Ecological niche of Streptococcus pneumoniae: Factors associated with survival and pathogenesis within the human host.

摘要

Streptococcus pneumoniae (pneumococcus) is an important human pathogen and a leading cause of morbidity and mortality worldwide. Gaining an understanding of this organism in its ecological niche is key to efforts geared towards treating and preventing the diseases it causes. Three aspects of pneumococcal disease are carriage, invasive disease, and the virulence factors involved in host damage.;Pneumococcal carriage in the nasopharynx of the host is required for disease establishment. Carriage is more likely to lead to disease in those with a decreased immune status, such as infection with human immunodeficiency virus (HIV). We studied pneumococcal carriage in HIV-infected individuals to identify carriage strain characteristics and to ascertain what role the introduction of the conjugate vaccine (PCV7) played in the rates of carriage and the types of strains being carried. We found that herd immunity effects of PCV7 administration have negatively impacted carriage: overall carriage and vaccine serotype carriage rates decreased. The presence of a high number of pneumococcus-like strains found in our population emphasizes the importance of highly specific tests for accurate pneumococcal identification in performance of epidemiological studies.;If the carriage state progresses to invasion, pneumococci can cause a number of diseases. Acute otitis media (AOM) is the most common and most costly presentation of pneumococcal infection in the United States. We studied pneumococcal ear isolates to identify characteristics that may be exploited for development of future treatment or prevention modalities. We found great variability based on genetic background and capsular serotype within the group of isolates. Similarities in the type of pneumococcal surface protein A expressed by these isolates makes this protein a candidate for future vaccines.;One virulence factor responsible for pneumococcal-associated pathology is the cytoplasmic protein pneumolysin (Ply). The mechanism of Ply's egress from the bacterial cell is unknown. We demonstrated a correspondence between Ply and the amount of RNA released from bacteria during growth, implying that differences in Ply release from different strains may be due to differences in cell turnover (cell lysis). However, data do not support our theory that differences in lysis are due to variation in the aliA gene.