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High In Vitro Infectivity of a Doxycycline-Insensitive Strain of Orientia tsutsugamushi
Min Su Kim1, Ji Hyeon Baek1, Jin-Soo Lee1
1Department of Internal Medicine, Inha University School of Medicine, Incheon, Korea.
Abstract:
We compared the infectivity and growth rates of 12 strains of Orientia tsutsugamushi in a cell culture system. ECV304 cells were infected with O. tsutsugamushi strains for 4 hr, and the culture was maintained for 72 hr. Immunofluorescence (IF) staining was performed at 4, 24, 48, and 72 hr after inoculation (hpi), and IF-positive foci were enumerated. The AFSC-4 strain, which is known to be insensitive to doxycycline, showed higher numbers of IF-positive foci than the other 11 strains at 4, 24, 48, and 72 hpi, which may explain its apparent insensitivity to antibiotics.
Insights
The AFSC-4 strain of Orientia tsutsugamushi showed higher infectivity in cell cultures compared to 11 other strains. This increased growth may explain its observed resistance to doxycycline antibiotics.
Area of Science:
- Microbiology
- Cell Biology
- Infectious Diseases
Background:
- Orientia tsutsugamushi is a bacterium causing scrub typhus.
- Understanding strain-specific infectivity is crucial for treatment strategies.
- Doxycycline is a primary antibiotic for scrub typhus, but resistance is a concern.
Purpose of the Study:
- To compare the infectivity and growth rates of 12 Orientia tsutsugamushi strains.
- To investigate the in vitro behavior of the doxycycline-insensitive AFSC-4 strain.
Main Methods:
- Utilized ECV304 cell cultures for O. tsutsugamushi infection.
- Infected cells with 12 different strains for 4 hours.
- Maintained cultures for 72 hours post-inoculation.
- Employed immunofluorescence staining to enumerate IF-positive foci at 4, 24, 48, and 72 hours post-inoculation.
Main Results:
- The AFSC-4 strain exhibited significantly higher numbers of IF-positive foci compared to the other 11 strains.
- This elevated infectivity was observed consistently at all time points (4, 24, 48, and 72 hpi).
Conclusions:
- The AFSC-4 strain demonstrates superior infectivity and growth in cell culture.
- Higher in vitro growth may underlie the observed antibiotic insensitivity of the AFSC-4 strain to doxycycline.
