Optimization of the transport mean free path and the absorption length in random lasers with non-resonant feedback.

We have studied numerically the optimal range of the transport mean free path lt and the absorption length (at the pumping wavelength) la, which minimize the threshold and maximize the slope efficiency of a random laser with non-resonant feedback. The results of the calculations are in a good agreement with the experimental results obtained in the GaAs/Al2O3 random laser.

Distribution of streptococcal inhibitor of complement variants in pharyngitis and invasive isolates in an epidemic of serotype M1 group A Streptococcus infection.

Streptococcal inhibitor of complement (Sic) is a highly polymorphic extracellular protein made predominantly by serotype M1 group A Streptococcus (GAS). New variants of the Sic protein frequently appear in M1 epidemics as a result of positive natural selection. To gain further understanding of the molecular basis of M1 epidemics, the sic gene was sequenced from 471 pharyngitis and 127 pyogenic and blood isolates recovered from 598 patients living in metropolitan Helsinki, Finland, during a 37-month population-based surveillance study. Most M1 GAS subclones recovered from pyogenic infections and blood were abundantly represented in the pool of subclones causing pharyngitis. Alleles shared among the pharyngitis, pyogenic, and blood samples were identified in throat isolates a mean of 9.8 months before their recovery from pyogenic infections and blood, which indicates that selection of most sic variants occurs on mucosal surfaces. In contrast, no variation was identified in the emm and covR/covS genes.

Rapid selection of complement-inhibiting protein variants in group A Streptococcus epidemic waves.

Serotype M1 group A Streptococcus strains cause epidemic waves of human infections long thought to be mono- or pauciclonal. The gene encoding an extracellular group A Streptococcus protein (streptococcal inhibitor of complement) that inhibits human complement was sequenced in 1,132 M1 strains recovered from population-based surveillance of infections in Canada, Finland and the United States. Epidemic waves are composed of strains expressing a remarkably heterogeneous array of variants of streptococcal inhibitor of complement that arise very rapidly by natural selection on mucosal surfaces. Thus, our results enhance the understanding of pathogen population dynamics in epidemic waves and infectious disease reemergence.

Rapid molecular genetic subtyping of serotype M1 group A Streptococcus strains.

Serotype M1 group A Streptococcus, the most common cause of invasive disease in many case series, generally have resisted extensive molecular subtyping by standard techniques (e.g., multilocus enzyme electrophoresis, pulsed-field gel electrophoresis). We used automated sequencing of the sic gene encoding streptococcal inhibitor of complement and of a region of the chromosome with direct repeat sequences to unambiguously differentiate 30 M1 isolates recovered from 28 patients in Texas with invasive disease episodes temporally clustered and thought to represent an outbreak. Sequencing of the emm gene was less useful for M1 strain differentiation, and restriction fragment length polymorphism analysis with IS1548 or IS1562 as Southern hybridization probes did not provide epidemiologically useful subtyping information. Sequence polymorphism in the direct repeat region of the chromosome and IS1548 profiling data support the hypothesis that M1 organisms have two main evolutionary lineages marked by the presence or absence of the speA2 allele encoding streptococcal pyrogenic exotoxin A2.

Hypervariability generated by natural selection in an extracellular complement-inhibiting protein of serotype M1 strains of group A Streptococcus.

In many countries, M1 strains of the human pathogenic bacterium group A Streptococcus are the most common serotype recovered from patients with invasive disease episodes. Strains of this serotype express an extracellular protein that inhibits complement [streptococcal inhibitor of complement (Sic)] and is therefore believed to be a virulence factor. Comparative sequence analysis of the 915-bp sic gene in 165 M1 organisms recovered from diverse localities and infection types identified 62 alleles. Inasmuch as multilocus enzyme electrophoresis and pulsed-field gel electrophoresis previously showed that most M1 organisms represent a distinct streptococcal clone, the extent of sic gene polymorphism was unexpected. The level of polymorphism greatly exceeds that recorded for all other genes examined in serotype M1 strains. All insertions and deletions are in frame, and virtually all nucleotide substitutions alter the amino acid sequence of the Sic protein. These molecular features indicate that structural change in Sic is mediated by natural selection. Study of 70 strains recovered from two temporally distinct epidemics of streptococcal infections in the former East Germany found little sharing of Sic variants among strains recovered in the different time periods. Taken together, the data indicate that sic is a uniquely variable gene and provide insight into a potential molecular mechanism contributing to fluctuations in streptococcal disease frequency and severity.

Medical students' confidence and the characteristics of their clinical experiences in a primary care clerkship.

PURPOSE: To investigate the relationship between medical students' confidence and their experiences in caring for patients within a primary care clerkship, because hands-on experience is assumed to be positively related to the development of confidence (a subjective marker of competence). METHOD: The participants were 60 students from the class of 1992 who completed a required third-year ambulatory care clerkship at the University of Kentucky Medical Center. The students documented their one-on-one experiences in patient care (under the supervision of preceptors in family practice, general pediatrics, or general internal medicine) by completing data cards on each patient encounter. Also, for each encounter, the students used a Likert scale to rate their levels of confidence in dealing with the patient's primary diagnosis. The variables recorded on the cards were then used to predict the students' levels of confidence during the encounters. The statistical analysis included descriptive statistics, Pearson correlations, and a stepwise multiple-regression procedure. RESULTS: The mean number of patient encounters per student was 99. The regression procedure selected three variables from the data cards as significant independent predictors of the students' confidence: management responsibility for the patient's problem (R2 = .40), prior exposure to the patient's problem (R2 = .08), and performance of laboratory work during the patient encounter (R2 = .06). These variables were responsible for predicting 54% of the observed variance in the students' confidence (R2 = .54). CONCLUSION: Hands-on clinical experience was more important for building students' confidence than any other encounter variable.

Velocity detection of Korotkoff sounds.

High-speed oscillograms were made showing the time relationships between the ECG and arterial pressure waves detected by three microphones successively placed beneath a standard blood pressure cuff along the brachial artery. As the cuff was deflated through the systolic/diastolic range, the indicated propagation velocity of the Korotkoff waves changed from approximately 1 m/sec near systolic pressure to about 2.5 m/sec near diastolic pressure. Non-Korotkoff waves (noise artifacts), on the other hand, were observed to propagate at much higher velocities, on the order of 5-10 m/sec. This phenomenon can be utilized to identify Korotkoff waves in the presence of other disturbances, particularly in exercise situations, and to determine diastolic pressure in the presence of arterially conducted valve and turbulence noise.