Genotyping of clinical methicillin-susceptible Staphylococcus aureus isolates in a Dutch teaching hospital

Methicillin-susceptible Staphylococcus aureus isolates, recovered from 204 patients in our hospital in a 22-month period, were characterized by pulsed-field gel electrophoresis. Among the multiple S. aureus types six clonal lineages dominated, comprising isolates from 158 patients. Despite the limited genetic variation, cross-transmission was made plausible only sporadically.     

Tip-oriented adherence of Treponema denticola to fibronectin.

The adherence of Treponema denticola to ligands on cell surfaces or in basement membranes of periodontal tissues might play an important role in its pathogenicity. A direct microscopic assay was used to examine the binding of T. denticola to fibronectin and other protein substrates adsorbed on plastic cover slips. All strains of T. denticola that were tested adhered to fibronectin but to different degrees. The strains which bound in high numbers frequently bound by their tips. Type strain ATCC 33520 bound to fibronectin in high numbers (149 +/- 11.3 bacteria per microscopic field), with 60% bound by the tips. Strain e' bound in high numbers (140 +/- 10.2) and had the highest percentage of tip binding (98%); strain e bound in lowest numbers (39 +/- 8.2) and had the lowest percentage of tip binding (15%). Laminin supported binding at a level similar to that of fibronectin, as did fibronectin fragments which contained the cell binding domain peptides, RGDS. Type IV collagen and non-RGDS peptides did not support binding. Binding to fibronectin and laminin was inhibited by the addition of antifibronectin and antilaminin antibodies. By lowering the incubation temperature from 37 to 4 degrees C, the number of cells that attached decreased by 60% and tip binding was reduced by 50%. Pretreatment of the cells with collagen did not affect binding, whereas fibronectin pretreatment enhanced binding by 50% and laminin pretreatment resulted in a decrease of 60%. T. denticola adheres by its tips to fibronectin-coated surfaces, which suggests that fibronectin-specific adhesins cluster at the tips.     

Chemical and immunological comparison of surface fibrils of strains representing six taxonomic groups of Actinomyces viscosus and Actinomyces naeslundii.

Human isolates of Actinomyces viscosus and Actinomyces naeslundii have been divided into six clusters in a numerical taxonomy study. Surface fibrils of strains representing these clusters were isolated and purified. Chemical analyses revealed that the major component of all fibrils was protein and that although differences in percentages of specific amino acid residues were found, the relative proportions of basic, acidic, polar uncharged, and nonpolar amino acids were rather similar among clusters. All of the fibrils except those from strain B236 (cluster 2) either failed to migrate or penetrated only slightly into gels during sodium dodecyl sulfate-polyacrylamide gel electrophoresis, even after boiling, reduction, or alkylation. Immunological studies by electron microscopic examination of fibril-antibody immunocomplexes, whole bacterial cell agglutination, inhibition of hemagglutination, and immunofluorescence by using antifibril antisera and antibodies demonstrated that strains of typical A. naeslundii (cluster 5) have a specific fibril-associated antigen(s) distinct from those of strains of other clusters. Cross-reactions for atypical A. naeslundii (cluster 3) were few. The fibrils from A. viscosus clusters 1, 2, 4, and 6 demonstrated several cross-reactions. By absorbing antifibril antibodies with cross-reactive strains it was possible to obtain cluster-specific antibodies, as determined by whole cell agglutination, only for cluster 5. Absorbed antifibril antisera for both A. naeslundii clusters 3 and 5 were specific by indirect immunofluorescence, whereas anti-cluster 1 fibril antisera cross-reacted only with other A. viscosus cluster representatives. Purification of Actinomyces fibrils by methods used for appendages of other species yields preparations containing common antigens among taxonomic groups. However, absorbing antifibril antisera, gamma globulin, or both has promise for producing cluster-specific reagents useful in identification.     

Are Viruses Important in Carcinogenesis?

The role of viruses in the etiology of animal cancers is fairly certain. Information derived under both natural and experimental conditions supports the concept that either DNA- or RNA-containing viruses can fulfill this function. The DNA-containing herpesviruses, especially the Epstein-Barr virus, are currently the primary objects of intense investigation concerning their role in human cancer. This article will focus on the properties of counterpart herpesviruses in lower animals as well as the human virus candidates with an assessment of the observations concerning their oncogenic potential.     

The pelvic epithelium of the rat kidney: A scanning and transmission electron microscopic study

The renal pelvis of the rat is characterized by extensions called specialized fornices that penetrate into the outer zone of the outer medulla (a type II as classified by Pfeiffer, 1968, 1970). The renal pelvic epithelium, therefore, covers areas of the kidney from the inner medulla, the inner and outer stripe of the outer medulla, and the cortex. The renal pelves of seven rats were studied by transmission and scanning electron microscopy. The transitional epithelium on the nonparenchymal surface of the pelvis was three to four cell layers thick (zone 0–1). This epithelium became thinner where it covered the renal cortex (zone 1–2) or the outer medulla. Although the apical cells of the epithelium retained the asymmetric luminal unit-membrane plaques, the number of cytoplasmic fusiform vesicles decreased as one studied the epithelium progressing over the zones from cortex toward papilla. Scanning electron microscopy demonstrated a small number of surface cells of a different morphology that were characterized by apical microvilli. The number of these microvillous lining cells increased as the epithelium covering the outer (zone 2–3) and inner (zone 3–4) stripe regions of the outer medulla was viewed, until the inner medulla was entirely covered by this cell type. In a reciprocal manner, the cells with the asymmetric apical plaques decreased in numbers and in their morphologic specialization in each successive region. The epithelium surrounding the inner medulla (zone 6–7) was completely devoid of this transitional cell type. Judging from the morphologic characteristics of the epithelia, one could surmise that little exchange of urea, water, and salts would occur with the extrarenal connective tissue or the cortical parenchyma. Recycling of urea might become more important physiologically with the outer stripe parenchyma, and even more so with the increased surfaces of the inner stripe parenchyma that lined the secondary pyramid, as well as with the epithelium lining the inner medulla.     

The impact of testing accommodations on MCAT scores: descriptive results.

PURPOSE: Medical College Admission Test (MCAT) examinees with disabilities who receive accommodations receive flagged scores indicating nonstandard administration. This report compares MCAT examinees who received accommodations and their performances with standard examinees. METHOD: Aggregate history records of all 1994-2000 MCAT examinees were identified as flagged (2,401) or standard (297,880), then further sorted by race/ethnicity (broadly identified as underrepresented minority and non-URM, at the time of testing) and gender. Those with flagged scores were also classified by disability (LD = learning disability, ADHD = attention deficit hyperactivity disorder, LD/ADHD = learning disability and attention deficit hyperactivity disorder, and Other = other disability) and type of accommodation. Mean MCAT scores were calculated for all groups. A group of 866 examinees took the MCAT first as a standard administration and subsequently with accommodations. In a separate analysis, their two sets of scores were compared. RESULTS: Less than 1% of examinees (2,401) had accommodations; of these, 55% were LD, 17% ADHD, 5% LD/ADHD, and 23% Other. Extended time was the most frequently provided accommodation. Mean flagged scores slightly exceeded mean standard scores on all MCAT sections. Examinees who retook the MCAT with accommodations after a standard administration increased their scores by six points, quadrupling the average gain Standard-Standard retest cohort from another study. CONCLUSION: The small but statistically significant different higher flagged scores may reflect either appropriate compensation or overly generous accommodations. Extended time had a positive impact on the scores of those who retested with this accommodation. The validity the flagged MCAT in predicting success in medical school is not known, and further investigation is underway.