Growth of microorganisms in total nutrient admixtures

It has been reported that intravenous fat emulsions, because of their isotonicity and neutral pH, support microbial growth, but traditional parenteral nutrition solutions, being hypertonic and more acidic, are not as supportive. To date, few studies have documented microbial growth in total nutrient admixtures (TNA) containing dextrose, amino acids, fat, electrolytes, vitamins, and trace elements. This study was undertaken to analyze the growth of Staphylococcus aureus, Candida albicans and four gram-negative enteric bacilli in three different nutrient admixtures, with and without the inclusion of 5% fat emulsion. The composition of the admixtures was either 5, 10, or 25% dextrose; either 0 or 5% fat; and 3% amino acids, electrolytes, vitamins, and trace elements. All admixtures were innoculated with 100 colony-forming units per milliliter, incubated at room (25 degrees C) or refrigerated (4 degrees C) temperature, with samples withdrawn at 0, 3, 6, 12, 24, and 48 hours and plated in triplicate. Only C. albicans demonstrated any significant growth regardless of fat content. The pH of the admixtures was similar (acidic), and all solutions were hypertonic and found to inhibit bacterial growth. Conclusions suggest that TNA, when formulated with normal concentrations of additives, is no more likely to support growth of contaminant organisms than the traditional solutions. This contradicts the notion that the addition of fat to total parenteral nutrition will enhance the ability of these admixtures to support microbial growth.