Antimicrobial Susceptibility Testing of Metronidazole and Clindamycin against Gardnerella vaginalis in Planktonic and Biofilm Formation

Table 1

Minimum inhibitory concentration (MIC) and minimum biofilm eradication concentrations (MBEC) for Gardnerella vaginalis at the planktonic and biofilm levels.

Isolate no.	Biofilm producer	Metronidazole				Clindamycin
		Planktonic MIC (μg/mL)	Biofilm MIC (μg/mL)	MIC ratio^a	MBEC (μg/mL)	Planktonic MIC (μg/mL)	Biofilm MIC (μg/mL)	MIC ratio^a	MBEC (μg/mL)
G1	Moderate	8	16	2	>128	0.0312	1	32	32
G2	Strong	16	>128	8	>128	≤0.0312	>64	2048	>64
G3	Moderate	2	8	4	>128	≤0.0312	0.5	16	8
G4	Moderate	2	>128	64	>128	≤0.0312	>64	2048	>64
G5	Moderate	8	>128	16	>128	≤0.0312	>64	2048	32
G6	Weak	0.25	>128	512	>128	≤0.0625	0.5	16	>64
G7	Weak	2	0.5	0.25	>128	≤0.0625	0.5	16	32
G8	Weak	8	>128	16	>128	0.5	0.5	1	32
G9	Weak	2	4	2	>128	0.125	0.5	4	32
G10	Weak	≤0.0625	≤0.125	2	>128	0.125	1	8	8
Standard strain^b	Moderate	32	128	4	>128	≤0.0625	0.5	16	8

MIC breakpoints adapted and interpreted as sensitive, resistant, or intermediate as defined by CLSI criteria for metronidazole (sensitive: ≤8 μg/mL; intermediate: = 16 μg/mL; resistant: ≥32 μg/mL) and clindamycin (sensitive: ≤2 μg/mL; intermediate: = 4 μg/mL; resistant: ≥8 μg/mL) were used for interpreting MIC results; The ^aMIC ratio was calculated using the following formula: MIC value with biofilm formation/MIC value without biofilm formation; ^bGardnerella vaginalis ATCC®14018 was used as a quality control bacterium and cultivated under anaerobic conditions.