Streptococcus pneumoniae antigen test using positive blood culture bottles as an alternative method to diagnose pneumococcal bacteremia.
ABSTRACT Recovery of Streptococcus pneumoniae from positive blood culture bottles may be difficult due to autolysis of pneumococci. Therefore, we evaluated the performance of the Binax NOW S. pneumoniae antigen test with samples from positive blood culture bottles and defined the duration of detectable pneumococcal antigen in these bottles. Use of the S. pneumoniae antigen test is an alternative method for identifying S. pneumoniae from positive blood culture bottles and may enable a diagnosis of pneumococcal bacteremia despite negative subcultures.
- The Lancet 11/2001; 358(9289):1273-4. · 39.06 Impact Factor
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ABSTRACT: Latex agglutination by use of the Pneumoslide test on clinical blood cultures detected 22 Streptococcus pneumoniae strains as the etiological agents in 47 streptococcal septic episodes. The other 25 isolates were identified as viridans streptococci or streptococci of groups A, B, D, or G. The test demonstrated 100% sensitivity, 92% specificity, and predictive values for positive and negative reactions of 91 and 92%, respectively. Two false-positive reactions were caused by strains of viridans streptococci. The two strains continued to give positive reactions when colonies from blood agar plates were tested according to the instructions of the manufacturer. This latex agglutination test is an effective tool for the rapid diagnosis of pneumococci in blood cultures.Journal of Clinical Microbiology 06/1984; 19(5):649-50. · 4.07 Impact Factor
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ABSTRACT: Most physicians recognize the false-positive blood cultures (generally due to contamination) are common. Bacteria such as pneumococci, however, may rapidly die in broth cultures, and viable bacteria may not be identified. Several patients were observed with pneumococcal infections that had false-negative blood cultures 24 hours after inoculation. Hemolysis and methemoglobin formation in the bottle suggested bacterial growth within 12 hours after incubation, and blind subcultures at that time yielded pneumococci. Pneumococcal antigen could be detected in the blood culture bottles using counter-immunoelectrophoresis, even though subculture at 24 hours yielded no growth. Physicians and laboratory personnel should be aware that false-negative blood cultures may occur, particularly with certain bacteria such as Streptococcus pneumoniae, and that the blood culture bottles should be observed visually for the presence of brown sediment or hemolysis.American Journal of Clinical Pathology 10/1982; 78(3):348-50. · 2.88 Impact Factor
JOURNAL OF CLINICAL MICROBIOLOGY, May 2005, p. 2510–2512
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Vol. 43, No. 5
Streptococcus pneumoniae Antigen Test Using Positive
Blood Culture Bottles as an Alternative Method
To Diagnose Pneumococcal Bacteremia
Cathy A. Petti,* Christopher W. Woods,
and L. Barth Reller
Clinical Microbiology Laboratory, Duke University Medical Center, and Departments
of Pathology and Medicine, Duke University School of Medicine,
Durham, North Carolina 27710
Received 24 June 2004/Returned for modification 14 September 2004/Accepted 28 January 2005
Recovery of Streptococcus pneumoniae from positive blood culture bottles may be difficult due to autolysis of
pneumococci. Therefore, we evaluated the performance of the Binax NOW S. pneumoniae antigen test with
samples from positive blood culture bottles and defined the duration of detectable pneumococcal antigen in
these bottles. Use of the S. pneumoniae antigen test is an alternative method for identifying S. pneumoniae from
positive blood culture bottles and may enable a diagnosis of pneumococcal bacteremia despite negative
Pneumococcal bacteremia is an important cause of severe
bloodstream infection worldwide and is associated with a high
mortality rate (13). Although standard culture-based methods
remain the mainstay for diagnosis, the Binax NOW Streptococ-
cus pneumoniae antigen test (Binax, Inc., Portland, Maine), an
immunochromatographic membrane assay that detects the
presence of the C polysaccharide cell wall antigen common to
all pneumococcal serotypes, has proven a valuable tool for the
rapid diagnosis from urine samples of invasive pneumococcal
disease (9, 12). The Food and Drug Administration recently
approved the use of this antigen test on cerebrospinal fluid for
the rapid diagnosis of pneumococcal meningitis (7).
Although S. pneumoniae grows rapidly in most conventional
and automated blood culture systems, it produces autolysin, a
cell wall enzyme responsible for its own lysis, during its sta-
tionary growth phase. Such autolysis may distort the appear-
ance of pneumococci on Gram stain or prevent growth on
subculture or both. Identification of S. pneumoniae from blood
cultures by a nonmolecular method that is not dependent on
growth may be useful, particularly when laboratory staffing
precludes prompt subculture of positive bottles. Therefore, we
evaluated the performance of the Binax NOW S. pneumoniae
antigen test for detecting pneumococcal antigen and assessed
persistence of the antigen in positive blood culture bottles.
All patients with culture-positive blood for S. pneumoniae
from December 2000 through March 2001 were included in the
study. Blood cultures were processed and incubated according
to each manufacturer’s instructions with the BacT/ALERT
(bioMe ´rieux, Durham, NC) or BACTEC 9240 (BD Diagnostic
Systems, Sparks, MD) or both automated continuously moni-
toring instrument systems. Blood culture bottles received in
the laboratory during this study period included BacT/ALERT
(FA, PF, PF [plastic], FN, and SN) and BACTEC (Plus Aer-
obic/F and Standard Anaerobic/F) bottles. When the instru-
ment flagged bottles as positive (day 0), an aliquot of blood-
broth mixture from positive blood cultures was Gram stained
and subcultured onto solid medium according to the results of
the Gram stain. Subsequent microbial identification was per-
formed by standard techniques (10). For all cultures identified
as S. pneumoniae, instrument-positive blood culture bottles
were removed from the instrument and held at room temper-
ature. Gram stain and subculture were performed from the
instrument-signaled bottles again on days 2 and 7 and at 7-day
intervals thereafter until there was no growth on subculture
(maximum, 30 days). On days 2, 7, 14, 21, and 30, 2 ml of
blood-broth mixture was removed from each instrument-sig-
naled bottle to perform the Binax NOW antigen test. The
antigen test was performed according to the manufacturer’s
instructions for urine samples. A swab was immersed into a
2-ml aliquot of blood-broth mixture from each blood culture
bottle and then inserted into the test device. The buffer solu-
tion was added, and after 15 min the test was read. The test was
interpreted as positive if both sample and control lines were
present. The test was interpreted as negative if only the control
line was present.
Each companion blood culture bottle that the instrument
did not flag positive (negative companion bottle) was removed
from the instrument on day 5 and subcultured and had an
antigen test performed by day 7. To assess specificity, the
antigen test was performed on blood culture bottles collected
during the study period that were positive for viridans group
streptococci (n ? 12), beta-hemolytic group A streptococci
(n ? 2), beta-hemolytic group B streptococci (n ? 4), and
nutritionally variant streptococci (n ? 1).
A total of 56 blood culture bottles from 18 patients with
pneumococcal bacteremia were evaluated during the study pe-
riod. Of 44 (79%) blood culture bottles that the instrument
flagged as positive, 42 had a Gram stain smear with gram-
* Corresponding author. Mailing address: ARUP Laboratories, 500
Chipeta Way, Salt Lake City, UT 84108. Phone: (801) 583-2787. Fax:
(801) 584-5207. E-mail: firstname.lastname@example.org.
positive diplococci or cocci in pairs and chains, and 43 grew S.
pneumoniae on subculture. Subsequent subculture and antigen
test results are shown in Table 1. All BacT/ALERT blood
culture bottles had negative subcultures on day 7. Of 23
BACTEC bottles that were flagged positive, the pneumococcus
was recovered on subculture from 16 bottles on day 7 and from
11 bottles on day 30. All 12 of 56 blood culture bottles that the
instrument failed to flag positive had no growth on terminal
S. pneumoniae antigen was detected in all 43 (100%) blood
culture bottles positive for pneumococci at days 2 and 30. S.
pneumoniae antigen was detected in only one (BacT/ALERT
PF plastic) of the seven negative companion bottles tested. Of
the 12 blood culture bottles that grew viridans group strepto-
cocci, 3 had false-positive pneumococcal antigen tests (Table
2). All three isolates were confirmed to be nonpneumococci by
sequencing the full 16S rRNA gene. Pneumococcal antigen
was not detected in blood culture bottles that grew beta-he-
molytic group A, group B, or nutritionally variant streptococci.
Historically, cultivation of S. pneumoniae has been challeng-
ing because autolysis resulted in decreased viability. When
subcultures were negative, microbiologists often relied on the
presence of “chocolatized” medium (the muddy brown sedi-
ment that develops in blood culture bottles) or performed
laborious latex agglutination tests to diagnose pneumococcal
infection (2, 3, 5, 6). The phenomenon of chocolatized medium
resulted from a number of complex interactions involving au-
tolysis of pneumococci, hydrogen peroxide production, lower-
ing of the pH, and activation of a hemolysin (5). Advances in
automated continuously monitored blood culture systems ob-
viated the need for these methods by enabling laboratorians to
process positive bottles before autolysis occurs. Although the
problem of false-negative subcultures was not observed in this
study, the issue may remain for laboratories with limited staff-
ing and/or resources that preclude prompt subculturing of pos-
itive blood culture bottles.
To our knowledge no publications have reported studies of
the Binax NOW S. pneumoniae antigen test for detecting the
presence of pneumococcal antigen in blood culture bottles. We
detected pneumococcal antigen in 100% of blood culture bot-
tles that grew S. pneumoniae. Also, pneumococcal antigen was
detected for 30 days following initial subculture for all bottles.
False-positive reactions may occur, and several authors have
demonstrated that viridans group streptococci, in particular
the Streptococcus mitis group, may cross-react with the pneu-
mococcal C polysaccharide antigen (1, 4, 8, 11). All three
false-positive results in our study were due to organisms within
the S. mitis group.
The Binax NOW antigen test is useful for detecting pneu-
mococcal antigen in positive blood culture bottles that have a
Gram stain smear compatible with S. pneumoniae. In the ap-
propriate clinical setting, particularly when subculture is neg-
ative or delayed due to limited staffing, the pneumococcal
antigen test may be used as an alternative method for making
a presumptive diagnosis of pneumococcal bacteremia.
We thank Sam Page and Wei Tang of ARUP Laboratories, Inc., for
excellent technical assistance.
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TABLE 1. Number of positive subculture and antigen results for S. pneumoniae
No. of positive blood culture bottles
aIncludes BACTEC Plus Aerobic/F and Standard Anaerobic/F bottles.
bOne additional bottle lost for follow-up.
cIncludes BacT/ALERT FA, PF glass, PF plastic, FN, and SN bottles.
TABLE 2. Antigen results for nonpneumococcal
positive blood bottles
No. of bottles
Viridans group streptococcus
?-hemolytic group A streptococcus
?-hemolytic group B streptococcus
Nutritionally variant streptococcus
aFull 16S rRNA gene sequencing identified isolates as Streptococcus sanguinis
(n ? 2) and Streptococcus mitis (n ? 1).
VOL. 43, 2005NOTES 2511
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