Gastric microbiota in elderly patients fed via nasogastric tubes for prolonged periods

Aspiration of oropharyngeal contents is a constant threat for elderly patients fed via a nasogastric tube (NGT). Colonization of the oropharynx of these patients by pathological flora and the development of biofilms on the feeding tube has been documented recently. In addition, the presence of the NGT may interfere with the gastro-oesophageal sphincter, leading to gastro-oesophageal reflux. Thus, the passage of pathogenic bacteria in both directions is facilitated. The purpose of this study was to explore the microbiota of the gastric juice and the oropharynx in NGT-fed elderly patients. Samples of gastric juice were drawn after an overnight fast, and microbial cultures and direct pH measurement were performed. Concomitant cultures were obtained from the oropharynx. Overall, 107 gastric and oropharyngeal cultures were obtained from 52 subjects. Pathogenic flora (Gram-negative bacteria or Staphylococcus aureus) were isolated from 74% of stomach samples and from 69% of oropharynx samples. Proteus spp. (26%) and Escherichia coli (22%) were the most common isolates in the gastric juice, and Proteus spp. (24%) and Pseudomonas spp. (21%) were the most common isolates in the oropharynx. Similarity in the composition of the oropharynx and gastric flora was observed in most cases. The gastric pH was relatively high (4.57 ± 0.65 at 3 h after feeding and 4.2 ± 0.9 at 12 h after feeding) and was highly correlated with the isolation of pathogenic bacteria (r = 0.58, P < 0.01). These results support the view that in addition to the oropharynx, the stomach of NGT-fed elderly patients constitutes a reservoir of pathogens that could be associated with the risk of aspiration pneumonia. The cause of the high gastric pH and its relation to pathogenic bacteria warrants further study.