Meconium enhances the growth of perinatal bacterial pathogens

Objective: To demonstrate the effects of meconium on growth of bacterial pathogens, which are common causes of intra-amniotic infection and neonatal sepsis. Methods: Meconium collected from 9 healthy neonates was suspended as a 20% solution using sterile saline. In experiment 1, separate test tubes of meconium solution and sterile saline (the control) were individually inoculated with 10⁶ colony-forming units of a single species of the following test pathogens: Escherichia coli, Enterococcus faecalis, group B Streptococcus, Staphylococcus aureus, Pseudomonas aeruginosa, and Listeria monocytogenes. After incubation at 37°C for 24 hours, 1 μL each of the bacterial-meconium and bacterial-saline solutions was inoculated onto 5% sheep blood agar. After 24 hours of incubation, the number of developing colonies was counted. In experiment 2, equal volumes of meconium and saline solutions were inoculated with 10⁵ colony-forming units of either E. coli or group B Streptococcus. At intervals of 6, 9, and 24 hours post-incubation, 1 μL each of the bacterial-meconium and bacterial-saline solutions was inoculated onto 5% sheep blood agar plates, and colonies were counted after overnight incubation. Results: In the first experiment, 24 hours of incubation resulted in bacterial amplification in the meconium solution from an initial inoculum of 10⁶ colony-forming units/mL to 10⁹ colony-forming units/mL. In contrast, the same inoculation of saline solution (control) showed no increase in colony counts over the same time interval. For E. coli and group B Streptococcus in experiment 2, growth enhancement in meconium was seen as early as 6 hours, as colony counts of a test species increased from 10⁵ colony-forming units/mL to 10⁹-10¹⁰ colony-forming units/mL. Conclusion: Enhanced growth of perinatal pathogens in meconium was constantly observed, and can occur as early as 6 hours after bacterial interaction of meconium.