Changing the Ecology of Pneumococci with Antibiotics and Vaccines

Abstract

This chapter describes the mechanisms and consequences for the pneumococcal population of the selective pressures imposed by antibiotics and vaccines. While inhibiting pneumococci can have effects on other species of upper respiratory tract (URT) bacteria, the chapter focuses on the selective effects of vaccines and antibiotics on pneumococci. The direct effects of antibiotics on S. pneumonia in the nasopharynx of the treated patient depend on the pharmacokinetics and pharmacodynamics of the agent. Streptococcus pneumoniae resistance to the beta-lactam antibiotic class evolved mainly by complex restructuring of the targets of the beta-lactams, the penicillin-binding proteins (PBPs). To summarize the effect of antibiotics on S. pneumoniae ecology, it is clear that antibiotic treatment in any community profoundly affects S. pneumoniae ecology. Furthermore, a significant reduction of carriage of antibiotic-resistant and multidrug resistant (MDR) S. pneumoniae in the younger siblings of the day care attendees as the result of vaccination of their older siblings was observed. The chapter emphasizes the effects of vaccines and antibiotics on the ecology of pneumococci taking place against a background of a genetically diverse population structured by direct and indirect ecological interactions between strains. The importance of understanding pneumococcal population structure has been appreciated since the earliest days. This understanding can be extended to reconcile the disparate results of clinical trials of antibiotics and vaccines, to evaluate the relative selective effect of different antibiotics for resistant strains, and to project the effects of vaccines and antibiotics on future patterns in the prevalence of serotypes and resistant strains.