Point mutations in wchA are responsible for the non-typability of two invasive Streptococcus pneumoniae isolates.
Non-typable Streptococcus pneumoniae (NTPn) strains are typically isolated from nasopharyngeal carriage or from conjunctivitis. Since the isolation of NTPn from invasive disease is rare, we characterized the genetic basis of the non-typability of two isolates obtained in Italy from two cases of bacteraemic pneumonia. MLST revealed that both NTPn belonged to ST191, which, according to the MLST database, is associated with serotype 7F. Sequencing of the capsular locus (cps) confirmed the presence of a 7F cps in both strains and revealed the existence of distinct single point mutations in the wchA gene (a glycosyltransferase), both leading to the translation of proteins truncated at the C terminus. To verify that these mutations were responsible for the non-typability of the isolates, a functional 7F WchA was overexpressed in both NTPn. The two NTPn along with their WchA-overexpressing derivatives were analysed by transmission electron microscopy and by high-resolution magic angle spinning NMR spectroscopy. Both NTPn were devoid of a polysaccharide capsule, and WchA overexpression was sufficient to restore the assembly of a serotype 7F capsule on the surface of the two NTPn. In conclusion, we identified two new naturally occurring point mutations that lead to non-typability in the pneumococcus, and demonstrated that WchA is essential for the biosynthesis of the serotype 7F capsule.
Novartis Vaccines & Diagnostics, Siena, Italy.
Sara
S
Melchiorre
Department of Infectious, Parasitic and Immune-Mediated Diseases, Istituto Superiore di Sanità, Rome, Italy.
Romina
R
Camilli
Department of Technology and Health, Istituto Superiore di Sanità, Rome, Italy.
Agostina
A
Pietrantoni
Novartis Vaccines & Diagnostics, Siena, Italy.
Monica
M
Moschioni
Novartis Vaccines & Diagnostics, Siena, Italy.
Francesco
F
Berti
Department of Infectious, Parasitic and Immune-Mediated Diseases, Istituto Superiore di Sanità, Rome, Italy.
Maria
M
Del Grosso
Department of Technology and Health, Istituto Superiore di Sanità, Rome, Italy.
Fabiana
F
Superti
Novartis Vaccines & Diagnostics, Siena, Italy.
Michèle Anne
MA
Barocchi
Department of Infectious, Parasitic and Immune-Mediated Diseases, Istituto Superiore di Sanità, Rome, Italy.
Annalisa
A
Pantosti
D000328:Adult; D000595:Amino Acid Sequence; D016667:Bacterial Capsules / Q000096:biosynthesis; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D015373:Bacterial Typing Techniques; D005260:Female; D016695:Glycosyltransferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D011008:Pneumococcal Infections / Q000382:microbiology*; D017354:Point Mutation; D016415:Sequence Alignment; D013296:Streptococcus pneumoniae / Q000145:classification / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification
D001426:Bacterial Proteins; D016695:Glycosyltransferases