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Outer membrane protein composition in disease isolates of Haemophilus influenzae: pathogenic and epidemiological
Abstract:
The outer membrane protein composition of 50 disease isolates of Haemophilus influenzae has been determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. All strains, including 28 strains of serotype b, one strain each of serotypes a, c, d, e, and f, and 17 untypable strains, had an outer membrane protein composition typical of gram-negative bacteria, i.e., these membranes contained two to three dozen proteins with four to six proteins accounting for most of their protein content. Variation in the mobility of these major outer membrane proteins from strain to strain was common but not universal; the observed patterns provided useful data and new insight into the epidemiology of type b disease. The basic findings can be summarized as follows: (i) All 50 strains possessed three proteins (one minor and two major) each having identical mobilities. The other proteins, both major and minor, varied in mobility. (ii) All type b strains possessed a fourth (major) protein of identical mobility. (iii) The 28 type b strains, on the basis of the mobility of the six major outer membrane proteins, could be divided into eight subtypes. Of all the other strains examined, both typable and untypable, only the serotype a strain belonged to one of these subtypes. (iv) The untypable strains showed considerable variation in the mobilities of their major outer membrane proteins. Of these 17 strains, 13 had an additional major outer membrane protein not present in encapsulated strains. (v) The outer membrane protein composition of a single strain remained unchanged after many passages on solid media, but varied with the growth phase. (vi) The outer membrane protein composition of isolates obtained from nine patients during an epidemic of type b meningitis varied, indicating that a single strain was not responsible for the epidemic. At least five different strains were responsible for these nine cases. (vii) Identical outer membrane protein compositions were observed in the following: in a type b strain and a mutant of this strain deficient in capsule production, indicating that the level of capsule synthesis is not obviously related to outer membrane protein composition; in type b strains isolated from different anatomic sites of patients acutely ill with meningitis, indicating that the strain associated with bacteremia is the same as that isolated from the cerebrospinal fluid; in type b strains isolated from siblings who contracted meningitis at about the same time, indicating infection with the same strain; and in type b strains isolated from the initial and repeat infection of a single patient, suggesting that reinfection was due to the same strain.
Insights
Outer membrane protein analysis of Haemophilus influenzae revealed distinct subtypes within serotype b strains, aiding in understanding the epidemiology of type b disease. This method also identified multiple strains responsible for meningitis epidemics.
Area of Science:
- Microbiology
- Molecular Biology
- Epidemiology
Background:
- Haemophilus influenzae is a significant pathogen, particularly serotype b, causing severe invasive diseases like meningitis.
- Understanding the genetic diversity and epidemiological relationships of H. influenzae strains is crucial for disease control.
Purpose of the Study:
- To characterize the outer membrane protein (OMP) composition of various Haemophilus influenzae disease isolates.
- To investigate the utility of OMP profiles for differentiating strains and understanding the epidemiology of H. influenzae infections, especially type b disease.
Main Methods:
- Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was employed to analyze the OMP profiles of 50 H. influenzae isolates.
- Isolates included serotype b, other serotypes (a, c, d, e, f), and untypable strains.
Main Results:
- All strains exhibited typical Gram-negative bacterial OMP profiles, with variations in major protein mobilities observed between strains.
- Serotype b strains were divisible into eight subtypes based on OMP mobility, with one serotype a strain sharing a subtype.
- Untypable strains showed significant OMP variability, with 13 of 17 possessing an additional major OMP not found in encapsulated strains.
- Analysis of isolates from a meningitis epidemic indicated at least five different strains were involved, not a single one.
- OMP composition remained stable in vitro but varied with growth phase; it was also consistent across different anatomical sites and in cases of reinfection.
Conclusions:
- Outer membrane protein profiling provides valuable insights into the epidemiology of Haemophilus influenzae type b disease.
- OMP analysis can differentiate between strains causing outbreaks and track infections within individuals and families.
- The OMP composition is a stable characteristic of a strain, useful for epidemiological studies, and not directly related to capsule synthesis levels.