Osmotic stress on dilution of acid injured Escherichia coli O157:H7.
To determine surviving numbers of Escherichia coli from cultures or food systems, dilution with 0.1% peptone is regularly used. Higher numbers of survivors could be obtained from an acid-treated culture if 0.5 mol l-1 sucrose was added to the 0.1% peptone. Sorbitol, glucose or sodium chloride, but not glycerol, could be used in place of sucrose. Using electron microscopy distinct differences could be seen between acid-treated and untreated cells. The osmolarity of the diluents ranged from 5 to 500 mosmol kg-1 H2O for the 0.5 mol l-1 sugar or glycerol solutions, to about 1000 mosmol kg-1 H2O for the salt solution. Maximum recovery diluent has an osmolarity of about 300 mosmol kg-1 H2O and resulted in recovery of similar numbers of injured cells as a 0.5 mol l-1 solution of sugar in 0.1% peptone. Taking into account the observed damage to acid-treated cells and the differences in osmolarity of the diluents, it is likely that dilution in 0.1% peptone imposed additional stress on the acid-injured cells which caused further cell damage. Dilution in a more osmotically stable solution alleviated this osmotic stress.
Jordan
K N
KN
Unilever Research Laboratory, Sharnbrook, Bedford, UK. kjordan@moorepark.teagasc.i.e
Hall
S
S
McClure
P J
PJ
D001431:Bacteriological Techniques; D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000302:isolation & purification* / Q000502:physiology* / Q000648:ultrastructure; D005516:Food Microbiology; D009997:Osmotic Pressure