Affiliation:
1. Cubist Pharmaceuticals, Inc., Cambridge, Massachusetts 02139
Abstract
ABSTRACT
We studied the in vitro emergence of resistance to daptomycin using three methods: spontaneous resistance incidence, serial passage in the presence of increasing drug concentrations, and chemical mutagenesis. No spontaneously resistant mutants were obtained for any organism tested (<10
−10
for
Staphylococcus aureus
, <10
−9
for
Staphylococcus epidermidis
, <10
−9
for
Enterococcus faecalis
, <10
−9
for
Enterococcus faecium
, <10
−8
for
Streptococcus pneumoniae
). Population analysis demonstrated that bacterial susceptibility to daptomycin is heterogeneous. Assay results were sensitive to calcium concentration and culture density, both of which can affect apparent resistance rates. Stable
S. aureus
mutants were isolated by both serial passage in liquid media and chemical mutagenesis. The daptomycin MICs for these isolates were 8- to 32-fold higher than for the parental strain. Many mutants with high MICs (>12.5 μg/ml) had significant growth defects but did not display phenotypes typical of
S. aureus
small colony variants. The voltage component (Δψ) of the bacterial membrane potential was increased in three independent resistant isolates. In vivo data showed that some daptomycin-resistant mutants had lost significant virulence. For other mutants, the degree of in vitro resistance was greater than the change in in vivo susceptibility. These results suggest that infection with some daptomycin-resistant organisms may still be easily treatable.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Pharmacology (medical),Pharmacology
Cited by
214 articles.
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