Relationship of Chemical Structure and Antimicrobial Activity of Alkyl Amides and Amines

Abstract

Contrary to the limited effects of alkyl amides and their corresponding N-derivatives, alkyl amines affected both gram-positive and gram-negative organisms. As with other alkyl derivatives the most sensitive gram-negative bacteria were usually more resistant than the most resistant gram-positive bacteria.Compounds with a chain-length of 11 to 15 are most active. Although some of the general properties relating the activity of fatty acids to their antimicrobial action are similar to those of amine compounds, the amines are unique in that monounsaturation does not increase compound activity.The possible modes of action of these compounds are discussed.Fatty acids are known to possess antimicrobial activity (4,5,19,28). In an attempt to study structure-activity relationships for fatty acids, a number of fatty acid derivatives were screened (18). From this study and others (17, 30), the wide-spectrum antimicrobial action for nitrogen compounds became of special interest. Therefore, a more extensive study of amine and amide compounds was undertaken.The present report concerns itself with two variables: (i) change of antimicrobial activity of amines and amides with changes in chain length and unsaturation, and (ii) the effect of these same compounds on different species of a given genus and on different strains of the same species. MATERIALS AND METHODSCompounds. Amines and amides of high purity (95 to 99.5%) were obtained, except where noted, from Lachat Chemicals, Inc., Chicago Heights, Ill. Lauric acid, lauryl N,N-dimethyl amide, pentylamine, and n-nonylamine were obtained from Sigma Chemical Co., St. Louis, Mo. Eastman Chemicals of Rochester, N.Y., supplied the docecylamine-HCl.A 0.2-g amount of amine or amide compound was dissolved in 0.5 ml of absolute methanol and quantitatively transferred to 200 ml of Trypticase soy broth (TSB; BBL). If the resulting suspension was granular or turbid, the suspension was carefully heated (approximately 70 C) to increase drug solubilization. Standard solutions (or suspensions) containing 1,000 jug/ml were serially diluted with additional broth to achieve desired concentrations. The serial dilutions were then dispensed into screw-cap tubes (16 by 125 mm), and the tubes were autoclaved at 15 p3i for 15 min. After sterilization, all tubes were cooled, incubated overnight at 35 C, and examined for demonstration of sterility. Control experiments indicated no change of compound activity after sterilization and comparison with an unheated control.Organisms. The organisms used in our survey were clinical isolates which have been maintained in our laboratory (18). The organisms used in the intraspecies survey were also clinical isolates (Providence Hospital, Southfield, Mich., 1970-1972; these had been stored in skim milk broth at -80 C.Inoculum. A test inoculum consisted of 0.05 ml of an 18-to 24-hr TSB culture (approximately 101 organism/ml). The inoculum was aseptically delivered into all dilutions of the compound, well mixed, and incubated at 36 C in a 5% CO2 atmosphere. A tube of i...

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