. 2018 Aug 7;9:1808. doi: 10.3389/fmicb.2018.01808

Table 1.

Results of checkerboard assays of colistin in combination with resveratrol.

Strains	Source	Phenotype	ST	Reference	Mechanism of colistin resistance	Colistin MICs (mg/L) at different resveratrol concentrations (mg/L)
						Resveratrol concentration (mg/L)
						0	8	16	32	64	128	256
E. coli LC711/14	Urine	COL-R	ST59	Cannatelli et al., 2017	PmrB Leu₁₀Pro	8	4	2^*	1^*	0.25^*	0.25^*	0.125^*
E. coli LC761/12	Urine	COL-R	ST131	This study	PmrA Asp₈₂Asn^c	4	0.5^*	0.5^*	0.25^*	0.125^*	0.125^*	0.125^*
E. coli FI-4451	Urine	COL-R	ST117	Cannatelli et al., 2016	mcr-1	8	8	8	4	4	4	4
E. coli FI-4531	Urine	COL-R	ST648	Cannatelli et al., 2016	mcr-1	8	4	4	4	4	2^*	2^*
E. coli FI-4592	Urine	COL-R	ST804	Cannatelli et al., 2016	mcr-1	8	4	4	4	4	4	4
E. coli LC902/14	Urine	COL-R	ST602	Cannatelli et al., 2016	mcr-1	8	4	4	4	4	2^*	2^*
C. braakii CA-26	Food	COL-R	–	Sennati et al., 2017	mcr-1	8	4	4	4	4	2^*	2^*
S. maltophilia 157	–	COL-R	n.d.	This study	n.d.^d	32	4	2^*	1^*	0.5^*	0.125^*	0.125^*
E. cloacae CIP6085	–	COL-R	n.d.	–	n.d.^e	128	128	32^*	8^*	0.5^*	0.25^*	0.125^*
K. pneumoniae KKBO-1^a	Blood	MDR/COL-S	ST258	Cannatelli et al., 2013	–	0.5	0.5	0.5	0.5	0.5	0.5	0.5
K. pneumoniae KKBO-4	Blood	MDR/COL-R	ST258	Cannatelli et al., 2013	IS5-like at nt.75 of mgrB	64	64	64	16^*	8^*	4^*	4^*
K. pneumoniae KPB-1^a	Blood	MDR/COL-S	ST512	Cannatelli et al., 2014a	–	0.5	0.5	0.5	0.5	0.5	0.5	0.5
K. pneumoniae KPB-2	Blood	MDR/COL-R	ST512	Cannatelli et al., 2014a	PmrB Leu₈₂Arg	4	4	4	4	2	1^*	0.5^*
K. pneumoniae KK207-1^a	Blood	MDR/COL-S	ST258	This study	–	0.5	0.5	0.5	1	0.5	0.5	0.5
K. pneumoniae KK207-2	Blood	MDR/COL-R	ST258	Cannatelli et al., 2014b	IS5-like at nt.75 of mgrB	64	64	64	64	4^*	1^*	0.5^*
K. pneumoniae 6884	Blood	MDR/COL-R	ST512	Di Pilato et al., 2016	mcr-1.2	8	8	8	8	4	1^*	1^*
K. pneumoniae KPFan^b	–	COL-R	ST674	Cannatelli et al., 2015	IS102-like at nt.69 of mgrB	32	32	16	8^*	2^*	1^*	1^*
K. pneumoniae KPGP1^b	–	COL-R	ST16	Cannatelli et al., 2015	ISkpn14-like at nt.124 of mgrB	32	32	32	32	2^*	1^*	1^*
A. baumannii N50	Respiratory tract	MDR/COL-R	ST2	D'Andrea et al., 2009	ISAva1 at nt. 531 of pmrB	64	64	64	64	8^*	1^*	1^*
S. marcescens CCUG1647^T	–	COL-R	n.d.	–	Naturally resistant	>128	>128	>128	>128	16^*	1^*	1^*
P. mirabilis NO-051	Cutaneous ulcer	COL-R	n.d.	D'Andrea et al., 2006	Naturally resistant	>128	>128	>128	>128	>128	>128	8^*

These strains were the COL-S precursors of COL-R K. pneumoniae KKBO-4, K. pneumoniae KPB-2, and K. pneumoniae KK207-2 strains, respectively. Resveratrol MICs were >512 mg/L for all tested strains.

These COL-R strains were selected in vitro, using two COL-S precursors (Cannatelli et al., 2015). Multidrug-resistant phenotypes (MDR) refer to strains resistant to carbapenems (imipenem and meropenem), ciprofloxacin, and amikacin. n.d. = not determined.

Colistin resistance in E. coli LC761/12 was putatively associate to PmrA Asp₈₂Asn novel allelic variant, being absent all other known mechanisms of acquired colistin resistance in E. coli (data not shown).

The colistin resistance mechanism in this strain is unknown.

Enterobacter CIP6085 was found to be negative for mcr-1 and mcr-2 detection. The colistin resistance mechanism in this strain is unknown.

Combinations in which colistin/resveratrol combinations yielded a synergistic activity (FICI ≤ 0.5). The lower concentration of resveratrol needed for restoring susceptibility to colistin is shaded in gray.