Massive shift in the composition of the nasopharyngeal flora after vaccination

ITQB PhD Seminar

Title: Massive shift in the composition of the nasopharyngeal flora of Streptococcus pneumoniae after vaccination of children with the 7-valent pneumococcal conjugate vaccine

Speaker: Nelson Frazão

Laboratory: Molecular Genetics (ITQB)

Abstract
Streptococcus pneumoniae remains one of the most important human pathogens in our era. The nasopharynx of young children, who are colonized very early in life, is the ecological reservoir of this microorganism. When the balance between host and pathogen is disturbed, the nasopharynx can become a launching pad for pneumococcal disease such as acute otitis media and pneumonia, or enter the bloodstream causing invasive infections such as sepsis and meningitis.
The extensive use of antibiotics led to the emergence of drug resistant strains, which found sanctuary in the nasopharynx of pre-school age children who are increasingly recruited into day care centers. Pneumococci can produce as many as 91 chemically different capsular types, which represent the primary virulence determinant of this pathogen. In 2000 a 7-valent pneumococcal conjugate vaccine (PCV7) against capsular types 4, 6B, 9V, 14, 18C, 19F and 23F, also known as vaccine types, became available in the United States and arrived in Portugal in July 2001. Since drug resistant strains of pneumococci most often belong to vaccine types, it was expected that vaccination would also reduce carriage of drug resistant pneumococci.
We assessed the impact of PCV7 on colonization in Portuguese children by carrying out epidemiological studies. Our results indicate that this vaccine decreases vaccine types and simultaneously selects for non-vaccine types that are genetically different but also drug resistant. Moreover, we determined that prevention of de novo acquisition of vaccine types is the mechanism of the vaccine’s effect.
To complement these studies, we have been analyzing the pathogenic potential of these non-vaccine types selected by PCV7 in animal models. Data obtained in mice show that non-vaccine types can invade the olfactory bulbs and the brain and are lethal in an animal pneumonia model of disease.

Short CV:
1997 to 2002 – Degree in Biology at Faculdade de Ciências da Universidade de Lisboa.
2002 to 2005 – Grant holder (BIC) in the Molecular Genetics Laboratory at ITQB. Supervision: Professora Hermínia de Lencastre, Professora Ilda Sanches, Doutora Rosario Mato.
2006 to present - PhD student in the Molecular Genetics Laboratory at ITQB; Visiting PhD student, The Rockefeller University. Supervision: Professora Hermínia de Lencastre, Professor Alexander Tomasz, Doutora Raquel Sá Leão.