Open AccessAssociation between Growth Rate and Pathogenicity of Spotted Fever Group Rickettsia
Author(s) -
Apichai Bourchookarn,
Christopher D. Paddock,
Kevin R. Macaluso,
Walairat Bourchookarn
Publication year - 2022
Publication title -
journal of pure and applied microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.149
H-Index - 16
eISSN - 2581-690X
pISSN - 0973-7510
DOI - 10.22207/jpam.16.1.31
Subject(s) - biology , spotted fever , vero cell , rickettsia , virology , scrub typhus , pathogenicity , pathogen , microbiology and biotechnology , infectivity , pathogenesis , tick , orientia tsutsugamushi , polymerase chain reaction , virus , immunology , gene , genetics
Rickettsia parkeri and Rickettsia amblyommatis are spotted fever group Rickettsia (SFGR) associated with Amblyomma ticks. R. parkeri is a recognized human pathogen that causes an eschar-associated febrile illness, while R. amblyommatis has not been confirmed as a causative agent of human disease. We hypothesized that the rate of replication is one of the factors contributing to rickettsial pathogenicity. In this study, growth and infectivity of R. parkeri and R. amblyommatis in mammalian (Vero E6) and tick-derived (ISE6) cell lines were assessed and compared over a 96-hour time course of infection using quantitative real-time polymerase chain reaction and microscopy. The pathogenic R. parkeri displayed a significantly higher level of infection in both Vero E6 and ISE6 cells than R. amblyommatis at 72 hours post-inoculation (hpi). Distinct growth profiles between rickettsial species with known and uncertain pathogenicity were identified. R. parkeri burdens were significantly greater than those of R. amblyommatis from 24 to 96 hpi. The relative fold changes of load were significantly higher in the pathogenic agent than in R. amblyommatis from 48 hpi onward and reached the maximum fold increase of ~2002- and ~296-fold in Vero E6 cells and ~1363- and ~161-fold in ISE6 cells, respectively, at 96 hpi. The results from the present study demonstrate that growth rate is associated with the pathogenicity of rickettsiae. Understanding SFGR growth characteristics in mammalian and tick cells will provide insight into rickettsial biology and pathogenesis.