Serum resistance and phase variation of a nasopharyngeal non-typeable Haemophilus influenzae isolate.
Haemophilus influenzae harbours a complex array of factors to resist human complement attack. As non-typeable H. influenzae (NTHi) strains do not possess a capsule, their serum resistance mainly depends on other mechanisms including LOS decoration. In this report, we describe the identification of a highly serum resistant, nasopharyngeal isolate (NTHi23) by screening a collection of 77 clinical isolates. For NTHi23, we defined the MLST sequence type 1133, which matches the profile of a previously published invasive NTHi isolate. A detailed genetic analysis revealed that NTHi23 shares several complement evading mechanisms with invasive disease isolates. These mechanisms include the functional expression of a retrograde phospholipid trafficking system and the presumable decoration of the LOS structure with sialic acid. By screening the NTHi23 population for spontaneous decreased serum resistance, we identified a clone, which was about 103-fold more sensitive to complement-mediated killing. Genome-wide analysis of this isolate revealed a phase variation in the N'-terminal region of lpsA, leading to a truncated version of the glycosyltransferase (LpsA). We further showed that a NTHi23 lpsA mutant exhibits a decreased invasion rate into human alveolar basal epithelial cells. Since only a small proportion of the NTHi23 population expressed the serum sensitive phenotype, resulting from lpsA phase-off, we conclude that the nasopharyngeal environment selected for a population expressing the intact and functional glycosyltransferase.
Institute of Molecular Biosciences, University of Graz, Humboldtstr. 50, 8010 Graz, Austria; Institute of Hygiene, Microbiology and Environmental Medicine, Medical University of Graz, Neue Stiftingtalstraße 2, 8010 Graz, Austria. Electronic address: sabine.lichtenegger@medunigraz.at.
Sabine
S
Lichtenegger
Institute of Molecular Biosciences, University of Graz, Humboldtstr. 50, 8010 Graz, Austria.
Isabelle
I
Bina
Institute of Molecular Biosciences, University of Graz, Humboldtstr. 50, 8010 Graz, Austria.
Sanel
S
Durakovic
Insitut Pasteur, 25-28 rue du docteur Roux, 75015 Paris, France.
Philippe
P
Glaser
Institute of Molecular Biosciences, University of Graz, Humboldtstr. 50, 8010 Graz, Austria.
Sarah
S
Tutz
Institute of Molecular Biosciences, University of Graz, Humboldtstr. 50, 8010 Graz, Austria; BioTechMed-Graz, Austria.
Stefan
S
Schild
Institute of Molecular Biosciences, University of Graz, Humboldtstr. 50, 8010 Graz, Austria; BioTechMed-Graz, Austria. Electronic address: joachim.reidl@uni-graz.at.
Joachim
J
Reidl
D000328:Adult; D056809:Alveolar Epithelial Cells / Q000382:microbiology; D000940:Antigenic Variation; D001770:Blood Bactericidal Activity; D002460:Cell Line; D002648:Child; D004705:Endocytosis; D005838:Genotype; D016695:Glycosyltransferases / Q000235:genetics / Q000378:metabolism; D006193:Haemophilus influenzae / Q000235:genetics / Q000276:immunology* / Q000302:isolation & purification / Q000502:physiology*; D006801:Humans; D057131:Immune Evasion; D058885:Multilocus Sequence Typing; D009305:Nasopharynx / Q000382:microbiology*
D016695:Glycosyltransferases
Haemophilus influenzae; Phase variation; Serum resistance; lpsA