Fig 5. Glucose in the pre-growth media is important for extreme acid survival of S. Typhi strains.

A. Bacteria were grown in commercial TSB supplemented with 0.25% glucose or TSB without added glucose for 18 hours and the pH of the cultures was determined. In the presence of glucose, the pH of Ty21a pGad and Ty21a pNW129 cultures dropped below 6.5 after 18 hours, whereas the pH of the Ty2 culture remained close to pH 7.2. The pH of the Sf culture dropped even further, to below pH 6. However, in the absence of glucose added to TSB, the pH drop was not observed with Ty21a strains, suggesting that glucose is responsible for the pH drop. The pH drop of Sf cultures was not dependent on glucose in the media. Data denoted by ** are significantly different (p < 0.05), but data marked * are not significant. B. Acid survival of bacteria was compared in the presence or absence of glucose in commercial TSB (pH 7.2). Acid survival ability of Ty21a pGad was greatly diminished (~ 3 logs after 3 hours) when the bacteria where grown in TSB without glucose. C. Acid survival of tested bacteria were compared in the presence and absence of glucose in TSB-MES pH 5.5. Acid survival ability of Ty21a pGad and Ty2 were significantly reduced (4 to 5 logs after 3 hours) when glucose was absent from the media. Even Ty21a acid survivability was reduced (~ 3 logs after 1 hour). However, Sf acid-survival was not affected by presence or absence of glucose in the media.