Growth of RB Population in the Conversion Phase of Chlamydia Life Cycle

Abstract

Upon infecting a host cell, the reticulate body (RB) form of the Chlamydia bacteria simply proliferates by binary fission for an extended period. Available data show only RB units in the infected cells 20 hours post infection (hpi), spanning nearly half way through the development cycle. With data collected every 4 hpi, conversion to the elementary body (EB) form begins abruptly at a rapid rate sometime around 24 hpi. By modeling proliferation and conversion as simple birth and death processes, it has been shown that the optimal strategy for maximizing the total (mean) EB population at host cell lysis time is a bang-bang control qualitatively replicating the observed conversion activities. However, the simple birth and death model for the RB proliferation and conversion to EB deviates in a significant way from the available data on the evolution of the RB population after the onset of RB-to-EB conversion. By working with a more refined model that takes into account a small size threshold eligibility requirement for conversion noted in the available data, we succeed in removing the deficiency of the previous models on the evolution of the RB population without affecting the optimal bang-bang conversion strategy.