Effects of Piperitone on the Antimicrobial Activity of Nitrofurantoin and on Nitrofurantoin Metabolism by Enterobacter cloacae.

Figures & data

Figure 1 Isobologram showing the synergistic effect of combination of piperitone with nitrofurantoin on the inhibition of Enterobacter cloacae..

Figure 2 HPLC chromatograms of nitrofurantoin extracts from the samples after 18 h of incubation with noninoculated medium (a), E. cloacae. (b), or E. cloacae. containing 1 µL/mL of piperitone (c). The peak eluted at 5.8 min represents nitrofurantoin.

Figure 3 Nitrofurantoin remaining in Mueller-Hinton medium before incubation (bar 1), after 18 h of sterile incubation (bar 2) with E. cloacae. and 1 µl piperitone (bar 3), and with E. cloacae. only (bar 4). The areas of the peaks found by HPLC were measured by integration.

Table 1.. Growth of nitrofurantoin-resistant E. cloacae. in media containing a noninhibitory concentration of nitrofurantoin in the presence and absence of a subinhibitory concentration of piperitone.

	Cell count (per mL)
Drugs	Zero time	18 h incubation
Nitrofurantoin (7.5 µg/mL)	2.75 × 10^5	1.28 × 10^7
Nitrofurantoin (7.5 µg/mL) + piperitone (1 µL/mL)	2.63 × 10^5	1.21 × 10^6
Piperitone (1 µL/mL)	2.34 × 10^5	4.90 × 10^7

Table 2.. Antibacterial activity of nitrofurantoin before and after incubation with Enterobacter cloacae. in the presence and absence of piperitone against a nitrofurantoin-sensitive strain of Escherichia coli..

	Diameter of zone of inhibition (mm)
Drugs	Zero time	18 h incubation
Nitrofurantoin (7.5 µg/mL)	9.0±1.0	None
Nitrofurantoin (7.5 µg/mL) + piperitone (1 µL/mL)	9.0±0.5	8.0±0.5
Piperitone (1 µL/mL)	None	None

Table 3.. Nitroreductase produced by nitrofurantoin-resistant E. cloacae. in the presence and absence of piperitone, units per Optimal Density unit of cells (A.₆₀₀).

	Units of nitroreductase activity
Conditions	Bacterial culture	Extracellular fraction
PNBA (30 µg/mL)	2.10±0.15	0
PNBA (30 µg/mL) + piperitone (0.5 µL/mL)	1.41±0.10	0
PNBA (30 µg/mL) + piperitone (1 µL/mL)	0.93±0.09	0

PNBA, 4-nitrobenzoic acid.