Melinda Mary Pettigrew PhD

Associate Professor of Epidemiology (Microbial Diseases); Associate Dean for Academic Affairs

Research Interests

Infectious diseases

Research Summary

Professor Pettigrew's research focuses on infectious diseases of infants, children, and young adults. Her current work utilizes a combined approach involving molecular biology and infectious disease epidemiology to identify bacterial virulence factors important for otitis media caused by the gram-positive pathogen Streptococcus pneumoniae. In collaboration with researchers in the Center for Perinatal, Pediatric and Environmental Epidemiology, Professor Pettigrew is also studying interactions between viruses and bacterial pathogens as they impact on upper respiratory tract infections in children.

Extensive Research Description

Dr. Pettigrew’s research is driven by a desire to understand processes that tip the balance between asymptomatic colonization and disease. Because the risks of colonization and disease are associated with host characteristics, the biological agent, and the environment, her research requires an understanding of several different disciplines including epidemiology, microbiology, and statistics. One major project utilizes a molecular epidemiologic approach to identify tissue specific virulence factors of the gram-positive pathogen Streptococcus pneumoniae. S. pneumoniaecolonizes the nasopharynx of up to 55% of healthy young children. Asymptomatic carriage is far more common than disease, yet these bacteria are important causes of otitis media, pneumonia, sepsis, and meningitis. Conjugate vaccine formulations are available for children, but these do not cover all 92 pneumococcal serotypes. Given these concerns, and increasing rates of antibiotic resistance among pneumococcal isolates, it is important to gain a better understanding of the virulence characteristics of S. pneumoniae that influence their propensity to cause disease. It is also important that we understand the distribution of these virulence determinants among strains in circulation at the population level. This will facilitate the development of novel strategies to prevent pneumococcal disease.

Additional research projects focuses on the epidemiology of polymicrobial interactions between S. pneumoniae and other bacteria that colonize the same niche in the upper respiratory tract. Colonization by S. pneumoniae is a critical early step in the disease process. Several hundred different bacterial species colonize the upper respiratory tract of a single individual. Our research indicates that competitive interactions between bacteria in the nasopharynx differ by the number and type of bacteria species present. These data have implications for the development of probiotics and for antibiotic and vaccination strategies that target carriage of colonizing bacterial species. Such strategies may alter the nasopharyngeal flora, which may in turn have unintended consequences for disease incidence. We are expanding our research to examine interactions between bacteria and respiratory tract viruses (e.g. respiratory syncytial virus and adenovirus) and by taking advantage of recent advances in pyrosequencing technology. Our newest projects utilize next generation 454 sequencing methods to characterize the microbial ecology of bacteria colonizing the upper respiratory tract of infants and young children. These data will also lead to increased understanding of the human microbiome and how competitive interactions between bacteria and viruses lead to disease.

Selected Publications