In vitro activity of rifaximin against isolates from patients with small intestinal bacterial overgrowth

Rifaximin, a non-absorbable rifamycin derivative, has published clinical efficacy in the alleviation of symptoms in patients with irritable bowel syndrome (IBS). Small intestinal bacterial overgrowth (SIBO) is associated with the pathogenesis of IBS. This study describes for the first time the antimicrobial effect of rifaximin against SIBO micro-organisms from humans. Fluid was aspirated from the third part of the duodenum from 567 consecutive patients; quantitative cultures diagnosed SIBO in 117 patients (20.6%). A total of 170 aerobic micro-organisms were isolated and the in vitro efficacy of rifaximin was studied by (i) minimum inhibitory concentration (MIC) testing by a microdilution technique and (ii) time–kill assays using bile to simulate the small intestinal environment. At a breakpoint of 32 μg/mL, rifaximin inhibited in vitro 85.4% of Escherichia coli, 43.6% of Klebsiella spp., 34.8% of Enterobacter spp., 54.5% of other Enterobacteriaceae spp., 82.6% of non-Enterobacteriaceae Gram-negative spp., 100% of Enterococcus faecalis, 100% of Enterococcus faecium and 100% of Staphylococcus aureus. For the time–kill assays, 11 E. coli, 15 non-E. coli Gram-negative enterobacteria and three E. faecalis isolates were studied. Rifaximin produced a >3 log₁₀ decrease in the starting inoculum against most of the tested isolates at 500 μg/mL after 24 h of growth. The results indicate that rifaximin has a potent effect on specific small bowel flora associated with SIBO. This conclusion should be regarded in light of the considerable time–kill effect at concentrations lower than those achieved in the bowel lumen after administration of conventional doses in humans.     

Worldwide dissemination of acquired carbapenem-hydrolysing class D β-lactamases in Acinetobacter spp. other than Acinetobacter baumannii

The aim of this study was to identify acquired OXA-type carbapenemases in Acinetobacter spp. other than Acinetobacter baumannii. From a total of 453 carbapenem-susceptible and -resistant Acinetobacter isolates collected worldwide, 23 were positive for bla_OXA genes by multiplex PCR. These isolates were identified as Acinetobacter pittii (n = 18), Acinetobacter nosocomialis (n = 2), Acinetobacter junii (n = 1) and Acinetobacter genomic species 14TU/13BJ (n = 2). The bla_OXA genes and associated insertion sequence (IS) elements were sequenced by primer walking. In 11 of these isolates, sequencing of the PCR products revealed that they were false-positive for bla_OXA. The remaining 12 isolates, originating from Europe, Asia, South America, North America and South Africa, harboured OXA-23 (n = 4), OXA-58 (n = 5), OXA-40-like (n = 1) and OXA-143-like (n = 1); one A. pittii isolate harboured both OXA-23 and OXA-58. IS elements were associated with bla_OXA in 10 isolates. OXA multiplex PCR showed a high degree of false-positive results (47.8%), indicating that detection of bla_OXA in non-baumannii Acinetobacter spp. should be confirmed using additional methods.     

High-level and novel mechanisms of carbapenem resistance in Gram-negative bacteria from tertiary hospitals in Nigeria

To determine the occurrence and molecular basis of carbapenem resistance in Gram-negative bacteria from tertiary hospitals in Nigeria, 182 non-duplicate Gram-negative bacterial isolates were investigated for antimicrobial susceptibility, presence of carbapenemases (tested phenotypically and genotypically), random amplified polymorphic DNA (RAPD) typing, plasmid sizing and replicon typing. Minimum inhibitory concentrations of carbapenems showed a high degree of resistance, with 67 isolates (36.8%) being resistant to all carbapenems, of which 40 (59.7%) produced enzymes able to hydrolyse imipenem. PCR and sequencing identified only 10 isolates (5.5%) carrying known carbapenemase genes, including bla_NDM, bla_VIM and bla_GES. The majority of phenotypically carbapenem-resistant and carbapenemase-producing isolates did not carry a known carbapenemase gene. Transconjugant or transformant plasmid sizes were estimated to be 115 kb for bla_NDM- and 93 kb for bla_VIM-carrying plasmids. These plasmids were untypeable for replicon/incompatibility and transferred various other genes including plasmid-mediated quinolone resistance (PMQR) genes and bla_CTX-M-15. Typing showed that the isolates in this study were not clonally related. There is a high level of carbapenem resistance in Nigeria. As well as the globally relevant carbapenemases (bla_NDM, bla_VIM and bla_GES), there are other unknown gene(s) or variant(s) in circulation able to hydrolyse carbapenems and confer high-level resistance.     

Comparison of two DNA microarrays for detection of plasmid-mediated antimicrobial resistance and virulence factor genes in clinical isolates of Enterobacteriaceae and non-Enterobacteriaceae

A DNA microarray was developed to detect plasmid-mediated antimicrobial resistance (AR) and virulence factor (VF) genes in clinical isolates of Enterobacteriaceae and non-Enterobacteriaceae. The array was validated with the following bacterial species: Escherichiacoli (n = 17); Klebsiellapneumoniae (n = 3); Enterobacter spp. (n = 6); Acinetobacter genospecies 3 (n = 1); Acinetobacterbaumannii (n = 1); Pseudomonasaeruginosa (n = 2); and Stenotrophomonasmaltophilia (n = 2). The AR gene profiles of these isolates were identified by polymerase chain reaction (PCR). The DNA microarray consisted of 155 and 133 AR and VF gene probes, respectively. Results were compared with the commercially available Identibac AMR-ve Array Tube. Hybridisation results indicated that there was excellent correlation between PCR and array results for AR and VF genes. Genes conferring resistance to each antibiotic class were identified by the DNA array. Unusual resistance genes were also identified, such as bla_SHV-5 in a bla_OXA-23-positive carbapenem-resistant A. baumannii. The phylogenetic group of each E. coli isolate was verified by the array. These data demonstrate that it is possible to screen simultaneously for all important classes of mobile AR and VF genes in Enterobacteriaceae and non-Enterobacteriaceae whilst also assigning a correct phylogenetic group to E. coli isolates. Therefore, it is feasible to test clinical Gram-negative bacteria for all known AR genes and to provide important information regarding pathogenicity simultaneously.     

Ceftolozane/tazobactam activity tested against Gram-negative bacterial isolates from hospitalised patients with pneumonia in US and European medical centres (2012)

During 2012, a total of 2968 isolates were consecutively collected from 59 medical centres in the USA and 15 European countries from hospitalised patients with pneumonia. Ceftolozane/tazobactam (tazobactam at a fixed concentration of 4 mg/L) and comparator agents were tested by reference methods, and MIC endpoints were interpreted by CLSI (2013) and EUCAST (2013) breakpoint criteria. Pseudomonas aeruginosa was the most common isolated pathogen (1019 strains; 34.3%), and ceftolozane/tazobactam was the most active β-lactam tested against P. aeruginosa (MIC_50/90, 0.5/4 mg/L; 94.1% inhibited at ≤8 mg/L). P. aeruginosa exhibited moderate susceptibility to meropenem (MIC_50/90, 0.5/>8 mg/L; 73.7% susceptible), ceftazidime (MIC_50/90, 2/>32 mg/L; 73.6% susceptible), cefepime (MIC_50/90, 4/>16 mg/L; 76.5% susceptible), piperacillin/tazobactam (MIC_50/90, 8/>64 mg/L; 69.5% susceptible), levofloxacin [MIC_50/90, 0.5/>4 mg/L; 69.9/61.0% susceptible (CLSI/EUCAST criteria)] and gentamicin (MIC_50/90, 2/>8 mg/L; 80.7% susceptible). Ceftolozane/tazobactam exhibited activity against many ceftazidime-non-susceptible, meropenem-non-susceptible and piperacillin/tazobactam-non-susceptible, multidrug-resistant (MDR) and extensively drug-resistant (XDR) P. aeruginosa isolates. Ceftolozane/tazobactam was active (MIC_50/90, 0.25/4 mg/L; 94.6% inhibited at ≤8 mg/L) against 1530 Enterobacteriaceae, including activity against many MDR and XDR strains. MDR and XDR prevalence varied widely between countries both for P. aeruginosa (24.1% MDR and 17.1% XDR overall) and Enterobacteriaceae (15.4% MDR and 2.7% XDR overall). All β-lactams had limited activity against Acinetobacter spp. and Stenotrophomonas maltophilia. Ceftolozane/tazobactam demonstrated greater in vitro activity than currently available cephalosporins, carbapenems and piperacillin/tazobactam when tested against P. aeruginosa. In addition, ceftolozane/tazobactam demonstrated greater activity than contemporary cephalosporins and piperacillin/tazobactam when tested against most Enterobacteriaceae.     

Shewanella species as the origin of blaOXA-48 genes: insights into gene diversity,associated phenotypes and possible transfer mechanisms

Chromosome-encoded beta-lactamases of Shewanella spp. have been indicated as probable progenitors of bla_OXA-48-like genes. However, these have been detected in few Shewanella spp. and dissemination mechanisms are unclear. Thus, our main objective was to confirm the role of Shewanella species as progenitors of bla_OXA-48-like genes.In silico analysis of Shewanella genomes was performed to detect bla_OXA-48-like genes and context, and 43 environmental Shewanella spp. were characterised. Clonal relatedness was determined by BOX-PCR. Phylogenetic affiliation was assessed by 16S rDNA and gyrB sequencing. Antibiotic susceptibility phenotypes were determined. The bla_OXA-48-like genes and genetic context were inspected by PCR, hybridisation and sequence analysis. Gene variants were cloned in Escherichia coli and MICs were determined. Shewanella isolates were screened for integrons, plasmids and insertion sequences.Analysis of Shewanella spp. genomes showed that putative bla_OXA-48-like is present in the majority and in an identical context. Isolates presenting unique BOX profiles affiliated with 11 Shewanella spp. bla_OXA-48-like genes were detected in 22 isolates from 6 species. Genes encoded enzymes identical to OXA-48, OXA-204, OXA-181, and 7 new variants differing from OXA-48 from 2 to 82 amino acids. IS1999 was detected in 24 isolates, although not in the vicinity of bla_OXA-48 genes. Recombinant E. coli strains presented altered MICs.The presence/absence of bla_OXA-48-like genes was species-related. Gene variants encoded enzymes with hydrolytic spectra similar to OXA-48-like from non–shewanellae. From the mobile elements previously described in association with bla_OXA-48-like genes, only the IS1999 was found in Shewanella, which indicates its relevance in bla_OXA-48-like genes transfer to other hosts.     

Alterations in acetylcholine,PGE2 and IL6 release from urothelial cells following treatment with pyocyanin and lipopolysaccharide

The effects of pseudomonal virulence factor pyocyanin, and LPS from Pseudomonas aeruginosa and Escherichia coli on urothelial mediator release and cytokine production were examined. RT4 urothelial cells were treated with pyocyanin (1–100 μM) or LPS (1–100 ng/mL) for 24-h. Effects were measured in terms of changes in cell viability, basal and stretch-induced acetylcholine (Ach) and PGE₂ release, and inflammatory cytokines (IL-6 and IL-12) production. Twenty-four hour pyocyanin (100 μM) treatment significantly decreased urothelial cell viability, while stretch-induced Ach release response was inhibited. E. coli LPS (100 ng/mL) produced a similar response with an additional significant increase in basal Ach release. All three virulence factors significantly increased urothelial PGE₂ release; under basal release for pyocyanin (100 μM), stretch-induced release for pseudomonal LPS (?10 ng/mL) and both basal and stimulated release for E. coli LPS (?10 ng/mL). IL-6 and IL-12 were not detected in control samples, however 24 h treatment with pyocyanin (100 μM) or LPS (100 ng/mL) resulted in IL-6 release from urothelial cells. The changes in urothelial Ach and PGE₂, and release of inflammatory cytokine IL-6 induced by exposure to the bacterial virulence factors may play a role in the symptoms of pain and urinary urgency experienced with urinary tract infections.     

Patterns of antimicrobial therapy in severe nosocomial infections: empiric choices,proportion of appropriate therapy,and adaptation rates—a multicentre,observational survey in critically ill patients

This prospective, observational multicentre (n = 24) study investigated relationships between antimicrobial choices and rates of empiric appropriate or adequate therapy, and subsequent adaptation of therapy in 171 ICU patients with severe nosocomial infections. Appropriate antibiotic therapy was defined as in vitro susceptibility of the causative pathogen and clinical response to the agent administered. In non-microbiologically documented infections, therapy was considered adequate in the case of favourable clinical response <5 days. Patients had pneumonia (n = 127; 66 ventilator-associated), intra-abdominal infection (n = 23), and bloodstream infection (n = 21). Predominant pathogens were Pseudomonas aeruginosa (n = 29) Escherichia coli (n = 26), Staphylococcus aureus (n = 22), and Enterobacter aerogenes (n = 21). In 49.6% of infections multidrug-resistant (MDR) bacteria were involved, mostly extended-spectrum β-lactamase (EBSL)-producing Enterobacteriaceae and MDR non-fermenting Gram-negative bacteria. Prior antibiotic exposure and hospitalisation in a general ward prior to ICU admission were risk factors for MDR. Empiric therapy was appropriate/adequate in 63.7% of cases. Empiric schemes were classified according to coverage of (i) ESBL-producing Enterobacteriaceae and non-fermenting Gram-negative bacteria (“meropenem-based”), (ii) non-fermenting Gram-negative bacteria (schemes with an antipseudomonal agent), and (iii) first-line agents not covering ESBL-Enterobacteriaceae nor non-fermenting Gram-negative bacteria. Meropenem-based schemes allowed for significantly higher rates of appropriate/adequate therapy (p < 0.001). This benefit remained when only patients without risk factors for MDR were considered (p = 0.021). In 106 patients (61%) empiric therapy was modified: in 60 cases following initial inappropriate/inadequate therapy, in 46 patients in order to refine empiric therapy. In this study reflecting real-life practice, first-line use of meropenem provided significantly higher rates of the appropriate/adequate therapy, irrespective of presence of risk factors for MDR.     

Xenopus laevis oocytes expressing human P-glycoprotein: Probing trans- and cis-inhibitory effects on [3H]vinblastine and [3H]digoxin efflux

P-glycoprotein (P-gp; MDR1) recognizes and actively transports many structurally diverse compounds (hydrophobic neutral and cationic). We studied MDR1-mediated drug transport using a high-throughput (96-well) oocyte expression system. MDR1-expressing oocytes contained sufficient ATP levels to conduct fundamental efflux studies; the optimal experimental temperature was 25 °C. [³H]Vinblastine efflux by MDR1-expressing oocytes was detectable and afforded a K_m of 145.5 ± 25.4 μM. [³H]Vinblastine (5.6 ± 0.3 μM) and [³H]digoxin (1.0 ± 0.1 μM) were individually injected into MDR1-expressing oocytes and their efflux monitored. Quinidine and verapamil, known MDR1 substrates/inhibitors, showed trans-inhibition on MDR1-mediated [³H]vinblastine and [³H]digoxin efflux. Conversely, doxorubicin demonstrated cis-inhibition without trans-inhibition on MDR1-mediated [³H]vinblastine efflux. The MDR1-expressing oocyte system offers researchers with an alternative in vitro method to screen compounds and may allow one to probe P-gp drug–drug and/or drug–inhibitor interactions.     

Assessment of bacterial quality of honey produced in Tamale metropolis (Ghana)

The bacterial quality of honey from different production sites within Tamale metropolis, Ghana, was estimated using standard microbiological methods. Honey samples were bought from six different production sites within Tamale metropolis and labeled. Samples that were taken from location B recorded the least mean bacterial count of 6.0 × 10⁴ colony forming units/mL with samples taken from location D showing the highest, 1.1 × 10⁵ colony forming units/mL. However, samples from production sites E and F recorded no bacteria growth. Bacteria isolated included Escherichia coli, Staphylococcus spp., Shigella spp., Streptococcus spp., and Bacillus spp. The pH values of honey samples from the various locations were found to be directly correlated to the average bacteria load. The variation in bacteria load and species at the various production sites and the absence of bacteria growth in two production sites is an indication of the differences in production practices, as well as hygienic conditions at these sites. The presence of these isolates is a cause for concern as pathogenic strains of these bacteria can cause serious health related problems.     

Toxicity evaluation of CdTe quantum dots with different size on Escherichia coli

Quantum dots (QDs) have a great potential for applications in nanomedicine. However, a few studies showed that they also exhibited toxicity. We used Escherichia coli (E. coli) as the model to study the effect of CdTe QDs on the cell growth by microcalorimetric technique, optical density (OD₆₀₀) and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectra. Three size aqueous-compatible CdTe QDs with maximum emission of 543 nm (green-emitting QDs, GQDs), 579 nm (yellow-emitting QDs, YQDs) and 647 nm (red-emitting QDs, RQDs) were tested. The growth rate constants (k) and half-inhibiting concentration (IC₅₀) were calculated from the microcalorimetric data. The results indicated that CdTe QDs exhibited a dose-dependent inhibitory effect on cell growth. The order of toxicity is GQDs > YQDs > RQDs. The smaller the particle size of QDs is, the more toxicity it is. ATR-FTIR spectra indicated that the outer membrane of the cell was changed or damaged by the QDs, which may induce QDs and harmful by-products to enter into the cells. These could be one of the reasons that CdTe QDs have cytotoxic effects on E. coli.     

N-(3,4-dimethoxyphenethyl)-4-(6,7-dimethoxy-3,4-dihydroisoquinolin-2[1H]-yl)-6,7-dimethoxyquinazolin-2-amine (CP-100,356) as a “chemical knock-out equivalent” to assess the impact of efflux transporters on oral drug absorption in the rat

The utility of the diaminoquinazoline derivative CP-100,356 as an in vivo probe to selectively assess MDR1/BCRP-mediated drug efflux was examined in the rat. CP-100,356 was devoid of inhibition (IC₅₀ >50 µM) against major human P450 enzymes including P4503A4. In human MDR1-transfected MDCKII cells, CP-100,356 inhibited acetoxymethyl calcein (calcein-AM) uptake (IC₅₀ ～0.5 ± 0.07 µM) and digoxin transport (IC₅₀ ～1.2 ± 0.1 µM). Inhibition of prazosin transport (IC₅₀ ～1.5 ± 0.3 µM) in human BCRP-transfected MDCKII cells by CP-100,356 confirmed the dual MDR1/BCRP inhibitory properties. CP-100,356 was a weak inhibitor of OATP1B1 (IC₅₀ ～66 ± 1.1 µM) and was devoid of MRP2 inhibition (IC₅₀ >15 µM). In vivo inhibitory effects of CP-100,356 in rats were examined after coadministration with MDR1 substrate fexofenadine and dual MDR1/BCRP substrate prazosin. Coadministration with increasing doses of CP-100,356 resulted in dramatic increases in systemic exposure of fexofenadine (36- and 80-fold increase in C_max and AUC at a CP-100,356 dose of 24 mg/kg). Significant differences in prazosin pharmacokinetics were also discernible in CP-100,356-pretreated rats as reflected from a 2.6-fold increase in AUC. Coadministration of CP-100,356 and P4503A substrate midazolam did not result in elevations in systemic exposure of midazolam in the rat. The in vivo methodology should have utility in drug discovery in selective and facile assessment of the role of MDR1 and BCRP efflux transporters in oral absorption of new drug candidates. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4914–4927, 2009     

Ceftaroline activity tested against uncommonly isolated Gram-positive pathogens: report from the SENTRY Antimicrobial Surveillance Program (2008–2011)

Ceftaroline was tested against 1859 clinically significant Gram-positive organisms from uncommonly isolated species. The organisms (31 species/groups) were collected from 133 medical centres worldwide over a 4-year period (2008–2011). Coagulase-negative staphylococci were generally susceptible to ceftaroline, with MIC₅₀ values (minimum inhibitory concentration required to inhibit 50% of the isolates) of 0.06–0.5 mg/L. Ceftaroline was active against Micrococcus spp. [minimum inhibitory concentration required to inhibit 90% of the isolates (MIC₉₀) = 0.06 mg/L], but showed more limited potency versus some Corynebacterium spp. and Listeria monocytogenes isolates. Ceftaroline was active against all β-haemolytic streptococci and viridans group streptococcal species/groups listed, with MIC₅₀ and MIC₉₀ values ranging from ≤0.015 mg/L to 0.03 mg/L and from ≤0.015 mg/L to 0.5 mg/L, respectively. Based on these in vitro findings, ceftaroline may have a potential role in the treatment of infections caused by these rarer species as guided by reference MIC test results.     

Extended-spectrum cephalosporins and the inoculum effect in tests with CTX-M-type extended-spectrum β-lactamase-producing Escherichia coli: Potential clinical implications of the revised CLSI interpretive criteria

Based on the new recommendations of the Clinical and Laboratory Standards Institute (CLSI), the revised cephalosporin breakpoints may result in many CTX-M-producing Escherichia coli being reported as susceptible to ceftazidime. We determined the activity of ceftazidime and other parenteral β-lactam agents in standard- and high-inoculum minimum inhibitory concentration (MIC) tests against CTX-M-producing E. coli isolates. Antimicrobial susceptibility was determined using a broth microdilution MIC method with inocula that differed 100-fold in density. An inoculum effect was defined as an eight-fold or greater increase in MIC on testing with the higher inoculum. When the revised CLSI ceftazidime breakpoint of 4 μg/mL was applied, 34 (34.3%) of the 99 CTX-M-producers tested were susceptible. More specifically, for 42 CTX-M-14-producing E. coli isolates, 32 (76.2%) were susceptible at 4 μg/mL. Cefotaxime, ceftazidime, cefepime and piperacillin/tazobactam were found to be associated with inoculum effects in 100% of the evaluable tests for extended-spectrum β-lactamase-producing E. coli isolates. The MIC₅₀ (MIC required to inhibit 50% of isolates) of ceftazidime was 16 μg/mL in the standard-inoculum tests and >512 μg/mL in the high-inoculum tests. In the high-inoculum tests including isolates encoding CTX-M-14, ceftazidime was dramatically affected, with susceptibility decreasing from 82.1% of isolates inhibited at 4 μg/mL in the standard-inoculum tests to 0% at high inoculum. Although further studies may demonstrate that ceftazidime has a role in the treatment of infections caused by these organisms, we suggest that until more data become available, clinicians should be cautious about treating serious CTX-M-producing E. coli infections with ceftazidime or cefepime.     

Influence of experimentally induced fever on the disposition of cefpirome in buffalo calves

The influence of Escherichia coli endotoxin-induced fever on the disposition of cefpirome was investigated in five male buffalo calves following a single intravenous dose of 10 mg kg⁻¹. Blood samples were collected from 1 min to 24 h of drug administration. The drug concentration in plasma was estimated by microbiological assay using E. coli as a test organism. The disposition of cefpirome followed two-compartment open model and the drug was detected above the minimum inhibitory concentration in plasma up to 12 h. The Vd_area and AUC were 0.75 ± 0.01 L kg⁻¹ and 35.1 ± 0.46 μg ml⁻¹ h, respectively. The elimination half-life of 1.81 ± 0.009 h and Cl_B of 0.29 ± 0.004 L kg⁻¹ h⁻¹ reflected rapid elimination and body clearance of cefpirome in febrile buffalo calves. Based on the results, a satisfactory dosage regimen of cefpirome in febrile buffalo calves was calculated to be 6 mg kg⁻¹ to be repeated at 8 h intervals.     

Rifaximin: a review of its use in the management of traveller's diarrhoea

Oral rifaximin, a semisynthetic rifamycin derivative, is an effective and well tolerated antibacterial for the management of adults with non-invasive traveller's diarrhoea. Rifaximin was significantly more effective than placebo and no less effective than ciprofloxacin in reducing the duration of diarrhoea after treatment initiation for illness contracted during travel to diverse geographic locations. While rifaximin is effective in patients with Escherichia coli-predominant traveller's diarrhoea, it appears ineffective in patients infected with inflammatory or invasive enteropathogens. Rifaximin has a broad spectrum of antibacterial activity in vitro and undergoes negligible systemic absorption (<0.4%). In contrast to systemically absorbed antibacterials, such as the fluoroquinolones and macrolides, the acquisition of resistance to rifaximin would have limited consequences for global public health, as rifaximin has no role in the management of systemic infections. Rifaximin shows promise as chemoprophylaxis against traveller's diarrhoea and is a valuable new option for the management of traveller's diarrhoea caused by non-invasive bacterial strains.     

Release of Prednisolone and Inulin from a New Calcium-Alginate Chitosan-Coated Matrix System for Colonic Delivery

Putative colonic release formulations of calcium (Ca)-alginate coated with chitosan containing two different actives, prednisolone and inulin, were prepared in three different sizes, beads (D₅₀ = 2104 μm) and microparticles (D₅₀ = 354 and 136 μm). The formulations were tested in standard phosphate buffer and biorelevant Krebs bicarbonate buffer at pH 7.4, and were further evaluated in the presence of the bacterium E. coli. Product yield and encapsulation were higher with prednisolone than with inulin. In Krebs bicarbonate buffer, a clear relationship between particle size and prednisolone release was observed. In contrast, release of inulin was independent of the particle size. In phosphate buffer, the particles eroded quickly, whereas in Krebs buffer, the particles swelled slowly. The difference in behavior can be attributed to the formation of calcium phosphate in the phosphate buffer medium, which in turn weakens the Ca-alginate matrix core. In the presence of E. coli, the formulations were fermented and the release of prednisolone was accelerated. In conclusion, the buffer media affects formulation behavior and drug release, with the bicarbonate media providing a better simulation of in vivo behavior. Moreover, the susceptibility of the formulations to bacterial action indicates their suitability as carriers for colonic drug delivery.     

Evaluation of dalbavancin,tigecycline, minocycline,tetracycline, teicoplanin and vancomycin against community-associated and multidrug-resistant hospital-associated meticillin-resistant Staphylococcus aureus

Dalbavancin is an investigational semisynthetic lipoglycopeptide that is structurally related to teicoplanin. We examined the activity of dalbavancin (DAL) compared with tigecycline (TIG), minocycline (MIN), tetracycline (TET), teicoplanin (TEC) and vancomycin (VAN) against community-associated meticillin-resistant Staphylococcus aureus (CA-MRSA) and multidrug-resistant hospital-associated meticillin-resistant S. aureus (MDR HA-MRSA). Two hundred and twenty clinical isolates of CA-MRSA and MDR HA-MRSA were utilised. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were determined according to Clinical and Laboratory Standards Institute guidelines. Selective time–kill studies were performed against CA-MRSA and MDR HA-MRSA in triplicate. Overall, DAL exhibited low MIC values against all strains of MRSA. Time–kill studies with CA-MRSA demonstrated DAL = VAN > TIG > MIN = TEC > TET (P < 0.006), and with MDR HA-MRSA demonstrated DAL = VAN = TEC > TIG = MIN > TET (P > 0.05). DAL demonstrated potent activity against clinical strains of CA-MRSA and MDR HA-MRSA, including tetracycline-resistant S. aureus.     

Chromosomal location of blaCTX-M genes in clinical isolates of Escherichia coli from Germany,The Netherlands and the UK

This study aimed to detect and characterise clinical Escherichia coli isolates suspected of carrying chromosomally encoded CTX-M enzymes. Escherichia coli (n = 356) obtained in Germany, The Netherlands and the UK (2005–2009) and resistant to third-generation cephalosporins were analysed for the presence of ESBL-/AmpC-encoding genes within the European SAFEFOODERA-ESBL project. β-Lactamases and their association with IS26 and ISEcp1 were investigated by PCR. Isolates were typed by phylogenetic grouping, MLST and PFGE. Plasmids were visualised by S1 nuclease PFGE, and the location of bla_CTX-M genes was determined by Southern hybridisation of XbaI-, S1- and I-CeuI-digested DNA. ESBL enzymes could not be located on plasmids in 17/356 isolates (4.8%). These 17 isolates, from different countries and years, were ascribed to phylogenetic groups D (9), B2 (6) and B1 (2), and to seven sequence types, with ST38 being the most frequent (7 phylogroup D isolates). Eleven isolates produced CTX-M-15. bla_CTX-M-15 genes were associated with ISEcp1. The remaining isolates expressed the CTX-M group 9 β-lactamases CTX-M-14 (4), CTX-M-9 (1) and CTX-M-51 (1). bla_CTX-M probes hybridised with I-CeuI- and/or XbaI-digested DNA, but not with S1-digested DNA, corroborating their chromosomal location. To summarise, only 4.8% of a large collection of ESBL-producing E. coli isolates harboured chromosomal bla_CTX-M genes. These isolates were of human origin and belonged predominantly to ST38 and ST131, which possibly indicates the role of these sequence types in this phenomenon. However, heterogeneity among isolates was found, suggesting that their spread is not only due to the dispersion of successful E. coli clones.     

Comparison of bidirectional lamivudine and zidovudine transport using MDCK,MDCK–MDR1, and Caco-2 cell monolayers

Bidirectional transport studies were conducted using Caco-2, MDCK, and MDCK–MDR1 to determine P-gp influences in lamivudine and zidovudine permeability and evaluate if zidovudine permeability changes with the increase of zidovudine concentration and/or by association of lamivudine. Transport of lamivudine and zidovudine separated and coadministrated across monolayers based on these cells were quantified using LC–MS–MS. Drug efflux by P-gp was inhibited using GG918. Bidirectional transport of lamivudine and zidovudine was performed across MDCK–MDR1 and Caco-2 cells. Statistically significant transport decrease in B → A direction was observed using MDCK–MDR1 for zidovudine and MDCK–MDR1 and Caco-2 for lamivudine. Results show increased transport in B → A and A → B directions as concentration increases but data from P_app increase in both directions for both drugs in Caco-2, decrease in MDCK, and does not change significantly in MDCK–MDR1. Zidovudine transport in A → B direction increases when coadministrated with increasing lamivudine concentration but does not change significantly in B → A direction. Zidovudine and lamivudine are P-gp substrates, but results assume that P-gp does not affect significantly lamivudine and zidovudine. Their transport in monolayers based on Caco-2 cells increase proportionally to concentration (in both directions) and zidovudine transport in Caco-2 cell monolayer does not show significant changes with lamivudine increasing concentrations. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4413–4419, 2009