Influence of acid tolerance response on survival, growth, and thermal cross-protection of Escherichia coli O157:H7 in acidified media and fruit juices

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Influence of acid tolerance response on survival,
growth, and thermal cross-protection of
Escherichia coli O157H7 in acidified media and
fruit juices

• Lee Young Jun
• Korea University
• Lab of Food Microbiology
• 2007. 5. 16

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Table of Contents

• Introduction
• Objective
• Experimental design
• Phase ?
• Survival of control, acid-adapted,
  acid-shocked cells of E. coli O157H7 inoculated
  into TSB acidified with acetic or lactic acid
• Phase ?
• Growth pattern of E. coli O157H7 in apple
  cider and orange juice incubated at 5 and 25?
• Phase ?
• D-values of three type of E. coli O157H7
  cells in TSB, apple cider, and orange juice at 52
  and 54?
• Conclusions

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E. coli O157H7

• Characteristics
• Gram negative
• Motile rods
• Facultative aerobes
• Diseases
• Diarrhea, Hemorrhagic colitis,
• Hemolytic uremic syndrom
• Reservoirs
• Cattle, Domestic animals,
• Humans

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• Acid-adapted?
• Acid-adapted cells are those which have been
  exposed to a gradual decrease in environmental pH
• Acid-shocked?
• Acid-shocked cells are those which have been
  exposed to an abrupt shift from high pH to low pH

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• D-value
• Time required to reduce population of
  microorganism to 1/10
• at certain temperature

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Objective

• To determine if survival and growth patterns of
  acid-adapted and acid-shocked cells of E. coli
  O157H7 differ in acidified TSB and in fruit
  juices
• To determine if acid adaptation of acid shock
  alter heat tolerance of cells in juices

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Experimental design

• Phase ?
• Survival of control, acid-adapted,
  acid-shocked cells of E. coli O157H7 inoculated
  into TSB acidified with acetic or lactic acid
• Phase ?
• Growth pattern of E. coli O157H7 in apple
  cider and orange juice incubated at 5 and 25?
• Phase ?
• D-values of three type of E. coli O157H7
  cells in TSB, apple cider, and orange juice at 52
  and 54?

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• Phase ?
• Survival of control, acid-adapted,
  acid-shocked cells of E. coli O157H7 inoculated
  into TSB acidified with acetic or lactic acid

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Materials and Methods

• Strains
• - E. coli O157H7
• Cell type
• - control, acid-adapted, acid-shocked cells
• Media
• - Tryptic soy broth(TSB)
• - Tryptic soy agar(TSA)
• - TSA containing 3 sodium chloride(TSAS)
• pH Incubation time
• - pH3.4 0, 1, 2(acetic)
• 0, 1, 3, 6, 8(lactic)
• - pH3.9 0, 5, 9, 12, 18, 24

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• Control cells
• - grown in TSB for 18h at 37?
• Acid-adapted cells
• - grown in TSB supplement with 1 glucose
  for 18h at 37?
• Acid-shocked cells
• - grown in TSB culture(16h)
• - adjusted to pH4.8 by adding 2M lactic acid
• - incubating for 2h at 37?

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0.1ml of a diluted 18-h cell-suspension into
9.9ml of TSB
Populations were monitored over a 24-h period
Two samples from each test parameter combination
were serially diluted in sterile 0.1 peptone
water
Surface plated on TSA and TSAS at each sampling
time
Incubated at 37? for 2448 h before colonies were
counted
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• Enhancement of acid tolerance is accompanied by
  decreased tolerance to sodium chloride, which is
  an indication of injury

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• Phase ?
• Growth pattern of E. coli O157H7 in apple
  cider and orange juice incubated at 5 and 25?

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Materials and Methods

• Strains
• - E. coli O157H7
• Cell type
• - control, acid-adapted, acid-shocked cells
• Juice type
• - Apple cider (AC1, AC2, AC3)
• - Orange juice (OJ1, OJ2, OJ3)
• pH
• - AC13.56, AC23.98, AC33.73
• - OJ13.82, OJ23.86, OJ33.86
• Temparature
• - 5 and 25?

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Apple cider and orange juice(9.9ml) were
transferred into test tube
Three type of E. coli O157H7 cells was added
Populations in inocula, cider, and juice held for
7, 14, 21, 28, 42, and 56 days were determined by
surface plating diluted samples on TSA
Incubated at 37? for 2448 h before colonies were
counted
Cultures were streaked on SMA, incubated 24h at
37?, and examined for E. coli O157H7 colonies
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• Phase ?
• D-values of three type of E. coli O157H7
  cells in TSB, apple cider, and orange juice at 52
  and 54?

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Materials and Methods

• Strains
• - E. coli O157H7
• Cell type
• - control, acid-adapted, acid-shocked cells
• Juice type
• - Apple cider (AC1, AC2)
• - Orange juice (OJ1, OJ2)
• Temparature (D-value)
• - 52 and 54?

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Conclusions

• Acid-adapted E. coli O157H7 cells have enhanced
  tolerance to lactic acid but not acetic acid
• Regardless of test parameter, there is not a
  strong indication that control, acid-adapted, and
  acid-shocked cells differ in tolerance to the
  acidic environment in apple cider or orange juice
• D-values of acid-adapted cells were considerably
  high than those of acid-shocked or control cells