Antimicrobial Susceptibility Testing of Chlamydophila pneumoniae: Pilot Study for Alternative Methods that Address the Complex Chlamydial Life Cycle

Conventional susceptibility testing of Chlamydophila pneumoniae does not account for the complex life cycle that takes place in an obligatory intracellular niche and involves multiple morphological forms. Some of these forms (elementary bodies and cryptic bodies) cause persistence and are not susceptible to antimicrobial agents. Therefore, we describe a pilot study for alternative methods of susceptibility testing of C. pneumoniae. These methods include delaying the addition of antimicrobial agents to cell cultures for 48 hours to allow the development of an established chlamydial infection as well as the use of reverse transcriptase quantitative PCR [RT-qPCR] to measure messenger RNA. Using these methods, susceptibility testing of an established infection in Hep2 cells was compared with conventional susceptibility testing of C. pneumoniae.\n\nConventional antimicrobial susceptibility testing of C. pneumoniae results in MICs and MBCs that would suggest that recommended treatment regimens of 2 to 3 weeks of antibiotics such as doxycycline, clarithromycin, levofloxacin, and rifabutin would be sufficient. However, susceptibility testing using an established chlamydial infection in HEp2 cells reveals that none of these agents are as inhibitory and/or bactericidal as indicated by conventional methods. The resultsof this pilot study suggest that further evaluation of chlamydial susceptibility testing methods using established infection in cell cultures and RT-qPCR to measure messenger RNA are needed to optimize treatment recommendations for chronic C. pneumoniae infections.