Previous studies have shown that various short- and medium-chain free fatty acids (FFAs) and their corresponding monoacylglycerol esters (MGs) have antibacterial activity in vitro against primarily gram-positive bacteria. More recent studies have also shown that the growth of Helicobacter spp. is inhibited by linoleic acid and arachidonic acid. The purpose of the present study was to evaluate the susceptibility of Helicobacter pylori to the in vitro bactericidal properties of medium-chain MGs and FFAs. Incubation of H. pylori with saturated MGs, ranging in carbon chain length from C10:0 to C14:0, at 1 mM caused a 4-log-unit or greater reduction in the number of viable bacteria after exposure for 1 h. Lower levels of bactericidal activity were observed with C9:0, C15:0, and C16:0 MGs. In contrast, lauric acid (C12:0) was the only medium-chain saturated FFA with bactericidal activity against H. pylori. The MGs and FFAs were bactericidal after incubation for as little as 15 min at neutral or acidic pHs. Higher levels of MGs and FFAs were required for bactericidal activity in the presence of higher amounts of protein in liquid diets. We also found that the frequency of spontaneous development of resistance by H. pylori was higher for metronidazole and tetracycline (10(-5) to 10(-6)) than for C10:0 MG, C12:0 MG, and C12:0 FFA (< 10(-8)). Collectively, our data demonstrate that H. pylori is rapidly inactivated by medium-chain MGs and lauric acid and exhibits a relatively low frequency of spontaneous development of resistance to the bactericidal activity of MGs. Further studies are needed to establish whether MGs may be useful either alone or with other known therapeutic agents in the management of H. pylori infections in humans.
Lactoferrin (Lf) is an iron-binding protein which has been shown to inhibit the growth of various bacterial pathogens and promote the growth of anaerobic bacteria of the genus Bijidobacterium in vitro. The present study was designed to investigate whether the bifidobacteria growth promotion activity of Lf is correlated with either the binding of Lf to bifidobacterial cells or the iron saturation of Lf. Bovine Lf (bLf) from mature milk increased the growth of B. infantis and B. breve in vitro in a dose-dependent fashion, while much less growth promotion activity was found for B. bijidum. In contrast, human Lf (huLf) from mature milk promoted the growth of B. bijidum and was inactive for B. infantis and B. breve, while bLf from colostrum was devoid of bifidobacteria growth promotion activity. Changes in the iron content of Lf did not alter the bifidobacteria growth promotion activity of either bLf or huLf preparations. Competitive binding studies with biotinylated milk bLf showed that binding of bLf was inhibited by unlabelled bLf and huLf but not by P-lactoglobulin, a-lactalbumin or transferrin. Binding of bLf to B. bijidum and B. breve was c. 40-fold higher than binding to Escherichia coli. Colostrum bLf was also found to bind to B. bijidurn and B. breve, despite a lack of in-vitro growth promotion activity. Collectively, these results demonstrate that the ability of Lf to promote the growth of Bzjidobacterium spp. in vitro is independent of the iron saturation level for Lf and suggest that binding of Lf to bifidobacteria cells may be involved but is not sufficient for stimulation of bifidobacterial growth.
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