Table.

Susceptibilities of P. gingivalis, P. intermedia, and P. nigrescens to antimicrobial agents

Antimicrobial agent	MIC breakpoint (μg/ml)a	MIC (μg/ml)
		P. gingivalis (31)b			P. intermedia (99)			P. nigrescens (13)
		Range	50%c	90%	Range	50%	90%	Range	50%	90%
Penicillin	≤0.5	≤0.125–0.5	≤0.125	0.25	≤0.125–16	≤0.125	1	≤0.125–16	≤0.125	1
Ampicillin	≤0.5	≤0.125–2	≤0.125	0.25	≤0.125–8	0.25	0.5	0.25–8	0.25	0.25
Amoxicillin	NA	≤0.125–1	≤0.125	0.25	≤0.125–8	0.25	1	≤0.125–8	0.25	0.25
Ticarcillin	≤32	≤0.125	≤0.125	≤0.125	≤0.125–16	≤0.125	2	≤0.125–16	≤0.125	0.25
Cephaloridine	NA	≤0.125–2	≤0.125	2	0.25–32	≤0.125	32	≤0.125–32	≤0.125	0.25
Cephalothin	NA	≤0.125–2	≤0.125	2	0.25–≥128	0.25	≥128	≤0.125–≥128	0.25	0.25
Cefamandole	≤8	0.25–2	0.25	0.5	0.25–4	0.25	4	≤0.125–4	0.25	1
Cefotaxime	≤16	0.25	0.25	0.25	≤0.125–4	0.5	4	≤0.125–4	0.25	2
Cefoxitin	≤16	0.25	≤0.125	≤0.125	≤0.125–2	0.5	2	≤0.125–2	0.5	2
Cefuroxime	NA	≤0.125–0.5	≤0.125	0.25	≤0.125–64	0.25	4	≤0.125–64	0.25	4
Imipenem	≤4	≤0.125	≤0.125	≤0.125	≤0.125	≤0.125	≤0.125	≤0.125	≤0.125	≤0.125
Piperacillin	≤32	≤0.125–2	0.25	1	≤0.125–16	0.25	1	≤0.125–16	≤0.125	1
Erythromycin	NA	≤0.125–1	0.25	1	0.25–0.5	0.5	1	≤0.125–8	0.5	1
Oleandomycin	NA	≤0.125–2	0.5	1	0.5–1	0.5	1	≤0.125–16	0.5	1
Spiramycin	NA	0.125	0.125	0.125	0.125–0.25	0.125	0.125	0.125–0.25	0.125	0.125
Clindamycin	≤2	≤0.125	≤0.125	≤0.125	≤0.125	≤0.125	≤0.125	≤0.125–≥256	≤0.125	≤0.125
Tetracycline	≤4	≤0.125–0.5	0.25	1	≤0.125–1	0.25	1	≤0.125–16	≤0.125	16
Metronidazole	≤8	0.125–2	0.125	0.125	0.125–32	0.125	0.125	0.125–1	0.125	0.125
Metronidazole-spiramycin	NA	≤0.032–0.125	≤0.032	≤0.032	≤0.032–0.125	≤0.032	≤0.032	≤0.032–0.125	≤0.032	≤0.032

^aBreakpoints correspond to susceptibility values recommended by the NCCLS (9). NA, not available. 

^bNumbers in parentheses indicate the numbers of strains tested. 

^c50% and 90%, MICs required to inhibit 50 and 90% of the isolates, respectively.