TABLE 2.

Microbiological activities of laboratory-grade gentamicin compared to artificial mixtures of gentamicin congeners that maximized gentamicin C1 and C2 (artificial mix 1) or minimized gentamicin C1 and C2 (artificial mix 2) within USP allowable ranges

Clinical isolate	Geometric mean MIC value (mg/liter)a
	Laboratory-grade gentamicin mix	Artificial mix 1b	Artificial mix 2c
K. pneumoniae CDC-AR-0003	1	1	2
K. pneumoniae CDC-AR-0004	0.25	0.25	1
K. pneumoniae CDC-AR-0005	0.5	0.25	1
K. pneumoniae CDC-AR-0012	8	16	64
K. pneumoniae CDC-AR-0047	0.5	0.25	1
K. pneumoniae CDC-AR-0097	2	2	8
K. pneumoniae CDC-AR-0129	0.5	0.5	1
E. coli CDC-AR-0061	16	32	32
Enterobacter cloacae CDC-AR-0002	2	2	4
E. cloacae CDC-AR-0053	2	2	4

^aMIC values are the geometric means of multiple independent measurements rounded to the nearest CLSI standard dilution increment. Experiments were performed using a clinical panel of CRE that harbor aac(6′)-Ib.

^bGentamicin artificial mixture 1 contained the following: C1, 50%; C1a, 10%; C2, 40%; and C2a, 0%.

^cGentamicin artificial mixture 2 contained the following: C1, 25%; C1a, 20%; C2, 0%; and C2a, 55%.