The objectives were to identify the source of Listeria monocytogenes in bulk tank milk (BTM), and to assess characteristics of Petrifilm Environmental Listeria (PEL) for detection of this pathogen in ...farm samples. Environmental and milk samples were collected from a dairy during two sampling periods. Follow-up samples of daily BTM and milk filters were collected. Isolates of L. monocytogenes were compared by use of Pulsed Field Gel Electrophoresis. Samples were plated on PEL and results classified into positive or negative. Of samples collected during the two sampling periods, L. monocytogenes was isolated from 66% of milk filters (19 of 29), 16% of BTM (7 of 44), 6% of water samples (two of 33) and one of 18 in-line milk samples. Except for one isolate, all were identical and of the same molecular type. Contamination of BTM with L. monocytogenes most likely originated from a common source, and results indicate that farms can develop persistent sources of contamination. The sensitivity of the PEL was high (100 and 74.1% for environmental and milk samples, respectively), but there was a high proportion of false-positive results and low specificity. These limitations need to be considered when using the PEL for on-farm screening of L. monocytogenes.
This study addressed the clinical reproducibility and validity of the thermodilution (TD) measurement of the right ventricular ejection fraction (RVEF). Forty-one patients underwent right heart ...catheterization, including TD RVEF, within 2 h of gated first pass (GFP) and gated blood pool (GBP) radionuclide ventriculography; 21 had single plane contrast right ventricular angiography (ANGIO) during the same catheterization. Analysis of variance showed no difference among three successive TD RVEF measurements. (table; see text) Stroke volume by RV ANGIO correlated with Fick (n = 10, r = .86) and thermodilution stroke volume (n = 21, r = .88). It is concluded that although the thermodilution method is an accurate way to measure flow, it is not an accurate way to measure right ventricular ejection fraction, and by inference, ventricular volumes. The most likely explanation for this finding is incomplete mixing as in previous studies of indicator methods of measuring left ventricular volumes.
