- To determine whether some bacteria are more susceptible
than others to quaternary ammonium compounds, the following bacteria
were grown on agar slants containing various concentrations of
alkyl dimethyl ethyl benzyl ammonium chloride (ADEBAC), and alkyl
dimethyl benzyl ammonium chloride (ADBAC): Aerobacter aerogenes
12658, Alcaligenes metalcaligenes, Brevibacterium linens, Chromobacterium
lividum, Escherichia coli 198, Micrococcus caseolyticus,
Microbacterium flavum, Microbacterium lacticum, Proteus vulgaris,
Pseudomonas aeruginosa, Pseudomonas fluorescens MI, Pseudomonas
fragi, Pseudomonas saliciperda, Pseudomonas syringae, Staphylococcus
aureus 209, and Streptococcus lactis E.
Gram-negative test organisms developed higher resistance
to both the ADEBAC and the ADBAC compounds. The gram-positive
bacteria were found to be more susceptible to the action of these
The higher lipid content of the gram-negative bacteria appears
to play a role in protecting these organisms against the injurious
effects of the quaternary ammonium compounds.
Quaternary ammonium resistant strains of the test organisms
were found to contain more fat bodies per cell than the sensitive
strains when stained with Sudan black B.
The ADEBAC sensitive and the ADEBAC resistant strains of
the following gram-negative test organisms were used for comparative
tests: A. aerogenes 12658, A. metalcaligenes, E. coli 198,
P. vulgaris, P. aeruginosa, P. fluorescens MI, P. fragi, P. saliciperda,
P. syringae, and S. marcescens.
It was found that the growth temperature had an effect on pigment
production in the case of the ADEBAC sensitive strains of
S. marcescens. The test organism failed to produce its characteristic
pink pigment when incubated at 37°C., a temperature above its
optimum. It is postulated that the higher growth temperature has
an effect on the cells' enzymatic composition.
No differences were observed among the ADEBAC sensitive
and the ADEBAC resistant strains of the test organisms with regard
to motility and growth patterns on TGY agar slants and in nutrient
broth. The ADEBAC apparently had an inhibitory effect on gelatinase,
nitratase, tryptophanase and various carbohydrase enzymes of the
ADEBAC resistant strains.
From the results obtained in this study, it may be concluded
that gram-negative bacteria are more resistant, and the gram-positive bacteria more susceptible to quaternary ammonium compounds;
and that the quaternary ammonium compounds have an
inhibitory effect on certain bacterial enzymes. Furthermore,
quaternary ammonium germicides may alter lipid metabolism of
cells as they become resistant and this change may eventually be
seen as involved in the mechanism of resistance.