A Metabolic Dependency for Host Isoprenoids in the Obligate Intracellular Pathogen Rickettsia parkeri Underlies a Sensitivity to the Statin Class of Host-Targeted Therapeutics.

Gram-negative bacteria in the order Rickettsiales have an obligate intracellular growth requirement, and some species cause human diseases such as typhus and spotted fever. The bacteria have evolved a dependence on essential nutrients and metabolites from the host cell as a consequence of extensive genome reduction. However, it remains largely unknown which nutrients they acquire and whether their metabolic dependency can be exploited therapeutically. Here, we describe a genetic rewiring of bacterial isoprenoid biosynthetic pathways in the Rickettsiales that has resulted from reductive genome evolution. Furthermore, we investigated whether the spotted fever group Rickettsia species Rickettsia parkeri scavenges isoprenoid precursors directly from the host. Using targeted mass spectrometry, we found that infection caused decreases in host isoprenoid products and concomitant increases in bacterial isoprenoid metabolites. Additionally, we report that treatment of infected cells with statins, which inhibit host isoprenoid synthesis, prohibited bacterial growth. We show that growth inhibition correlates with changes in bacterial size and shape that mimic those caused by antibiotics that inhibit peptidoglycan biosynthesis, suggesting that statins lead to an inhibition of cell wall synthesis. Altogether, our results describe a potential Achilles' heel of obligate intracellular pathogens that can potentially be exploited with host-targeted therapeutics that interfere with metabolic pathways required for bacterial growth.IMPORTANCE Obligate intracellular pathogens, which include viruses as well as certain bacteria and eukaryotes, are a subset of infectious microbes that are metabolically dependent on and unable to grow outside an infected host cell because they have lost or lack essential biosynthetic pathways. In this study, we describe a metabolic dependency of the bacterial pathogen Rickettsia parkeri on host isoprenoid molecules that are used in the biosynthesis of downstream products, including cholesterol, steroid hormones, and heme. Bacteria make products from isoprenoids, such as an essential lipid carrier for making the bacterial cell wall. We show that bacterial metabolic dependency can represent a potential Achilles' heel and that inhibiting host isoprenoid biosynthesis with the FDA-approved statin class of drugs inhibits bacterial growth by interfering with the integrity of the cell wall. This work supports the potential to treat infections by obligate intracellular pathogens through inhibition of host biosynthetic pathways that are susceptible to parasitism.

Evaluation of the possible use of genus Mentha derived essential oils in the prevention of SENLAT syndrome caused by Rickettsia slovaca.

ETHNOPHARMACOLOGICAL RELEVANCE: Essential oils and essential oil bearing medicinal and culinary plants have a long tradition of being used to combat infection, treat various conditions, and promote and restore health. Mint oils are traditionally applied to repel insects and treat various conditions including wounds, skin infections, inflammation, eczema, urticaria, psoriasis, scabies and insect bites. They are among essential oils promoted as a natural way to prevent tick-borne diseases and recommended as ingredients in various homemade repellent mixtures and tick-bite treatments. AIM OF THE STUDY: The aim of this study was to evaluate the effect of three most common mint oils - peppermint (Mentha x piperita L.), cornmint (M. arvensis L.), and spearmint (M. spicata L.) on obligate intracellular tick-borne bacterium Rickettsia slovaca. MATERIALS AND METHODS: Influence of mint oils on R. slovaca replication in Vero cells initially infected by lower (106) or higher (108) number of rickettsial particles was tested during in vitro cultivation with daily change of medium. qPCR and RT-qPCR based growth curves and linear mixed effect models were applied to evaluate the growth inhibition. Peppermint oil was further tested in pilot in vivo study on experimentally infected ticks. RESULTS: Two of the tested essential oils, peppermint and cornmint, significantly inhibited rickettsial growth. On average, peppermint oil reduced the amount of rickettsiae present on day 4 post infection up to 0.05% of the rickettsial load present in the respective controls. Cornmint oil decreased the amount of rickettsiae to 0.09% of control. Peppermint oil also significantly reduced the number of living rickettsiae in artificially infected ticks. CONCLUSIONS: Present study showed that essential oils with antimicrobial properties may also inhibit tick-transmitted bacteria, and thus their possible use as preventative measures against tick-borne diseases is worth further research.

Nutritional studies of Rickettsia guintana: nature of the hematin requirement.

Rickettsia quintana grew in a liquid medium consisting of a brain-heart infusion base supplemented with starch and hematin. The growth requirement for hematin could not be substituted by compounds of known catalytic activity for H(2)O(2), viz., catalase, potassium pyruvate, or charcoal, or by the reducing compounds sodium sulfite and sodium thioglycollate. R. quintana was catalase-negative, but no H(2)O(2) production could be demonstrated by the catalase-aminotriazole technique. A minimum inoculum giving 10(5) cells/ml was required to initiate growth. The generation time at 33 C was 10 hr. The temperature range for growth was 28 to 37 C. Growth was enhanced when succinate or glutamate was added as energy source.