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Cultures of Wolinella succinogenes were adapted to grow in the presence of 1 mM [Formula: see text] or 10 mM [Formula: see text]. Both selenium salts were reduced to red, amorphous, elemental selenium but only after the culture reached the stationary growth phase. Bacterial cells taken from a culture actively reducing selenium were examined by transmission electron microscopy and were found to have large, electron-dense granules in the cytoplasm. These granules were verified by energy-dispersive X-ray spectroscopy to consist of selenium. Wolinella succinogenes was unable to grow with [Formula: see text] or [Formula: see text] as the final electron acceptor. Key words: Wolinella, selenium, cytology, selenate.

The sizing of restriction fragments is the chief analytical technique utilized in the production of DNA fingerprints. Few techniques have been able to compete with pulsed-field gel electrophoresis (PFGE), which is capable of discriminating among bacteria at species and strain levels by resolving restriction fragments. However, an ultrasensitive flow cytometer (FCM) developed in our lab has also demonstrated the ability to discriminate bacteria at species and strain levels. The abilities of FCM warrant a quantitative parallel comparison with PFGE to assess and evaluate the accuracy and precision of DNA fragment sizing by both techniques. Replicate samples of Staphylococcus aureus Mu50 were analyzed along with two clinical S. aureus isolates. The absolute fragment sizing accuracy was determined for PFGE (5% ؎ 2%) and FCM (4% ؎ 4%), with sequence-predicted Mu50 SmaI fragment sizes used as a reference. Precision was determined by simple arithmetic methods (relative standard deviation for PFGE [RSD PFGE ] ‫؍‬ 3% ؎ 2% and RSD FCM ‫؍‬ 1.2% ؎ 0.8%) as well as by the use of dendrograms derived from Dice coefficient-unweighted pair group method with arithmetic averages (UPGMA) and Pearson-UPGMA analyses. All quantitative measures of PFGE and FCM precision were equivalent, within error. The precision of both methods was not limited by any single sample preparation or analysis step that was tracked in this study. Additionally, we determined that the curve-based clustering of fingerprint data provided a more informative and useful assessment than did traditional bandbased methods.DNA fragment sizing is arguably the most widely used analytical method in molecular biology, biochemistry, and microbiology. Specific applications of DNA fragment sizing include microbe identification and discrimination, genotyping, and sequencing. Traditionally, DNA fragments are characterized via size-dependent separation methods such as gel electrophoresis.Conventional gel electrophoresis, using a solid polymer (e.g., agarose or polyacrylamide) and a static electric field, is ubiquitous in today's molecular biology and biochemistry labs. Such methods are routinely used to separate and size DNA fragments of Յ20 kb (4).Pulsed-field gel electrophoresis (PFGE), developed in 1984 by Schwartz et al. (44), extended the fragment sizing range to over 1 Mb (4,6,9,19,44). For PFGE, large DNA fragments (i.e., Ͼ10 kb) are separated in an agarose gel by a pulsed electric field. A popular application of PFGE has been strainlevel bacterial fingerprinting through the sizing of DNA fragments resulting from the digestion of whole genomic DNAs with rare-cutting restriction endonucleases (5,11,28,35,47,49). Macrorestriction-based bacterial fingerprinting has found applications primarily in the public health and food safety industries. For example, the Centers for Disease Control and Prevention (CDC) have formed PulseNet, the National Molecular Subtyping Network for Foodborne Disease Surveillance (46; http://www.cdc.gov/pulsenet). PulseNet utilizes macrorestriction fi...

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 walis was estimated by calculating the ratio of the total hexosamine content (Morgan-Elson-reactive material) A unified model for the action of inhibitors of cell wall synthesis (21, 26) predicts that in all susceptible organisms, cell wall antibiotics initially act by inhibiting the assembly of insoluble peptidoglycan (PG), which in turn leads to bacteriostasis. The subsequent (secondary) events are species dependent and, on the basis of recent reports, can also be related to growth rate (4) and medium composition (14). Apparently, some bacteria die and then lyse, whereas others lyse immediately, and still others undergo nonlytic death. An additional response, tolerance, is considered in the model as a continuation of stasis (21) and has been suggested to be associated with specific regulatory mechanisms (19,21). A central feature of lytic phenotypes is the secondary expression of endogenous PG hydrolases (autolysins) after exposure to antibiotics (21,26). It follows that a prerequisite for nonlytic phenotypes is an absent, weakly expressed, or tightly regulated autolytic system. PG hydrolase activities are considered to be essential for normal surface growth and cell division processes (5) and are therefore presumed to be present in all bacterial cells. Considering the following phenomena: (i) the demonstrated unity in the primary mechanism of action of, for example, P-lactams in the binding to penicillin-binding proteins and inhibition of their function(s) (2, 9), (ii) the requirement of autolytic activities for growth (5), ahd (iii) the documented relationship between inhibition of PG assembly and deregulation of autolysins in lytic phenotypes (21, 26), hydrolysis of a small number of bonds insufficient to cause cellular lysis (nicking) has been suggested as a possible secondary and potentially fatal outcome of inhibition of PG synthesis in bacteria which undergo nonlytic death (8).In this report, we present results of experiments designed to assess the role of PG nicking in penicillin-induced nonlytic death in a group A streptococcus (GAS). Preliminary characterization of the autolytic system of GAS is also presented.( Quantitative comparison of growth inhibition. Conventional methods for determining MICs were considered to be unsatisfactory for use in these studies, since they rely on small, physiologically poorly defined inocula and long incubation intervals. Therefore, 50% growth inhibitory concentrations (GIC50s) were determined for each strain as described previously (17). For these studies we used GIC50s obtained after exposure of exponentially growing cultures at the time that exponentially growing control cultures had increased fourfold in turbidity. Potassium PenG (1,595 U/mg) used in these experim...

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We report the first acoustical vibration studies on chicken eggs. Measurements of the acoustic resonances offer the potential of simple, noninvasive, and rapid characterization of eggs. The technique appears at least partially sensitive to yolk puncture, shell cracks, and the presence of Salmonella bacteria. There may be practical quality control applications.