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Frequency and properties of naturally occurring adherent piliated strains of Haemophilus influenzae type b
Insights
Haemophilus influenzae type b colonization is common in children. Piliated bacteria in the nasopharynx may lose pili for invasion, explaining disease progression.
Area of Science:
- Microbiology
- Pediatrics
- Infectious Diseases
Background:
- Haemophilus influenzae type b (Hib) is a significant cause of invasive disease in children.
- Understanding the transition from colonization to invasive disease is crucial for prevention.
Purpose of the Study:
- To investigate the characteristics of Hib strains causing invasive disease versus colonization.
- To explore the role of bacterial adherence and piliation in Hib pathogenesis.
Main Methods:
- Nasopharyngeal (NP) and systemic isolates from children with Hib disease and upper respiratory infections were analyzed.
- Adherence to buccal epithelial cells, biotyping, serotyping, antibiotic susceptibility, outer membrane protein profiles, and electron microscopy (piliation) were assessed.
Main Results:
- Hib colonization was detected in 55% of children with invasive disease and 1.7% with upper respiratory infections.
- 16% of NP strains from children with systemic Hib disease adhered to buccal cells; systemic strains did not.
- Adherent NP strains were highly piliated and agglutinated erythrocytes, unlike non-adherent systemic strains.
Conclusions:
- Piliation may not be essential for NP colonization by Hib.
- Loss of pili might be a critical step for Hib to invade host tissues and cause systemic disease.
Abstract:
We found that 41 of 75 (55%) children with Haemophilus influenzae type b disease (70 cases of meningitis, 2 of cellulitis, 2 of septic arthritis, and 1 of epiglottitis) and 2 of 120 (1.7%) children with upper respiratory infection were colonized with H. influenzae type b in the nasopharynx (NP). Of these 43 NP strains from children with systemic H. influenzae type b disease, 7 (16%) adhered to human buccal epithelial cells. The strains isolated from the systemic site of all children, including children from whose NP adherent bacteria were isolated, did not adhere to buccal epithelial cells in vitro. Each adherent NP strain had biotype (I), serotype (b), and antibiotic susceptibility (sensitive) similar to that of the corresponding nonadherent systemic isolate. With one exception, all NP-systemic pairs had similar major outer membrane proteins. Six of the seven NP strains had a protein band in the whole cell lysate preparation with a molecular weight between 22,000 and 23,000, which could not be seen in the nonadherent cerebrospinal fluid strains. Electron micrographs of all adherent strains showed that more than 95% of the organisms examined were highly piliated, whereas the nonadherent strains were not piliated. All piliated strains agglutinated human erythrocytes. Adherence to buccal epithelial cells and agglutination of erythrocytes could not be blocked by mannose or alpha-methyl-D-mannoside. We speculate that piliation is not important for NP colonization by H. influenzae type b and that the loss of pili may be required for host invasion.