Comparison of the glutamate-, arginine- and lysine-dependent acid resistance systems in Escherichia coli O157:H7.
OBJECTIVE
The objective of this study was to investigate the effect of growing conditions on the glutamate-, arginine- and lysine-dependent acid resistance (AR) systems of Escherichia coli O157:H7.


RESULTS
Seven E. coli O157:H7 strains were grown in five different media at neutral or acidic pH under aerobic or anaerobic conditions, and the survival rate after acid shocks (pH 2.0, 1 h, 37 degrees C) in the presence of glutamate, arginine and lysine was determined. Six strains induced the glutamate-dependent AR at stationary phase, and maximal survival were observed (> or =10%) when grown in pH 5- Luria-Bertani media with glucose (LBG) and in pH 4.5-anaerobic media. The arginine- and lysine-dependent systems were also present, but were only induced if cells had grown in LBG. For strain ATCC 43895, the minimum glutamate concentration that resulted in at least 10% survival rate was 10 micromol l(-1), but it required at least 10-fold more arginine and lysine.


CONCLUSIONS
The lysine-dependent AR system could be as important as the arginine-mediated one, but the contribution of both systems to E. coli O157:H7 overall AR response might be minor compared with the glutamate-dependent system.


CONCLUSIONS
Under typical environmental conditions, the glutamate-dependent AR system might be solely responsible for protecting cells against acidic pH.
Diez-Gonzalez
F
F
Department of Food Science and Nutrition, University of Minnesota, St Paul, MN, USA. fdiez@umn.edu
Karaibrahimoglu
Y
Y
D000596:Amino Acids / Q000494:pharmacology*; D001120:Arginine / Q000494:pharmacology; D003470:Culture Media; D004305:Dose-Response Relationship, Drug; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000254:growth & development* / Q000502:physiology; D005516:Food Microbiology; D018698:Glutamic Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008239:Lysine / Q000494:pharmacology
D000596:Amino Acids; D003470:Culture Media; D018698:Glutamic Acid; D001120:Arginine; D008239:Lysine