Nitrate- and nitrite-reducing bacteria in the achlorhydric stomach

Abstract

Summary. The microbial composition of samples of gastric juice from eight achlorhydric patients was determined by aerobic and rigorously anaerobic culture techniques. Bacteria from 16 genera were commonly isolated, but representatives of only three genera, (streptococci, neisseriae and haemophili) were isolated from every patient. Nitrate and nitrite were both reduced by veillonellae, haemophili, staphylococci, corynebacteria, lactobacilli, flavobacteria and fusobacteria, but the potential rate of nitrate reduction by suspensions of veillonellae, Haemophilus parainjluenzae and members of the Enterobacteriaceae were up to ten times more rapid than the rate of nitrite reduction. Conversely, although all Neisseria spp. reduced nitrite only some strains reduced nitrate. Streptococci did not reduce nitrate. Streptococcus sanguis reduced nitrite when grown with haematin ; other streptococci did not reduce nitrite. Bacterial nitrate and nitrite reduction were active over the pH range 6-8, similar to thepH range of the achlorhydric stomach.From a knowledge of the composition of the bacterial flora and their potential rates of nitrate and nitrite reduction under prevailing conditions, predictions were made about the tendency of nitrite to accumulate during nitrate reduction. Studies of the transient accumulation of nitrite by mixed cultures of H . parainjluenzae and N . subjlava were consistent with these predictions. Haemophili and veillonellae could be responsible for the accumulation of nitrite in the gastric juice of some patients, whereas streptococci and neisseriae would tend to remove nitrite from the stomach as rapidly as it formed.

Nitrite Accumulatin during Anaerobic Nitrate Reduction by Binary Suspensions of Bacteria Isolated from the Achlorhydric Stomach

“…Values comparable to those reported by Forsythe et al (1987) were obtained. No nitrate reductase activity was detected with suspensions of N. subflava or S.…”

“…The rates of nitrite accumulation and removal were 640 and 580 U ml-l at a density of 4 x lo9 bacteria ml-l, 370 and 330 U ml-l with 2 x lo9 bacteria ml-l, 200 and 140 U ml-l with 1 x lo9 bacteria ml-l, and 120 and 100 U ml-l with 5 x lo8 bacteria ml-l. dry wt)-l for veillonellae. These values are again similar to those determined with pure culture suspensions (Forsythe et al, 1987). The slower rate of nitrite reduction by streptococci than by neisseriae was reflected in the times taken for nitrite to disappear from binary suspensions (Fig.…”

“…It is perhaps significant that the average bacterial density in gastric juice from hypogammaglobulinaemic patients is lo6 ml-l compared with lo7 ml-l in pernicious anaemic patients (Dolby et al, 1984;Borriello et al, 1986). Although nitrite is found in gastric juice from both types of patient, the highest concentrations detected in hypogammaglobulinaemic patients, 1 mM, is tenfold greater than the 0.1 m~ maximum nitrite concentration detected in pernicious anaemic patients (Dolby et al, 1984;Forsythe et al, 1987). This correlates with the observation that hypogammaglobulinaemic patients are ten times more prone to gastric cancer than those with pernicious anaemia and 50 times more prone than the general population (Kinlen et al, 1985).…”

“…Nitrite has been shown to accumulate in the gastric juice of achlorhydric patients, so this might be a contributing factor to their raised incidence of gastric cancer compared with the general population (Dolby et al 1984;Kinlen et al 1985). Forsythe et al (1987) identified the predominant nitrate-reducing and nitrite-reducing bacteria from the achlorhydric stomach and determined the nitrate reductase and nitrite reductase activities of washed cell suspensions of these organisms. Haemophilus parainzuenzae and Veiltonella parvula were suggested to be the predominant organisms responsible for nitrite accumulation because their nitrate reductase activities' exceeded their nitrite reductase activities.…”

A reassessment of the genetic determinants, the effect of growth conditions and the availability of an electron donor on the nitrosating activity of Escherichia coli K-12

“…Highest activities were reported for denitrifying bacteria, but these organisms are rarely isolated from the gastro-intestinal tract, even when the p H of gastric juice is abnormally high due to achlorhydria (Forsythe et al, 1988). Consequently, despite their 10-fold lower catalytic activity, the far larger population of enteric bacteria can be predicted to contribute the majority of nitrosation activity in the human body.…”