Evolution of Streptococcus pneumoniae serotypes and penicillin susceptibility in Latin America, Sireva-Vigía Group, 1993 to 1999. PAHO Sireva-Vigía Study Group. Pan American Health Organization

Fil: Di Fabio, José Luis. Pan American Health Organization. Division of Vaccines and Immunization; Estados Unidos.Fil: Castañeda, Elizabeth. Instituto Nacional de Salud; Colombia.Fil: Agudelo, Clara Inés. Instituto Nacional de Salud; Colombia.Fil: De La Hoz, Fernando. Universidad Nacional de Colombia. Facultad de Medicina. Departamento de Salud Pública. Instituto de Salud Pública; Colombia.Fil: Hortal, María. Departamento de Laboratorios de Salud Pública; Uruguay.Fil: Camou, Teresa. Departamento de Laboratorios de Salud Pública; Uruguay.Fil: Echániz-Avilés, Gabriela. Instituto Nacional de Salud Pública; México.Fil: Barajas, María Noemi Carnalla. Instituto Nacional de Salud Pública; México.Fil: Heitmann, Ingrid. Instituto de Salud Pública, Chile.Fil: Hormazabal, Juan Carlos. Instituto de Salud Pública, Chile.Fil: Brandileone, María Cristina C. Instituto Adolfo Lutz; Brasil.Fil: Dias Vieira, Vera Simonsen. Instituto Adolfo Lutz; Brasil.Fil: Regueira, Mabel. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas; Argentina.Fil: Ruvinski, Raúl. Hospital Municipal M. Durand; Argentina.Fil: Corso, Alejandra. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas; Argentina.Fil: Lovgren, Marguerite. National Centre for Streptococcus; Canadá.Fil: Talbot, James A. National Centre for Streptococcus; Canadá.Fil: De Quadros, Ciro. Pan American Health Organization. Division of Vaccines and Immunization; Estados Unidos.Background: Since 1993 the Pan American Health Organization has coordinated a surveillance network with the National Reference Laboratories of Argentina, Brazil, Chile, Colombia, Mexico and Uruguay aimed at monitoring capsular types and antimicrobial susceptibility of Streptococcus pneumoniae causing invasive disease in children <6 years of age. Methods: The surveillance system included children 6 years of age and younger with invasive disease caused by S. pneumoniae. The identification, capsular typing and susceptibility to penicillin of the isolates were conducted using a common protocol, based on standard methodologies. Results: By June, 1999, 4,105 invasive pneumococcal isolates had been collected mainly from pneumonia (44.1%) and meningitis (41.1%) cases. Thirteen capsular types accounting for 86.1% of the isolates (14, 6A/6B, 5, 1, 23F, 19F, 18C, 19A, 9V, 7F, 3, 9N and 4) remained the most common types during the surveillance period. Diminished susceptibility to penicillin was detected in 28.6% of the isolates, 17.3% with intermediate and 11.3% with high level resistance. Resistance varied among countries and increased during this period in Argentina, Colombia and Uruguay. Serotypes 14 and 23F accounted for 66.6% of the resistance. Conclusion: These surveillance data clearly demonstrate the potential impact of the introduction of a conjugate vaccine on pneumococcal disease and the need for more judicious use of antibiotics to slow or reverse the development of antimicrobial resistance

Vibrational Properties of Metal Nanoparticles: Atomistic Simulation and Comparison with Time-Resolved Investigation

International audienceKnowledge of the vibrational spectrum of metal clusters and nanoparticles is of fundamental interest since it is a signature of their morphology, and it can be used to determine their mechanical, thermodynamical, and other physical properties. It is expected that such a vibrational spectrum depends on the material, size, and shape of clusters and nanoparticles. In this work, we report the vibrational spectra and density of states of Au, Pt, and Ag nanoparticles in the size range of 0.5-4 nm (13-2057 atoms), with icosahedral, Marks decahedral, and FCC morphologies. The vibrational spectra were calculated through atomistic simulations (molecular dynamics and a normal-mode analysis) using the many-body Gupta potential. A discussion on the dependence of the vibrational spectrum on the material, size, and shape of the nanoparticle is presented. Linear relations with the nanoparticle diameter were obtained for the periods of two characteristic oscillations: the quasi-breathing and the lowest frequency (acoustic gap) modes. These linear behaviors are consistent with the calculation of the periods corresponding to the breathing and acoustic gap modes of an isotropic, homogeneous metallic nanosphere, performed with continuous elastic theory using bulk properties. Additionally, experimental results on the period corresponding to isotropic volume oscillations of Au nanoparticles measured by time-resolved pump-probe spectroscopy are presented, indicating a linear variation with the mean diameter in the size range of 2-4 nm. These, and similar results previously obtained for Pt nanoparticles with size between 1.3 and 3 nm, are in good agreement with the calculated quasi-breathing mode periods of the metal nanoparticles, independently of their morphologies. On the other hand, the calculated period of the mode with the highest (cutoff) frequency displays weak size and shape dependencies up to 4 nm, for all nanoparticles under study. In contrast with the behavior of other physicochemical properties, the clear consistency between experiments with atomistic and continuous media approaches resulting from this work indicates the existence of simple relations with size and weak dependence with the material and shape, for vibrational properties of metal nanoparticles