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Journal of Clinical Microbiology, October 2000, p. 3907-3907, Vol. 38, No. 10
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
LETTERS TO THE EDITOR
PCR Can Add to Detection of Pneumococcal Disease in Pneumonic
Patients Receiving Antibiotics at Admission
 |
LETTER |
We wish to add to the debate on PCR for the detection of
bacteremia in patients on antibiotics (3). We evaluated a
nested PCR (nPCR) for Streptococcus pneumoniae DNA in the
blood of 86 consecutive adult acute medical admissions in which the
admitting intern considered blood culture to be indicated. EDTA blood
samples taken at admission were tested by the nPCR, DNA being extracted by the method of Bell et al. (1), using proteinase K
digestion and chloroform extraction. The nPCR targeted the pneumolysin
gene. The first-round primers (amplifying a region of 501 bp) were
5'-ATGGCAAATAAAGCAGTAAATGACT-3' and
5'-AGAACCAAACTTGACCTTGAGTTGT-3'. An internal amplification control which coamplified to give a 316-bp product was incorporated. The nested primers amplified a 170-bp region within the first-round amplicon but outside of the amplification control and were
5'-TTTGCCTGGTTTGGCAAGTAGC-3' and 5'-CCATGCTGTGAGCCGTTATTTTTT-3'.
Amplification consisted of 35 cycles for each round, and products were
detected by ethidium bromide-stained gels. The nPCR was shown to be
specific for S. pneumoniae when tested against a wide range
of nonpneumococcal streptococci and unrelated bacterial species. Using
serial dilutions of a broth culture of S. pneumoniae NCTC
7466, the first-round amplification detected 7.5 × 103 CFU
and the full nPCR detected 75 CFU.
The nPCR was positive in only one of 42 patients with either
nonpneumococcal bacteremia (Escherichia coli in 2 patients
and Staphylococcus aureus in 1 patient), localized
nonpneumococcal infection, or noninfective conditions. This patient had
Streptococcus mitis endocarditis. This apparently anomalous
result is, in fact, consistent with recent observations (4).
The reaction was inhibited in two samples in this group.
Of three patients with proven bacteremic pneumococcal pneumonia, the
nPCR was positive for two and inhibited for one. However, nine
nPCR-positive and two inhibited reactions occurred in the remaining 41 patients with negative blood cultures but in whom pneumococcal disease
could not confidently be excluded, although it was much more likely in
some than in others. Seven positive results occurred in 14 patients
presenting with radiological pneumonia but with negative blood cultures
compared to only two (one patient with meningitis and one with chronic
obstructive pulmonary disease) in 27 patients without pneumonia
(P < 0.001). Twelve of these 41 patients were on
antibiotics and the nPCR was positive in 7 of these, in contrast to
only 2 of the 29 patients not receiving antibiotics (P < 0.001). All seven patients with pneumonia and a positive nPCR result
were on antibiotics compared to only three of the seven pneumonic
patients with a negative nPCR result. The nPCR results are summarized
in Table 1.
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TABLE 1.
Results of nPCR for S. pneumoniae DNA for EDTA
blood samples from 86 adult medical admissions presenting with possible
bacteremia related to clinical assessment
category
|
|
Our limited study supports the contention of Heininger et al. that PCR
may be useful in bacteremic patients in which antibiotics have
prevented cultural diagnosis (2) but also suggests that organism-specific PCRs are most productively targeted at particular syndromes (in this case, an S. pneumoniae PCR for pneumonia
patients). Whereas PCR might yet be too expensive for management of
individual patients with common conditions such as pneumonia, it will
be a valuable additional tool in surveys, the results of which can guide initial empirical therapy.
| |
FOOTNOTES |
*
Phone: 44 1912738987 Fax: 44 1912260365 E-mail:
newrfree{at}north.phls.nhs.uk
| |
REFERENCES |
| 1.
|
Bell, G. I.,
J. H. Karam, and W. J. Rutter.
1981.
Polymorphic DNA region adjacent to the 5' end of the human insulin gene.
Proc. Natl. Acad. Sci. USA
78:5759-5763[Abstract/Free Full Text].
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| 2.
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Heininger, A.,
M. Binder,
S. Schmidt,
K. Unertl,
K. Botzenhart, and G. Doring.
1999.
PCR and blood culture for the detection of Escherichia coli bacteremia in rats.
J. Clin. Microbiol.
37:2479-2482[Abstract/Free Full Text].
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Shah, P. M.
2000.
PCR for detection of bacteremia.
J. Clin. Microbiol.
38:943[Free Full Text].
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Whatmore, A. M.,
A. Efstratiou,
A. P. Pickerill,
K. Broughton,
G. Woodard,
D. Sturgeon,
R. George, and C. G. Dowson.
2000.
Genetic relationships between clinical isolates of Streptococcus pneumoniae, Streptococcus oralis, and Streptococcus mitis: characterization of "atypical" pneumococci and organisms allied to S. mitis harboring S. pneumoniae virulence factor-encoding genes.
Infect. Immun.
68:1374-1382[Abstract/Free Full Text].
|
| | | | |
Janice Wheeler
Olive M. Murphy
Roger Freeman*
Angela M. Kearns
Newcastle Regional Public Health Laboratory
Newcastle
General Hospital
Newcastle upon Tyne, NE4 6BE, United
Kingdom
|
| | | | |
Michael Steward
Maureen J. S. Lee
Novocastra Laboratories Ltd.
Newcastle
upon Tyne, NE12 8EW, United Kingdom
|
Journal of Clinical Microbiology, October 2000, p. 3907-3907, Vol. 38, No. 10
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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