Identification of the high-virulence clone of group B streptococci in Mexican isolates by growth characteristics at 40 degrees C

Group B streptococci (GBS) colonizing the vagina and rectum of pregnant women cause invasive disease of the offspring in a small number of cases. The immune status of the host and differences in virulence among strains appear to be the main determinants for neonatal infection. A high-virulence clone (HVC) was proposed to cause much of the morbidity and mortality when a collection of GBS isolates was examined by multilocus enzyme electrophoresis. HVC isolates could be further distinguished by their inability to grow at 40 degrees C. This characteristic was used in the present study to examine a collection of 57 GBS isolates from Mexico City for the HVC. Three serotype III invasive strains were classified in the HVC. The other eleven invasive strains and all carrier isolates had growth curves unaffected at 40 degrees C. These results demonstrate the presence of the HVC in Mexico. Such a low prevalence could explain in part the low rate of GBS invasive neonatal disease in Mexico.     

The inhibition of calcium oxalate monohydrate crystal growth by maleic acid copolymers

The crystallization of calcium oxalate monohydrate (COM) was investigated at conditions of constant supersaturation both in the absence and in the presence of synthetic maleic acid copolymers at 37C, 0.15 M NaCl. The dependence of the rates of COM crystallization in the absence of inhibitors was found to be second order at low and first order at higher supersaturations suggesting a surface diffusion controlled mechanism. The presence of all copolymers tested at concentration levels up to 5 ppm retarded the rates of COM crystal growth up to 90%. The decrease of the COM crystal growth rates by the polymers depended on the nature of the comonomer polymerized with maleic acid and the order of inhibition was found to be vinyl acetate > N-vinylpyrrolidone > styrene. Taking into consideration kinetics data published in the literature concerning the inhibition of COM crystal growth, it is suggested that molecular weight also plays a role, with more inhibition at higher molecular weights. The morphology of the COM crystals grown was unaffected yet the crystals growing at lower rates in the presence of the copolymers were larger and their size more uniform. It is concluded that maleic acid copolymers are strong inhibitors of the crystallization of COM, the inhibitory activity being more pronounced in the case of the linear copolymers.     

Impact of scale standardization on images of digital radiography systems

OBJECTIVES: To test the effect of altering image size on diagnostic quality. METHODS: Endodontic files, size 10 and 15 were prepared to full root length and 1.5 mm short, in upper and lower molars and premolars. Digital images of the Sidexis (S) and Visualix/Vixa (V) system were reduced in size to Digora (D) scale, and the D images were enlarged to S scale. ROC analysis was performed and data analysed with MANOVA statistics. RESULTS: Assessment of root canal length with file size 10 was less accurate for the S images reduced in size, compared with the original S images (P < 0.011). All other differences were not significant (P > 0.081). CONCLUSIONS: Relevant diagnostic information may be lost when images are reduced in size. Therefore, for optimal presentation, the smaller images should be enlarged rather than the larger ones reduced.     

Tuberculosis meningitis in Hong Kong: experience in a regional hospital

Tuberculous meningitis (TBM) remains common in Hong Kong. From January 1996 to June 1997, 11 adult patients with TBM presented to Queen Mary Hospital, a regional hospital in Hong Kong. The annual incidence of TBM was estimated at 1.8 per 100,000 population. Nine patients were local Chinese, and only one patient had the acquired immune-deficiency syndrome (AIDS). In contrast to the classical presentation as a chronic indolent disease, our patients presented acutely: the mean duration from onset of symptoms to presentation was 4.8 days (range 0-10). The most common presenting symptoms were headache (64%), fever (46%), or both (36%), with focal deficits occurring in 64% of patients. Cerebrospinal fluid (CSF) culture and polymerase chain reaction (PCR) were positive in 30% and 29% of cases. Mean CSF cell count, protein and glucose levels were 340 x 10(6)/L, 267 mg/dL, and 2.3 mmol/L, respectively. Extra-neural tuberculosis occurred in 46% of cases. All patients survived and responded to treatment. Drug-induced hepatotoxicity was common; 64% of patients developed biochemical hepatitis.     

In vitro encystment and experimental infections of Blastocystis hominis

Cultures of Blastocystis hominis were induced to encyst using three encystation media: (a) an encystation medium (EM) comprising yeast extract in buffered saline containing 50% horse serum, (b) an encystation medium (CEM) comprising EM conditioned with bacterial soluble products and (c) an encystation medium (TEM) containing 0.5% trypticase in EM. Two isolates of B. hominis were studied, an axenized isolate C and a non-axenized isolate MS. In EM, isolate C did not encyst, whereas 6.1% of isolate MS had encysted by day 1. However, in CEM and TEM, 17.4% and 25.7% of isolate C, respectively, had encysted by day 5. In all three media, isolate MS encysted more readily than isolate C, with as much as 91.7% of the former encysting in TEM. As viewed by phase-contrast microscopy, cyst-like stages appeared highly refractile. Direct stool examination of juvenile Wistar rats infected with 10,000 cyst-like stages of both C and MS isolates showed Blastocystis at day 2 post-infection. At autopsy on day 7, large numbers of Blastocystis were seen in the cecum, with smaller numbers being observed in the large intestine. In contrast, rats fed with various inocula of the vacuolar stages of isolates C and MS did not become infected, indicating the importance of the encysted stages in the transmission of the parasite.     

Think-aloud approaches to cognitive assessment and the articulated thoughts in simulated situations paradigm

In addition to widely used endorsement methods, one way to get at people's thoughts is to have them verbalize while engaged in a task or situation. The articulated thoughts in simulated situations (ATSS) paradigm is a think-aloud approach to cognitive assessment that has several advantages: an unstructured production response format, on-line rather than retrospective assessment, situational specificity and control, and flexibility of situation and cognitions. The authors review experiments that have examined articulated thoughts in clinically relevant contexts. ATSS does have certain limitations and further research into its psychometric properties is needed, but it seems promising as a versatile and adaptable method of cognitive assessment, especially when little is known of the cognitive terrain of interest.