Antibacterial and anti-biofilm activities of thiazolidione derivatives against clinical staphylococcus strains

Figures & data

Table 1 The biofilm-forming abilities of the clinical staphylococcal isolates

Strains^a	Biofilm-negative^b (number (%))	Biofilm-positive^b (number (%))
-	+	++	+++
MRSA	32 (57.6)	15 (27.3)	3 (6.0)	5 (9.1)
MSSA	22 (54.1)	13 (33.3)	3 (8.3)	2 (4.3)
MRSE	16 (37.2)	11 (25.7)	9 (20.0)	8 (17.1)
MSSE	10 (41.6)	7 (29.2)	3 (12.5)	4 (16.7)

^aBiofilm formation by the clinical isolates was assessed by semiquantitative assay with microtiter plates.

^bThe clinical strains were classified into four groups according to their abilities to form biofilms as measured by OD_570. The cutoff OD value (ODc) was 0.16. The four groups were as follows: no biofilm producer (−), OD₅₇₀≤0.16; weak biofilm producer (+), 0.16<OD₅₇₀≤0.32; moderate biofilm producer (++), 0.32<OD₅₇₀≤0.64; and strong biofilm producer (+++), OD₅₇₀>0.64.

short-legendFigure 1

Table 2 MIC values of the four derivatives against the clinical staphylococcal isolates

Strains	Derivatives^a	The range of MIC^b (μM)	MIC50^c (μM)	MIC90^c (μM)
MRSE (44)	H2-38	0.75–12.5	3.13	6.25
	H2-39	3.125–12.5	3.13	6.25
	H2-74	3.125–12.5	6.25	12.5
	H2-81	0.75–6.25	3.13	6.25
MSSE (24)	H2-38	0.75–6.25	3.13	6.25
	H2-39	1.5–12.5	3.13	6.25
	H2-74	3.13–25	6.25	12.5
	H2-81	0.75–12.5	3.13	6.25
MRSA (55)	H2-38	0.75–12.5	6.25	12.5
	H2-39	1.5–25	6.25	12.5
	H2-74	1.5–25	6.25	12.5
	H2-81	0.75–12.5	3.13	6.25
MSSA (40)	H2-38	0.75–12.5	3.13	6.25
	H2-39	1.5–12.5	3.13	6.25
	H2-74	3.125–100	6.25	12.5
	H2-81	0.75–12.5	3.13	6.25

^aStock solutions of the compounds were prepared in 0.1% DMSO.

^bMIC represents the minimal inhibitory concentration of the derivatives against the test strains as determined by broth micro-dilution testing on a microtiter plate according to the standards of the American Clinical and Laboratory Standards Institute.

^cThe MIC₅₀ is the concentration below which 50% of the clinical isolate MIC values lie, and MIC₉₀ is the concentration below which 90% of the isolate MIC values lie.

Table 3 The MIC distribution for the four derivatives and the clinical staphylococcal isolates

Derivatives	MIC^a
	≤12.5 (μM)		25–50 (μM)		>50 (μM)
SE^b	SA^b	SE	SA	SE	SA
H2-38	68	95	0	0	0	0
H2-39	68	91	0	4	0	0
H2-74	67	91	1	3	0	1
H2-81	68	95	0	0	0	0

^aMIC represents the minimal inhibitory concentration of the derivatives against the test strains as determined by broth micro-dilution testing on a microtiter plate according to the standards of the American Clinical and Laboratory Standards Institute.

^bSE represents S. epidermidis (68 clinical stains) and SA represents S. aureus (95 clinical strains).

short-legendFigure 2

Table 4 The percentages of viable cells in the biofilms of the six strains treated with H2-81 and H2-38

		Strains^a
	Treatment^a	MRSA 1000234	MRSA 916054	MSSA 1815	MRSE 1020081	MRSE 915296	MSSE 914111
Viable cells/total (%)	H2-81	1.6	7.8	8.2	11.6	7.9	8.9
	H2-38	3.5	10.4	7.5	16.2	8.6	12.3
	Vancomycin	80.1	75.6	77.8	75.4	80.8	79.6
	DMSO^b	92.4	89.1	88.5	91.8	91.4	93.6
MIC (μM)	H2-81	1.5	12.5	1.5	3.1	3.1	1.5
	H2-38	1.5	12.5	1.5	6.3	3.1	1.5

^a The six strains were selected randomly from 19 strong biofilm producers (MRSA 1000234, MRSA 916054, MSSA 1815, MRSE 1020081, MRSE 915296 and MSSE 914111).

^bStock solutions of the compounds were prepared in 0.1% DMSO. Biofilms treated with 0.1% DMSO were used as the negative control.