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Infect. Immun., 07 1997, 2792-2802, Vol 65, No. 7
C Frehel, C Offredo and C de Chastellier
Murine bone marrow-derived macrophages (Mphis) infected with virulent
strains of Mycobacterium avium (TMC 724 and a human clinical isolate) or
with an avirulent opaque variant that spontaneously dissociates from the
virulent human clinical isolate were subjected to a prolonged and
continuous treatment with clarithromycin added at the MIC. The efficiency
of this antibiotic in terms of inhibition of bacterial growth and bacterial
degradation was evaluated during a 21-day treatment period. Growth was
assessed by determination of CFU of intracellular bacteria and by a
quantitative ultrastructural analysis which allowed us also to determine
the extent of bacterial degradation. A similar treatment was applied to the
same strains growing in liquid medium. Our data show that in liquid medium,
clarithromycin caused a 90% decrease in CFU within 7 days of treatment.
When applied to Mphis infected with virulent M. avium, clarithromycin
immediately arrested bacterial growth but was unable to fully kill and
degrade intracellularly growing virulent bacteria. After 21 days of
treatment, 25% of intracellular bacteria were still morphologically intact.
These bacteria resumed growth upon removal of the antibiotic, with a normal
replication rate. These bacteria had not become more resistant to the drug,
since the MIC was unchanged as compared to the one determined for the
initial stock used to infect Mphis. Our data therefore suggest that the
intraphagosomal environment protects bacteria from degradation. We propose
that the inability of the drug to completely destroy bacteria is the result
of a limited accessibility of the drug due to prevention of fusions between
the immature phagosomes in which virulent bacteria reside and lysosomes in
which clarithromycin accumulates. In accord with our proposal, we show that
the avirulent opaque variant, which does not prevent phagosome-lysosome
fusions (unpublished data), is finally destroyed by clarithromycin even
within the phagosomal environment.
Copyright © 1997, American Society for Microbiology
The phagosomal environment protects virulent Mycobacterium avium from killing and destruction by clarithromycin
INSERM U411, Laboratoire de Microbiologie, UFR de Medecine Necker Enfants Malades, Paris, France.
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