Background: Pseudomonas aeruginosa is an opportunistic, gram-negative pathogen associated with many hospital-acquired infections and disease states. In particular, P. aeruginosa has been identified as a crucial factor in the pathogenesis of neonatal necrotizing enterocolitis (NEC). This condition presents more frequently in infants fed a formula-based diet, which may be a result of the specific monosaccharide content of this diet. We hypothesized that P. aeruginosa would express virulence genes differentially when exposed to monosaccharides present in formula versus those in human milk.
Methods: Using the results of a metabolomics study on infant diets and their resulting fecal samples, we identified several monosaccharides that distinguished milk from formula diets. Of these compounds, four were found to be metabolized by P. aeruginosa. We subsequently grew P. aeruginosa in tryptic soy broth (TSB) supplemented with these four monosaccharides and used quantitative reverse transcriptase-polymerase chain reaction to measure the expression of 59 major P. aeruginosa virulence genes. The results were standardized to an external control of P. aeruginosa grown in TSB alone.
Results: P. aeruginosa did not respond differentially to the monosaccharides after 6 h of growth. However, after 24 h, the organism grown in arabinose (present in formula), xylose (present in human milk), and galactose (present in both formula and feces from milk-fed infants) displayed a significant increase in the expression of virulence genes in all categories. In contrast, P. aeruginosa grown in mannose (present in the feces of milk-fed infants) displayed a significant decrease in virulence gene expression.
Conclusion: These results demonstrate the importance of nutrient content on the relative expression of virulence genes in pathogens that colonize commonly the gut of infants. Understanding the effect of current dietary formulas on virulence gene expression in various gut-colonizing pathogens may present a new approach to elucidating the differences between human milk and formula in the development of NEC.