Infect Chemother.  2014 Sep;46(3):182-188. 10.3947/ic.2014.46.3.182.

In vitro Synergism between Chloroquine and Antibiotics against Orientia tsutsugamushi

• Son D
• Chung MH

• KMID: 2284975
• DOI: http://doi.org/10.3947/ic.2014.46.3.182

Abstract

BACKGROUND
To investigate whether chloroquine enhances the effect of antibiotics against Orientia tsutsugamushi, the causative organism of scrub typhus, we compared the effect of antibiotics in combination with chloroquine with the effect of antibiotics alone in vitro.
MATERIALS AND METHODS
The Boryong or AFSC-4 strain was inoculated into ECV304 cells, and incubated in medium containing doxycycline (4 microg/mL), rifampin (4 microg/mL), azithromycin (0.5 microg/mL), chloroquine (1 microg/mL), and each of these antibiotics in combination with chloroquine for 7 d. Immunofluorescence (IF) staining for O. tsutsugamushi was performed 4 hr and 7 d after inoculation of the bacteria, and IF-positive foci were enumerated.
RESULTS
Chloroquine inhibited the growth of O. tsutsugamushi by 15.5%. In combination with chloroquine, the antimicrobial effects increased by 4.4% for doxycycline (a 92.9% reduction of bacterial numbers for doxycycline versus a 97.3% reduction for doxycycline plus chloroquine), 4.6% for rifampin (90.0% versus 94.6%), and 8.3% for azithromycin (86.9% versus 95.2%). The antimicrobial effect of the antibiotics alone was significantly different compared to the combined effect of antibiotics and chloroquine (Wilcoxon signed-rank test, P = 0.001).
CONCLUSIONS
The combined use of chloroquine with an antibiotic for the treatment of O. tsutsugamushi infections may be useful for increasing the efficacy of the antibiotics.

Keyword

Azithromycin; Chloroquine; Combination drug therapy; Doxycycline; Drug synergism; Orientia tsutsugamushi; Rifampin; Scrub typhus

MeSH Terms

Anti-Bacterial Agents*
Azithromycin
Bacteria
Chloroquine*
Chungcheongnam-do
Doxycycline
Drug Synergism
Drug Therapy, Combination
Fluorescent Antibody Technique
Orientia tsutsugamushi*
Rifampin
Scrub Typhus
Anti-Bacterial Agents
Azithromycin
Chloroquine
Doxycycline
Rifampin

Figure

• 

  Figure 1 Inhibition of Orientia tsutsugamushi growth by antibiotics and their combinations with chloroquine. The Boryong or AFSC-4 strain of O. tsutsugamushi was inoculated into ECV304 cells and incubated in medium containing no antibiotic (N), chloroquine (C), doxycycline (D), doxycycline plus chloroquine (DC), rifampin (R), rifampin plus chloroquine (RC), azithromycin (A), or azithromycin plus chloroquine (AC) for 7 days. The number of immunofluorescence (IF)-positive foci was counted on day 8 post-inoculation. Chloroquine inhibits the growth of O. tsutsugamushi and augments the antimicrobial effect of the antibiotics against the bacterium. aP=0.043 by Wilcoxon signed-rank tests.

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