Fastidiosos

Haemophilus influenzae

Small Gram-negative coccobacilli

Identification & Growth

Identification

Requires factor X (hemin) and factor V (NAD) — X, V and XV disk test
Satellitism around S. aureus on blood agar

Growth Conditions

Chocolate agar with 5% CO₂, 35 °C, 24 h; translucent, greyish colonies
Does not grow on plain sheep blood agar

Clinical Significance

Otitis media, sinusitis, COPD exacerbation, pneumonia, meningitis (unvaccinated patients)

Intrinsic Resistance

Glycopeptides, clindamycin, linezolid, daptomycin, penicillin G (EUCAST Expected Resistant Phenotypes v1.2)

Bench Alerts

Disk diffusion on Mueller-Hinton Fastidious (MH-F) agar with CO₂
Beta-lactamase-positive: ampicillin R — confirm directly with a nitrocefin test
BLNAR: resistance via PBP alteration even in the absence of beta-lactamase

Clinical Notes

Clinical presentations

Causes acute otitis media, sinusitis, and exacerbations of chronic obstructive pulmonary disease, typically by nontypeable strains.
Encapsulated serotype b (Hib) strains cause bacterial meningitis, epiglottitis, and septic arthritis, especially in unvaccinated children.
Can cause community-acquired pneumonia and bacteremia in elderly adults or those with chronic lung disease.

Specimens and collection

Cerebrospinal fluid, blood culture, and joint fluid culture are indicated according to the suspected site of invasive infection.
Respiratory specimens should be processed promptly because the organism is fastidious and sensitive to desiccation.
Culture requires medium supplemented with factors X and V (chocolate agar) for adequate growth.

Epidemiology and at-risk populations

Hib vaccination has dramatically reduced invasive disease incidence in children in countries with established immunization programs.
Nontypeable strains remain a common cause of respiratory infection across all age groups, not prevented by the conjugate vaccine.
Splenectomized patients and those with complement deficiencies have increased risk of invasive disease.

Resistance and therapeutic implications

Plasmid-mediated beta-lactamase production confers ampicillin resistance in a significant proportion of isolates.
Strains with beta-lactam resistance via altered penicillin-binding proteins (BLNAR) may not be detected by beta-lactamase testing alone.
Third-generation cephalosporins are preferred empirically for meningitis pending susceptibility confirmation.

Bench and reporting notes

Satellite test around Staphylococcus aureus colonies on blood agar aids presumptive identification.
Beta-lactamase testing should be performed routinely on invasive isolates to guide initial empiric therapy.
Capsular serotyping should be performed on invasive isolates for post-vaccination epidemiologic surveillance.

Sources

Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.

FAQ: Frequently Asked Questions

How to identify Haemophilus influenzae in the lab?

Haemophilus influenzae is identified through requires factor x (hemin) and factor v (nad) — x, v and xv disk test, satellitism around s. aureus on blood agar.

What are the intrinsic resistances of Haemophilus influenzae?

This organism is naturally resistant to glycopeptides, clindamycin, linezolid, daptomycin, penicillin g (eucast expected resistant phenotypes v1.2). These drugs should not be reported as susceptible.

Where is Haemophilus influenzae commonly found?

It is typically associated with otitis media, sinusitis, copd exacerbation, pneumonia, meningitis (unvaccinated patients).

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