Bacterial killing in gastric juice – effect of pH and pepsin on Escherichia coli and Helicobacter pylori

Abstract

The susceptibility of Escherichia coli and Helicobacter pylori to pH and the effect of pepsinmediated proteolysis were investigated. This was to establish the relative importance of their bacterial killing properties in gastric juice. Solutions in the pH range 1?5-7?4 with or without pig pepsin A were used, together with seven gastric juice samples obtained from patients undergoing routine gastric collection. Escherichia coli C690 (a capsulate strain), E. coli K-12 (a rough mutant) and Helicobacter pylori E5 were selected as the test organisms. Suspensions of bacteria (1610 6 E. coli ml "1 and 1610 8 H. pylori ml) were pre-incubated with test solutions at 37 6C for up to 2 h, and then cultured to establish the effect on subsequent growth. Survival of bacteria was diminished at pHs of less than 3?5, whereas killing required a pH of less than 2?5. Preincubation with pig pepsin at 0?5, 1?0 and 2?0 mg ml "1 at pH 3?5 reduced viable counts by 100 % for E. coli 690 and E. coli K-12 after 100 min incubation. With H. pylori, the viable counts decreased to 50 % of the control after 20 min incubation in 1 mg pepsin ml "1 at pH 2?5, 3?0 and 3?5. The gastric juices showed bactericidal activity at pH 3?5, and the rate of killing was juice dependent, with complete death of E. coli 690 occurring between 5 and 40 min post-incubation. Thus, killing of E. coli and H. pylori occurs optimally at pHs of less than 2?5. At pH 3?5, little effect is observed, whereas addition of pepsin alone or in gastric juice causes a marked increase in bacterial susceptibility, suggesting an important role for proteolysis in the killing of bacteria.

Microencapsulation of Bacteriophage Felix O1 into Chitosan-Alginate Microspheres for Oral Delivery

“…For example, during a meal, gastric pH increases to an average value of 5.0 in humans (13). In addition, the ingested food constituents may provide protection for phage against extreme pH values, which has been demonstrated in a study involving bacteria (49). O'Flynn et al (34) have previously reported that phage Felix O1 can survive exposure to gastric contents directly collected from porcine stomachs at pH 2.5 for up to 2 h; this disagreement is presumably due to the difference in assay medium used.…”

pH-dependent antibacterial effects on oral microorganisms through pure PLGA implants and composites with nanosized bioactive glass

“…pylori [26]. PLGA brought the pH in the same range during incubation, which explains the CFU decline.…”

“…However, even if counterproductive in the orthopaedic field, one might think of the pH drop induced by PLGA as an antimicrobial tool useful in dentistry, especially, as this biomaterial design would function according to the same principle as the barrier put up by the stomach, which is known to be an effective obstacle for harmful bacteria [26].…”

Acid Resistance inMycobacterium tuberculosis

“…Thus, nitrite diffusing into an acidified compartment generates another round of bactericidal RNI (53). The phagosomal milieu in the activated macrophage thus resembles to some degree the intragastric environment, whose microbicidal efficiency depends on the combined action of acid and RNI (10,60,106). In addition, like many other elements of the innate immune response, phagosomal acid serves to link the innate and adaptive immune systems.…”