Successes and failures in the search for antibiotics.
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Elongation factor (EF) G promotes tRNA translocation on the ribosome. We present three-dimensional reconstructions, obtained by cryo-electron microscopy, of EF-G-ribosome complexes before and after translocation. In the pretranslocation state, domain 1 of EF-G interacts with the L7/12 stalk on the 50S subunit, while domain 4 contacts the shoulder of the 30S subunit in the region where protein S4 is located. During translocation, EF-G experiences an extensive reorientation, such that, after translocation, domain 4 reaches into the decoding center. The factor assumes different conformations before and after translocation. The structure of the ribosome is changed substantially in the pretranslocation state, in particular at the head-to-body junction in the 30S subunit, suggesting a possible mechanism of translocation.
Rapid protein synthesis in bacteria requires the G proteins IF2, EF-Tu, EF-G, and RF3. These factors catalyze all major steps of mRNA translation in a GTP-dependent manner. Here, it is shown how the position of peptidyl-tRNA in the ribosome and presence of its peptide control the binding and GTPase activity of these translation factors. The results explain how idling GTPase activity and negative interference between different translation factors are avoided and suggest that hybrid sites for tRNA on the ribosome play essential roles in translocation of tRNAs, recycling of class 1 release factors by RF3, and recycling of ribosomes back to a new round of initiation. We also propose a model for translocation of tRNAs in two separate steps, which clarifies the roles of EF-G.GTP and GTP hydrolysis in this process.
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We report a case of pulmonary actinomycosis, stimulating a bronchial neoplasm, in which serological tests for actinomycosis were positive.
Staphylococcus epidermidis is an infrequent cause of native valve endocarditis. We describe two cases associated with mitral valve prolapse, and discuss the significance, diagnosis and management of this condition.
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Growth of Staphylococcus aureus in the presence of salicylate leads to reduced ciprofloxacin and ethidium accumulation and increased resistance to ethidium. Salicylate induced reduction in ciprofloxacin accumulation is energy-independent while salicylate induced alterations in ethidium accumulation and efflux is proton motive force-dependent. NorA is an intrinsic multidrug efflux pump that contributes to intrinsic levels of fluoroquinolone and ethidium resistance in S. aureus. The NorA inhibitor reserpine did not dramatically affect the ability of salicylate to induce increased ciprofloxacin and ethidium resistance. Inactivation of norA did not alter the ability of salicylate to induce increased ciprofloxacin and ethidium resistance levels and a reduction in ciprofloxacin accumulation. These data demonstrate that NorA is not absolutely required for the salicylate-inducible multidrug resistance mechanism of S. aureus.
The use of Cerebro-Spinal-Fluid-shunts (CSF-shunts) is often associated with infectious complications, because bacteria tend to colonize plastic material. The use of plastic materials with antibacterial activity may reduce catheter related bacterial colonization. A novel CSF-shunt impregnated with a broad-spectrum antimicrobial combination was designed in order to meet two requirements; lack of toxicity and persistence of antimicrobial efficacy. Incorporation of three antibiotics up to 10% (wt/wt) into the shunt material (polydimethyl-siloxane) was required for sustained release for more than 100 days, measured by HPLC. The combination of antimicrobials showed additive and synergistical effects as measured by the checker-board and time kill technique. These antimicrobial combinations prevented mutations in resistance inducing experiments with several S. epidermidis and S. aureus strains. Using large challenge doses of S. aureus in a catheter colonization model, antimicrobially modified catheters were protected against bacterial colonization for more than 14 days. Using a C3a-des-Arg-ELISA-test and a CH50-hemolysis test the modified catheter was as biocompatible as the unmodified shunt material. These encouraging results indicate that such antibiotic-bonded catheters substantially reduce the incidence and magnitude of catheter-related bacterial colonization and may substantially reduce CSF-shunt infection.