Effect of environmental and substrate factors on survival and growth of Helicobacter pylori.

The effect of temperature (4 to 42 degrees C), NaCl concentration (0.5 to 7.5%), NaNO2 concentration (0 to 400 micrograms/ml), water activity (aw level of 0.6 to 0.995), pH (3.5 to 7.3) and urea (8 mM) on the survival and growth of Helicobacter pylori in a nutrient-rich laboratory culture medium was investigated. Under microaerobic conditions (5% O2, 10% CO2, and 85% N2), the organism grew well in brain heart infusion broth supplemented with 7% horse serum and antibiotics (BHI-HS-TVA) in a temperature range of 30 to 37 degrees C with agitation. H. pylori (initial population of ca. 5 x 10(3) CFU/ml) survived for 14 days at 4 degrees C, for 2 days at 25 degrees C, and for less than 1 day at 40 and 42 degrees C. The optimal NaCl concentration for growth of H. pylori was 0.5 to 1.0%; 2.0% NaCl inhibited growth. Up to 400 micrograms of NaNO2 per ml did not prevent growth. The minimum aw (adjusted with glycerol) and pH (acidified with HCl) for growth of H. pylori was 0.98 and 4.5, respectively. The addition of urea to broth greatly enhanced the growth of H. pylori at both pH 4.5 and 5.5. Although H. pylori did not grow at pH 3.5, the presence of urea in broth enhanced its survival. Considering the apparent fastidious conditions for growth of H. pylori in BHI-HS-TVA broth, H. pylori is unlikely to grow well, if at all, in most foods. The bacterium may, however, survive for extended periods of time in low acid-high moisture environments under refrigerated storage.