Comparative genomic analysis of Haemophilus haemolyticus and non-typeable Haemophilus influenzae and a new testing scheme for their discrimination.

Hu F1, Rishishwar L2, Sivadas A3, Mitchell GJ4, Jordan IK2, Murphy TF5, Gilsdorf JR6, Mayer LW1, Wang X1.

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Abstract

Haemophilus haemolyticus (H. haemolyticus) has been recently discovered to have the potential to cause invasive disease. It is closely related to non-typeable Haemophilus influenzae (NT H. influenzae). NT H. influenzae and H. haemolyticus are often misidentified because none of the existing tests targeting the known phenotypes of H. haemolyticus are able to specifically identify H. haemolyticus Through comparative genomic analysis of H. haemolyticus and NT H. influenzae, we identified genes unique to H. haemolyticus that can be used as targets for the identification of H. haemolyticus A real-time PCR targeting purT (encoding phosphoribosylglycinamide formyltransferase 2 in the purine synthesis pathway) was developed and evaluated. The lower limit of detection was 40 genomes/PCR reaction; the sensitivity and specificity in detecting H. haemolyticus were 98.9% and 97%, respectively. To improve the discrimination of H. haemolyticus and NT H. influenzae, a testing scheme combining two targets (H. haemolyticus purT and H. influenzae hpd encoding protein D lipoprotein) was also evaluated and showed 96.7% sensitivity and 98.2% specificity for the identification of H. haemolyticus, and 92.8% sensitivity and 100% specificity for the identification of H. influenzae The dual-target testing scheme can be used for the diagnosis and surveillance of infection disease caused by H. haemolyticus and NT H. influenzae.