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Also called Pfeiffer bacillus. Richard Pfeiffer first described this bacteria in 1892 during an influenza pandemic
First free-living organism to be sequenced in 1995 by Craig Venter and his team who used the whole-genome shotgun.
external image moz-screenshot.pngH.fluGenome.jpeg
The circular chromosome of H. influenzae
(http://www.textbookofbacteriology.net/haemophilus.html)

Phylogenic tree
Kingdom Bacteria => Phylum Proteobacteria => Class Gammaproteobacteria => Order Pasteurellales => Family Pasteurellaceae => Genus Haemophilus => Species H. influenzae
Morphology
Encapsulated, gram-negative, pleomorphic, non-motile coccobacillus
H.flu.jpegGram stain of H.influenzae from sputum
(http://www.textbookofbacteriology.net/haemophilus.html)


Serovar
Two serotypes exist for H. influenzae:
1) Encapsultated strains: six different types called type a, b, c, d, e and f. Serotype b (called Hib) can cause diseases and affect different organs.
2) an un-encapsulated strain are classified using "multilocus sequence typing". This molecular biology technique sequences housekeeping genes and internal fragments.

Diseases
Most of H. influenzae strains are opportunistic pathogens which means that they live in their host without causing diseases but when an infection occurs, they can cause pneumonia, bacterial meningitis and infectious arthritis.
Hib (Haemophilus influenzae type b) is the most dangerous type .
(http://www.youtube.com/watch?v=ogqrgd3i_mQ)

H. influenzae type b is the most virulent strain. It contains a polyribosyl ribitol phosphate capsule which is an anti-phagositic material and avoid any phagocytosis by macrophages. Also it avoids activation of complement pathway (helps immune cells to clear pathogens) and thus bacteria can invode bloodstream and cerebrospinal fluid.

How to diagnose this bacteria ? Bacterial culture is the main diagnosis technique to diagnose H. influenzae presence and is done on chocolate agar plates. This chocolate agar is a non selective medium and contains lysed red blood cells in order to provide growth factor, NAD and hematin (an iron-containing porphyrin).
More sensitive methods can be used, called the latex particle agglutination test, which is used to detect antibodies accumulation in produced in response to H. influenza infection and Polymerase Chain Reaction, which is not yet a routine technique used in laboratories.

Who are the people at risks ? young children

Treatment
H. influenzae is resistant to penicillin but cephalosporin antibiotics ( β-Lactam antibiotics ) can be used to treat patients due to its capacity to penetrate meninges which make it efficient against bacterial meningitis caused by H.influenzae.
H. influenzae can interact with another bacteria called Streptococcus pneumoniae and they can both be found in the human respiratory tract.

Haemophilus influenzae type b vaccine
In 1985, a polysacharride vaccine was produced but immune response was dependent on age of patients. Indeed, young children didn't have a positive immune response.
In 2006, a "conjugate vaccine" was studied. A protein carrier was linked to Hib polysaccharide and scientists discovered that children developp immunity against Hib pathogens.
Usually Hib vaccine is combined with diphteria, pertussis, tetanus, polio and Hepatitis B vaccines.


Links
The Comprehensive Microbial Resource (CMR) is a database containing general information about all bacterial genome sequences
**http://cmr.jcvi.org/cgi-bin/CMR/GenomePage.cgi?database=ghi**
http://emedicine.medscape.com/article/218271-overview
http://www.who.int/mediacentre/factsheets/fs294/en/index.html

Books
"Haemophilus influenzae protocols" Edited by Mark A. Herbert, E. Richard Moxon, Derk W.Hood (2003) 333 pages. Methods in molecular medicine
**//http://www.textbookofbacteriology.net/haemophilus_1.html//** (2011) Kenneth Todar, PhD