Antimicrobial Resistance in Chlamydiales, Rickettsia, Coxiella, and Other Intracellular Pathogens

The three groups of microbes considered in this article share some general lifestyle features. First, they are all multihost pathogens with the ability to infect diverse species ranging from arthropods, reptiles, and birds to mammalian species including companion animals, livestock, and humans and are thus considered as zoonoses. Second, they are all highly adapted to survival within their intracellular niche and, as such, have undergone significant genomic reduction that is largely responsible for their obligate requirement for intracellular growth (1, 2). This has been partially overcome in the case of Coxiella, whereby genomic sequencing provided insights into the nutritional requirements for propagation of this microbe and an axenic medium was subsequently produced (see section below). Both the Chlamydiales and Coxiella share the ability to produce small cell variants and larger replicative forms. These small cell variants facilitate environmental persistence that is key to long-term survival under adverse conditions. © 2018 American Society for Microbiology. All rights reserved.