Infect Chemother.  2013 Dec;45(4):431-434. 10.3947/ic.2013.45.4.431.

High In Vitro Infectivity of a Doxycycline-Insensitive Strain of Orientia tsutsugamushi

• Kim MS
• Baek JH
• Lee JS
• Chung MH
• Lee SM
• Kang JS

• KMID: 2170447
• DOI: http://doi.org/10.3947/ic.2013.45.4.431

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.

Keyword

Orientia tsutsugamushi; Scrub typhus; Virulence; Drug resistance

MeSH Terms

Anti-Bacterial Agents
Cell Culture Techniques
Doxycycline
Drug Resistance
Fluorescent Antibody Technique
Orientia tsutsugamushi*
Scrub Typhus
Virulence
Anti-Bacterial Agents
Doxycycline

Figure

• 

  Figure 1 Infectivity and growth rates of Orientia tsutsugamushi strains in ECV304 cells. The number of immunofluorescence (IF)-positive foci observed in ECV304 cells was quantified at 4, 24, 48, and 72 hr after inoculation (hpi) as an indication of the number of O. tsutsugamushi bacteria present. The amount of bacteria present at 4 hpi represents the infectivity of each O. tsutsugamushi strain or isolate. The increments of IF-positive numbers from 4 to 72 hpi represent the growth rate of each strain or isolate. The AFSC-4 strain demonstrates higher infectivity and larger bacterial numbers than the other 11 strains throughout the experiment.

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