A 70 year old female presents with bronchiectasis with acute exacerbation. She is a non-smoker, although claims to have been exposed to secondhand smoke, and she has chronic sinusitis. The patient recently traveled to Savannah, Georgia where she developed a productive cough. She was prescribed doxycycline and was then sent home. She returned to the pulmonary clinic for a follow up consultation after her cough worsened.
The Gram stain and smear showed 4+ neutrophils, 4+ gram negative coccobacilli and little to no mixed respiratory flora. The following day, the culture grew 1+ respiratory flora on the blood plate, no growth on the MacConkey plate, and 4+ translucent colonies on the chocolate plate.
The predominant organism was identified by the MALDI-TOF as Haemophilus influenzae. The Gram stain and culture findings are consistent with the MALDI-TOF identification. H. influenzae is an oxidase positive, gram negative coccobacilli known for its requirement of X (hemin) and V (NAD) factors found in chocolate agar. Because of its growth requirements, H. influenzae will not grow on MacConkey agar despite being a gram negative organism. It may be cultured on blood agar if the agar is inoculated with an organism such as Staphylococcus aureus, which can provide the V factor, while the X factor is provided by the agar itself. This phenomenon is known as satelliting. Identification of H. influenzae may also be done using a Haemophilus ID Quad plate. Each section of the plate contains varying factors and allows for Haemophilus identification to the species level based on the growth and hemolysis pattern.
H. influenzae is normal flora of mucous membranes and frequently colonizes the human oral cavity and upper respiratory tract. Commonly, H. influenzae causes pneumonia, as with our patient, bronchitis, and ear infections. However, it is also a known cause for bacterial meningitis, endocarditis, and osteomyelitis. Transmission of H. influenzae occurs through respiratory droplets so proper PPE precautions must be taken by clinicians when working with infected patients. It is important for laboratory professionals to work with the organism using proper PPE and BSL-2 practices and plating of respiratory specimens should occur in a biosafety cabinet.
Susceptibility testing is not routinely performed on isolates of H. influenzae. β-lactamase production can be determined by using nitrocefin, a chromogenic cephalosporin spot test.
- Haemophilus influenzae Disease (Including Hib). (2018, February 13). Retrieved June 28, 2018, from https://www.cdc.gov/hi-disease/index.html
- (2012, March 15). Retrieved June 28, 2018, from https://www.cdc.gov/meningitis/lab-manual/chpt09-id-characterization-hi.html. Identification and Characterization of Haemophilus influenzae
- Manual of Clinical Microbiology, 11th edition
-Madaine Saguinsin, MLS (ASCP), graduated from Purdue University with a BS in Medical Laboratory Sciences and is a medical technologist at NorthShore University Health System. Her interests are microbiology and parasitology.
-Erin McElvania, PhD, D(ABMM), is the Director of Clinical Microbiology NorthShore University Health System in Evanston, Illinois.