Novel enterocin E20c purified from Enterococcus hirae 20c synergised with ß-lactams and ciprofloxacin against Salmonella enterica

Table 4 MIC and FICI of E20c alone and in combination with antibiotics against S. enterica

Antibiotic	MIC (µg/ml)			FIC of antibiotic	FIC of enterocin 20c	FICI antibiotic + E20c	Fold decrease in MIC of antibiotic
Antibiotic	Antibiotic	E20c	Antibiotic/E20c	FIC of antibiotic	FIC of enterocin 20c	FICI antibiotic + E20c	Fold decrease in MIC of antibiotic
Ampicillin	12.5	0.5	1.81/0.07	0.14	0.14	0.28	6.9
Penicillin	25	0.5	1.9/0.156	0.08	0.32	0.39	13.1
Ceftriaxone	43.5	0.5	6.7/0.07	0.15	0.14	0.29	6.4
Ciprofloxacin	400	0.5	31.2/0.15	0.078	0.31	0.38	12.8
Carbenicillin	21.7	0.5	6.5/0.15	0.29	0.31	0.60	3.3

FICI = FIC of antibiotic + FIC of E20c = (MIC of antibiotic in combination/MIC of antibiotic alone) + (MIC of E20c in combination/MIC of E20c alone). The interaction was interpreted as follows: synergy, FICI ≤ 0.5; indifference, 0.5 < FICI < 2; and antagonism, FICI > 2. The values are mean ± SD of experiments performed in triplicate

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