The most important test for new isolates of C. diphtheriae is to determine if they are toxigenic, which has important implications for patient care and public health. The ideal test should be simple, sensitive, rapid, reliable, and inexpensive, and it should also correlate well with the biological activity of diphtheria toxin. Bioassays performed in susceptible animals or cultured cells are the gold standard, but unfortunately they are slow, complicated, and costly. Molecular methods based on immunochemical properties of diphtheria toxin or nucleotide sequences of the toxin structural gene serve as surrogates for bioassays and provide indirect assessments for potential toxigenicity of C. diphtheriae isolates. Elek tests, based on formation of toxin-antitoxin precipitates in agar during growth of tox+ isolates of C. diphtheriae, require rigidly controlled execution by skilled personnel, although recent modifications have improved their speed and cost-effectiveness. An immunochromatographic strip assay for diphtheria toxin offers great advantages in sensitivity, speed, and applicability for direct use on clinical specimens. Polymerase chain reaction-based methods to detect specific segments of the tox gene have been optimized for speed, sensitivity, and reliability, but they do not assess the ability of C. diphtheriae to produce the diphtheria toxin protein. Because some isolates of C. diphtheriae contain all or part of the toxin gene but do not produce diphtheria toxin, some positive PCR results may lead to false-positive identification of tox+ C. diphtheriae isolates unless bioassays are also performed.
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The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.