Invited Lecture AbstractsISPPD-0534 Pneumococcal Colonization and Carriage: GENOMICS AND PNEUMOCOCCAL EPIDEMIOLOGY IN THE NASOPHARYNXC. Chewapreecha1, S.R. Harris1, N.J. Croucher2, C. Turner3, P. Marttinen4, L. Cheng5, A. Pessia5, D. Aanensen6, S.J. Salter1, A.E. Mather1, A.J. Page1, D. Harris1, F. Nosten7, D. Goldblatt8, J. Corander5, J. Parkhill1, P. Turner3, S.D. Bentley11Pathogen genomics, The Wellcome Trust Sanger Institute, Cambridge, United Kingdom; 2Center for Communicable Disease Dynamics, Harvard School of Public Health, Boston, USA; 3Cambodia-Oxford Medical Research Unit, Angkor Hospital for Children, Siem Reap, Cambodia 4Department of Information and Computer Science, Aalto University, Helsinki, Finland; 5Department of Mathematics and Statistics, University of Helsinki, Helsinki, Finland; 6Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom; 7Shoklo Malaria Research Unit, Mahidol-Oxford Tropical Medicine Research Unit, Tak, Thailand; 8Immunobiology Unit, Institute of Child Health University College London, London, United KingdomHomologous recombination is one of the main evolutionary forces affecting Streptococcus pneumoniae. The highly recombinogenic nature of this species allows introduction of genetic material with selective advantages in carriage, the state that is a prerequisite for the development of pneumococcal invasive diseases. To study the impact of recombination on the evolution of a carriage pneumococcal population, whole genome sequencing was used to characterize 3,085 pneumococcal carriage isolates from a 2.4 km2 Thai refugee camp collected over a 3-year period. This high sampling density allowed us to characterized genetic exchanges in the pneumococcal population at a high resolution. Recombination ‘hotspots’ showed remarkable consistency between lineages, some of which were associated with drug resistance. Temporal trends in recombination at these sites reflected changes in antibiotic consumption, suggesting recombination facilitates adaptation to changing selection pressures. The highest frequencies of receipt and donation of DNA fragments exchanged through homologous recombination were observed in non-encapsulated lineages, implying a potential role in diversification and adaptation of the overall population played by these non-vaccine target lineages. These findings expand our understanding of pneumococcal population in carriage and help inform the design of future intervention strategies.No conflict of interestISPPD-0550 Pneumococcal Colonization and Carriage: INTERACTIONS BETWEEN STREPTOCOCCUS PNEUMONIAE AND THE RESPIRATORY MICROBIOME IN RELATION TO RESPIRATORY HEALTHD. Bogaert11The NetherlandsIndividuals differ markedly in their susceptibility to and clinical presentation of respiratory infections, despite that most young children and many adults are colonized with potential bacterial pathogens like Streptococcus pneumoniae. The reasons for these individual differences are not yet fully understood, but clearly multifactorial. Besides pathogen-related (virulence)-factors, host-related factors like immune-status and genetic background and environmental factors, a possible fourth factor might be of relevance, i.e. the commensal community of bacteria ‘hosting’ these potential pathogens. The collective genomes of these commensal inhabitants are referred to as the human microbiome. This microbiome contains highly complexity communities of bacteria, which differ between individuals and even more between niches. The human microbiome in general has shown crucial for an appropriate development of our immune system and our mucosal barriers, and for prevention of pathogen adherence and expansion. We studied the development and composition of microbiota of the upper respiratory tract in different age-groups and in relation to environmental and disease characteristics. We observed highly complex and niche-specific communities of bacteria. Even within the upper respiratory tract, the microbiota composition differs depending on the exact anatomical location. Furthermore, the composition of respiratory microbiota varies with host and environmental factors like age, season, infant feeding, and viral presence. Moreover, our data suggest a correlation between the presence and abundance of specific bacteria and stability of microbiota, as well as susceptibility to respiratory infections. Finally, clear evidence has been found for patterns of bacterial interactions within the respiratory microbiota, with a central role played by Streptococci.No conflict of interest