6,881views
00:00 / 00:00
of complete
of complete
2024
2023
2022
2021
Haemophilus influenzae p. , 140
Haemophilus influenzae p. , 140
for Haemophilus influenzae p. , 140
Haemophilus influenzae p. , 124, 140
Haemophilus influenzae p. , 140
Haemophilus influenzae p. , 140
Haemophilus influenzae p. , 140
biofilm production p. 127
cephalosporins p. 186
chloramphenicol p. 189
culture requirements p. 124
Gram-negative algorithm p. 139
influenza p. 166
penicillins for p. 185
pneumonia p. 176
postviral infection p. 176
rhinosinusitis p. 691
vaccine p. 177
Haemophilus influenzae p. , 140
Haemophilus influenzae p. , 127, 140
Haemophilus influenzae p. , 140
Haemophilus influenzae p. , 140, 177
Haemophilus influenzae is a small Gram-negative coccobacillus which can normally colonize the human respiratory tract. There are two major categories of H. influenzae - encapsulated strains and unencapsulated strains.
Encapsulated strains are classified into six serotypes based on their capsular antigens - a, b, c, d, e and f, and unencapsulated strains are called nontypable, because they lack the polysaccharide capsule, and, consequently, capsular antigens.
The strains that cause disease in humans are most often Haemophilus influenzae type b, or Hib for short and Haemophilus influenzae nontypable.
Now, Haemophilus influenzae has a thin peptidoglycan layer, so it doesn’t retain the crystal violet dye during Gram staining. Instead, like any other Gram-negative bacteria, it stains pink with safranin dye.
And since it’s a coccobacillus, it’s shaped somewhere between round, like a coccus, and linear, like a bacillus. Haemophilus influenzae is non-motile, so it doesn’t move, and facultative anaerobic which means it can survive both in aerobic and anaerobic environments. It’s also catalase and oxidase positive which means it produces both these enzymes.
Finally, Haemophilus influenzae can be cultivated on chocolate agar, because this medium contains essential nutrients that Haemophilus influenzae needs to grow, like factor X, also called hemin, and factor V, also called nicotinamide adenine nucleotide.
Another way to grow it is to grow it with Staphylococcus aureus colonies, on blood agar, which provides factor V via red blood cells hemolysis.
On both blood agar and chocolate agar, Haemophilus influenzae grows into convex, smooth, gray or transparent colonies. Now, Haemophilus influenzae has a number of virulence factors, that are like assault weaponry that help it attack and destroy the host cells, and evade the immune system.
So first, encapsulated strains of Haemophilus influenzae are covered by a polysaccharide layer called a capsule. Now, this capsule is a major virulence factor for Haemophilus influenzae because of its antiphagocytic ability, meaning that it protects the bacteria against phagocytosis by macrophages or neutrophils.
This allows Haemophilus influenzae to escape destruction and attach to epithelial cells in the airways. Also, on the capsule, there are pili, which are hair-like extensions, and adhesion proteins such as HMW1 and HMW2 that help the bacteria attach to host cells.
Haemophilus influenzae, or just H. influenzae, is a gram-negative, facultatively anaerobic, non-motile coccobacillus. Haemophilus influenzae bacteria are classified into encapsulated strains and unencapsulated strains. Based on their capsular antigen type, encapsulated strains are further classified into six serotypes (serotypes a, b, c, d, e, and f). Unencapsulated strains are also referred to as nontypable because they lack the polysaccharide capsule, and capsular antigens.
Nontypeable strains of Haemophilus influenzae are known to cause relatively simple mucosal infections, like otitis media, sinusitis, and pneumonia. On the other hand, encapsulated strains such as Haemophilus influenza type b can cause more severe infections such as meningitis and epiglottitis, but such severe infections are not so common nowadays due to vaccination.
Copyright © 2024 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.
Cookies are used by this site.
USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.