Comparison of polymerase chain reaction and Chlamydiazyme for the detection ofChlamydia trachomatis in clinical specimens

An attempt was made to improve laboratory diagnosis ofChalmydia trachomatis and to validate the Abbott Chlamydiazyme confirmatory test used at present by comparing the polymerase chain reaction (PCR) procedure and the Abbott enzyme immunoassay. A total of 275 routine clinical specimens representing a range of positive and negative findings by Chlamydiazyme were retested by PCR. The procedures demonstrated 99 % concordance for specimens with optical density (OD) readings above the Chlamydiazyme cut-off of 0.1, but PCR was confirmed to be significantly more sensitive (p<0.025) for specimens with OD values between 0.05 and 0.09. Specimens in this range should be retested routinely by PCR.     

Epidemiologists in the United States: an assessment of the current supply and the anticipated need

We provide 1985 estimates of the work force of epidemiologists in the United States, the number of graduates from training programs in epidemiology, and a projection of the future need for these health professionals. Our methods included a search of mailing lists from professional organizations, mail contact with graduate training programs, telephone interviews with experts, and a review of job announcements in professional journals. The study indicates that the current work force of epidemiologists in the United States is estimated to include 4,600 persons, more than half of whom are physicians; most epidemiologists are located in either a state with a major federal public health agency or one with a large population; and programs in epidemiology graduate an average of 475 persons with one or two years of master's level education and approximately 80 with doctoral-level education each year. After considering the factors that influence the supply of epidemiologists, we project a substantial need for more epidemiologists in the future than current sources will provide.     

Physiological evidence that periodontal collagen in the rat exists as fibres prior to histological fixation

The hypothesis that the collagen in the periodontal membrane forms a thixotropic gel in life and that the arrangement seen in histological preparations is a fixation artifact was tested by comparing the effects of various agents on the position of teeth in isolated unfixed mandibles and on the length of bundles of rat tail tendon collagen. Changing from Ringer solution to deionized water produced a reversible shortening of fibres and extrusion of teeth. Sucrose solutions produced irreversible lengthening and intrusion. Glutaraldehyde generally produced no length changes in the fibres or movements of the teeth but made both the fibres and teeth unresponsive to further changes of solution. Six mandibles in Ringer solution were heated in 5 °C increments to 70 °C. Between 60 and 65 °C (denaturation temperature of soft tissue collagens) the incisor extruded by 60 ± 15 (SD) μm. This extrusion did not occur in mandibles that had been stored in formalin. These results are consistent with at least part of the periodontal collagen existing as obliquely oriented fibres before fixation. This orientation is such that contraction of the fibres could produce an eruptive force.     

Stability of regional cerebral glucose metabolism in the normal brain measured by positron emission tomography

Cerebral glucose utilization (LCMRGI) was measured using the [18F]fluorodeoxyglucose method with PET in two groups of ten healthy young volunteers, each scanned in a resting state under different methodological conditions. In addition, five subjects had a second scan within 48 hr. Mean hemispheric values averaged 45.8 +/- 3.3 mumol/100 g/min in the right cerebral hemisphere and 47.0 +/- 3.7 mumol/100 g/min in the left hemisphere. A four-way analysis of variance (group, sex, region, hemisphere) was carried out on the results using three different methods of data manipulation: (a) the raw values of glucose utilization, (b) LCMRGI values "normalized" by the mean hemispheric gray matter LCMRGI value, and (c) log transformed LCMRGI values. For all analysis techniques, significantly higher LCMRGI values were consistently seen in the left mid and posterior temporal area and caudate nucleus relative to the right, and in the right occipital region relative to the left. The coefficient of variation of intrasubject regional differences (9.9%) was significantly smaller than the coefficient of variation for regions between subjects (16.5%). No differences were noted between the sexes and no effect of repeat procedures was seen in subjects having multiple scans. In addition, inter-regional LCMRGI correlations were examined both in values from the 20 normal subjects, as well as in a set of hypothetical "abnormal" values. Results were compared with those reported from other PET centers; despite certain methodological differences, the intersubject and inter-regional variation of LCMRGI is fairly constant.     

Do semantic categories activate distinct cortical regions? Evidence for a distributed neural semantic system

A key issue in cognitive neuroscience concerns the neural representation of conceptual knowledge. Currently, debate focuses around the issue of whether there are neural regions specialised for the processing of specific semantic attributes or categories, or whether concepts are represented in an undifferentiated neural system. Neuropsychological studies of patients with selective semantic deficits and previous neuroimaging studies do not unequivocally support either account. We carried out a PET study to determine whether there is any regional specialisation for the processing of concepts from different semantic categories using picture stimuli and a semantic categorisation task. We found robust activation of a large semantic network extending from left inferior frontal cortex into the inferior temporal lobe and including occipital cortex and the fusiform gyrus. The only category effect that we found was additional activation for animals in the right occipital cortex, which we interpret as being due to the extra visual processing demands required in order to differentiate one animal from another. We also carried out analyses in specific cortical regions that have been claimed to be preferentially activated for various categories, but found no evidence of any differential activation as a function of category. We interpret these data within the framework of cognitive accounts in which conceptual knowledge is represented within a nondifferentiated distributed system.     

Detection of the aerolysin gene in Aeromonas hydrophila by the polymerase chain reaction.

Synthetic oligonucleotide primers were used in a polymerase chain reaction (PCR) technique to detect the gene for aerolysin in strains of Aeromonas hydrophila and to screen for identical genes in A. caviae, A. sobria, and A. veronii isolated from patients with diarrheal disease. Primers targeted a 209-bp fragment of the aer gene coding for the beta-hemolysin and detected template DNA only in the PCR using nucleic acid (NA) from hemolytic strains of A. hydrophila which were also cytotoxic to Vero and CHO cells and enterotoxic in suckling-mouse assays. PCR amplification of NA from hemolytic A. sobria or nonhemolytic A. hydrophila and A. caviae strains was consistently negative. Primer specificity was determined in the PCR by using NA extracted from 56 strains of bacteria, including hemolytic Escherichia coli and Listeria monocytogenes as well as several recognized enteric pathogens defined in terms of their toxigenicity. The detection limit for the aerolysin gene by PCR amplification was 1 ng of total NA. The PCR clearly identified aerolysin-producing strains of A. hydrophila and may have application as a species-specific virulence test because other hemolytic Aeromonas species tested were negative.