Effect of pH on an in vitro model of gastric microbiota in enteral nutrition patients

Abstract

Patients with dysphagia due to oropharyngeal disease or cerebrovascular accident require long-term nutritional support via enteral feeding, which often results in microbial overgrowth in the upper gastrointestinal (GI) tract. Gastric acid is the primary innate defense mechanism in the stomach and has been assumed to provide an effective barrier to microbial colonization at pH values of <4. To evaluate the efficacy of gastric acid as a barrier to overgrowth, the microbiota of gastric and duodenal aspirates was assessed by culturing methods. Additionally, a fermentor-based model incorporating enteral nutrition tubing of the gastric microbiota of enteral nutrition (EN) patients was constructed to assess the effect of pH on the microbiota. Results showed that gastric acidity had a relatively small effect on the numbers of microorganisms recovered from intestinal aspirates but did influence microbiota composition. Similarly, at pH 3 in the fermentor, a complex microbiota developed in the planktonic phase and in biofilms. The effect of pH on microbiota composition was similar in aspirates and in the fermentors. Candidas and lactobacilli were aciduric, while recoveries of Escherichia coli and Klebsiella pneumoniae decreased as pH was reduced, although both were still present in significant numbers at pH 3. Only Staphylococcus aureus and Bifidobacterium adolescentis persisted at higher pH values both in vitro and in vivo. Lactate and acetate were the main organic acids detected in both aspirates and fermentors. These data show that the simulator used in this investigation was capable of modeling the effects of environmental influences on the upper GI microbiota of EN patients and that gastric pH of <4 is not sufficient to prevent microbial overgrowth in these individuals.

FIG. 1.

Effect of pH on chemostat steady-state planktonic populations. (A) E. coli (•), K. pneumoniae (○), C. albicans (□), and C. famata (▪); (B) L. paracasei (▵), L. sharpeae (▴), S. parasanguis (▿), and S. intermedius (▾). Data are means of triplicate determinations ± standard deviation.

FIG. 2.

Effect of pH on chemostat steady-state biofilm populations. (A) E. coli (•), K. pneumoniae (○), C. albicans (□), and C. famata (▪); (B) L. paracasei (▵), L. sharpeae (▴), S. parasanguis (▿), and S. intermedius (▾). Data are means of triplicate determinations ± standard deviation.

FIG. 3.

BacLight Live/Dead-stained fluorescence microscopy images of PEG tube surface biofilms immersed in the chemostat at pH 6.0 (A) pH 5.0 (B), pH 4.0 (C), and pH 3.0 (D). Scale bar, 10 μm.