TABLE 5.

Effect of inoculum size on activity of RWJ-54428 against MRSA and MSSA strains with various types and levels of production of β-lactamase, as determined using the agar dilution assay

S. aureus strain	β-Lactamasea		Antibiotic	MIC (μg/ml) at CFU/spot inoculum size:
	Type	Level		5 × 104	5 × 105	5 × 106	5 × 107
MSSA
ATCC 25923	Neg.b	0	RWJ-54428	0.125	0.125	0.25	0.25
			Cefamandole	0.25	0.5	0.5	0.5
			Cefaclor	1	1	2	2
			Penicillin G	≤0.03	≤0.03	≤0.03	≤0.03
ATCC 29213	A	0.006	RWJ-54428	0.25	0.25	0.25	0.25
			Cefamandole	0.5	0.5	1	1
			Cefaclor	1	2	2	8
			Penicillin G	0.125	0.25	2	32
NCTC 9789	A	0.088	RWJ-54428	0.25	0.25	0.25	0.5
			Cefamandole	0.5	1	1	4
			Cefaclor	2	4	8	>8
			Penicillin G	1	8	>64	>64
			Vancomycin	0.5	1	2	16
22260	B	0.24	RWJ-54428	0.25	0.25	0.25	0.25
			Cefamandole	0.5	1	2	4
			Cefaclor	2	2	4	8
			Penicillin G	0.5	2	32	>64
V137	C	0.034	RWJ-54428	0.25	0.25	0.5	0.5
			Cefamandole	1	1	2	8
			Cefaclor	2	4	8	>8
			Penicillin G	1	8	64	>64
FAR19	D	0.03	RWJ-54428	0.25	0.25	0.25	0.25
			Cefamandole	0.5	0.5	1	2
			Cefaclor	1	2	4	8
			Penicillin G	0.25	1	32	>64
MRSA
COL	Neg.b	NAd	RWJ-54428	1	1	1	1
			Cefamandole	>8	>8	>8	>8
			Penicillin G	16	32	32	32
			Vancomycin	2	2	2	4
76	Pos.c	NA	RWJ-54428	1	1	1	1
			Cefamandole	>8	>8	>8	>8
			Penicillin G	32	64	>64	>64
			Vancomycin	1	1	2	8

^aFrom Kernodle et al. (20, 21). The activity was reported as micromoles of nitrocefin degraded per minute per cell mass after induction.

^bNeg., β-lactamase-negative strain.

^cPos., β-lactamase-positive strain for which the enzyme type was not determined.

^dNA, not available.