Analysis of genetic relatedness of Haemophilus influenzae isolates by multilocus sequence typing.

The gram-negative bacterium Haemophilus influenzae is a human-restricted commensal of the nasopharynx that can also be associated with disease. The majority of H. influenzae respiratory isolates lack the genes for capsule production and are nontypeable (NTHI). Whereas encapsulated strains are known to belong to serotype-specific phylogenetic groups, the structure of the NTHI population has not been previously described. A total of 656 H. influenzae strains, including 322 NTHI strains, have been typed by multilocus sequence typing and found to have 359 sequence types (ST). We performed maximum-parsimony analysis of the 359 sequences and calculated the majority-rule consensus of 4,545 resulting equally most parsimonious trees. Eleven clades were identified, consisting of six or more ST on a branch that was present in 100% of trees. Two additional clades were defined by branches present in 91% and 82% of trees, respectively. Of these 13 clades, 8 consisted predominantly of NTHI strains, three were serotype specific, and 2 contained distinct NTHI-specific and serotype-specific clusters of strains. Sixty percent of NTHI strains have ST within one of the 13 clades, and eBURST analysis identified an additional phylogenetic group that contained 20% of NTHI strains. There was concordant clustering of certain metabolic reactions and putative virulence loci but not of disease source or geographic origin. We conclude that well-defined phylogenetic groups of NTHI strains exist and that these groups differ in genetic content. These observations will provide a framework for further study of the effect of genetic diversity on the interaction of NTHI with the host.

Rapid laboratory detection of meningococcal disease outbreaks caused by serogroup C Neisseria meningitidis.

Molecular subtyping is of significant importance to the recognition of outbreaks of meningococcal disease caused by serogroup C Neisseria meningitidis. We describe the application of multilocus variable number tandem repeat analysis (MLVA) for the molecular subtyping of N. meningitidis and compare its performance to that of pulsed-field gel electrophoresis (PFGE). For MLVA, a multiplex PCR assay targeting five variable number tandem repeat regions was developed and evaluated using a panel of sporadic and outbreak-associated serogroup C N. meningitidis isolates. MLVA was highly reproducible and provided results within 6 h. Overall, the discriminatory power of MLVA was equivalent to that of PFGE. The utilization of MLVA for subtyping N. meningitidis isolates provides a rapid and safer alternative to PFGE for identifying outbreaks of meningococcal disease. As such, it may provide public health officials with timely information that may minimize the spread of outbreak-related cases through prophylaxis.

Nucleic acid-based methods for the detection of bacterial pathogens: present and future considerations for the clinical laboratory.

BACKGROUND: Recent advances in nucleic acid-based methods to detect bacteria offer increased sensitivity and specificity over traditional microbiological techniques. The potential benefit of nucleic acid-based testing to the clinical laboratory is reduced time to diagnosis, high throughput, and accurate and reliable results. METHODS: Several PCR and hybridization tests are commercially available for specific organism detection. Furthermore, hundreds of nucleic acid-based bacterial detection tests have been published in the literature and could be adapted for use in the clinical setting. Contamination potential, lack of standardization or validation for some assays, complex interpretation of results, and increased cost are possible limitations of these tests, however, and must be carefully considered before implementing them in the clinical laboratory. CONCLUSIONS: A major area of advancement in nucleic acid-based assay development has been for specific and broad-range detection of bacterial pathogens.

High level of sequence diversity in the 16S rRNA genes of Haemophilus influenzae isolates is useful for molecular subtyping.

A molecular typing method based on the 16S rRNA sequence diversity was developed for Haemophilus influenzae isolates. A total of 330 H. influenzae isolates were analyzed, representing a diverse collection of U.S. isolates. We found a high level of 16S rRNA sequence heterogeneity (up to 2.73%) and observed an exclusive correlation between 16S types and serotypes (a to f); no 16S type was found in more than one serotype. Similarly, no multilocus sequence typing (MLST) sequence type (ST) was found in more than one serotype. Our 16S typing and MLST results are in agreement with those of previous studies showing that serotypable H. influenzae isolates behave as highly clonal populations and emphasize the lack of clonality of nontypable (NT) H. influenzae isolates. There was not a 1:1 correlation between 16S types and STs, but all H. influenzae serotypable isolates clustered similarly. This correlation was not observed for NT H. influenzae; the two methods clustered NT H. influenzae isolates differently. 16S rRNA gene sequencing alone provides a level of discrimination similar to that obtained with the analysis of seven genes for MLST. We demonstrated that 16S typing is an additional and complementary approach to MLST, particularly for NT H. influenzae isolates, and is potentially useful for outbreak investigation.

Use of real-time PCR to resolve slide agglutination discrepancies in serogroup identification of Neisseria meningitidis.

Neisseria meningitidis is a leading cause of bacterial meningitis and septicemia in children and young adults in the United States. Rapid and reliable identification of N. meningitidis serogroups is crucial for judicious and expedient response to cases of meningococcal disease, including decisions about vaccination campaigns. From 1997 to 2002, 1,298 N. meningitidis isolates, collected in the United States through the Active Bacterial Core surveillance (ABCs), were tested by slide agglutination serogrouping (SASG) at both the ABCs sites and the Centers for Disease Control and Prevention (CDC). For over 95% of isolates, SASG results were concordant, while discrepant results were reported for 58 isolates. To resolve these discrepancies, we repeated the SASG in a blinded fashion and employed ctrA and six serogroup-specific PCR assays (SGS-PCR) to determine the genetic capsule type. Seventy-eight percent of discrepancies were resolved, since results of the SGS-PCR and SASG blinded study agreed with each other and confirmed the SASG result at either state health laboratories or CDC. This study demonstrated the ability of SGS-PCR to efficiently resolve SASG discrepancies and identified the main cause of the discrepancies as overreporting of these isolates as nongroupable. It also reemphasized the importance of adherence to quality assurance procedures when performing SASG and prompted prospective monitoring for SASG discrepancies involving isolates collected through ABCs in the United States.

Development of a real-time fluorescence PCR assay for rapid detection of the diphtheria toxin gene.

We developed and evaluated a real-time fluorescence PCR assay for detecting the A and B subunits of diphtheria toxin (tox) gene. When 23 toxigenic Corynebacterium diphtheriae strains, 9 nontoxigenic C. diphtheriae strains, and 44 strains representing the diversity of pathogens and normal respiratory flora were tested, this real-time PCR assay exhibited 100% sensitivity and specificity. It allowed for the detection of both subunits of the tox gene at 750 times greater sensitivity (2 CFU) than the standard PCR (1,500 CFU). When used directly on specimens collected from patients with clinical diphtheria, one or both subunits of the tox gene were detected in 34 of 36 specimens by using the real-time PCR assay; only 9 specimens were found to be positive by standard PCR. Reamplification by standard PCR and DNA sequencing of the amplification product confirmed all real-time PCR tox-positive reactions. This real-time PCR format is a more sensitive and rapid alternative to standard PCR for detection of the tox gene in clinical material.