RESUMEN
Our high technology society continues to rely more and more upon sophisticated measurements, technical standards, and associated testing activities. This was true for the industrial society of the 20th century and remains true for the information society of the 21st century. Over the last half of the 20th century, information technology (IT) has been a powerful agent of change in almost every sector of the economy. The complexity and rapidly changing nature of IT have presented unique technical challenges to the National Institute of Standards and Technology (NIST) and to the scientific measurement community in developing a sound measurement and testing infrastructure for IT. This measurement and testing infrastructure for the important non-physical and non-chemical properties associated with complex IT systems is still in an early stage of development. This paper explains key terms and concepts of IT metrology, briefly reviews the history of the National Bureau of Standards/National Institute of Standards and Technology (NBS/NIST) in the field of IT, and reviews NIST's current capabilities and work in measurement and testing for IT. It concludes with a look at what is likely to occur in the field of IT over the next ten years and what metrology roles NIST is likely to play.
RESUMEN
By using in vitro assays, a group of related, filamentous gram-negative bacteria isolated from subgingival plaque deposits of patients with periodontal disease were found to colonize intact teeth. Tentatively identified as members of the genus Cytophaga, these isolates exhibited a preference for colonizing the cementum surface of the root. Examination of intact teeth after several weeks of colonization revealed that the root substructure had been extensively demineralized.
Asunto(s)
Cytophaga/crecimiento & desarrollo , Cemento Dental/microbiología , Raíz del Diente/microbiología , Medios de Cultivo , Descalcificación Patológica , Placa Dental/microbiología , Humanos , Streptococcus mutans/crecimiento & desarrolloRESUMEN
The effect of extracellular products from Streptococcus salivarius on sucrose-dependent adherence to smooth surfaces by other oral bacteria was studied in vitro. Strains of Streptococcus mitis, Streptococcus pyogenes, and Veillonella parvula without innate ability to adhere to a steel wire were able to do so when incubated with sucrose and cell-free culture fluid from S. salivarius strains 9759, 25975, CNII, and MEPI. These culture fluids synthesized more adherent material and water-insoluble glucan than those from Streptococcus mutans C67-1 and seven other S. salivarius strains. Among the S. salivarius strains, glucosyltransferase (GT; dextransucrase, EC 2.4.1.5) activity varied more than 100-fold. Cells of Veillonella and S. mitis S3 that had been incubated in culture fluids from S. salivarius 25975 and 9759, respectively, and then washed adhered upon subsequent incubation with sucrose. This was due to adsorbed GT because (i) the adherence was sensitive to dextranase; (ii) it was observed only with the high-GT culture fluids; (iii) it was dependent on sucrose; and (iv) the washed Veillonella cells synthesized glucan, but not fructan, from sucrose. These results suggest that sucrose-dependent adherence of bacteria without such innate ability can be mediated by (i) entrapment in insoluble glucan synthesized by S. salivarius culture fluids, and (ii) prior adsorption of GT from S. salivarius culture fluids. The possibility that GT formed by high-yield strains of S. salivarius is distributed through the mouth by the action of salivary flow and contributes to sucrose-dependent adherence and plaque formation is considered.