Rapid determination of X/V growth requirements of Haemophilus species in broth

Abstract

A broth system was developed for rapid identification of the requirement for X factor (hemin), or V factor (NAD), or both for growth of Haemophilus species. This system was compared to growth around paper discs/strips impregnated with factors X and/or V. The broth system consisted of three tubes, each containing brain-heart infusion broth supplemented with V factor, X factor, or both. Each tube was inoculated with a saline suspension of an Haemophilus isolate, and the broths were shaken for aeration at 37 degrees C. Under these conditions turbidity or clumping was usually evident after 4-5 hr only in the broth(s) containing the required supplement(s). A few strains requiring only V factor required overnight incubation. One hundred fifty-six Haemophilus isolates were tested for growth around supplemented discs/strips or in supplemented broths: 129 were H. influenzae/aegypticus, 25 were of various species that required only V factor, and 2 were H. aphrophilus. Ten of 89 H. influenzae isolates from the respiratory tract were misidentified by satellitism. All isolates were correctly identified by growth in supplemented broths. The cost of the broth assay was about 60 cents/test, whereas the satellite assay cost about 120 cents/test. Serotyping and antibiotic sensitivity testing could be performed directly from the broth culture. Determination of X and/or V requirement by Haemophilus species with supplemented broths was sensitive, rapid, and inexpensive.