pgi Genotyping Is a Surrogate for Serotyping of Encapsulated Haemophilus influenzae

Abstract

Study of the epidemiology of invasive infections caused by encapsulated Haemophilus influenzae has been complicated by the poor sensitivity and specificity of the serologic assays used to identify specific capsular polysaccharides. The population structure of these bacteria is highly clonal, however, and serotype is highly correlated with other genetic characteristics. We sought to determine if alleles of the highly conserved phosphoglucose isomerase (pgi) gene correspond to the serotypes of encapsulated H. influenzae strains. pgi alleles of 52 well-characterized encapsulated H. influenzae isolates were amplified by PCR, sequenced, and compared to one another and to additional previously reported H. influenzae pgi alleles. Overall, 83% of the strains possessed pgi alleles associated with the major serotype a, b, e, and f clonotypes that cause the most invasive disease in the United States. Six strains (four type a and two type f) had unusual pgi alleles, which suggested that these strains belonged to less common clonotypes of encapsulated bacteria or were actually nontypeable strains. pgi genotyping may provide a simple and stable surrogate for capsular serotyping. Further studies correlating pgi typing with the expression of capsule are likely to increase our understanding of the epidemiology and pathogenesis of these infections.

Clonal relationship of recent invasive Haemophilus influenzae serotype f isolates from Denmark and the United States

“…The limited genetic diversity of the recent Danish clinical isolates of Hif revealed by our phylogenetic analysis (Fig. 1) is in full agreement with previous observations from the USA (Anyanwu et al, 2003;Omikunle et al, 2002) and Spain (Campos et al, 2003). The close relationship of our isolates to strains representing cases from the USA suggests that these recent cases of Hif disease are caused by a single clone (according to the definition of Maynard Smith, 1995) in which genetic diversity is very limited.…”

Genotypic characteristics of Haemophilus influenzae isolates from pediatric pneumonia patients in Chengdu city, Sichuan, China

“…It cannot be used to distinguish between noncapsulate strains and capsule-deficient mutants of type b strains (b -strains) because some of these bacteria exhibited nonspecific agglutination. This discrepancy may be due to the low specificity of antiserum which results in difficulty in interpreting the agglutination test (Falla et al, 1994;CDC, 2002;Anyanwu et al, 2003). The findings of this study is consistent with previous data.…”

“…We believe that serotyping should be confirmed by PCR genotyping to minimize the errors of conventional serotyping using the slide agglutination test (CDC, 2002) because PCR sero-genotyping is more sensitive and specific than traditional slide agglutination assays. Nontypeable H.influenzae is also responsible for pediatric pneumonia (Heath et al, 2001;Anyanwu et al, 2003;LaClaire et al, 2003). We found that 77.7% cases occurred under 1 year old.…”

Capsule Gene Analysis of Invasive Haemophilus influenzae : Accuracy of Serotyping and Prevalence of IS 1016 among Nontypeable Isolates

“…Strains containing capsule-specific genes (region 2) may be phenotypically and serologically nontypeable if critical elements of the gene cluster such as the capsule export gene bexA (region 1) or transport genes hcsA and hcsB (region 3) are missing (18,25,32,43). The nucleotide sequences of the highly conserved housekeeping gene for phosphoglucose isomerase (pgi, one of the seven housekeeping loci used in multilocus sequence typing [MLST]) are conserved within capsule types, and this additional molecular scheme has been suggested as a surrogate for capsule typing (2).…”