Antibacterial and Antibiotic Modifying Potential of Crude Extracts, Fractions, and Compounds from Acacia polyacantha Willd. against MDR Gram-Negative Bacteria

Table 3

MICs (in μg/mL) of crude leaf extract (APL), active fractions (APLa and APLd), 3-O-[β-galactopyranosyl-(1→4)-β-galactopyranosyl]-oleanolic acid (8) and chloramphenicol in the presence of PAßN and fold increase of activity (in parenthesis) against a panel of selected Gram-negative bacteria.

Bacterial strains	Tested samples, MIC in μg/mL in presence of PAßN and fold increase of activity (in parenthesis)
	Leaf extract	Fractions from APL		Isolated compound	Reference antibiotic
	APL	APLb	APLd	8	Chloramphenicol
Escherichia coli
ATCC8739	256 (4)	4 (4)	2 (8)	≤2 (≥ 16)	≤ 2 (≥ 1)
AG102	64 (8)	32 (2)	8 (16)	≤ 2 (≥ 16)	4 (8)
Enterobacter aerogenes
ATCC13048	64 (4)	4 (2)	≤4 (≥ 64)	≤ 2 (≥ 16)	2 (8)
EA27	16 (64)	64 (2)	4 (128)	64 (4)	4 (8)
Klebsiella pneumoniae
ATCC11229	128 (8)	≤ 4 (≥ 4)	≤ 4 (≥ 16)	≤ 2 (≥ 16)	4 (8)
KP55	128 (8)	32 (2)	4 (4)	≤ 2 (≥ 16)	16 (4)
Pseudomonas aeruginosa
PA01	128 (0.5)	32 (2)	32(4)	≤2 (≥ 128)	8 (8)
PA124	128 (2)	32 (2)	128 (2)	16 (2)	64 (4)
Providencia stuartii
ATCC29916	≤ 4 (≥ 2)	32 (16)	32(4)	16 (4)	16 (4)

(-): MIC > 1024 μg/mL for crude extract APL, >512 for fractions APLb and APLd, 256 μg/mL for 3-O-[β-galactopyranosyl-(1→4)-β-galactopyranosyl]-oleanolic acid (8); (): values in parenthesis are fold increase of activity in the presence of PAßN at 30 μg/mL; MIC values in bold: significant antibacterial effects for MIC [18] and significant increase of activity in the presence of PAßN [19, 20]; fold increase of activity determined MIC of sample tested alone (Tables 1 and 2) versus MIC of the sample in the presence of PAßN. The MIC of PAßN was >256 mg/L for E. coli, E. aerogenes, K. pneumoniae, P. aerogenes, and P. stuartii strains.