Manipulation of Host Diet To Reduce Gastrointestinal Colonization by the Opportunistic Pathogen Candida albicans

Abstract

Candida albicans, the most common human fungal pathogen, can cause systemic infections with a mortality rate of ~40%. Infections arise from colonization of the gastrointestinal (GI) tract, where C. albicans is part of the normal microflora. Reducing colonization in at-risk patients using antifungal drugs prevents C. albicans-associated mortalities. C. albicans provides a clinically relevant system for studying the relationship between diet and the microbiota as it relates to commensalism and pathogenicity. As a first step toward a dietary intervention to reduce C. albicans GI colonization, we investigated the impact of dietary lipids on murine colonization by C. albicans. Coconut oil and its constituent fatty acids have antifungal activity in vitro; we hypothesized that dietary coconut oil would reduce GI colonization by C. albicans. Colonization was lower in mice fed a coconut oil-rich diet than in mice fed diets rich in beef tallow or soybean oil. Switching beef tallow-fed mice to a coconut oil diet reduced preexisting colonization. Coconut oil reduced colonization even when the diet also contained beef tallow. Dietary coconut oil also altered the metabolic program of colonizing C. albicans cells. Long-chain fatty acids were less abundant in the cecal contents of coconut oil-fed mice than in the cecal contents of beef tallow-fed mice; the expression of genes involved in fatty acid utilization was lower in C. albicans from coconut oil-fed mice than in C. albicans from beef tallow-fed mice. Extrapolating to humans, these findings suggest that coconut oil could become the first dietary intervention to reduce C. albicans GI colonization. IMPORTANCE Candida albicans, the most common human fungal pathogen, can cause infections with a mortality rate of ~40%. C. albicans is part of the normal gut flora, but when a patient's immune system is compromised, it can leave the gut and cause infections. By reducing the amount of C. albicans in the gut of susceptible patients, infections (and the resulting fatalities) can be prevented. Currently, this is done using antimicrobial drugs; to "preserve" drugs for treating infections, we looked for a dietary change to reduce the amount of C. albicans in the gut. Using a mouse model, we showed that adding coconut oil to the diet could become the first drug-free way to reduce C. albicans in the gut. More broadly, this model lets us study the interactions between our diet and the microbes in our body and the reasons why some of those microbes, under certain conditions, cause disease. Podcast: A podcast concerning this article is available.

Keywords: Candida; Candida albicans; carbon metabolism; commensal; fatty acids; host-pathogen interactions; medium-chain fatty acids; microbiome; pathogenesis.

Figures

FIG 1

Fatty acid composition of beef tallow, soybean oil, and coconut oil and weight of mice fed diets containing those fats. (A) Fatty acid composition data from the USDA Nutritional Nutrient Database for Standard Reference (release 27, http://ndb.nal.usda.gov/). (B) Mice fed a high-fat diet containing coconut oil, beef tallow, or soybean oil (18% by weight) or a standard diet (AIN-93G) were inoculated with C. albicans by oral gavage on day 0 (n = 8 to 12 mice per diet; mice from Fig. 2). Mice were weighed periodically throughout the experiment and were sacrificed 21 days postinoculation. (C) Mice fed a high-fat diet containing either coconut oil or beef tallow (30% by weight), a high-fat diet containing both (12% coconut oil and 18% beef tallow), or a standard diet (AIN-93G) were inoculated with C. albicans by oral gavage on day 0 (n = 8 to 12 mice per diet; mice from Fig. 4). Mice were weighed periodically throughout the experiment and were sacrificed 21 days postinoculation.

FIG 2

C. albicans murine gastrointestinal colonization is lower in mice fed a diet containing coconut oil than in mice fed a diet containing beef tallow or soybean oil. Mice fed a high-fat diet containing coconut oil, beef tallow, or soybean oil (18% by weight) or a standard diet (AIN-93G) were inoculated with C. albicans, and colonization (CFU per gram of material) was determined 21 days postinoculation. (A) Colonization was significantly lower in the stomach contents of mice fed the coconut oil diet than in the stomach contents of mice fed the beef tallow diet, soybean oil diet, or AIN-93G. (B) Colonization was significantly lower in the cecal contents of mice fed the coconut oil diet than in the cecal contents of mice fed the beef tallow or soybean oil diet but not AIN-93G. (C) Colonization was significantly lower in the fecal pellets of mice fed the coconut oil diet than in the fecal pellets of mice fed the beef tallow or soybean oil diet but was not significantly different from colonization in mice fed AIN-93G. Each symbol represents one mouse (n = 8 to 12 mice per diet); bars represent geometric means. NS, P > 0.05; *, P < 0.05; **, P < 0.01; ***, P < 0.001, Tukey’s HSD test.

FIG 3

Changing to a coconut oil-containing diet reduces preexisting GI colonization by C. albicans. Mice on a beef tallow-containing diet (18% by weight) were inoculated with C. albicans, and colonization was measured using fecal pellets collected on the days indicated. Fourteen days postinoculation, mice were switched to a coconut oil-containing diet (18% by weight); data from mice maintained on the beef tallow- or coconut oil-containing diet throughout the experiment are shown for comparison. Eighteen days postinoculation (4 days after the change in diet), colonization in mice switched from the beef tallow to the coconut oil diet was lower than that in mice maintained on the beef tallow diet and was not significantly different from that in mice fed the coconut oil-containing diet throughout the experiment. Data shown as geometric means ± standard errors; n = 8 to 12 mice per diet. **, P ≤ 0.01, Tukey’s HSD test.

FIG 4

Dietary coconut oil inhibits GI colonization by C. albicans. Mice fed a high-fat diet containing both coconut oil (12% by weight) and beef tallow (18%) or isocaloric diets containing either coconut oil or beef tallow (30%) or a standard diet (AIN-93G) were inoculated with C. albicans, and CFU per gram of material was determined 21 days postinoculation. (A) Colonization was significantly lower in the stomach contents of mice fed the coconut oil diet or the diet containing both coconut oil and beef tallow than in the stomach contents of mice fed the beef tallow diet. (B) Colonization was significantly lower in the cecal contents of mice fed the coconut oil diet, the diet containing both coconut oil and beef tallow, or AIN-93G than in the cecal contents of mice fed the beef tallow diet. (C) Colonization was significantly lower in the fecal pellets of mice fed the coconut oil diet, the diet containing both coconut oil and beef tallow, or AIN-93G than in the fecal pellets of mice fed the beef tallow diet. Each symbol represents one mouse (n = 8 to 12 mice per diet); bars represent geometric means. NS, P > 0.05; *, P < 0.05; **, P < 0.01; ***, P ≤ 0.001, Tukey’s HSD test.

FIG 5

Fatty acid profile (molar percentage) of the GI contents of mice fed diets containing either coconut oil or beef tallow, a diet containing both coconut oil and beef tallow, or a standard diet (AIN-93G). To determine the effect of dietary coconut oil and beef tallow on the fatty acid composition of the GI contents, mice were fed diets containing coconut oil or beef tallow (30%), a diet containing both (12% coconut oil and 18% beef tallow), or AIN-93G. Organ contents were harvested from throughout the GI tract, and the fatty acid profiles of these samples, as well as of the original diets, were determined by gas chromatography and expressed as molar percentages. Data represent the averages for three mice per diet.

FIG 6

Fatty acid profile (micrograms per milligram, wet weight) of the GI contents of mice fed diets containing either coconut oil or beef tallow, a diet containing both coconut oil and beef tallow, or a standard diet (AIN-93G). To determine the effect of dietary coconut oil and beef tallow on the fatty acid composition of the GI contents, mice were fed diets containing coconut oil or beef tallow (30%), a diet containing both (12% coconut oil and 18% beef tallow), or AIN-93G. Organ contents were harvested from throughout the GI tract, and the fatty acid profiles of these samples, as well as of the original diets, were determined by gas chromatography and expressed as micrograms of fatty acid per milligram (wet weight). Data represent the averages for three mice per diet.

FIG 7

Long-chain fatty acids are less abundant in the cecal contents of coconut oil-fed mice than in the cecal contents of beef tallow-fed mice. Mice were fed a high-fat diet containing either coconut oil or beef tallow (30% by weight) or both (12% coconut oil and 18% beef tallow). (A) The concentration of octadecanoic acid (18:0) was significantly lower in the cecal contents of mice fed the coconut oil diet or the diet containing both coconut oil and beef tallow than in the cecal contents of mice fed the beef tallow diet. (B) The concentration of hexadecanoic acid (16:0) was significantly lower in the cecal contents of mice fed the coconut oil diet than in the cecal contents of mice fed the beef tallow diet; the concentration of hexadecanoic acid was also lower in the cecal contents of mice fed the diet containing both coconut oil and beef tallow than in the cecal contents of beef tallow-fed mice, but this difference was not statistically significant (P = 0.06). Composite results from two experiments are shown, one in which n was 3 mice per diet and one in which samples from three mice per diet were pooled. Each symbol represents one sample; bars represent averages. NS, P > 0.05; *, P < 0.05; **, P < 0.01, Tukey’s HSD test.

FIG 8

Expression of C. albicans fatty acid catabolic genes is lower in the cecal contents of coconut oil-fed mice than in the cecal contents of beef tallow-fed mice. (A) Schematic of fatty acid catabolism in C. albicans. The pathways of fatty acid β-oxidation, acetyl-CoA transport (carnitine shuttle), the glyoxylate cycle, gluconeogenesis, and glycolysis are depicted, and the names of C. albicans genes differentially regulated in response to experimental diets are shown. (B to H) The expression of C. albicans genes was measured in the cecal contents of mice fed a high-fat diet containing either coconut oil or beef tallow (30%) or both (12% coconut oil and 18% beef tallow) or a standard diet (AIN-93G). (B to G) Expression of the fatty acid β-oxidation genes POT1 (B) and POX1-3 (C), the carnitine acetyltransferase genes CTN1 (D) and CTN3 (E), and the glyoxylate cycle genes ICL1 (F) and MLS1 (G) was lower in C. albicans from mice fed the coconut oil diet or the diet containing both beef tallow and coconut oil than in C. albicans from mice fed the beef tallow diet. (H) Expression of the glycolytic gene CDC19 was higher in C. albicans from mice fed the coconut oil diet or the diet containing both beef tallow and coconut oil than in C. albicans from mice fed the beef tallow diet. Data are expressed as fold change relative to the mean expression in mice fed the coconut oil diet; all gene expression data (measured via RT-qPCR) have been normalized to reference genes. Symbols indicate means ± standard errors; n = 8 to 12 mice per diet. NS, P > 0.05; *, P < 0.05; **, P < 0.01; ***, P < 0.001, Bonferroni-corrected pairwise t test following one-way ANOVA.