Temperature-dependent effect of sublethal levels of cinnamaldehyde on viability and morphology of  Escherichia coli.
OBJECTIVE
Effects of sublethal levels of cinnamaldehyde (CIN) on the viability and morphology of Escherichia coli O157:H7 and E. coli 8 WT were investigated at 6 and 37°C.


RESULTS
The minimum inhibitory concentration of CIN against E. coli O157:H7 and E. coli 8WT was 400 mg l(-1). At 37°C and ≤300 mg l(-1), CIN delayed the multiplication of both strains, causing a ≤5 and ≤13 h lag, respectively. Delayed multiplication at ≤300 mg l(-1) was partly due to cell elongation and injury as determined by LIVE/DEAD viability, CTC vitality and bis-(1,3-dibutylbarbituric acid) trimethine oxonol staining. The greatest extent of cell elongation (87%) and greatest mean length (6.4 μm) occurred with E. coli O157:H7 at 2-h exposure to 200 mg l(-1) CIN. After initial delays in multiplication, both E. coli O157:H7 and E. coli 8WT returned to exponential growth and normal morphology before reaching the stationary phase. In contrast at 6°C, CIN at ≥100 mg l(-1) prevented cell elongation which occurred in untreated control cells. Treatment with 200 or 300 mg l(-1) CIN at 6°C was lethal to both E. coli strains. At 300 mg l(-1) , CIN caused a ≥5 log CFU ml(-1) reduction at ≤3 days and completely inactivated both of these organisms, causing ≥7 log CFU ml(-1) reduction at 7 days.


CONCLUSIONS
Sublethal levels of CIN at 37°C delayed the multiplication of E. coli cells by causing transient cell elongation, but at 6°C ≥200 mg l(-1) CIN was lethal to E. coli.


CONCLUSIONS
Inhibition of cold-induced cell elongation and the enhanced lethal effect of CIN at 6°C against E. coli O157:H7 suggest that CIN may be useful for control of this pathogen at refrigeration temperatures.
Department of Food Science, University of Manitoba, Winnipeg, MB, Canada.
J
J
Visvalingam
R A
RA
Holley
D000171:Acrolein / Q000031:analogs & derivatives* / Q000494:pharmacology; D003080:Cold Temperature; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000166:cytology / Q000187:drug effects / Q000254:growth & development; D019453:Escherichia coli O157 / Q000166:cytology / Q000187:drug effects / Q000254:growth & development*; D005516:Food Microbiology; D006863:Hydrogen-Ion Concentration; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects*; D013696:Temperature
D000171:Acrolein; C012843:cinnamaldehyde