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Journal of Clinical Microbiology, Apr 1997, 969-972, Vol 35, No. 4
LA Thal, J Silverman, S Donabedian and MJ Zervos
Contour-clamped homogeneous gel electrophoresis has increasingly been used
and has generally been considered the method of choice for the delineation
of enterococcial strains. It has been suggested that the contour-clamped
homogeneous electric field (CHEF) electrophoresis digestion patterns of
genomic DNA indicate the relatedness of strains when SmaI patterns differ
by six or fewer bands. To evaluate the potential reasons for the diversity
of bands among clonally related isolates, we studied plasmid-free
Enterococcus faecalis FA2-2 and derivatives with transposon Tn916 (encoding
for tetracycline resistance) insertions on the chromosome. We obtained
derivatives with seven different Tn916 insertion sites and up to two copies
of Tn916 on the chromosome, resulting in differences of one to seven bands
by CHEF electrophoresis; eight different patterns were observed. With Tn916
insertions, there was either (i) loss of a band(s) with the generation of a
new band(s), (ii) the generation of a new band(s) only, or (iii) the loss
of a band(s) with no new visible band(s). These results indicate that
strains can have up to seven different SmaI bands by CHEF electrophoresis
and still be closely related.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
The effect of Tn916 insertions on contour-clamped homogeneous electrophoresis patterns of Enterococcus faecalis
Department of Medicine, William Beaumont Hospital, Royal Oak, Michigan 48073, USA.
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