Sampling variability in the microbiological evaluation of expectorated sputa and endotracheal aspirates

A five-center study was conducted with the aim of determining how reproducibly expectorated sputa and tracheal aspirates could be sampled when preparing Gram-stained smears and inoculating cultures. With both specimen types, excessive variation was noted among Gram stain results obtained from replicate smears. Less variation was noted among culture results, especially with tracheal aspirates.

Variation and persistence of methicillin-resistant Staphylococcus aureus strains among individual patients over extended periods of time

To determine the strain variation and persistence among isolates of methicillin-resistant Staphylococcus aureus (MRSA) cultured from patients with colonization over extended time spans, pulsed-field gel electrophoresis was used to analyze the isolates from 47 patients for whom at least two mecA-positive isolates collected a minimum of six months apart were available. For 22 (47%) patients, the isolates represented multiple distinct strains of Staphylococcus aureus, while 20 (43%) patients had only a single strain detected; five (11%) patients had similar, genetically related isolates. MRSA were frequently associated with mucocutaneous abnormalities; 29 (62%) patients had focal cutaneous defects, and ten (21%) had chronic dermatitis. Multiple strains of MRSA were detected more frequently than single strains among patients in whom the initial focus of MRSA resolved clinically and another mucocutaneous defect subsequently developed compared to patients with clinically persistent foci (11/15 versus 9/23, respectively; p = 0.05, Fisher's exact test). Among the 21 patients in this series for whom isolates cultured within a two-month time span were available, there were seven (33%) patients with multiple strains of MRSA, including one patient with polyclonal bacteremia. In summary, patients with long-term MRSA colonization often have several different strains of MRSA, which typically change overtime in association with removal or resolution of a colonized focus and the recurrence of mucocutaneous defects.

Ultrastructural observations of X-ray induced chromatid gaps

A combination of light microscopy, transmission electron microscopy of whole-mount preparations and sectioned material, and scanning electron microscopy was employed to examine the fine structure of X-ray induced gaps and breaks in mammalian chromosomes, in an effort to determine the true nature of these aberrations. The results suggest that, rather than being completely separate phenomena, gaps and breaks are different manifestation of the same events and that gaps may be incomplete breaks. It was determined that light microscopy alone is inadequate for making accurate quantitative assessments of these aberrations, and it is therefore proposed that electron microscopy be used to supplement light microscopy for the analysis of gaps and breaks.