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Journal of Clinical Microbiology, 10 1996, 2619-2622, Vol 34, No. 10
CH Chiu and JT Ou
In order to make a rapid and definite diagnosis of Salmonella enteritis in
children, an enrichment broth culture-multiplex PCR combination assay was
devised to identify Salmonella serovars directly from fecal samples. Two
pairs of oligonucleotide primers were prepared according to the sequences
of the chromosomal invA and plasmid spvC genes. PCR with these two primers
would produce either one amplicon (from the invA gene) or two amplicons
(from the invA and spvC genes), depending on whether or not the Salmonella
bacteria contained a virulence plasmid. The fecal sample was diluted 10- to
20-fold into gram-negative enrichment broth and incubated to eliminate
inhibitory compounds and also to allow selective enrichment of the
bacteria. One or two amplicons were obtained, the expected result if
Salmonella bacteria were present. The detection limit of this PCR was about
200 bacteria per reaction mixture. The primers were specific, as no
amplification products were obtained with 18 species and 22 isolates of
non- Salmonella bacteria tested which could be present in the feces or
cause contamination. In contrast, when 23 commonly seen Salmonella serovars
(38 isolates) were tested, all were shown to carry the invA gene and seven
concomitantly harbored the spvC gene of the virulence plasmid. This assay
was applied to the diagnosis of Salmonella enteritis in 57 children who
were suffering from mucoid and/or bloody diarrhea. Of the 57 children, 38
were PCR positive and 22 were culture positive. There were two
culture-positive samples that were not detected by PCR. Thus, this PCR
assay showed an efficiency of 95% (38 of 40), which is much higher than the
60% (24 of 40) by culture alone. Not only is this method more sensitive,
rapid, and efficient but it will cause only an incremental increase in the
cost of stool processing, since enrichment cultivation of fecal samples
from diarrheal patients using gram- negative enrichment broth is a routine
practice for identification in many diagnostic microbiology laboratories.
This PCR method, therefore, has clinical application.
Copyright © 1996 by the American Society for Microbiology. All rights reserved.
Rapid identification of Salmonella serovars in feces by specific detection of virulence genes, invA and spvC, by an enrichment broth culture-multiplex PCR combination assay
Department of Pediatrics, Chang Gung Children's Hospital, Taoyuan, Taiwan.
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