Identification of Haemophilus spp. from clinical specimens by biochemical tests compared with PCR method

Haemophilus influenzae is a part of normal upper respiratory flora of human, which can cause a wide variety of infections. Other members of genus Haemophilus rarely cause human infection but are frequently isolated from clinical specimens, such as sputum. The pathogenicity between H. influenzae and other Haemophilus species is different therefore a reliable method for identification of H. influenzae is essential. The aim of this study was to compare the identification methods for Haemophilus by four phenotypic tests with that by a PCR-based method. A total of 101 Haemophilus isolates were identified by biochemical tests and the XV requirement test by using XV paper strip technique, porphyrin test and Staphylococcus streak technique. The PCR-based method was performed using specific primers for 16S rDNA, p6 genes of H. influenzae and sodA gene of H. parainfluenzae . Using the XV paper strip technique, porphyrin test and biochemical tests, 88 and 13 isolates were identified as H. influenzae and H. parainfluenzae respectively, whereas 54 H. influenzae and 47 H. parainfluenzae were identified by using Staphylococcus streak technique (66.4 % agreement with that of the three tests). The PCR-based method revealed that 83 H. influenzae and 12 H. parainfluenzae were identified, whereas 6 isolates could not be categorized into both species. This study showed that identification of Haemophilus by the XV paper strip technique, porphyrin test and biochemical test gave 93.1 % agreement with that of the PCR method, whereas the Staphylococcus streak technique gave only 71.3 % agreement.