In a sinus culture, small pinpoint colonies growing around medium white colonies on sheep blood agar are most likely which organism?

In a sinus culture, small pinpoint colonies growing around medium white colonies on sheep blood agar are most likely which organism?

• A. Burkholderia pseudomallei
• B. Campylobacter jejuni
• C. Haemophilus influenzae
• D. Yersinia pestis

Answer: (C)

The pattern tests recognition of Haemophilus influenzae growth on blood agar due to a dependency on growth factors, specifically the need for V factor (NAD) in addition to X factor (hemin). Haemophilus influenzae often cannot grow well on plain blood agar, but if a neighboring colony provides NAD, the bacterium can expand as small pinpoint colonies around that “helper” organism. In the sinus culture context, Haemophilus influenzae is a common pathogen, and the classic satellite phenomenon occurs around colonies of Staphylococcus aureus on sheep blood agar. The white medium-sized colonies are the helper organism, and the tiny colonies radiating around them are Haemophilus influenzae, which could not grow as well on its own without the NAD provided by the nearby colonies. Other organisms listed do not show this satellite growth pattern on standard blood agar. Burkholderia pseudomallei, Campylobacter jejuni, and Yersinia pestis do not rely on this NAD-dependent satellite phenomenon for growth on this medium, and their colony morphologies and growth requirements differ from the described pattern.

The pattern tests recognition of Haemophilus influenzae growth on blood agar due to a dependency on growth factors, specifically the need for V factor (NAD) in addition to X factor (hemin). Haemophilus influenzae often cannot grow well on plain blood agar, but if a neighboring colony provides NAD, the bacterium can expand as small pinpoint colonies around that “helper” organism. In the sinus culture context, Haemophilus influenzae is a common pathogen, and the classic satellite phenomenon occurs around colonies of Staphylococcus aureus on sheep blood agar. The white medium-sized colonies are the helper organism, and the tiny colonies radiating around them are Haemophilus influenzae, which could not grow as well on its own without the NAD provided by the nearby colonies.

Other organisms listed do not show this satellite growth pattern on standard blood agar. Burkholderia pseudomallei, Campylobacter jejuni, and Yersinia pestis do not rely on this NAD-dependent satellite phenomenon for growth on this medium, and their colony morphologies and growth requirements differ from the described pattern.