In vitro susceptibility of clinical isolates of Mycobacterium tuberculosis to cefadroxil—a cephalosporin antibiotic

The bactericidal activity (BA) of cefadroxil, a semisynthetic cephalosporin antibiotic, against M. tuberculosis H37Rv was studied in Middlebrook 7H9 medium, Cefadroxil showed good BA (average fall of viable counts = log10 0.32 colony forming units/ml/day) against the log phase culture of M. tuberculosis H37Rv. Its minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were found to be 15 μg/ml or less. The MIC of cefadroxil for 29 clinical isolates of M. tuberculosis and a laboratory strain, M. tuberculosis H37Rv was also determined by agar dilution method using Middlebrook 7H11 agar as a screening procedure. The MIC of cefadroxil was found to be 10 μg/ml or less for M. tuberculosis H37Rv and 16 (55.1%) of 29 clinical isolates tested. The MIC for 3 of 10 drug sensitive and 9 of 19 drug resistant isolates was 40 or more, a concentration much higher than the peak plasma concentration (28 μg/ml) attained in human beings. The higher MIC observed in 12 of 29 clinical isolates irrespective of their susceptibility pattern requires further studies to assess the usefulness of cefadroxil in the treatment of tuberculosis

Reply to ``Comment on `Inverse exciton series in the optical decay of an excitonic molecule' "

As a reply to the Comment by I.S. Gorban {\it et al.} (Phys. Rev. B, preceding paper) we summarize our criticism on their claim of the first observation of the $M$ series in $\beta$-ZnP$_2$. We support our analysis by reporting the first observation of inverse {\it polariton} series from the excitonic molecules selectively generated at ${\bf K}_m \simeq {\bf 0}$ in a CuCl single crystal. This observation and its explanation within the bipolariton model complete our proof of the biexcitonic origin of the inverse series.Comment: The Comment by I.S. Gorban et al. has been rejecte

In vitro susceptibility of Mycobacterium tuberculosis to trifluoperazine

The reference strain, Mycobacterium tuberculosis H37Rv, 19 drug-sensitive and 15 drug resistant clinical isolates of M. tuberculosis were tested for their in vitro susceptibility to trifluoperazine (TFP), an antipsychotic drug, by broth dilution method. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of TFP against M. tuberculosis H37Rv were 8 and 32 mg/l, respectively. The distribution of the sensitive and resistant isolates, with respect to the MIC of TFP, was similar. The distribution of the sensitive and resistant isolates, with respect to the MBC of TFP, was different and the difference was statistically significant. The findings suggest that TFP is more bactericidal to drug-resistant isolates than to the sensitive isolates

Bioluminescence assay of adenosine triphosphate in drug susceptibility testing of Mycobacterium tuberculosis

Twenty three clinical isolates of M. tuberculosis and the reference strain, M. tuberculosis H37Rv were tested for their susceptibility to trifluoperazine (TFP) by the standard broth dilution method and the bioluminescence assay. The results showed that in 15 of the 23 isolates, the minimal inhibitory concentration (MIC) was identical in both the methods and in the remaining 8 isolates the difference in the MIC values between the methods, was less than two fold and was not significant. The findings suggest that the measurement of adenosine triphosphate (ATP) by bioluminescence assay can be employed as an alternative method for the rapid screening of clinical isolates for their susceptibility to anti-mycobacterial agents

EXCITON-PHONON INTERACTION AND PHONON FREQUENCY SHIFT IN QUANTUM DOTS

We present a theory of LO phonon renormalization by coupling with the excitonin semiconductor quantum dots. We find that the one phonon side band of theexciton ground state shows an anticrossing with the excited exciton states. Evenaway from such a resonant coupling, the phonon frequency shift is significant.For example, in CuCl quantum dots in the weak confinement regime, the phononfrequency in the presence of a single exciton is reduced by about 10% from its valuein the ground state. Similar results are predicted for CdS and GaAs quantum dotsin the strong confinement regime.24th International Conference on the Physics of Semiconductors : Jerusalem, Israel August 2-7, 199

Hopfield coefficients measured by inverse polariton series

We report observation of the inverse polariton series and a detailed experimental study of the exciton components in polaritons (Hopfield coefficients). Spontaneous emission of excitonic molecules into outgoing polaritons associated with the i(=1,2,3,4,5)th exciton states in bulk CuCl is detected and analyzed by the bipolariton model. Because the intensities of the emission lines, which form the inverse polariton series, are determined by the exciton components in the final-state polaritons, we are able to measure the Hopfield coefficients for the highly composite outgoing polaritons. Quantum interference in the optical decay of excitonic molecules, due to the multiple exciton components in the polariton and biexciton states, is also demonstrated

LO Phonon Renormalization in Optically Excited CuCl Nanocrystals

We have revealed sharp structures in the absorption spectrum of CuCl nanocrystals using persistent hole-burning spectroscopy and observed sidebands due to phonon-assisted absorption. The LO phonon frequency in the excited state of the nanocrystal is reduced by about 10% from the free value due to mixing with the exciton. When the mixing becomes resonant, the phonon sideband anticrosses with the excited exciton state. We present a theory of the phonon renormalization in nanocrystals and obtain results in excellent agreement with the experiment

Exciton-phonon coupled states in CuCl quantum cubes

The size dependence of excitonic states and vibrational modes in CuCl cubic quantum dots embedded in NaCl crystals was studied by means of site-selective persistent spectral hole burning spectroscopy. It is shown that the interaction of the longitudinal optical (LO) phonon with the exciton results in the formation of coupled exciton-phonon modes when the energy of the LO phonon approaches the energy spacings between the ground and excited states of the exciton. The energy anticrossings of the LO phonon modes with two higher optically allowed excited states of the exciton in CuCl QD’s were clearly observed at confinement energies of about 10 and 6 meV, respectively. In addition, the linewidth of the LO phonon sideband in CuCl QD’s in NaCl crystals was found to increase abruptly from 0.3 meV to about 1.2 meV at a confinement energy of about 23 meV, which appears to result from the exciton-phonon mixing of the LO phonon mode with the first excited state of the exciton. The experimental results are qualitatively understood by the LO phonon renormalization theory

External-field effects on the optical spectra of self-assembled InP quantum dots

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