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PCR of DNA extracted from different dilutions of the three Listeria spp. was undertaken to determine the minimal number of cells required for successful amplification of the conserved region of their 16S rRNA gene using PfuTurbo polymerase. A detectable PCR product was obtained using either set of primer pairs with as little as 1.3 ng DNA from 1.3 x 104 colony forming units (cfu) of L. innocua. A detectable PCR product was obtained with as little as 1.6 ng DNA from 5.2 x 103 cfu of L. monocytogenes using primer pair 1055F and 1406R with GC-clamp. Ten times this amount of L. monocytogenes DNA was required to obtain a detectable PCR product using the primer pair 341F with GC-clamp and 534R. A detectable PCR product was obtained with as little as 7.7 ng DNA from 6.9 x 103 cfu of L. seeligeri using primer pair 1055F and 1406R with GC-clamp, whereas, the other primer pair required ten times this amount of L. seeligeri DNA for a detectable product. The minimum quantity of DNA from these Listeria spp. that was required for successful amplification of fragments by PCR was generally less than that (25500 ng) recommended by the suppliers of the polymerase.
L. monocytogenes was distinguished from L. innocua and L. seeligeri when
fragments of their 16S rRNA gene(s), amplified by PCR using PfuTurbo polym
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