Non-typeable Haemophilus influenzae contains an N6-adenine DNA-methyltransferase (ModA) that is subject to phase-variable expression (random ON/OFF switching). Five modA alleles, modA2, modA4, modA5, modA9 and modA10, account for over two-thirds of clinical otitis media isolates surveyed. Here, we use single molecule, real-time (SMRT) methylome analysis to identify the DNA-recognition motifs for all five of these modA alleles. Phase variation of these alleles regulates multiple proteins including vaccine candidates, and key virulence phenotypes such as antibiotic resistance (modA2, modA5, modA10), biofilm formation (modA2) and immunoevasion (modA4). Analyses of a modA2 strain in the chinchilla model of otitis media show a clear selection for ON switching of modA2 in the middle ear. Our results indicate that a biphasic epigenetic switch can control bacterial virulence, immunoevasion and niche adaptation in an animal model system.
The acellular pertussis vaccine was protective among adolescents and adults, and its routine use might reduce the overall disease burden and transmission to children.
Outer-membrane proteins from isolates of Haemophilus influenzae type b were examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Sarcosinate-insoluble membrane preparations contained one peptide with a molecular weight of 16,000 and four major peptides with molecular weights of 25,000-40,000. A peptide with a molecular weight of 49,000 (50,000 in some strains) was observed after the samples were heated at 100 C. Fifty-one isolates obtained from patients hospitalized with invasive diseases, primarily meningitis, could be subclassified into nine categories based on reproducible and clearly resolvable differences in the outer-membrane protein profiles. Five categories accounted for 92% of the isolates. Complete concordance was observed in subtypes of strains obtained from epidemiologically related cases and contacts. Thus, comparison of the major outer-membrane proteins of H. influenzae type b is a useful technique for investigating the transmission of the organism and may provide a basis for further immunologic characterization of the outer-membrane proteins.
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