TABLE 1.

Strains used

Strain	Strain backgrounda	Vanco- mycin MIC (μg ml−1)	Acquisition of vancomycin resistance
RN450	Mcs, 8325-4	1	Failed to acquire
COL	Mcr (ho)	2	Slow
COLV5	GISA	6	Slow; 5 cycles in 7 wk
COLV10	GISA	8	Slow; 7 cycles in 11 wk
13136p−m+	Mcr (he)	1.5	Rapid
13136p−m+V5	GISA	8	Rapid; 2 cycles in 1 wk
13136p−m+V20	GISA	16	Rapid; 5 cycles in 5 wk
BB270V15	Mcr (he), 8325 line	12	Rapid; 5 cycles in 5 wk
BB568V15	Mcr (ho), COL	12	Rapid; 5 cycles in 5 wk
BB399V12	Mcr (ho), DU4916 line	12	Slow; 7 cycles in 8 wk
HIP5836	GISAb	6
HIP5827	GISAb	8

^aAbbreviations: Mc^s, methicillin susceptible; Mc^r, methicillin resistant; he, heterogeneous resistance expression; ho, homogeneous resistance expression.

^bClinical isolate.