tailieunhanh - Chapter 139. Haemophilus Infections (Kỳ 1) Harrison's Internal Medicine Chapter 139.

Harrison's Internal Medicine Chapter 139. Haemophilus Infections Haemophilus influenzae Microbiology Haemophilus influenzae was first recognized in 1892 by Pfeiffer, who erroneously concluded that the bacterium was the cause of influenza. The bacterium is a small (1- by ) gram-negative organism of variable shape; hence, it is often described as a pleomorphic coccobacillus. In clinical specimens such as cerebrospinal fluid (CSF) and sputum, it frequently stains only faintly with phenosafranin and therefore can easily be overlooked. H. influenzae grows both aerobically and anaerobically. Its aerobic growth requires two factors: hemin (X factor) and nicotinamide adenine dinucleotide (V factor). . | Chapter 139. Haemophilus Infections Kỳ 1 Harrison s Internal Medicine Chapter 139. Haemophilus Infections Haemophilus influenzae Microbiology Haemophilus influenzae was first recognized in 1892 by Pfeiffer who erroneously concluded that the bacterium was the cause of influenza. The bacterium is a small 1- by gram-negative organism of variable shape hence it is often described as a pleomorphic coccobacillus. In clinical specimens such as cerebrospinal fluid CSF and sputum it frequently stains only faintly with phenosafranin and therefore can easily be overlooked. H. influenzae grows both aerobically and anaerobically. Its aerobic growth requires two factors hemin X factor and nicotinamide adenine dinucleotide V factor . These requirements are used in the clinical laboratory to identify the bacterium. Caution must be used to distinguish H. influenzae from H. haemolyticus a respiratory tract commensal that has identical growth requirements. H. haemolyticus has classically been distinguished from H. influenzae by hemolysis on horse blood agar. However a significant proportion of isolates of H. haemolyticus have recently been recognized as nonhemolytic. Analysis of 16S ribosomal sequences is one reliable method to distinguish these two species. Six major serotypes of H. influenzae have been identified designated a through f they are based on antigenically distinct polysaccharide capsules. In addition some strains lack a polysaccharide capsule and are referred to as nontypable strains. Type b and nontypable strains are the most relevant strains clinically Table 139-1 although encapsulated strains other than type b can cause disease. H. influenzae was the first free-living organism to have its entire genome sequenced. Table 139-1 Characteristics of Type b and Nontypable Strains of Haemophilus influenzae Feature Type b Strains Nontypable Strains Capsule Ribosyl-ribitol phosphate Unencapsulated Pathogenesis Invasive infections due to hematogenous spread Mucosal .