Linezolid alone or combined with rifampin against methicillin-resistant Staphylococcus aureus in experimental foreign-body infection.

We investigated the activity of linezolid, alone and in combination with rifampin (rifampicin), against a methicillin-resistant Staphylococcus aureus (MRSA) strain in vitro and in a guinea pig model of foreign-body infection. The MIC, minimal bactericidal concentration (MBC) in logarithmic phase, and MBC in stationary growth phase were 2.5, >20, and >20 microg/ml, respectively, for linezolid; 0.01, 0.08, and 2.5 microg/ml, respectively, for rifampin; and 0.16, 0.63, >20 microg/ml, respectively, for levofloxacin. In time-kill studies, bacterial regrowth and the development of rifampin resistance were observed after 24 h with rifampin alone at 1x or 4x the MIC and were prevented by the addition of linezolid. After the administration of single intraperitoneal doses of 25, 50, and 75 mg/kg of body weight, linezolid peak concentrations of 6.8, 12.7, and 18.1 microg/ml, respectively, were achieved in sterile cage fluid at approximately 3 h. The linezolid concentration remained above the MIC of the test organism for 12 h with all doses. Antimicrobial treatments of animals with cage implant infections were given twice daily for 4 days. Linezolid alone at 25, 50, and 75 mg/kg reduced the planktonic bacteria in cage fluid during treatment by 1.2 to 1.7 log(10) CFU/ml; only linezolid at 75 mg/kg prevented bacterial regrowth 5 days after the end of treatment. Linezolid used in combination with rifampin (12.5 mg/kg) was more effective than linezolid used as monotherapy, reducing the planktonic bacteria by >or=3 log(10) CFU (P < 0.05). Efficacy in the eradication of cage-associated infection was achieved only when linezolid was combined with rifampin, with cure rates being between 50% and 60%, whereas the levofloxacin-rifampin combination demonstrated the highest cure rate (91%) against the strain tested. The linezolid-rifampin combination is a treatment option for implant-associated infections caused by quinolone-resistant MRSA.

Oscillation modes of microtubules.

Microtubules are long, filamentous protein complexes which play a central role in several cellular physiological processes, such as cell division transport and locomotion. Their mechanical properties are extremely important since they determine the biological function. In a recently published experiment [Phys. Rev. Lett. 89 (2002) 248101], microtubule's Young's and shear moduli were simultaneously measured, proving that they are highly anisotropic. Together with the known structure, this finding opens the way to better understand and predict their mechanical behavior under a particular set of conditions. In the present study, we modeled microtubules by using the finite elements method and analyzed their oscillation modes. The analysis revealed that oscillation modes involving a change in the diameter of the microtubules strongly depend on the shear modulus. In these modes, the correlation times of the movements are just slightly shorter than diffusion times of free molecules surrounding the microtubule. It could be therefore speculated that the matching of the two timescales could play a role in facilitating the interactions between microtubules and MT associated proteins, and between microtubules and tubulins themselves.

Regulation of foreign gene in fowlpox virus by a vaccinia virus promoter.

A vaccinia virus promoter was evaluated for regulation of a foreign gene in fowlpox virus by a transient expression assay. Fowlpox virus-infected quail cells, transfected with plasmid DNA containing chloramphenicol acetyltransferase (CAT) gene ligated to a vaccinia virus promoter, expressed CAT activity. No CAT activity was detected either in uninfected cells or fowlpox virus-infected cells. These results indicated that a heterologous vaccinia virus promoter can regulate expression of a foreign gene in fowlpox virus.

Mutations inducing divergent shifts of constitutive activity reveal different modes of binding among catecholamine analogues to the beta(2)-adrenergic receptor.

1. We compared the changes in binding energy generated by two mutations that shift in divergent directions the constitutive activity of the human beta(2) adrenergic receptor (beta(2)AR). 2. A constitutively activating mutant (CAM) and the double alanine replacement (AA mutant) of catechol-binding serines (S204A, S207A) in helix 5 were stably expressed in CHO cell lines, and used to measure the binding affinities of more than 40 adrenergic ligands. Moreover, the efficacy of the same group of compounds was determined as intrinsic activity for maximal adenylyl cyclase stimulation in wild-type beta(2)AR. 3. Although the two mutations had opposite effects on ligand affinity, the extents of change were in both cases largely correlated with the degree of ligand efficacy. This was particularly evident if the extra loss of binding energy due to hydrogen bond deletion in the AA mutant was taken into account. Thus the data demonstrate that there is an overall linkage between the configuration of the binding pocket and the intrinsic equilibrium between active and inactive receptor forms. 4. We also found that AA mutation-induced affinity changes for catecholamine congeners gradually lacking ethanolamine substituents were linearly correlated to the loss of affinity that such modifications of the ligand cause for wild-type receptor. This indicates that the strength of bonds between catechol ring and helix 5 is critically dependent on the rest of interactions of the beta-ethanolamine tail with other residues of the beta(2)-AR binding pocket.

Präoperative Azidose und Entwicklung von Säuglingen nach Operation angeborener Herzfehler Preoperative acidosis and infant development following surgery for congenital heart disease.

OBJECTIVE: Prenatal diagnosis has been shown to decrease pre-operative acidosis and might prevent the occurrence of disturbed developmental outcome. The aim of this study is to evaluate parameters for acidosis and their predictive value on developmental outcome in newborns with congenital heart disease. METHODS: A total of 117 patients requiring surgery for structural heart disease in the first 31 days of life were included. Diagnosis was established either pre- or postnatally. Preoperative values of lactate, pH and base excess levels were compared to the occurrence of disturbed developmental outcome, i.e. an underperformance of more than 10% on the P90 of a standardized Dutch developmental scale. Patients were divided into groups according to blood levels of acidosis parameters, using receiver operating characteristics curves to determine cut-off values for pH, base excess and lactate. RESULTS: No significant difference in developmental outcome was found using values for pH or base excess as a cut-off level. Preoperative lactate values exceeding 6.1 mmol/l resulted in a significant increase in impaired development compared to infants with a pre-operative lactate lower than 6.1 mmol/l: 40.9% vs 15.1% in (p=0.03). CONCLUSIONS: Pre-operative lactate values might have a prognostic value on developmental outcome in newborns with congenital heart disease. The limited prognostic value of pH can be explained by the fact that pH can be easily corrected, while lactate better reflects the total oxygen debt experienced by these patients.

Gentamicin Improves the Activities of Daptomycin and Vancomycin against Enterococcus faecalis In Vitro and in an Experimental Foreign-Body Infection Model.

For enterococcal implant-associated infections, the optimal treatment regimen has not been defined. We investigated the activity of daptomycin, vancomycin, and gentamicin (and their combinations) against Enterococcus faecalis in vitro and in a foreign-body infection model. Antimicrobial activity was investigated by time-kill and growth-related heat production studies (microcalorimetry) as well as with a guinea pig model using subcutaneously implanted cages. Infection was established by percutaneous injection of E. faecalis in the cage. Antibiotic treatment for 4 days was started 3 h after infection. Cages were removed 5 days after end of treatment to determine the cure rate. The MIC, the minimal bactericidal concentration (MBC) in the logarithmic phase, and the MBC in the stationary phase were 1.25, 5, and >20 μg/ml for daptomycin, 1, >64, and >64 μg/ml for vancomycin, and 16, 32, and 4 μg/ml for gentamicin, respectively. In vitro, gentamicin at subinhibitory concentrations improved the activity against E. faecalis when combined with daptomycin or vancomycin in the logarithmic and stationary phases. In the animal model, daptomycin cured 25%, vancomycin 17%, and gentamicin 50% of infected cages. In combination with gentamicin, the cure rate for daptomycin increased to 55% and that of vancomycin increased to 33%. In conclusion, daptomycin was more active than vancomycin against adherent E. faecalis, and its activity was further improved by the addition of gentamicin. Despite a short duration of infection (3 h), the cure rates did not exceed 55%, highlighting the difficulty of eradicating E. faecalis from implants already in the early stage of implant-associated infection.