Original articleBactericidal effects of fatty acids and monoglycerides on Helicobacter pylori
Introduction
Helicobacter pylori is found in chronic gastritis and duodenal ulceration and is a risk factor in gastric cancer due to inflammatory mechanisms. H. pylori has been found to colonise the stomachs of 30–50% of individuals in Western Europe and the infection rate is nearly 100% in the developing world. A reservoir of H. pylori outside the human stomach has not been found and its transmission is not yet understood, although spread by contaminated water or food might occur in developing countries [1]. Development of resistant strains of H. pylori may cause relapse after termination of therapy [2] and this problem along with the cost of treatment mean that there is a need for new methods to prevent or to treat gastrointestinal infections caused by H. pylori.
In recent years, we have studied the microbicidal effects of medium- and long-chain fatty acids and their corresponding 1-monoglycerides. They have been found to have a broad spectrum of microbicidal activity against enveloped viruses and various bacteria in vitro [3], [4], [5], [6], [7], including pathogens such as herpes simplex virus (HSV) [5], [8], Neisseria gonorrhoeae [9], Chlamydia trachomatis [10], group B streptococci (GBS), group A streptococci (GAS), Staphylococcus aureus [11], Candida albicans [12] and H. pylori [13]. These lipids are commonly found in natural products and are, therefore, likely to be non-toxic to the mucosa, at least at low concentrations. Fatty acids are considered to have an antimicrobial function in human milk, skin and mucosal membranes and it has been suggested that they might be useful as microbicides for protection against human pathogens that colonise skin and mucosa [7], [13], [14]. The aim of this study was to define the range of activity of medium- and long-chain fatty acids and their 1-monoglycerides against H. pylori after short incubation times. The Escherichia coli and Salmonella spp. were included in the study because they are common foodborne pathogens [15], [16] and have become a serious health threat due to increased drug resistance [17], [18]. Microbicidal lipids could be used to treat infections caused by these gastroenteric bacteria, either alone or together with other antimicrobial agents.
It was also of interest to compare the susceptibilities of these three Gram-negative bacteria to lipids, as they have structural differences in their outer membrane.
Section snippets
Lipids
Fatty acids and 1-monoglycerides were purchased from Sigma Chemical Co., St. Louis, MO (purest grade). Stock solutions were made in ethanol, 0.5 M for monomyristin and 1 M for all the other fatty acids and monoglycerides.
Bacterial strains and culture conditions
One H. pylori strain was obtained from the American Type Culture Collection (ATCC 43504). Two strains were recent clinical isolates. For each experiment, cultures were prepared from frozen stocks and grown on blood agar plates. The plates were incubated in a gas jar with an
Results
An inactivation time of 10 min or less was selected as the criterion for fast and effective bactericidal activity of a lipid. A comparison of the activities of lipids against H. pylori is presented in Table 1 which shows the mean titres of colony-forming bacteria (log10 cfu/ml) of all three strains of H. pylori after incubation with fatty acids and monoglycerides for 10 min at 37 °C. Each strain was tested at least twice. At 10, 5, and 2.5 mM concentrations capric acid (10:0 [no. carbon
Discussion
The bactericidal activity of medium- and long-chain fatty acids and their corresponding 1-monoglycerides has been recognised for decades [3], [4]. In the present study we have shown a difference in killing activity of these lipids for three Gram-negative pathogens after short incubation times. All the lipids tested except oleic acid, monocaprylin, and monoolein had activity against H. pylori at 10 mM concentration and 10 min incubation time. When tested at lower concentrations and shorter
Acknowledgements
This work was supported by grants from the Research Fund of the University of Iceland and the Icelandic Research Council. We thank Erla Sigvaldadóttir and Sigfús M. Karlsson for much help in this work.
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