Evaluation of the Xpert vanA/vanB assay using enriched inoculated broths for direct detection of vanB vancomycin-resistant Enterococci.

Rapid and accurate detection of VRE (vancomycin-resistant enterococci) is required for adequate antimicrobial treatment and infection prevention measures. Previous studies using PCR for the detection of VRE, including Cepheid's Xpert vanA/vanB assay, reported accurate detection of vanA VRE; however, many false-positive results were found for vanB VRE. This is mainly due to nonenterococcal vanB genes, which can be found in the gut flora. Our goal was to optimize the rapid and accurate detection of vanB VRE and to improve the positive predictive value (PPV) by limiting false-positive results. We evaluated the use of the Xpert vanA/vanB assay on rectal swabs and on enriched inoculated broths for the detection of vanB VRE. By adjusting the cycle threshold (CT) cutoff value to ≤ 25 for positivity by PCR on enriched broths, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 96.9%, 100%, 100%, and 99.5% for vanB VRE, respectively. As shown in this study, CT values of ≤ 25 acquired from enriched broths can be considered true positive. For broths with CT values between 25 and 30, we recommend confirming the results by culture. CT values of >30 appeared to be true negative. In conclusion, this study shows that the Cepheid's Xpert vanA/vanB assay performed on enriched inoculated broths with an adjusted cutoff CT value is a useful and rapid tool for the detection of vanB VRE.

Effect of theophylline on CD11b and L-selectin expression and density of eosinophils and neutrophils in vitro.

The nonspecific phosphodiesterase inhibitor theophylline, widely used in asthma therapy, may cause a decrease in inflammatory responses of airways. In asthma, eosinophils migrate to the airway wall and become activated. Activated eosinophils are characterized by low cell density, as well as increased expression of CD11b and reduced expression of L-selectin, two adhesion molecules involved in transendothelial migration. To study the anti-inflammatory effect of theophylline on granulocyte adhesion molecules in vitro, the platelet-activating factor (PAF)-induced density shift was determined by density centrifugation and the modulation of CD11b and L-selectin expression by flow cytometry on eosinophils and neutrophils in human whole blood. A relatively high concentration of theophylline (10(-3) M) inhibited the increase in the percentage of hypodense eosinophils and neutrophils in whole-blood samples after PAF stimulation in vitro. A more pharmacological concentration (10(-4) M) inhibited the CD11b upregulation and L-selectin shedding induced by PAF (10(-7) M) on both eosinophils and neutrophils. The effect of isoproterenol on the inhibitory effect of theophylline was mainly additive, but a small synergistic effect could not be excluded. In conclusion theophylline can attenuate eosinophil and neutrophil activation in vitro at the level of adhesion molecule expression and changes in cell density. This may have implications for transendothelial migration of these cells in asthma.

Inhibition of PAF-induced expression of CD11b and shedding of L-selectin on human neutrophils and eosinophils by the type IV selective PDE inhibitor, rolipram.

We quantitatively determined whether the selective phosphodiesterase (PDE) inhibitor, rolipram, inhibits changes in the adhesion molecules CD11b and L-selectin on platelet-activating factor (PAF)-stimulated human neutrophils and eosinophils in vitro. Incubations were performed in human whole blood obtained from healthy volunteers, to restrict activation by purification procedures and to simulate in vivo conditions, in which different cell types may interact, more closely. Receptor expression was measured after fixation of cells, using monoclonal antibodies and flow cytometry. Concentration-dependent inhibition of the PAF-induced CD11b expression and L-selectin shedding for neutrophils and eosinophils was observed with rolipram, dibutyryl cyclic adenosine monophosphate (cAMP), prostaglandin E2 (PGE2), and isoproterenol. However, these inhibitions did not exceed 50%. Preincubation with rolipram (10(-8) M) and subsequent incubation with isoproterenol (0.5x10(-8) M) or PGE2 (10(-8) M) induced a cumulative, but not synergistic, effect. Using the combination of rolipram with isoproterenol or PGE2, inhibition of PAF-induced L-selectin shedding from eosinophils was as high as 71+/-28 and 67+/-21%, respectively. Other inhibitions were below 50%. In conclusion, rolipram inhibits CD11b expression and L-selectin shedding of platelet-activating factor-stimulated neutrophils and eosinophils in whole blood in a concentration-dependent fashion. Inhibitions did not exceed 50%, even at high concentrations. The inhibition of platelet-activating factor induced shedding of L-selectin from eosinophils with a combination of rolipram and prostaglandin E2 or isoproterenol, however, was found to be approximately 70%. Inhibition of rolling adhesion of eosinophils may, therefore, be a mode of action of type IV phosphodiesterase inhibitors.

Dextran sedimentation induces a difference in the percentage of hypodense eosinophils in peripheral blood between children with allergic asthma and healthy controls.

Considerable differences in the percentage of hypodense eosinophils in the peripheral blood of asthmatics have been reported by different investigators. In these previous studies dextran sedimentation was used for removal of erythrocytes prior to density centrifugation. We hypothesized that the sedimentation procedure might induce the presence of hypodense eosinophils in the peripheral blood of asthmatic patients. In order to test this hypothesis, we compared eosinophil density profiles from peripheral blood of children with asthma and of age-matched healthy controls, using different procedures. In the first method (direct method) blood samples were directly layered on a discontinuous Percoll gradient. Erythrocytes were removed by isotonic lysis. In the second method (dextran sedimentation) erythrocytes were removed by sedimentation with dextran prior to gradient centrifugation. Results of the direct method show no significant difference in percentage of hypodense eosinophils between children with asthma and healthy controls (9.19% and 6.84% respectively). However, after dextran sedimentation, children with asthma had a significantly higher percentage of hypodense eosinophils than healthy controls (15.40% and 8.84% respectively; P < 0.05). The percentage of hypodense eosinophils was correlated with the number of eosinophils and with the lung function, measured as the Tiffeneau index (FEV1/VC), in the whole group of subjects when the direct method was used. We conclude that an increased percentage of hypodense eosinophils is not present in the circulation of children with asthma, but can be induced in vitro by dextran sedimentation. Therefore, in vitro generation of hypodense eosinophils in the blood of patients with asthma seems to be related with the primed state of eosinophils.

Induction of low density and up-regulation of CD11b expression of neutrophils and eosinophils by dextran sedimentation and centrifugation.

Neutrophils and eosinophils circulating in an activated state are of low density. However, purification procedures such as dextran sedimentation and centrifugation may influence the density and function of cells. In the present study we have evaluated the effect of dextran sedimentation and subsequent centrifugation on the density and CD11b expression of neutrophils and eosinophils. Direct density separation of whole blood resulted in 17.7 +/- 9.0% low density neutrophils (< 1.090 g/ml) and 8.7 +/- 3.5% low density eosinophils (< 1.093 g/ml). Dextran sedimentation at room temperature prior to density separation yielded 57.8 +/- 14.7% low density neutrophils and 43.2 +/- 8.0% of low density eosinophils. Additional centrifugation after dextran sedimentation resulted in an increase of these numbers to 91.7 +/- 3.1 and 69.8 +/- 11.7% respectively. The density shifts were found with hypertonic as well as isotonic Percoll. Furthermore, it was shown that dextran sedimentation resulted in an increased CD11b expression on neutrophils as well as eosinophils. During subsequent washing by centrifugation, a further increase in CD11b expression was observed together with lactoferrin release. The effects of dextran sedimentation on density and CD11b expression were independent of extracellular calcium. These results indicate that dextran sedimentation induces the release of specific granule compartments with subsequent expression of CD11b, resulting in changes in granulocyte density.

Expression of CD35 (CR1) and CD11b (CR3) on circulating neutrophils and eosinophils from allergic asthmatic children.

Complement receptors on neutrophils and eosinophils play a role in activation and adhesion. During asthmatic reactions these receptors have been found elevated on circulating granulocytes. In the present study we compared the expression of CD35 (complement receptor type 1) and CD11b (complement receptor type 3) on neutrophils and eosinophils from asthmatic and non-asthmatic children. This was done in whole blood samples using depolarized light scattering for the discrimination of neutrophils and eosinophils. The non-stimulated expression as well as the upregulated expression of receptors by the chemotactic peptide N-formylmethionyl-leucyl-phenyl-alanine (fMLP) were studied. The results showed that without prior stimulation only the expression of CD35 on neutrophils was significantly elevated in children with asthma (P<0.05). After up-regulation with fMLP, the CD11b expression on neutrophils (P<0.005, fMLP: 0.002 microM) and eosinophils (P<0.05, fMLP: 0.02 microM) was significantly higher in asthmatic children than in the controls. These results indicate that the inducible expression of CD11b on neutrophils and eosinophils from allergic asthmatic children is primed in vivo.