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Figure 2. a) Population analysis of parent isolates and reference
strains. PC3, vancomycin- intermediate Staphylococcus aureus (VISA)
reference strain (published vancomycin MIC 8 mg/L (19);
MIC 4 mg/L by our assay); ATCC, methicillin-resistant S. aureus
(MRSA) reference strain ATCC 33591 (MIC 1 mg/L by our assay); clinical
isolates exhibiting growth on screening media (MIC in parentheses, in
mg/L, followed by MIC of subclone)—302 (1, 4), 354 (0.5, 1), 1150 (1,2),
1203 (1,2); clinical isolates with no growth on screening media (MIC in
parentheses, in mg/L)—328 (1), 736 (1), 744 (1), 1149 (1). Isolates with
growth on screening media are represented by solid lines; isolates with
no growth are represented by broken lines. Isolates 354 and 1150 were
cultured from the same patient, 14 months apart. b) Population analysis
of an MRSA bloodstream isolate exhibiting heterogeneously reduced susceptibility
to vancomycin, and its subclone, compared with reference strains. ATCC,
MRSA reference strain ATCC 33591 (MIC 1 mg/L by our assay); PC3, VISA
reference strain (published MIC 8 mg/L (19);
MIC 4 mg/L by our assay); 1337, clinical isolate (MIC 1 mg/L); 1337d,
subclone of 1337 grown on screening media (MIC 2 mg/L). While the population
curve representing 1337d closely resembles that of PC3, this subclone
did not meet MIC criteria for VISA. CFU, colony-forming units.
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