Real-time detection of DNA during gel electrophoresis using a Zeeman refractive index detector.

We have developed a new method for detecting unstained, untagged, unlabeled DNA bands in real-time during gel electrophoresis. This technique is based on the use of a Zeeman refractive index detector with lambda/12,000 resolution and outstanding stability. Current sensitivity in a polyacrylamide gel is 0.2 ng of DNA in the probe beam. We believe this can be significantly improved. We don't understand why the DNA initially decreases, then dramatically increases, the local refractive index as it passes through the gel, although we propose three possible mechanisms.

Absence of autolytic activity (peptidoglycan nicking) in penicillin-induced nonlytic death in a group A streptococcus.

The extent of sublytic autolysin activity (peptidoglycan [PG] nicking) after exposure of exponentially growing cultures of a group A streptococcus (GAS) to benzylpenicillin (PenG) was studied by determining changes in the glycan chain length of PG polymers. The average PG chain length in isolated cell walls was estimated by calculating the ratio of the total hexosamine content (Morgan-Elson-reactive material) to reducing-end group content established via quantitation of [3H]borohydride reduction products. Comparison of the average PG chain length obtained from untreated control cultures of GAS with those obtained after exposure to a saturating dose of PenG revealed no decrease over a time interval equivalent to four mass doublings of the control cultures. Exposure to this concentration of PenG for a time equivalent to only two mass doublings resulted in approximately 90% loss of viability. In contrast, exposure of the lytic bacterium, Streptococcus faecium ATCC 9790, to a 50% growth inhibitory dose of PenG produced a 20% reduction in the average PG chain length concomitant with only a 65% loss of viability. Preliminary characterization of the autolytic system of GAS indicated that this streptococcus has a hexosaminidase-type autolysin. The results presented indicate the lack of autolytic activity in PenG-induced nonlytic death.

Theory of attachment in Giardia.

Using a low Reynold's number hydrodynamic model, the adhesive force in Giardia is calculated. It is shown that this force is larger than typical forces that would tend to detach the organism.