Small, G –ve bacilli bacteria

Small, G –ve bacilli bacteria:
Includes: (1) Haemophilus, (2) Bordetella, (3). Brucella.
1. Haemophilus:
The most important pathogen is H. influenzae type b, which may causes meningitis, epiglutitis, pneumonia, conjunctivitis, nasopharyngitis, otitis media and externa.
Haemophilus is opportunistic pathogen found normally in upper respiratory tract. This bacteria derives its name from essential growth factor in blood represented by:
1. X-factor: It is heat stable and physiologically known as Hemin.
2. V-factor: It is heat labile known as NAD coenzyme. Haemophilus produce no exotoxine, non hemolytic.
General characteristics and morphology:
G –ve , pleomorphic, cocco bacilli in young cultures (6-8 hr.) and bacilli in old culture (up to 1 day), arranged in single, pairs or short chains, non spore forming, non motile, oxidase +ve, catalase +ve, some strains are capsulated produce polysaccharide, capsular Ag. which is the most important virulence factor in H. inf. and according to this capsule H. inf. can be classified into 6 serotype: a, b, c, d, e and f.
The commonest virulence one is type b which is called PRP (polyribose, Ribitol-phosphate), some strains have fimbriae.
Lab. Diagnosis:
1. Specimens ? CSF, blood, pus, throat swab.
2. Culture: Blood agar is done on blood agar supplemented with (NAD) and incubated at 37?C of 10% CO2. The media can be made selective by adding penicillin and bacitracin. H. inflenzae also not grow on sheep blood agar except around colonies of Staphylococcus (Satellite phenomenon).
- On chocolate agar: flat, grayish-brown at 37?C and 10% CO2.
- Serology:
1. Agglutination test.
2. Coagulation resemble to Quilling test for capsular strains (serum + capsular Ag ? swelling of capsule (capsular swelling reaction).)
3. Immunoflourescence.
- H. influenzae requires V and X factors and non haemolytic.
- H. parainfluenzae requires V only and non haemolytic.
- H. parahaemolyticus and H. haemolyticus are haemolytic