVs.

A combined pharmacodynamic quantitative and qualitative model reveals the potent activity of daptomycin and delafloxacin against Staphylococcus aureus biofilms.

Abstract: Biofilms are associated with persistence of Staphylococcus aureus infections and therapeutic failures. Our aim was to set up a pharmacodynamic model comparing antibiotic activities against biofilms and examining in parallel their effects on viability and biofilm mass. Biofilms of S. aureus ATCC 25923 (methicillin-sensitive S. aureus [MSSA]) or ATCC 33591 (methicillin-resistant S. aureus [MRSA]) were obtained by culture in 96-well plates for 6 h/24 h. Antibiotic activities were assessed after 24/48 h of exposure to concentrations ranging from 0.5 to 512 times the MIC. Biofilm mass and bacterial viability were quantified using crystal violet and the redox indicator resazurin. Biofilms stained with Live/Dead probes were observed by using confocal microscopy. Concentration-effect curves fitted sigmoidal regressions, with a 50% reduction toward both matrix and viability obtained at sub-MIC or low multiples of MICs against young biofilms for all antibiotics tested. Against mature biofilms, maximal efficacies and potencies were reduced, with none of the antibiotics being able to completely destroy the matrix. Delafloxacin and daptomycin were the most potent, reducing viability by more than 50% at clinically achievable concentrations against both strains, as well as reducing biofilm depth, as observed in confocal microscopy. Rifampin, tigecycline, and moxifloxacin were effective against mature MRSA biofilms, while oxacillin demonstrated activity against MSSA. Fusidic acid, vancomycin, and linezolid were less potent overall. Antibiotic activity depends on biofilm maturity and bacterial strain. The pharmacodynamic model developed allows ranking of antibiotics with respect to efficacy and potency at clinically achievable concentrations and highlights the potential utility of daptomycin and delafloxacin for the treatment of biofilm-related infections.

Stability and compatibility of vancomycin for administration by continuous infusion

Abstract: Methods: Vancomycin stability [defined as recovery ≥93% of the original content (validated HPLC assay)] was examined throughout the whole process of centralized preparation, storage and use in the ward by infusion for up to 48 h, with allowances for deviations from recommended practice [exposure to high temperature; use of concentrated solutions (up to 83 g/L)]. Compatibility was assessed by mimicking co-administration in a single line via Y-shaped connectors with contact of 1 h at 258C, followed by visual inspection (professional viewer), detection of particulate matter (particle analyser) and HPLC assay of vancomycin. Results: Vancomycin was stable during the whole process and also during 72 h exposure of concentrated solutions at temperatures up to 378C. Major incompatibilities were seen with b-lactams (temocillin, piperacillin/ tazobactam, ceftazidime, imipenem, cefepime and flucloxacillin) and moxifloxacin, but not with ciprofloxacin, aminoglycosides and macrolides. Propofol, valproic acid, phenytoin, theophylline, methylprednisolone and furosemide were also incompatible, whereas ketamine, sufentanil, midazolam, morphine, piritramide, nicardipine, urapidil, dopamine, dobutamine and adrenaline were compatible. No effect or incompatibility with N-acetylcysteine or amino acid solutions was detected. Conclusions: Centralized preparation of vancomycin and its use by continuous infusion in wards is safe concerning stability, but careful attention must be paid to incompatibilities. Several drugs (including all b-lactams) require distinct intravenous lines or appropriate procedures to avoid undue contact.

Pharmacodynamic evaluation of the intracellular activity of antibiotics towards Pseudomonas aeruginosa PAO1 in a model of THP-1 human monocytes.

Abstract: Pseudomonas aeruginosa invades epithelial and phagocytic cells, which may play an important role in the persistence of infection. We have developed a 24-h model of THP-1 monocyte infection with P. aeruginosa PAO1 in which bacteria are seen multiplying in vacuoles by electron microscopy. The model has been used to quantitatively assess antibiotic activity against intracellular and extracellular bacteria by using a pharmacodynamic approach (concentration-dependent experiments over a wide range of extracellular concentrations to calculate bacteriostatic concentrations [Cs] and maximal relative efficacies [Emax]; Hill-Langmuir equation). Using 16 antipseudomonal antibiotics (three aminoglycosides, nine β-lactams, three fluoroquinolones, and colistin), dose-response curves were found to be undistinguishable for antibiotics of the same pharmacological class if data were expressed as a function of the corresponding MICs. Extracellularly, all of the antibiotics reached a bacteriostatic effect at their MIC, and their Emax exceeded the limit of detection (-4.5 log(10) CFU compared to the initial inoculum). Intracellularly, Cs values remained unchanged for β-lactams, fluoroquinolones, and colistin but were approximately 10 times higher for aminoglycosides, whereas Emax values were markedly reduced (less negative), reaching -3 log(10) CFU for fluoroquinolones and only -1 to -1.5 log(10) CFU for all other antibiotics. The decrease in intracellular aminoglycoside potency (higher Cs) can be ascribed to the acid pH to which bacteria are exposed in vacuoles. The decrease in the Emax may reflect a reversible alteration of bacterial responsiveness to antibiotics in the intracellular milieu. The model may prove useful for comparison of antipseudomonal antibiotics to reduce the risk of persistence or relapse of pseudomonal infections.

A survey of beta-lactam antibiotics and vancomycin dosing strategies in intensive care units and general wards in Belgian hospitals

Abstract: Extended and continuous infusions with beta-lactam antibiotics have been suggested as a means of pharmacokinetic and pharmacodynamic optimisation of antimicrobial therapy. Vancomycin is also frequently administered in continuous infusion, although more for practical reasons. A survey was undertaken to investigate the recommendations by the local antibiotic management teams (AMTs) in Belgian acute hospitals concerning the administration (intermittent, extended or continuous infusion) and therapeutic drug monitoring of four beta-lactam antibiotics (ceftazidime, cefepime, piperacillin-tazobactam, meropenem) and vancomycin for adult patients with a normal kidney function. A structured questionnaire survey comprising three domains was developed and approved by the members of the Belgian Antibiotic Policy Coordination Committee (BAPCOC). The questionnaire was sent by e-mail to the official AMT correspondents of 105 Belgian hospitals, followed by two reminders. The response rate was 32 %, with 94 %, 59 %, 100 %, 100 % and 100 % of the participating Belgian hospitals using ceftazidime, cefepime, piperacillin-tazobactam, meropenem and vancomycin, respectively. Comparing intensive care unit (ICU) with non-ICU wards showed a higher implementation of extended or continuous infusions for ceftazidime (81 % vs. 41 %), cefepime (35 % vs. 10 %), piperacillin-tazobactam (38 % vs. 12 %), meropenem (68 % vs. 35 %) and vancomycin (79 % vs. 44 %) on the ICU wards. A majority of the hospitals recommended a loading dose prior to the first dose. For vancomycin, the loading dose and the trough target concentration were too low based on the current literature. This survey shows that extended and continuous infusions with beta-lactams and vancomycin are widely implemented in Belgian hospitals.

Activity of ceftaroline against extracellular (broth) and intracellular (THP-1 monocytes) forms of methicillin-resistant Staphylococcus aureus: comparison with vancomycin, linezolid and daptomycin

Abstract: BACKGROUND: Ceftaroline fosamil is approved for treatment of acute bacterial skin and skin structure infections caused by methicillin-resistant Staphylococcus aureus (MRSA). We examined the activity of its active metabolite (ceftaroline) against intracellular forms of S. aureus in comparison with vancomycin, daptomycin and linezolid. METHODS: Two methicillin-susceptible S. aureus (MSSA) and 11 MRSA strains with ceftaroline MICs from 0.125 to 2 mg/L [two strains vancomycin- and one strain linezolid-resistant (EUCAST interpretative criteria); VISA and cfr+] were investigated. The activity was measured in broth and after phagocytosis by THP-1 monocytes in concentration-dependent experiments (24 h of incubation) to determine: (i) relative potencies (EC(50)) and static concentrations (C(s)) (mg/L and × MIC); and (ii) relative activities at human C(max) (E(C)(max)) and maximal relative efficacies (E(max)) (change in log(10) cfu compared with initial inoculum). Ceftaroline stability and cellular accumulation (at 24 h) were measured by mass spectrometry. RESULTS: Ceftaroline showed similar activities in broth and in monocytes compared with vancomycin, daptomycin and linezolid, with no impact of resistance mechanisms to vancomycin or linezolid. For all four antibiotics, intracellular E(C)(max) and E(max) were considerably lower than in broth (∼0.5 log(10) versus 4-5 log(10) cfu decrease), but the EC(50) and C(s) showed comparatively little change (all values between ∼0.3 and ∼6× MIC). The mean cellular to extracellular ceftaroline concentration ratios (20 mg/L; 24 h) were 0.66 ± 0.05 and 0.90 ± 0.36 in uninfected and infected cells, respectively. CONCLUSION: In vitro, ceftaroline controls the growth of intracellular MRSA to an extent similar to that of vancomycin, linezolid and daptomycin for strains with a ceftaroline MIC ≤ 2 mg/L.

Analysis of the Membrane Proteome of Ciprofloxacin-Resistant Macrophages by Stable Isotope Labeling with Amino Acids in Cell Culture (SILAC)

Abstract: Overexpression of multidrug transporters is a well-established mechanism of resistance to chemotherapy, but other changes may be co-selected upon exposure to drugs that contribute to resistance. Using a model of J774 macrophages made resistant to the fluoroquinolone antibiotic ciprofloxacin and comparing it with the wild-type parent cell line, we performed a quantitative proteomic analysis using the stable isotope labeling with amino acids in cell culture technology coupled with liquid chromatography electrospray ionization Fourier transform tandem mass spectrometry (LC-ESI-FT-MS/MS) on 2 samples enriched in membrane proteins (fractions F1 and F2 collected from discontinuous sucrose gradient). Nine hundred proteins were identified with at least 3 unique peptides in these 2 pooled fractions among which 61 (F1) and 69 (F2) showed a significantly modified abundance among the 2 cell lines. The multidrug resistance associated protein Abcc4, known as the ciprofloxacin efflux transporter in these cells, was the most upregulated, together with Dnajc3, a protein encoded by a gene located downstream of Abcc4. The other modulated proteins are involved in transport functions, cell adhesion and cytoskeleton organization, immune response, signal transduction, and metabolism. This indicates that the antibiotic ciprofloxacin is able to trigger a pleiotropic adaptative response in macrophages that includes the overexpression of its efflux transporter.