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Journal of Clinical Microbiology, March 2006, p. 1074-1076, Vol. 44, No. 3
0095-1137/06/$08.00+0 doi:10.1128/JCM.44.3.1074-1076.2006
Molecular Diagnosis of Bordetella pertussis Infection by Evaluation of Formalin-Fixed Tissue Specimens
Kathleen M. Tatti,1*
Kai-Hui Wu,2
Gary N. Sanden,2
Patricia Greer,1
John Sumner,1
Jeannette Guarner,1
Christopher D. Paddock,1 and
Sherif R. Zaki1
Centers for Disease Control and Prevention, National Center for Infectious Diseases, Division of Viral and Rickettsial Disease, Infectious Disease Pathology Activity, Atlanta, Georgia 30333,1
Centers for Disease Control and Prevention, National Center for Infectious Diseases, Division of Bacterial and Mycotic Disease, Meningitis and Special Pathogens Branch, Epidemiologic Investigations Laboratory, Atlanta, Georgia 303332
Received 12 December 2005/
Accepted 13 December 2005

ABSTRACT
Formalin-fixed lung or trachea tissue specimens from four infants
and one adolescent who died of respiratory illness were tested
for
Bordetella pertussis by conventional and real-time PCR assays.
B. pertussis was confirmed in all cases. PCR can be an invaluable
retrospective diagnostic tool for evaluating archival tissues
from patients with suspected fatal pertussis.

TEXT
Bordetella pertussis, a gram-negative coccobacillus, is the
primary etiologic agent of pertussis (whooping cough). Pertussis
is an important cause of morbidity among children of <4 months
of age (
10), and some studies of sudden infant death syndrome
(SIDS) have shown an epidemiologic association with
B. pertussis cases (
1-
4). Laboratory diagnosis of
Bordetella sp. infections
has traditionally been determined by culture of the agent; however,
because of the enhanced sensitivity of PCR, this assay is increasingly
being used for the diagnosis of
B. pertussis infection.
Minimal DNA can be recovered from formalin-fixed tissues; thus, the use of a multicopy target for PCR detection, such as IS481, is advantageous. This study demonstrates that PCR assays targeting IS481 and the pertussis toxin gene can be used to identify B. pertussis in formalin-fixed, paraffin-embedded autopsy tissues from patients with unexplained deaths and in fixed tissues from suspected pertussis patients for whom fresh samples are not available.
(Part of this work was presented at the 105th meeting of the American Society for Microbiology, Atlanta, Ga., 6 June 2005.)
Study samples consisted of formalin-fixed autopsy tissues from three patients suspected of having Bordetella infection, one suspected of having influenza, and one whose death was attributed to SIDS. Four patients ranged in age from 35 days to 3 months, and one patient was 13 years old. The clinical histories of the five patients varied, but all had a cough and other respiratory symptoms; one patient was immunosuppressed. Four patients had an epidemiologic link with an ill family member. Except for the SIDS patient (patient 4), all patients were on antibiotics and had laboratory evidence of pertussis by culture or PCR.
Hematoxylin and eosin staining of lung tissues from the patients showed bronchopneumonia comprised of intra-alveolar infiltrates of neutrophils and macrophages (Fig. 1A), with foci of necrosis and intra-alveolar hemorrhage as the predominant pulmonary pathologies. The trachea of patient 4 exhibited focal areas of denuded epithelium accompanied by mild to moderate submucosal mononuclear cell infiltrates. Silver staining (Steiner's method) demonstrated coccobacilli in all patients (Fig. 1B), while Gram's staining (Brown and Hopps method) showed gram-negative bacilli in only patients 2 and 4.
Clinical isolates of
Bordetella spp. (Table
1) were fixed in
formalin, minced with uninfected tissues, and embedded in paraffin.
DNA was extracted from one 10-µm section of each formalin-fixed
tissue by use of a QIAamp DNA Mini kit (QIAGEN, Valencia, CA)
and was eluted in 100 µl of 10 mM Tris buffer (pH 7.5).
To determine whether the extracted DNAs could be amplified by
PCR, a 167-bp region of the ß-globin gene was amplified
from the tissue specimens (
6). The PCR amplification assay for
B. pertussis was performed using primers IS
481F (5'-GATTCAATAGGTTGTATGCATGGTT)
and IS
481R (5'-TTCAGGCACACAAACTTGATGGGCG), which were designed
by Templeton et al. (
8). Each PCR mixture consisted of a 300
nM concentration of each primer, 10 µl of DNA extract,
high-fidelity PCR master mix (containing 1.5 mM MgCl
2 and a
0.2 mM concentration of each deoxynucleoside triphosphate),
and an enzyme mixture of
Taq and
Tgo DNA polymerases in a 50-µl
volume. The DNA was denatured for 3 min at 94°C and then
subjected to 40 cycles of amplification (94°C for 15 s,
60°C for 20 s, and 72°C for 30 s) followed by a final
extension of 10 min at 72°C. The PCR results for the assay
of IS
481 from different clinical isolates of
Bordetella spp.
demonstrated that this assay detects both
B. pertussis and
B. holmesii but not
B. parapertussis or
B. bronchiseptica (Table
1). This result correlates with previous studies that showed
that
B. holmesii contains the insertion sequence IS
481 at 8
to 10 copies per cell (
5). Since IS
481 is present at one copy
only in some
B. bronchiseptica strains (S. Gladbach, S. Hanauer,
and U. Reischl, Abstr. 7th Int. Symp. Pertussis, abstr. 34,
2002), the IS
481 sequence may not have been present in these
particular test strains or the conventional assay may not have
detected the sequence because the total DNA concentration was
nominal. When we used DNAs extracted from clinical samples of
lung tissue infected with
Bacillus anthracis, group A
Streptococcus,
group B
Streptococcus,
Haemophilus influenzae,
Legionella pneumophila,
Staphylococcus aureus,
Streptococcus pneumoniae, or
Yersinia pestis and from liver tissue infected with spotted-fever-group
Rickettsia, the IS
481 PCR assay did not generate an amplicon.
The IS
481 PCR assay amplified a 181-bp fragment from lung or
trachea specimens from the five patients, suggesting that either
B. pertussis or
B. holmesii was present.
We next sequenced the 181-bp amplicons of the IS
481 gene from
the clinical isolates and the five patients. Comparison of the
DNA sequences of the 181-bp amplicons of
B. pertussis and
B. holmesii illustrated one consistent difference between the two
species: at nucleotide 100 in all five clinical isolates of
B. holmesii, a mixture of nucleotide bases C and A occurred,
with C slightly more predominant than A (data not shown). This
mixture of C and A has been documented previously (
5) and is
indicated as "m" at nucleotide 133 in the
B. holmesii IS
481 insertion sequence (accession number AF349431). In contrast,
an A was always present at the same nucleotide position in all
five patient and clinical isolates of
B. pertussis. An analysis
of the sequence from the reverse strand confirmed that a mixture
of nucleotide bases G and T occurred at the homologous position
in all five
B. holmesii isolates, while only a T occurred in
the
B. pertussis isolates and the five patient isolates. Although
the mixture of nucleotides at this position in IS
481 appears
to be indicative of
B. holmesii isolates, an amplicon with an
A at this nucleotide position can only be used as suggestive
information that a patient might be infected with
B. pertussis.
The patient history and clinical information are beneficial
in differentiating between
B. holmesii and
B. pertussis. Although
B. holmesii is known to cause septicemia (
11) and, in some instances,
respiratory illnesses (
7) in adolescents and adults, the respiratory
illness caused by
B. holmesii is mild compared with that caused
by
B. pertussis, and no deaths have been attributed to
B. holmesii.
All real-time PCR assays were performed using a LightCycler instrument (Roche Applied Science, Indianapolis, IN). To quantify the amounts of DNA extracted from human tissues, a real-time assay to detect an 80-bp region of the human RNase P gene was performed (Table 2). The real-time IS481 assay targets a region downstream from the inverted repeat that generates a 66-bp amplicon (K.-H. Wu and G. N. Sanden, unpublished data). The region targeted by the real-time IS481 PCR assay is different from that targeted by the conventional IS481 PCR assay. A real-time assay specific for a 55-bp region of the pertussis toxin gene was developed (Wu and Sanden, unpublished data). The weakest PCR signal for the pertussis toxin gene was obtained from patient 5, the same patient with the negative Gram's and Steiner stains (Table 2). The results from real-time IS481 PCRs substantiated the results of the conventional IS481 assay, verifying that all five patients were infected with either B. pertussis or B. holmesii, while the specific real-time pertussis toxin assay, which targets a single-copy gene, demonstrated that all specimens from the five patients were positive for B. pertussis (Table 2). An analysis of the real-time data illustrated that cycle threshold (CT) values for the real-time IS481, pertussis toxin, and RNase P assays are concordant. The IS481 assay generates relatively higher CT values because the insertion element is present in multiple copies, and assay results for specimens with low DNA concentrations suggested that the IS481 assay may be more sensitive than single-copy targets at detecting B. pertussis (Table 2).
This study demonstrates the utility of various PCR assays for
the detection of
B. pertussis DNA in formalin-fixed tissue specimens.
For further analysis, lung tissue samples were obtained from
an additional 10 infants whose deaths were suspected to be due
to pertussis. PCR analysis utilizing the assays described in
this study demonstrated that the infants were infected with
B. pertussis (data not shown). Of the five patients diagnosed
with
B. pertussis infection in this study, the epidemiologic
data support the PCR results for four who were in contact with
ill family members. Patient 2 presented as a laboratory-confirmed
influenza case without an epidemiologic link but was determined
to be infected with
B. pertussis by hospital PCR tests and the
PCR tests in this study. Patient 4 presented as a presumed SIDS-related
fatality; however, conventional and real-time PCR tests, an
immunohistochemical assay (C. D. Paddock, unpublished data),
and an epidemiologic link to a known
B. pertussis case established
that the infant was infected with
B. pertussis. Studies by several
groups using PCR analysis (
1,
2) or surveys of statistical records
and epidemiologic studies (
3,
4) have suggested that between
5% and 18% of SIDS cases may be attributable to
B. pertussis.
Future studies using molecular and immunohistochemical assays
are planned to explore the role of
B. pertussis in SIDS deaths.

ACKNOWLEDGMENTS
We thank Laurie Mueller for her assistance with graphics, Jeanine
Bartlett for her special stains, Pamela Cassiday for growing
strains of the
Bordetella spp., and Claudia Chesley for her
editorial expertise. In addition, we thank the following people
for submitting tissue specimens for analysis and consultation:
B. Fulton, Pathology and Laboratory Medicine Spectrum Health,
Grand Rapids, MI; J. Wyatt-Ashmead, The University of Mississippi
Medical Center; S. Ladd-Wilson, Oregon Health Division/EIP Department
of Human Services; D. Drehner, Children's Hospital and Clinic,
Minneapolis, MN; and K. Lemon, Children's Hospital Medical Center,
Boston, MA.
The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the funding agency.

FOOTNOTES
* Corresponding author. Mailing address: Centers for Disease Control and Prevention, 1600 Clifton Rd., NE, Mailstop G30, Atlanta, GA 30333. Phone: (404) 639-3133. Fax: (404) 639-3043. E-mail:
ket2{at}cdc.gov.


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Journal of Clinical Microbiology, March 2006, p. 1074-1076, Vol. 44, No. 3
0095-1137/06/$08.00+0 doi:10.1128/JCM.44.3.1074-1076.2006
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