TABLE 1.

Percentages of anaerobic gram-negative rods resistant to clindamycin and metronidazole before and after therapy

Group	Visit	No. of isolates tested	No. (%) of drug-resistant isolates from patients treated witha:
			Clindamycin		Metronidazole
			Clindamycin resistant	Metronidazole resistant	Clindamycin resistant	Metronidazole resistant
P. bivia	Pretreatment	60	5 (8)	0	10 (17)	0
	7-12 days	39	20 (51)	0	2 (5)	0
	35-45 days	61	23 (38)	0	7 (11)	0
	70-90 days	53	22 (42)	0	5 (9)	0
Nonpigmented Prevotella spp.	Pretreatment	108	15 (14)	0	7 (6)	1 (1)
	7-12 days	40	17 (43)	0	3 (8)	1 (3)
	35-45 days	85	24 (28)	0	7 (8)	0
	70-90 days	68	17 (25)	0	9 (13)	0
Black-pigmented Prevotella spp.	Pretreatment	56	6 (11)	0	7 (13)	0
	7-12 days	22	15 (68)	0	2 (9)	0
	35-45 days	44	16 (36)	0	3 (7)	1 (2)
	70-90 days	36	17 (47)	0	4 (11)	0
Porphyromonas spp.	Pretreatment	89	3 (3)	0	2 (2)	0
	7-12 days	14	2 (14)	0	2 (14)	0
	35-45 days	41	15 (37)	0	2 (5)	0
	70-90 days	31	13 (50)	0	3 (10)	0
Bacteroides spp.	Pretreatment	5	0	0	0	0
	7-12 days	3	0	0	0	0
	35-45 days	5	1 (20)	0	2 (40)	0
	70-90 days	5	1 (20)	0	1 (20)	0

^aP values are from chi-square tests for linear trend. P values for clindamycin results are as follows: for P. bivia, <0.001; for nonpigmented Prevotella spp., 0.08; for black-pigmented Prevotella spp., <0001; for Porphyromonas spp., <0.001; and for Bacteroides spp., 0.2. P values for metronidazole results are as follows: for P. bivia, 0.3; for nonpigmented Prevotella spp., 0.2; for black-pigmented Prevotella spp., 0.6; for Porphyromonas spp., 0.1; and for Bacteroides spp., 0.2.