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Journal of Clinical Microbiology, June 2003, p. 2697-2699, Vol. 41, No. 6
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.6.2697-2699.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Identification of Neisseria meningitidis Serogroups Y and W135 by siaD Nucleotide Sequence Analysis
C. Lewis1,2 and S. C. Clarke2,3*
Scottish Centre for Infection and Environmental Health, Clifton House, Clifton Place, Glasgow G3 7LN,1
Scottish Meningococcus and Pneumococcus Reference Laboratory, Stobhill Hospital, Glasgow G21 3UW, Glasgow,2
Faculty of Biomedical and Life Sciences, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, Scotland3
Received 27 January 2003/
Returned for modification 16 March 2003/
Accepted 24 March 2003

ABSTRACT
Rapid serogrouping of meningococci is essential for the effective
public health management of cases of the disease and the contacts
of infected patients. Here we describe an accurate nucleotide-sequencing
method for the confirmation of serogroup Y and W135 meningococci
by
siaD gene analysis from cultures of
Neisseria meningitidis.

TEXT
Neisseria meningitidis is one of the major causes of bacterial
meningitis, and serogroups A, B, C, Y, and W135 account for
most disease worldwide (
11). The rapid and accurate characterization
of meningococci is crucial for effective public health management.
Swift serogroup determination is essential, particularly during
case clusters and outbreaks, while the changing epidemiology
of this important pathogen makes serogrouping increasingly important.
Meningococcal serogroup C conjugate vaccines have now been introduced
in the United Kingdom and elsewhere, there have been two outbreaks
associated with serogroup W135 disease and the Hajj pilgrimage
(
13) (M. K. Taha, M. Achtman, J. M. Alonso, B. Greenwood, M.
Ramsay, A. Fox, S. Gray, and E. Kaczmarski, Letter, Lancet
356:2159,
2000), and serogroup Y now accounts for a significant percentage
of disease in the United States (
14).
Current methods for serogrouping meningococci rely on phenotypic methods, such as latex agglutination, or genotypic methods, such as PCR restriction fragment length polymorphism (RFLP) (2, 3). However, the former lacks sensitivity and specificity while the latter is based on the presence of RFLPs and, therefore, their longer-term accuracy is questionable with an organism that is both highly competent in the uptake of genetic material by transformation and undergoing epidemiological change worldwide (6, 9, 12). Nucleotide sequencing is being used increasingly in the modern microbiology laboratory and is accurate, digitally based, and, therefore, portable. We therefore developed a nucleotide-sequencing method which compares numerous nucleotide differences between serogroups Y and W135. The siaD gene is part of the operon in meningococci that is responsible for capsule synthesis and has been studied quite extensively (1, 3, 4, 8, 15). It is highly conserved between serogroup B and C meningococci but is less conserved among serogroup Y and W135 meningococci (3, 4, 8). In particular, there is a variable region towards the end of the first third of the gene in which numerous nucleotide differences occur between serogroup Y and W135. We therefore took advantage of this and designed oligonucleotide primers external to this variable region for PCR amplification and internal primers for nucleotide sequencing.
Ninety-six clinical isolates of N. meningitidis (isolated in Scotland between 1998 and 2002) were analyzed. Of the serogroups B, C, Y, and W135, 24 isolates of each were chosen. The serogroup Y isolates were from cerebrospinal fluid (n = 1), blood (n = 3), eye (n = 1), knee aspirate (n = 1), sputum (n = 8), throat (n = 8), urethra (n = 1), and unknown (n = 1). The cases of 6 patients were considered to be invasive serogroup Y infections, while the remaining 18 patients were carriers. The serogroup W135 isolates were from cerebrospinal fluid (n = 4), blood (n = 4), sputum (n = 4), throat (n = 6), vagina (n = 1), rectum (n = 1), and unknown (n = 4). The cases of 8 patients were considered to be invasive serogroup W135 infections, while the remaining 16 patients were carriers. Using standard methods as part of the service provided by the Scottish Meningococcus and Pneumococcus Reference Laboratory (3, 4, 7), all isolates had previously been serogrouped by latex agglutination and PCR-RFLP. PCR and nucleotide sequencing were performed as previously described (5) except that sequencing was performed on a MegaBACE 1000 automated DNA sequencer (Amersham Pharmacia Biotech, Little Chalfont, Buckinghamshire, United Kingdom). Oligonucleotide primers WYxampF (5'-GCTGGAAGAAATGCATTCC-3') and WYxampR (5'-CAGGATTGGTTAGCTCGA-3') were used for PCR; the PCR cycle was 95°C for 5 min, followed by 35 cycles of 94°C for 25 s, 53°C for 40 s, and 72°C for 1 min, with a final extension step of 72°C for 5 min. Using oligonucleotide primers WyxseqF (5'-gAATCTTCCGAGCAGGAA-3') and WyxseqR (5'-TGCGCGGAAGAATAGTG-3'), sequence labeling was performed as previously described; the sequence-labeling cycle was 30 cycles of 92°C for 20 s, 50°C for 15 s, and 60°C for 1 min. Nucleotide sequences from each strain were aligned using the AlignIR program (LICOR Biosciences, Cambridge, United Kingdom) and the ALIGN program at the Genestream Resource Center (http://www2.igh.cnrs.fr/bin/align-guess.cgi). These sequences were then compared against the consensus sequences gained from GenBank (accession numbers Y13969 and Y13970 for serogroups Y and W135, respectively). PCR was performed on all 96 strains, but only the 48 serogroup Y and W135 strains gave positive results. The PCR products were sequenced, and a total of 29 nucleotide differences were noted which could be used for determination of their serogroups by sequence alignment (Fig. 1). No polymorphism differences were noted between the test strains and the reference sequences in this study. However, as polymorphisms develop over time, an alignment database can be used to determine the serogroup (10). The nucleotide-sequencing results were compared with those gained from latex agglutination and PCR-RFLP. The results gained by genotyping were identical to those gained by phenotyping and PCR-RFLP, indicating that the test was 100% specific for serogroups Y and W135.
Rapid tools are required for the serogroup determination of
meningococci causing disease, and they must be accurate so that
effective public health management can take place. Also, the
handling of clusters and outbreaks, or even the description
of new strains, relies on methods that currently depend on the
analysis of RFLPs. Such analysis cannot be relied on as a robust,
long-term method for serogrouping strains. In this study, a
total of 50 nucleotide sequences were compared within the variable
region of the
siaD gene in serogroup Y and W135 meningococci.
Of these sequences, 48 were from clinical meningococcal isolates
which were serogrouped using phenotypic and genotypic methods.
Nucleotide sequencing provides a more robust method, because
it is based on the analysis of multiple nucleotide differences
and takes into account nucleotide changes that can occur over
time by mutation or recombination. It has been shown that this
methodology can be applied to meningococcal cultures but could
also possibly be applied to body fluids containing meningococcal
DNA. Such a methodology is important for accurately serogrouping
meningococcal strains that commonly cause disease in the United
States and also those strains associated with the Hajj pilgrimage.

ACKNOWLEDGMENTS
Funding for the liquid-handling robot and automated DNA sequencer
was generously provided by the Meningitis Association (Scotland).
This work was also supported, in part, by the Chief Scientist's
Office of The Scottish Executive.

FOOTNOTES
* Corresponding author. Mailing address: Scottish Meningococcus and Pneumococcus Reference Laboratory, Stobhill Hospital, Balornock Rd., Glasgow G21 3UW, United Kingdom. Phone: 44 141 201 3836. Fax: 44 141 201 3663. E-mail:
stuart.clarke{at}northglasgow.scot.nhs.uk.


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Journal of Clinical Microbiology, June 2003, p. 2697-2699, Vol. 41, No. 6
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.6.2697-2699.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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