ABSTRACT
INTRODUCTION This chapter discusses susceptibility testing for rickettsial agents including Rickettsia, Ehrlichia, Anaplasma, and Coxiella burnetii. Because of the intracellular lifestyle of these bacteria, the susceptibility testing that has been carried out has been somewhat limited in terms of both the number of isolates tested and the number of different anti-infective agents evaluated. In an attempt to better understand the susceptibility to antibiotics of these bacteria, several in vitro cell culture methods of evaluation of the susceptibility to antibiotics have been developed. The major drawbacks of these methods were the absence of reproducibility and the subjectivity of enumeration of the bacteria, which made comparison of the results difficult. Thus, the complexity of the methods needed to propagate these organisms argues for an attempt to standardize the methods used for susceptibility testing. This has been recently addressed by the use of molecular methods for quantification of bacteria and in vitro antibiotic susceptibility testing for fastidious and intracellular bacteria (1) that are reviewed in this chapter. This new methodology will allow testing of more isolates. This is important, because resistance will continue to remain unconfirmed if testing is not carried out (2). Resistance to antimicrobials has been infrequent among these organisms, but recent findings regarding molecular support of resistance to antibiotics have been recently reported.
