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Antimicrobial Agents and Chemotherapy, Mar 1997, 578-582, Vol 41, No. 3
TJ Ives, P Manzewitsch, RL Regnery, JD Butts and M Kebede
The in vitro susceptibilities of Bartonella (Rochalimaea) henselae, B.
quintana, B. elizabethae, Rickettsia akari, R. conorii, R. prowazekii, and
R. rickettsii to different concentrations of azithromycin, clarithromycin,
dirithromycin, erythromycin, and roxithromycin in Vero cell cultures were
evaluated. Bartonella and Rickettsia spp. were allowed to initiate
infection of the antibiotic-free Vero cell monolayers, which were
maintained in 16-chamber microscope slides in the absence of antibiotics at
32 degrees C in a CO2-enriched atmosphere. The monolayers were then
incubated for 3 h to allow for initial host cell intracellular penetration
by infecting species. After inoculation, inocula were replaced and tested
with media containing 12 different concentrations of each antibiotic in
replicate (10 wells of each antibiotic dilution) for each species, and the
monolayers were reincubated. Tetracycline served as the control. Growth
status of Bartonella spp. and Rickettsia spp. was determined by evaluation
of immunofluorescent staining bacilli. Five days later, when antibiotic-
free, control-infected cell monolayers demonstrated significant
fluorescence, media were removed for all cell monolayers, the monolayers
were fixed, and all specimens were stained with standard indirect
immunofluorescent antibody reagents. Fluorescent foci were enumerated by
counting such foci on random fields visualized with an epifluorescence
microscope. The extent of antibiotic-induced focus inhibition was recorded
for each dilution of antibiotic and compared with that of an
antibiotic-negative control. Effective antibiotic dilution endpoints for
inhibition of Bartonella and Rickettsia proliferation, as judged by absence
of increase of significant fluorescence (as compared with no-growth
controls), were enumerated by determining the number of cell culture
chambers at various antibiotic dilutions that were negative or positive for
significant Bartonella- or Rickettsia-specific fluorescence. All of the
macrolide agents tested were readily active against all three Bartonella
organisms, and azithromycin, clarithromycin, and roxithromycin may have
potential in the treatment of Rickettsia infections. Animal model-based
clinical trials are warranted to define the specific treatment role of the
newer macrolide antibiotics.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
In vitro susceptibilities of Bartonella henselae, B. quintana, B. elizabethae, Rickettsia rickettsii, R. conorii, R. akari, and R. prowazekii to macrolide antibiotics as determined by immunofluorescent- antibody analysis of infected Vero cell monolayers
School of Pharmacy, University of North Carolina at Chapel Hill 27599- 7595, USA. tjives@med.unc.edu
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