Haemophilus influenzae
species of bacterium
Haemophilus influenzae (formerly called Pfeiffer's bacillus or Bacillus influenzae) is a Gram-negative, non-motile, coccobacillary, facultatively anaerobic, capnophilic pathogenic bacterium of the family Pasteurellaceae. The bacteria are mesophilic and grow best at temperatures between 35 and 37 °C.
H. influenzae was first described in 1893 by Richard Pfeiffer during an influenza pandemic when he incorrectly identified it as the causative microbe, which is why the bacterium was given the name "influenzae". H. influenzae is responsible for a wide range of localized and invasive infections, typically in infants and children, including pneumonia, meningitis, or bloodstream infections. Treatment consists of antibiotics; however, H. influenzae is often resistant to the penicillin family, but amoxicillin/clavulanic acid can be used in mild cases. Serotype B H. influenzae (hib) can cause illness, called Hib infections, among other names. It has been a major cause of meningitis in infants and small children, frequently causing deafness and mental degradation. However, the development in the 1980s of a vaccine effective in this age group (the Hib vaccine) has almost eliminated this in developed countries.
This species was the first organism to have its entire genome sequenced.
Physiology and metabolism
Structure
H. influenzae is a small Gram-negative bacterium, approximately 0.3 micrometer to 1 micrometer. Like other Gram-negative bacteria, H. influenzae has a thin peptidoglycan layer surrounded by an outer membrane containing lipopolysaccharide.
Begin with the source’s own compact description: “Haemophilus influenzae” is species of bacterium. The dossier treats that line as a proposition to test through Haemophilus, influenzae and species, not as a finished interpretation.
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Datasets, specimens, observations and peer-reviewed methods provide the appropriate test for the technical claims summarized here. The source revision retrieved here is dated Sep 16, 2026. The linked authority identifier is Q1141979. The Library of Congress control number is sh85060220. 1 of 1 selected statements include explicit references; 1 carry qualifiers and 0 use preferred rank. The first chronological checks are 1893.
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This entry incorporates text from “Haemophilus influenzae” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.