Methicillin-Resistant Staphylococcus aureus: Comparison of Susceptibility Testing Methods and Analysis of mecA-Positive Susceptible Strains

Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for an increasing number of serious nosocomial and community-acquired infections. Phenotypic heterogeneous drug resistance (heteroresistance) to antistaphylococcal beta-lactams affects the results of susceptibility testing. The present study compared the MRSA-Screen latex agglutination test (Denka Seiken Co., Ltd., Tokyo, Japan) for detection of PBP 2a with agar dilution, the VITEK-1 and VITEK-2 systems (bioMérieux, St. Louis, Mo.), and the oxacillin agar screen test for detection of MRSA, with PCR for the mecA gene used as the "gold standard" assay. Analysis of 107 methicillin-susceptible S. aureus (MSSA) isolates and 203 MRSA isolates revealed that the MRSA-Screen latex agglutination test is superior to any single phenotype-based susceptibility testing method, with a sensitivity of 100% and a specificity of 99.1%. Only one isolate that lacked mecA was weakly positive by the MRSA-Screen latex agglutination test. This isolate was phenotypically susceptible to oxacillin and did not contain the mecA gene by Southern blot hybridization. The oxacillin agar screen test, the VITEK-1 system, the VITEK-2 system, and agar dilution showed sensitivities of 99.0, 99.0, 99.5, and 99%, respectively, and specificities of 98.1, 100, 97.2, and 100%, respectively. The differences in sensitivity or specificity were not statistically significant. Oxacillin bactericidal assays showed that mecA- and PBP 2a-positive S. aureus isolates that are susceptible to antistaphylococcal beta-lactams by conventional methods are functionally resistant to oxacillin. We conclude that the accuracy of the MRSA-Screen latex agglutination method for detection of PBP 2a approaches the accuracy of PCR and is more accurate than any susceptibility testing method used alone for the detection of MRSA.     

Acute hypothalamic-pituitary-adrenal responses to the stress of treadmill exercise. Physiologic adaptations to physical training

To study the effects of physical conditioning on the hypothalamic-pituitary-adrenal axis, we examined the plasma ACTH, cortisol, and lactate responses in sedentary subjects, moderately trained runners, and highly trained runners to graded levels of treadmill exercise (50, 70, and 90 percent of maximal oxygen uptake) and to intravenous ovine corticotropin-releasing hormone (1 microgram per kilogram of body weight). Basal evening concentrations of ACTH and cortisol, but not of lactate, were elevated in highly trained runners as compared with sedentary subjects and moderately trained runners. Exercise-stimulated ACTH, cortisol, and lactate responses were similar in all groups and were proportional to the exercise intensity employed. These responses, however, were attenuated in the trained subjects when plotted against applied absolute workload. Only the highly trained group had diminished responses of ACTH and cortisol to ovine corticotropin-releasing hormone, consistent with sustained hypercortisolism. We conclude that physical conditioning is associated with a reduction in pituitary-adrenal activation in response to a given workload. Alterations of the hypothalamic-pituitary-adrenal axis consistent with mild hypercortisolism and similar to findings in depression and anorexia nervosa were found only in highly trained runners. Whether these alterations represent an adaptive change to the daily stress of strenuous exercise or a marker of a specific personality profile in highly trained athletes is unknown.     

The phage T4 nrdB intron: a deletion mutant of a version found in the wild

Bacteriophage T4 possesses three self-splicing group I introns. Two of the three introns are mobile elements; the third, in the gene encoding a subunit of the phage nucleotide reductase (nrdB), is not mobile. Because intron mobility offers a reasonable explanation for the paradoxical occurrence of large intervening sequences in a space-efficient eubacterial phage, it is puzzling that the nrdB intron is not mobile like its compatriots. We have discovered a larger nrdB intron in a closely related phage, and we infer from comparative sequence data that the T4 intron is a deletion mutant derived from this larger intron. This larger nrdB intron encodes an open reading frame of 269 codons, which we have cloned and overexpressed. The overexpressed protein shows a dsDNA endonuclease activity specific for the intronless nrdB gene, typical of mobile introns. Thus, we believe that all three introns of T4 are or were mobile "infectious introns" and that they have entered into and been maintained in the phage population by virtue of this efficient mobility.     

Amphiphysin IIm, a novel amphiphysin II isoform, is required for macrophage phagocytosis

Phagocytosis of pathogens by macrophages initiates the innate immune response, which in turn orchestrates the adaptive immune response. Amphiphysin II participates in receptor-mediated endocytosis, in part, by recruiting the GTPase dynamin to the nascent endosome. We demonstrate here that a novel isoform of amphiphysin II associates with early phagosomes in macrophages. We have ablated the dynamin-binding site of this protein and shown that this mutant form of amphiphysin II inhibits phagocytosis at the stage of membrane extension around the bound particles. We define a signaling cascade in which PI3K is required to recruit amphiphysin II to the phagosome, and amphiphysin II in turn recruits dynamin. Thus, amphiphysin II facilitates a critical initial step in host response to infection.     

Mitogenicity of Entamoeba histolytica extracts for murine lymphocytes.

Aqueous extracts or aqueous extracts of delipidated Entamoeba histolytica (E.h.e.) contain a mitogenic principle for murine lymphocytes. As detected by [3H]-thymidine incorporation and blast transformation, E.h.e. acted predominantly on T cells of splenic origin, but not on thymocytes or bone marrow cells. Furthermore, E.h.e. induced proliferation of a subset of non-T-cells which is present in the spleen of athymic nude mice, adhered to nylon wool, but could not be activated to produce antibody. It seems possible that polyclonal activation of lymphocytes by E. histolytica might play a role in the disturbance of the immune system as manifested in the impaired cell mediated immune response of E. histolytica infected hosts.     

Hypothalamic obesity following knife cuts that minimize arterial damage

Parasagittal knife cuts that separate the medial hypothalamus from the lateral hypothalamus produce obesity. It has been assumed that the obesity results from the cutting of axons. However, these cuts also appear to sever arteries. The present study demonstrates that the severing of arteries is not necessary for the production of obesity. Knife cuts were placed at an angle so as to separate the medial hypothalamus from the lateral hypothalamus with minimal damage to arteries. These rats overate and became obese just as rapidly as rats with parasagittal cuts.     

Antigenic and immunologic characterization of an allogeneic colon carcinoma vaccine

In the present prospective, census-based study we have investigated the prevalence of organ-specific and non-organ-specific autoantibodies (AAb) in 152 unselected Cameroonians aged 60 years and older living in the community. AAb were detected in 49% of the participants. Non-organ-specific AAb (47%) predominated over organ-specific AAb (7%). Anti-TPO, anti-Tm, anti-Tg and anti-PC AAb were completely absent. RF was the most frequent AAb, being found in 57 (38%) cases. The prevalences of anti-SMA and RF were significantly higher in women than in men (respectively, P=0.023 and P=0.016). Higher serum concentrations of gammaglobulins were accompanied by a higher prevalence of RF (P < 0.0001) and a lower prevalence of ANA (P=0.036). The overall prevalence of AAb was higher in the filaria-infected (60%) compared to the non-infected (42%) participants (P=0.046). There was no significant influence of the vitamin D status, number of pregnancies, physical activity or medication use on the prevalence of AAb. In this study a heterogeneous pattern for the presence of the various AAb was found. Some AAb, which are commonly encountered in other studies on elderly subjects, were completely absent in this population. This diversified pattern of AAb prevalence therefore argues in favour of exogenous influences in the occurrence of AAb in elderly populations.