High Intake of Milk Fat Inhibits Intestinal Colonization of Listeria but Not of Salmonella in Rats

Abstract

During fat digestion, fatty acids and monoglycerides are liberated in the gastrointestinal tract. Generally, these lipids are potent inhibitors of gram-positive bacteria in vitro but have less effect on gram-negative microbes. Considering this, we hypothesized that increased intake of bovine milk fat would result in enhanced gastrointestinal killing of Listeria monocytogenes (gram-positive) but have little effect on infection with Salmonella enteritidis (gram-negative) in rats. To test this, rats were fed either low milk fat diets (10% of energy obtained from milk fat, corresponding to 4. 2 g fat/100 g diet) or high milk fat diets (40% of energy obtained from milk fat, corresponding to 19.6 g fat/100 g diet). After adaptation to these diets, rats were orally infected with Listeria or Salmonella. Greater milk fat consumption in Listeria-infected rats diminished intestinal colonization of Listeria (P < 0.05) and reduced diarrhea (P < 0.05). Analysis of gastrointestinal contents showed that killing of Listeria occurred predominantly in the stomach. High milk fat intake significantly augmented this gastric listericidal capacity (P < 0.05) and raised the concentration of medium-chain and saturated long-chain free fatty acids and of monoglycerides of C12:0, C14:0, C16:0, C18:0, and C18:1 in gastric chyme (P < 0.05). Considering the in vitro listericidal capacity of these agents, it was concluded that particularly the free fatty acids C10:0, C12:0 and C14:0 and the monoglycerides of C12:0, C14:0, and C16:0 seem to play a pivotal role in this enhanced Listeria killing. In contrast, Salmonella infection was not affected by milk fat consumption. In conclusion, high milk fat intake results in higher concentrations of gastric bactericidal lipids and thereby protects against Listeria infection but not against Salmonella.

Small-Molecule Modulators of Listeria monocytogenes Biofilm Development

“…Because sphingosine and palmitoyl-D,Lcarnitine had similar structures, with a charged head group coupled to a C 16:0 acyl chain, we further examined the effects of saturated fatty acids on biofilm formation. Although some fatty acids impair the growth of L. monocytogenes (46,48), their effects on biofilm formation have not been reported. Saturated fatty acids with chain lengths ranging from C 9:0 to C 18:0 were tested for their effects on biofilm development (Table 4).…”

“…A number of recent studies have implicated microbially produced fatty acids or derivatives as diffusible signal factors that control, among other phenotypes, biofilm formation by heterologous species (43). Bovine milk, which contains a variety of fatty acids, has been shown to reduce the amount of viable L. monocytogenes cells in vitro, as well as to prevent intestinal colonization of rats in a chain length-dependent manner (46)(47)(48). Sprong et al showed that shorter-chain-length saturated fatty acids (C 4:0 , C 6:0 , and C 8:0 ) lack bactericidal activity toward L. monocytogenes even at 500 M. In addition, neither C 16:0 nor C 18:0 had bactericidal activity at 500 M, which is consistent with our results.…”

Nonhuman Primate Model for Listeria monocytogenes -Induced Stillbirths

“…This suggests that L. monocytogenes may be better able to colonize the gastrointestinal tract when delivered to animals in a higher-fat vehicle. Sprong et al (34) determined that in rats a diet high in fat inhibits colonization of L. monocytogenes in the gut; however, in their study, L. monocytogenes was administered in a saline solution. This approach is different from our study, where L. monocytogenes was administered in a high-fat vehicle to animals on a normal monkey diet.…”

Bactericidal Activities of Milk Lipids

“…Stock solutions of bacteria were routinely stored at Ϫ80°C in culture media (listed in Table 2) containing 20% (vol/vol) glycerol. Bacterial cells were cultured as described before (20) using the agar plates, broth, and culture conditions described in Table 2. Bactericidal activity of fatty acids (all obtained from Fluka, Buchs, Switzerland) was tested in citrate buffer at pH 5 (100 mmol of potassium citrate per liter) and 37°C as described before (20).…”

“…Bacterial cells were cultured as described before (20) using the agar plates, broth, and culture conditions described in Table 2. Bactericidal activity of fatty acids (all obtained from Fluka, Buchs, Switzerland) was tested in citrate buffer at pH 5 (100 mmol of potassium citrate per liter) and 37°C as described before (20). Because the strictly anaerobic bacterium C. perfringens did not survive the washing procedure in an aerobic environment, overnight cultures were directly diluted in sterile saline and immediately placed in an anaerobic cabinet (Coy Laboratory Products Inc., Ann Harbor, Mich.).…”