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Bacterial structure and functions
Bacillus anthracis (Anthrax)
Bacillus cereus (Food poisoning)
Corynebacterium diphtheriae (Diphtheria)
Clostridium botulinum (Botulism)
Clostridium difficile (Pseudomembranous colitis)
Clostridium tetani (Tetanus)
Streptococcus agalactiae (Group B Strep)
Streptococcus pyogenes (Group A Strep)
Bartonella henselae (Cat-scratch disease and Bacillary angiomatosis)
Legionella pneumophila (Legionnaires disease and Pontiac fever)
Salmonella typhi (typhoid fever)
Yersinia pestis (Plague)
Vibrio cholerae (Cholera)
Bordetella pertussis (Whooping cough)
Francisella tularensis (Tularemia)
Haemophilus ducreyi (Chancroid)
Mycobacterium tuberculosis (Tuberculosis)
Mycobacterium avium complex (NORD)
Gardnerella vaginalis (Bacterial vaginosis)
Coxiella burnetii (Q fever)
Ehrlichia and Anaplasma
Rickettsia rickettsii (Rocky Mountain spotted fever) and other Rickettsia species
Borrelia burgdorferi (Lyme disease)
Borrelia species (Relapsing fever)
Treponema pallidum (Syphilis)
Haemophilus Influenzae Disease
Haemophilus influenzae Characteristics
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.
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.
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