- Vitamin K₅, 4-amino-2-methyl-1-naphthol hydrochloride, a
water soluble analog of vitamin K has been shown to possess an antimicrobial
activity toward many bacteria, molds, and yeast. Much
of the work reported in the literature is on its use as a food preservative,
and it was the purpose of this study to investigate some of the
factors which might affect the antimicrobial activity of vitamin K₅
in order to add insight into its more effective use as a food preservative.
Pure cultures of Escherichia coli, Bacillus subtilis, Proteus
vulgaris, Staphlococcus aureus, and Pseudomonas fluorescens were
utilized. The effect of the method of application of vitamin K₅ on
Escherichia coli; the effect of purity of vitamin K₅ against
Escherichia coli; the bactericidal concentrations required for Escherichia coli, Bacillus subtilis, Proteus vulgaris, Staphlococcus
aureus, and Pseudomonas fluorescens; the effect of an absence of
oxygen; the effect of contact time with Escherichia coli; the effect of
initial count/ml of Escherichia coli; and the synergistic action in
combination with propylene glycol were studied.
The results demonstrated that air oxidation of vitamin K₅ was
necessary to obtain maximum inhibitory activity against Escherichia
coli. The use of white, crystalline vitamin K₅ synthesized in the
laboratory, as compared to partially oxidized commercial preparations,
gave better results against Escherichia coli.
It was shown that some species variation, with the five microorganisms
tested, did exist with respect to the antimicrobial activity
of vitamin K₅. The bactericidal concentrations ranged from 60 ppm
for Staphlococcus aureus to 220 ppm for Escherichia coli, using an
initial count of 160,000 to 200,000 cells/ml and a contact time of 12
hours in Bacto-nutrient broth. The gram-positive bacteria tested
were more susceptible to the antimicrobial activity of vitamin K₅
than the gram-negative bacteria tested.
In the studies conducted under nitrogen atmosphere the percent
inhibition showed an inverse relation to the bactericidal concentrations
required for complete inhibition in studies conducted under air
atmosphere. This finding suggested that there might be different
factors responsible for inhibition depending on the species of bacteria being tested and also might help explain the difference in concentrations
necessary for inhibition.
Cells of Escherichia coli were not inhibited immediately on
coming into contact with vitamin K₅. Fifty percent inhibition occurred after 25 minutes. A rapid inhibition rate was maintained until
approximately 90 percent inhibition occurred, afterwhich, a rapid
decrease in the rate of inhibition was noted.
An increase in the initial number of cells of Escherichia coli
utilized required an increase in the concentration of vitamin K₅ for
complete inhibition, although the concentration of vitamin K₅ was not
the limiting factor.
A synergistic effect does exist between vitamin K₅ and
propylene glycol, and the bactericidal concentrations necessary for
the different bacteria can be reduced depending on the species of
bacteria and the concentration of propylene glycol utilized.