Trends in the susceptibility of methicillin-resistant Staphylococcus aureus to nine antimicrobial agents, including ceftobiprole, nemonoxacin, and tyrothricin: results from the Tigecycline In Vitro Surveillance in Taiwan (TIST) study, 2006-2010.

This study investigated the in vitro susceptibilities of methicillin-resistant Staphylococcus aureus (MRSA) to nine antimicrobial agents in Taiwan. A total of 1,725 isolates were obtained from 20 hospitals throughout Taiwan from 2006 to 2010. The minimum inhibitory concentrations (MICs) of the nine agents were determined by the agar dilution method. The MICs of mupirocin and tyrothricin were determined for 223 MRSA isolates collected from 2009 to 2010. For vancomycin, 99.7 % were susceptible; however, 30.0 % (n = 517) exhibited MICs of 2 µg/ml and 0.3 % (n = 6) demonstrated intermediate susceptibility (MICs of 4 µg/ml). Nearly all isolates (≥ 99.9 %) were susceptible to teicoplanin, linezolid, and daptomycin. The MIC90 values were 2 µg/ml for ceftobiprole and 1 µg/ml for nemonoxacin. The MIC90 values of mupirocin and tyrothricin were 0.12 and 4 µg/ml, respectively. MIC creep was noted for daptomycin during this period, but not for vancomycin, teicoplanin, linezolid, or tigecycline. For isolates with vancomycin MICs of 2 µg/ml, the MIC90 values were 2 µg/ml for teicoplanin, 0.5 µg/ml for daptomycin, and 0.5 µg/ml for tigecycline. Those values were four- to eight-fold higher than those among isolates with vancomycin MICs of 0.5 µg/ml (2, 0.06, and 0.12 µg/ml, respectively). Of the nine MRSA isolates exhibiting non-susceptibility to vancomycin (n = 6), teicoplanin (n = 1), daptomycin (n = 2), or tigecycline (n = 1), all had different pulsotypes, indicating the absence of intra-hospital or inter-hospital spread. The presence of a high proportion of MRSA isolates with elevated MICs (2 µg/ml) and MIC creep of daptomycin might alert clinicians on the therapy for serious MRSA infections in Taiwan.

Optical negative refraction in ferrofluids with magnetocontrollability.

We numerically demonstrate optical negative refraction in ferrofluids containing isotropic Fe3O4 nanoparticles, each having an isotropic Ag shell, in the presence of an external dc magnetic field H. The all-angle broadband optical negative refraction with magnetocontrollability arises from H-induced chains or columns. They result in hyperbolic equifrequency contour for transverse magnetic waves propagating in the system. The finite element simulations verify the analyses using the effective medium approximation. Experimental demonstration and potential applications are suggested and discussed.

Dynamic polarizability of rotating particles in electrorheological fluids.

A rotating particle in electrorheological (ER) fluid leads to a displacement of its polarization charges on the surface which relax toward the external applied field E0, resulting in a steady-state polarization at an angle with respect to E0. This dynamic effect has shown to affect the ER fluid properties dramatically. In this paper, we develop a dynamic effective medium theory (EMT) for a system containing rotating particles of finite volume fraction. This is a generalization of established EMT to account for the interactions between many rotating particles. While the theory is valid for three dimensions, the results in a special two-dimensional configuration show that the system exhibits an off-diagonal polarization response in addition to a diagonal polarization response, which resembles the classic Hall effect. The diagonal response monotonically decreases with increasing rotational speed, whereas the off-diagonal response exhibits a maximum at a reduced rotational angular velocity omega0, compared to the case of isolated rotating particles. This implies a way of measurement on the interacting relaxation time. The dependencies of the diagonal and off-diagonal responses on various factors, such as omega0, the volume fraction, and the dielectric contrast, are discussed.

Electromagnetic transparency by coated spheres with radial anisotropy.

We establish an account of electromagnetic scattering by coated spheres with radial dielectric and magnetic anisotropy. Within full-wave scattering theory, we show that the total scattering cross section Qs is strongly dependent on both the dielectric anisotropy and magnetic anisotropy. As a consequence, by a suitable adjustment of the radius ratio, one may make the anisotropic coated particle nearly transparent or invisible. In the quasistatic case, we take one step forward to derive the effective permittivity and permeability for the coated particle, and the near-zero scattering radius ratio can be well described within effective medium theory. To one's interest, the introduction of radial anisotropy is helpful to achieve better transparency quality such as a much smaller Qs and wider range of near-zero scattering ratio. Moreover, when the coated particle is anisotropic, the position of the near-zero scattering radius ratio can be tunable, resulting in a tunable electromagnetic cloaking.

Dielectrophoresis of an inhomogeneous colloidal particle under an inhomogeneous field: a first-principles approach.

In reality, colloidal particles often possess an arbitrary inhomogeneity profile. We present a first-principles approach to dielectrophoresis of such an inhomogeneous colloidal particle under an inhomogeneous field of an oscillating electric dipole moment. For numerical simulations, we treat the inhomogeneous particle as a specific graded one with a physically motivated dielectric model and conductivity profile. We find that both multipolar interactions and spatial fluctuations inside the particle can affect the dielectrophoretic spectrum of the particle significantly.

Central venous catheter-related Stenotrophomonas maltophilia bacteraemia and associated relapsing bacteraemia in haematology and oncology patients.

This retrospective study investigated the clinical significance and impact of Stenotrophomonas maltophilia bacteraemia in 49 haematology and oncology patients at a tertiary referral medical centre in Taipei between July 1999 and December 2003. Sixteen patients had 24 episodes of central venous catheter (CVC)-related bacteraemia, with the main clinical characteristics being a nosocomial bacteraemia (100%), preceding antibiotic therapy (94%), bacteraemia developed in a general ward (87%), immunosuppressive therapy (75%), in-situ CVC-related bacteraemia (75%), and neutropenia (63%). Only four (25%) patients had inflammatory signs at the CVC site following diagnosis of bacteraemia. Five patients had recurrent bacteraemia, with risk-factors being long-lasting (>10 days) neutropenia (p 0.036) and an initial failure to remove the CVC (p 0.001). These cases did not involve re-infection, as the same S. maltophilia strain was identified following random amplified polymorphic DNA (RAPD) analysis of the initial and subsequent isolates. However, relapses could occur after long latency periods (maximum, 200 days). Most patients were cured after removal of the CVC, even without appropriate antibiotic treatment. Physicians should have a high index of suspicion for CVC-related bacteraemia with haematology and oncology patients with CVCs and S. maltophilia bacteraemia. In addition to appropriate antibiotic therapy, removal of the CVC is crucial for successful treatment of CVC-related S. maltophilia bacteraemia and prevention of relapses.

Dynamic effects on nonlinear alternating current responses in electrorheological fluids.

By using a perturbation approach, we investigate dynamic effects on nonlinear alternating current (ac) responses in electrorheological (ER) fluids under an ac or direct current electric field. We show that the dynamic effect due to a shear flow, which exerts a torque on ER particles and thus leads to the rotation of the particles about their centers, plays a significant role in the responses. Our results can be well interpreted in the dielectric dispersion spectral representation, and they offer a convenient method to determine the relaxation time and rotation velocity of ER particles by measuring the nonlinear ac responses.

Application of bioreactor system for large-scale production of Eleutherococcus sessiliflorus somatic embryos in an air-lift bioreactor and production of eleutherosides.

Embryogenic callus was induced from leaf explants of Eleutherococcus sessiliflorus cultured on Murashige and Skoog (MS) basal medium supplemented with 1 mg l(-1) 2,4-dichlorophenoxyacetic acid (2,4-D), while no plant growth regulators were needed for embryo maturation. The addition of 1 mg l(-1) 2,4-D was needed to maintain the embryogenic culture by preventing embryo maturation. Optimal embryo germination and plantlet development was achieved on MS medium with 4 mg l(-1) gibberellic acid (GA(3)). Low-strength MS medium (1/2 and 1/3 strength) was more effective than full-strength MS for the production of normal plantlets with well-developed shoots and roots. The plants were successfully transferred to soil. Embryogenic callus was used to establish a suspension culture for subsequent production of somatic embryos in bioreactor. By inoculating 10 g of embryogenic cells (fresh weight) into a 3l balloon type bubble bioreactor (BTBB) containing 2l MS medium without plant growth regulators, 121.8 g mature somatic embryos at different developmental stages were harvested and could be separated by filtration. Cotyledonary somatic embryos were germinated, and these converted into plantlets following transfer to a 3l BTBB containing 2l MS medium with 4 mg l(-1) GA3. HPLC analysis revealed that the total eleutherosides were significantly higher in leaves of field grown plants as compared to different stages of somatic embryo. However, the content of eleutheroside B was highest in germinated embryos. Germinated embryos also had higher contents of eleutheroside E and eleutheroside E1 as compared to other developmental stages. This result indicates that an efficient protocol for the mass production of E. sessiliflorus biomass can be achieved by bioreactor culture of somatic embryos and can be used as a source of medicinal raw materials.

Theory of nondegenerate nonlinear optical susceptibilities of graded composites with high-volume fractions.

We present a theory for the effective nondegenerate third-order nonlinear optical susceptibility (NDTNOS) of composite media in which the graded metallic particles with weak nonlinearity and the linear dielectric grains are randomly distributed. In combination with an effective medium approximation, the recently established nonlinear differential effective dipole approximation (NDEDA), which is valid for the degenerate third-order optical nonlinearity of the composites in the dilute limit, is generalized to deal with the effective NDTNOS of graded composites of high-volume fractions. Numerical results show that for high-volume fractions, the presence of gradation makes the effective NDTNOS enhanced, but the linear optical absorption reduced, thus, yielding an attractive figure of merit. In addition, by using NDEDA and Maxwell-Garnett approximation, we study the effective NDTNOS of the graded composite media with the Hashin-Shtrikman microgeometry. The nondegenerate optical nonlinearity enhancement is found to be sensitive to the composite topology.

Spectral representation of the effective dielectric constant of graded composites.

We generalize the Bergman-Milton spectral representation, originally derived for a two-component composite, to extract the spectral density function for the effective dielectric constant of a graded composite. This work has been motivated by a recent study of the optical absorption spectrum of a graded metallic film [Huang and Yu, Appl. Phys. Lett. 85, 94 (2004)] in which a broad surface-plasmon absorption band was shown to be responsible for enhanced nonlinear optical response and an attractive figure of merit. It turns out that, unlike in the case of homogeneous constituent components, the characteristic function of a graded composite is a continuous function because of the continuous variation of the dielectric function within the constituent components. Analytical generalization to three-dimensional graded composites is discussed, and numerical calculations for multilayer composites are given as a simple application.

Macrophage-stimulating activity of exo-biopolymer from cultured rice bran with Monascus pilosus.

To find a new use of rice bran, five fungi were examined for the production of exo-biopolymer with macrophage-stimulating activity from rice bran. Among the exo-biopolymers produced from the cultures, Monascus pilosus had the most potent macrophage stimulating activity in a liquid culture rather than in a solid culture. In order to improve the yield of exo-biopolymer with macrophage-stimulating activity, a suitable medium for exo-biopolymer was tested in submerged culture of M. pilosus. The highest amount of exo-biopolymer (13.9 mg/mL) was obtained in a medium containing rice bran as an only carbon source followed by media with additional maltose and sucrose (13.8 and 13.7 mg/mL, respectively). The addition of peptone resulted in the production of high amount of exo-biopolymer (15.1 mg/mL), meanwhile the addition of ammonium chloride resulted in 264.0 microg/mL of glucosamine content. Among eight different kinds of inorganic salts tested, potassium phosphate (0.1%) was the most effective inorganic salt for the mycelial growth and exo-biopolymer production. Therefore the optimal medium composition was as follows (g/L): 20 g of rice bran, 5 g of peptone, and 1 g of KH2PO4. The optimal culture pH and time for mycelial growth and exo-biopolymer production was pH 5.0 and 25 degrees C, respectively. The maximum exo-biopolymer (20.1 mg/mL) was observed at the fourth day of cultivation. Exo-biopolymer, a crude polysaccharide fraction, mainly contained neutral sugar (81.8%) with considerable amounts of uronic acid (18.2%). Component sugar analysis showed that the active fraction consisted mainly of arabinose, galactose, glucose, which was digested from starch of rice bran during cultivation, and uronic acid (molar ratio; 0.8:1.0:0.7:0.8).

Evidence of transmission of Mycobacterium tuberculosis by random amplified polymorphic DNA (RAPD) fingerprinting in Taipei City, Taiwan.

AIMS: To determine, by strain identification of Mycobacterium tuberculosis, whether transmission has occurred between individuals or whether new strains are present. METHODS: A rapid protocol for random amplified polymorphic DNA (RAPD) analysis was developed. This protocol was applied to 64 strains of M tuberculosis that had been confirmed by culture and microbiological methods. RESULTS: There are five groups of M tuberculosis prevalent in Taipei city, Taiwan. The major types are groups I and III. Groups I and II had been prevalent until the end of last year when, according to our group analysis, they had been eradicated. However, group III was continuously present from the middle of 1995 to the middle of 1996, and group IV was present at the end of both years, which indicated that both groups were transmitted continuously. These clustered strains had demographic characteristics consistent with a finding of transmission tuberculosis. Also, there were 13 of 64 strains with unique RAPD fingerprints that were inferred to be due primarily to the reactivation of infection. In the drug resistance analysis, the major type represented included group III and part of group IV. CONCLUSIONS: Our preliminary data imply, not only that the prevalence of M tuberculosis in Taipei city is due to transmission rather than reactivation, but that drug resistance also may play a role in tuberculosis transmission.

Antibacterial activity and beta-lactamase stability of MDL 19,592, an oral cephalosporin.

We compared the in vitro activity and beta-lactamase stability of MDL 19,592, an orally absorbed cephalosporin, with that of cephalexin and cefaclor. It inhabited Staphylococcus aureus at less than or equal to 4 micrograms/ml, Streptococcus pyogenes at 0.25 microgram/ml, sero groups B, C and G streptococci at 1 microgram/ml, and Streptococcus pneumoniae at 2 micrograms/ml. It was slightly more active than cefaclor and cephalexin. MDL 19,592 did not significantly inhibit Enterobacteriaceae, enterococci, Listeria monocytogenes, Pseudomonas aeruginosa, and Acinetobacter spp. strains (MIC greater than or equal to 32 micrograms/ml). MDL 19,592 was not hydrolyzed by the plasmid beta-lactamases TEM-1 and SHV-1 of Klebsiella but was hydrolyzed by the TEM-3, Staphylococcus aureus beta-lactamase, and the chromosomal-mediated Enterobacter cloacae P99 enzymes.

Antibacterial activity of rokitamycin compared with that of other macrolides.

The activity of rokitamycin, a 16-membered macrolide, was compared with other macrolides and agents used to treat respiratory infections. Rokitamycin had in vitro activity against streptococci and Streptococcus pneumoniae comparable to the other macrolides, inhibiting most organisms at less than 0.03 to 0.5 microgram/ml. It was the most active macrolide agent against Staphylococcus aureus, inhibiting 90% at 1 microgram/ml. Macrolide-resistant streptococci and staphylococci in which resistance was inducible were inhibited, but constitutively resistant Gram-positive bacteria were resistant. Rokitamycin was less active than erythromycin against Haemophilus influenzae, but had activity comparable to erythromycin against Moraxella catarrhalis and Neisseria gonorrhoeae. It inhibited Clostridium spp. and peptostreptococci, but had poor activity against Bacteroides species. Rokitamycin was bactericidal for streptococci and staphylococci, but not for enterococci. Overall rokitamycin has in vitro activity comparable to currently available 14-membered macrolides. Its clinical utility will be influenced by the degree of metabolism to less active metabolites since 70% is rapidly metabolized.

Isolation of Aeromonas hydrophila in children with diarrhea.

Aeromonas species are gram-negative bacilli that lead to a wide spectrum of infectious diseases in human. In the present study, these bacilli were reviewed to assess their significance as enteric pathogens in this area. During the years of 1994 to 1998, the clinical microbiology laboratory received 2150 stool specimens of children with diarrhea. Medical charts of patients who had positive culture for Aeromonas hydrophila were reviewed. A. hydrophila were isolated from 50 (2.3%) of 2150 children with diarrhea. Most patients were outpatients with ages ranging from 5 months to 16 years old (mean age 3.5 years). The male to female ratio was 0.85:1. All patients suffered from watery or loose diarrhea, some with blood-tinged stool. Whether or not they received medication, all patients had uneventful recoveries. The results of antibiotic susceptibility testing revealed that all strains were not susceptible to ampicillin. In summary, A. hydrophila may be considered as a causative agent of gastrointestinal illness in children.

Characteristics of patients with Burkholderia cepacia bacteremia.

Burkholderia cepacia has become an important pathogen of infections in immunocompromised and nosocomial patients. The characteristics of 42 episodes of B. cepacia bacteremia in 40 patients admitted to the Taipei Veterans General Hospital between January 1997 and December 1999 were retrospectively analyzed. Factors that adversely influenced the mortality rate included respiratory failure, an unknown infection source, a period in an intensive care unit, and shock. Most of the patients had serious underlying diseases, such as diabetes mellitus, malignancy, congestive heart failure, and chronic obstructive pulmonary disease. The mean time for a positive blood culture was 45 days after admission. The overall mortality rate was 28.6% (12/42), and 44.4% (12/27) of all deaths were directly related to B. cepacia bacteremia. Polymicrobial bacteremia was found in 5 patients. Ceftazidime was the most effective antimicrobial agent in vitro, whereas chloramphenicol, imipenem, and trimethoprim/sulfamethoxazole were less effective alternatives. Appropriate antibiotic therapy was given to 30 patients, most of whom responded to the therapy except for 5 who died despite receiving appropriate treatment. Although B. cepacia infection develops in a relatively small proportion of hospitalized individuals, it has a major impact on morbidity and mortality. In view of the fact that B. cepacia develops resistance to a wide range of antimicrobial agents, ceftazidime and/or trimethoprim/sulfamethoxazole should be the drug of choice for empiric therapy.

Field-induced structure transformation in electrorheological solids.

We have computed the local electric field in a body-centered tetragonal (bct) lattice of point dipoles via the Ewald-Kornfeld formulation, in an attempt to examine the effects of a structure transformation on the local-field strength. For the ground state of an electrorheological solid of hard spheres, we identified a different structure transformation from the bct to the face-centered cubic (fcc) lattices by changing the uniaxial lattice constant c under the hard-sphere constraint. In contrast to the previous results, the local field exhibits a nonmonotonic transition from bct to fcc. As c increases from the bct ground state, the local field initially decreases rapidly towards the isotropic value at the body-centered cubic lattice, decreases further, reaching a minimum value and increases, passing through the isotropic value again at an intermediate lattice, reaches a maximum value and finally decreases to the fcc value. An experimental realization of the structure transformation is suggested. Moreover, the change in the local field can lead to a generalized Clausius-Mossotti equation for the bct lattices.

Ground state of a polydisperse electrorheological solid: beyond the dipole approximation.

The ground state of an electrorheological (ER) fluid has been studied based on our recently proposed dipole-induced dipole (DID) model. We obtained an analytical expression of the interaction between chains of particles which are of the same or different dielectric constants. The effects of dielectric constants on the structure formation in monodisperse and polydisperse electrorheological fluids are studied in a wide range of dielectric contrasts between the particles and the base fluid. Our results showed that the established body-centered tetragonal ground state in monodisperse ER fluids may become unstable due to a polydispersity in the particle dielectric constants. While our results agree with that of the fully multipole theory, the DID model is much simpler, which offers a basis for computer simulations in polydisperse ER fluids.

Interparticle force in electrorheological solids: many-body dipole-induced dipole model.

One often investigates electrorheological (ER) solids by using the point-dipole (PD) approximation, which, however, is known to err considerably for touching particles due to the existence of many-body (local-field) effects and multipolar interactions. Beyond the PD model, previous attempts have been restricted to either local-field effects only or multipolar interactions only, but not both. In the present work, we have developed a many-body dipole-induced dipole model for an ER solid the lattice structure of which can be changed due to the application of external fields, in an attempt to take into account both local-field effects and multipolar interactions. The results show that the multipolar interaction can indeed be dominant over the dipolar interaction, while the local-field effect may yield an important correction. Also, the results are well understood with the aid of spectral representation theory.

Statistics of level spacing of geometric resonances in random binary composites.

We study the statistics of level spacing of geometric resonances in the disordered binary networks. For a definite concentration p within the interval [0.2,0.7], numerical calculations indicate that the unfolded level spacing distribution P(t) and level number variance Sigma(2)(L) have general features. It is also shown that the short-range fluctuation P(t) and long-range spectral correlation Sigma(2)(L) lie between the profiles of the Poisson ensemble and Gaussion orthogonal ensemble. At the percolation threshold p(c), crossover behavior of functions P(t) and Sigma(2)(L) is obtained, giving the finite size scaling of mean level spacing delta and mean level number n, which obey the scaling laws, delta=1.032L(-1.952) and n=0.911L(1.970).