D. Mlynarčík

Quantitative relationships between structure and antimicrobial activity of new “Soft” bisquaternary ammonium salts

New surface-active bisquaternary ammonium salts derived from bis-(2-dimethylaminoethyl) ester of glutaric acid are highly effective against representatives of Gram-positive, Gram-negative bacteria and yeasts. Relationships between structure, lipophilicity and antimicrobial effectiveness were demonstrated by quantitative structure-activity methodology. The nonlinear dependence of biological activity on the structure as well as lipophilicity (expressed as critical micelle concentration—CMC) was shown using Kubinyi’s bilinear model. The most effective compounds were those with the alkyl chain of 11–12 carbon atoms and with the CMC values around 0.7−1.0 mmol/L. These derivatives possessed higher antimicrobial activity particularly to Gram-negative bacteria.

INTERACTION OF AMINE OXIDES AND QUATERNARY AMMONIUM SALTS WITH MEMBRANE AND MEMBRANE-ASSOCIATED PROCESSES IN E. COLI CELLS: MODE OF ACTION

The antimicrobials (1-methyldodecyl)dimethylamine oxide and (1-methyldodecyl)trimethylammonium bromide affect the cytoplasmic membrane of E. coli. The interaction results in release of intracellular material (K+, 260nm-absorbing material), an effect on dehydrogenase enzyme activity and inhibition of respiration. The final effect of both substances is the same; they differ only in their dynamics. The effect of the membrane was correlated with parameters characterizing these surfactants i.e. critical micelle concentration (c.m.c.) minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) over the concentration range of 10(-4) to 10(-1) mmol/dm3 of active substance. The three stage mode of action model can be summarized as follows: 1-polar (coulombic) interactions, 2-polar and hydrophobic interactions, 3-hydrophobic interactions (extraction and solubilization). The polar and hydrophobic interactions (1st and 2nd stage) are discussed also in relation to model membranes.

Antimicrobial efficiency of saturated heterocyclic amine oxides

Aromatic and heterocyclic I~-oxides are known to have antimicrobial, detergent and solubilization properties and are used as detergents, foam stabilizers, preservatives and pesticides (Ochiai 1967). They are less toxic than quaternary ammonium salts and biodegradable. Little is known about the antimicrobial efficiency of sa turated heterocyclic amine oxides. We have already published a report on the subject (MlynarSik et al. 1974). The site of action on the cell was studied especially with 1-dodecylpiperidine-l-oxide (MlynarSik et al. 1975a, b) and 4-dodecylmorpholine-4-oxide (~ubik et al. 1977). In the present work the relation was studied between the antimicrobial efficiency and the structure of amine oxides derived from saturated heterocyclic amines. The synthesis and physico-chemical properties of some compounds of this group were described by Devinsky et al. (1977) and the method of assay of their antibacterial and antifungal effect was described in our preceding paper (MlynarSik and ~i~ms 1976). I t follows from the results (Table I) tha t the most efficient compound of all the amine oxides tested was 1-pentadecylpiperidine-l-oxide, the MIC of which was at the level of commonly available disinfectants (benzyldodeeyldimethylammonium bromide [Ajatin| and [2-(ethoxyearbonyl)pentadecyl] tr imethylammonium bromide [Septonex| The effect of the amine oxides depended in the first place on the length of the alkyl chain on the nitrogen atom; its extension to hexadecyl had a negative influence on efficiency against Escher i ch ia coll. The derivatives of piperidine and pyrrolidine (six-membered and five-membered heterocycles) appeared to be most suitable while an enlargement of the ring to seven or eight members (perhydroazepine and perhydroazocine) or the presence of oxygen in the heteroeyclic ring (morpholine) resulted in an activity decrease.

Stereoisomeric effect on antimicrobial activity of a series of quaternary ammonium salts

Two homologous series of diastereoisomeric racemic +/- cis and +/- trans-N,N-dimethyl-N-alkyl-2-benzoyloxycyclohexylmethylammonium bromides with the number of carbon atoms in the alkyl chain from six to twenty (m = 6,8 ... 20) were synthesised. Their structures have been elucidated by IR, UV and in some cases also with 1H and 13C NMR spectrometry. The title compounds were assayed for their antimicrobial activity on microorganisms S. aureus, E. coli and C. albicans. The highest antimicrobial activity was observed against S. aureus (log 1/MIC = 5.5 mol-1 dm3) and the lowest against E. coli (log 1/MIC = 4.5 mol-1 dm3). The +/- cis and +/- trans stereoisomers of all eight couples of diastereoisomeric compounds show differences in their physico-chemical characteristics (including partition coefficient and lipophilicity) which is also reflected in the different antimicrobial activity of these diastereoisomers.

Antimicrobial effect of bis-quaternary ammonium salts derived from 1,3-propanediamine.

Antimicrobial activity of bis-quaternary ammonium salts derived from 1,3-propanediamine and 1,3-diamino-2-propanol is described. Effect of the length of alkyl chain and the substitution in the connecting chain on this activity was studied.

Inhibitory effect of 1-methyldodecyldimethylamine oxide and N,N-bis(dodecyldimethyl)-1,2-ethanediammonium dibromide on the spores of Bacillus cereus.

Abstract1-Methyldodecyldimethylamine oxide (MDDO) and N, N’-bis(dodecyldimethyl)-l, 2-ethanediammonium dibromide (BDED) exhibit a significant affinity for the surface ofBacillus cereus spores and adsorb very rapidly to the cells; they have a pronounced inhibitory effect on spore outgrowth. In order to alter the affinity of the spore surface for these inhibitors, the spores were pretreated with sodium dodecyl sulfate (SDS), and with an electronegative (Tween 80) and electropositive (histone) compound. In SDS-pretreated spores the inhibitory effect of MDDO and BDED was abolished to a considerable extent. Whereas the development of intact spores was inhibited already after germination, in SDS-pretreated spores the postgermination development continued but was not completed. In Tween.80-pretreated spores the addition of BDED led only to a retardation of outgrowth and division; BDED added only during the division stage interrupted further development completely. Histone-pretreated spores stopped their development instantaneously after the addition of BDED at any phase of the postgermination development. The possible mechanisms of the interaction of the compounds used with spore surface or rather with the state of its structures are discussed.

The effect of quaternary ammonium compounds and amine oxides on spores of bacillus cereus

The effect of 1-dodecylpiperidine 1-oxide and N,N’-bis(dodecyldimethyl)-1,2-ethane diammonium dibromide on the spores ofBacillus cereus. particularly their binding to intact spores and spores with reduced cystine bonds, was investigated. The Langmuir type of binding is involved in both cases. Both compounds decreased the thermoresistance of spores. DPNO decreased the fraction of non-germinating spores, the effect of the drug increasing with increasing concentration. This phenomenon was associated with a faster release of dipicolinic acid to the medium. Only microgermination proceeded in the presence of BDED and dipicolinic acid was released only in substantially lower amounts. Both compounds also influenced respiration.

Primary biodegradation of amine oxide and quaternary ammonium amphiphiles

Biodegradation of two amphiphilic “soft” antimicrobially active derivatives of lauric (dodecanoic) acid, a quaternary ammonium salt and an amine oxide bearing an amide or ester group, was followed using microorganisms from activated sludge. Primary biodegradation was determined by ion-selective electrodes, total biodegradation as the chemical oxygen demand. Though organic ammonium salts quickly undergo primary biodegradation, the rest of the molecule is difficult to destroy. In contrast, amine oxides are easily biodegradable.

Activation of human leukocytes by lipid A from E. coli strains adapted to quaternary ammonium salt and amine oxide.

The immunomodulatory activities of monophosphoryl lipid A (MLA) and diphosphoryl lipid A analogues obtained from the sensitive strain ofE. coli and from the resistant strains adapted to a quaternary ammonium salt and an amine oxide were compared. All analogues considerably stimulated the activity of human leukocytes although the analogue from the sensitive strain at a higher concentration significantly suppressed phagocytosis. The MLA analogue exhibited a suppressive effect on the microbicidal activity of human leukocytes againstE. coli and the peroxidase activity. Adaptation of bacteria to amphiphilic antimicrobial compounds, which is accompanied by chemical changes in their lipid A, only slightly reduced their immunomodulatory activity when compared with the analogue from the sensitive strain. On the other hand, the diphosphoryl analogues were less active than MLA.

Antimicrobial efficacy of some N,N'-dialkyl-N,N'-dimethyl-1,6-hexanediamine dioxides.

A total of 17 N,N’-dialkyl-N,N’-diinethyl-1,6-hexanediamine dioxides were tested for activity against three microorganisms. A relationship was found between the length of the alkyl substituent and antimicrobial activity.