Adaptive responses of Salmonella enterica serovar Typhimurium DT104 and other S. Typhimurium strains and Escherichia coli O157 to low pH environments.
OBJECTIVE
Cattle are a known main reservoir for acid-resistant Escherichia coli O157 and Salmonella enterica serovar Typhimurium DT104. We studied the response of S. Typhimurium DT104 to extreme low pH environments and compared their response to that of acid-resistant E. coli O157 and other S. Typhimurium phage types.


RESULTS
Bacteria were grown in nutrient-rich medium and subsequently acid challenged at pH 2.5. We found that stationary phase cultures of various S. Typhimurium strains were able to survive a challenge for 2 h at pH 2.5. As in E. coli, the ability of S. Typhimurium to survive at pH 2.5 was shown to be dependent on the presence of amino acids, specifically arginine. The amount of proton pumping H+/ATPase, both in E. coli O157 and S. Typhimurium strains, was lower when grown at pH values <6 than after growth at pH 7.5. Cyclo fatty acid content of membranes of bacteria grown at pH values <6 was higher than that of membranes of bacteria grown at pH 7.5.


CONCLUSIONS
Various S. Typhimurium strains, both DT104 and non-DT104, are able to survive for a prolonged period of time at pH 2.5. Their response to such low pH environment is seemingly similar to that of E. coli O157.


CONCLUSIONS
Food-borne pathogens like S. Typhimurium DT104 and E. coli O157 form a serious threat to public health since such strains are able to survive under extreme low pH conditions as present in the human stomach. The emergence these acid-resistant strains suggests the presence of a selection barrier. The intestinal tract of ruminants fed a carbohydrate-rich diet might be such a barrier.
de Jonge
R
R
National Institute for Public Health and the Environment, Microbiological Laboratory for Health Protection, Bilthoven, The Netherlands. rob.de.jonge@rivm.nl
Ritmeester
W S
WS
van Leusden
F M
FM
D000222:Adaptation, Physiological; D000596:Amino Acids / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D003470:Culture Media; D019453:Escherichia coli O157 / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism; D005516:Food Microbiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006180:Proton-Translocating ATPases / Q000502:physiology; D012486:Salmonella typhimurium / Q000145:classification / Q000187:drug effects / Q000254:growth & development*
D000596:Amino Acids; D003470:Culture Media; D005227:Fatty Acids; D006180:Proton-Translocating ATPases