Comparison of Petrifilm Staph Express Count System with the bacteriological analytical manual direct-plating method for enumeration of Staphylococcus aureus in artificially contaminated hard cheese

The 3M Petrifilm Staph Express Count System was compared with the U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM) direct-plate count method for the enumeration of Staphylococcus aureus in 6 types of artificially contaminated hard cheese (Asiago, Cheddar, Gruyère, Parmesan, Romano, and Swiss). Five different samples of each cheese type were inoculated with S. aureus (ATCC 25923) to achieve low, medium, and high inoculum levels. S. aureus was enumerated by the Petrifilm and BAM methods, and the results were compared. Multivariate analysis of variance revealed no significant differences (P<0.05) between the 2 methods. The Petrifilm method compared favorably with the BAM procedure. The rapid method was more convenient to use, considerably faster, and less expensive to perform than the BAM method.     

Detecting functional magnetic resonance imaging activation in white matter: Interhemispheric transfer across the corpus callosum

Background  

It is generally believed that activation in functional magnetic resonance imaging (fMRI) is restricted to gray matter. Despite this, a number of studies have reported white matter activation, particularly when the corpus callosum is targeted using interhemispheric transfer tasks. These findings suggest that fMRI signals may not be neatly confined to gray matter tissue. In the current experiment, 4 T fMRI was employed to evaluate whether it is possible to detect white matter activation. We used an interhemispheric transfer task modelled after neurological studies of callosal disconnection. It was hypothesized that white matter activation could be detected using fMRI.     

Rapid detection of the Vibrio cholerae ctx gene in food enrichments using real-time polymerase chain reaction

A real-time polymerase chain reaction (qPCR) assay for the detection of the ctxA gene of toxigenic Vibrio cholerae (Vc) was validated against standard culture techniques. The first experimental phase determined optimal enrichment conditions for detection by culture and qPCR of Vc in shrimp, bottled water, milk, and potato salad. The conditions tested included temperature (35 and 42 degrees C), time (6 and 18 h), and effect of shaking (0 and 100 rpm). No definitive trends were found with enrichment temperature or shaking on Vc isolation frequency or detection by qPCR. Generally, Vc was detected by qPCR more frequently than Vc was isolated, but this difference was significant only in the 35 degrees C 6 h enrichment without shaking. In the second phase of experiments, shrimp, bottled water, milk, potato salad, and oysters were inoculated with each of 3 toxigenic Vc strains (Latin American O1 strain, an O139 strain, and an O1 strain from the U.S. Gulf Coast) and enriched under static conditions at 42OC for 6 and 18 h. Overall, detection frequency of ctx by qPCR was 98% (88/90) and 100% (90/90) after 6 and 18 h enrichments, respectively, while Vc isolation frequency was 87% (78/90) and 83% (75/90) after 6 and 18 h, respectively. Toxigenic Vc can be detected by qPCR within an 8 h work day using the 6 h enrichment procedure, assuming an initial level of at least 1-2 colony-forming units/g; however, overnight enrichment may be necessary to detect lower levels. These data indicate that the qPCR assay for ctx is a more reliable, sensitive, and rapid alternative to standard Vc culture methods and is applicable to diverse food products.