Title: Influence of acid tolerance response on survival, growth, and thermal cross-protection of Escherichia coli O157:H7 in acidified media and fruit juices
1Influence 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
2Table 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
3E. coli O157H7
- Characteristics
- Gram negative
- Motile rods
- Facultative aerobes
- Diseases
- Diarrhea, Hemorrhagic colitis,
- Hemolytic uremic syndrom
- Reservoirs
- Cattle, Domestic animals,
- Humans
4- 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
5- D-value
- Time required to reduce population of
microorganism to 1/10 - at certain temperature
6Objective
- 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
7Experimental 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?
8- Phase ?
- Survival of control, acid-adapted,
acid-shocked cells of E. coli O157H7 inoculated
into TSB acidified with acetic or lactic acid
9Materials and Methods
- Strains
- - E. coli O157H7
- Cell types
- - control, acid-adapted, acid-shocked cells
- Media
- - Tryptic soy broth(TSB)
- - Tryptic soy agar(TSA)
- - TSA containing 3 sodium chloride(TSAS)
- pH Incubation time(h)
- - pH3.4 0, 1, 2(acetic)
- 0, 1, 3, 6, 8(lactic)
- - pH3.9 0, 5, 9, 12, 18, 24
10- 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 for 16h (pH6.0)
- - adjusted to pH4.8 by adding 2M lactic acid
- - incubating for 2h at 37?
11E. coli O157H7
TSB (adjusted to pH 3.9 or 3.4 with acetic or
lactic acid)
TSA and TSAS
Incubated at 37? for 2448 h
12Table 1. Number of control, acid-adapted, and
acid-shocked cells of E. coli O157H7 inoculated
into TSB acidified at pH 3.9 or 3.4 with acetic
or lactic acids, incubated for up to 24h, and
recovered on TSA or TSAS
13Fig. 1. Differences(log10cfu/ml) in populations
of control cells(), acid-adapted cells(?), and
acid-shocked cells(?) of E. coli O157H7
recovered from TSB acidified at pH 3.9 with
lactic acid incubated at 37? for up to 12h when
plated on TSA and TSAS
14- Phase ?
- Growth pattern of E. coli O157H7 in apple
cider and orange juice incubated at 5 and 25?
15Materials and Methods
- Strains
- - E. coli O157H7
- Cell types
- - control, acid-adapted, acid-shocked cells
- Juice types
- - 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?
16E. coli O157H7
Apple cider and orange juice
TSA
Incubated at 37? for 2448 h
17Table 2. Populations(log10cfu/ml) of E. coli
O157H7 in apple cider(AC1, AC2, AC3) and orange
juice(OJ1, OJ2, OJ3) incubated at 5 and 25?
18- Phase ?
- D-values of three type of E. coli O157H7
cells in TSB, apple cider, and orange juice at 52
and 54?
19Materials and Methods
- Strains
- - E. coli O157H7
- Cell types
- - control, acid-adapted, acid-shocked cells
- Juice types
- - Apple cider (AC1, AC2)
- - Orange juice (OJ1, OJ2)
- Temparature (D-value)
- - 52 and 54?
20E. coli O157H7
Apple cider and orange juice (adjusted to 52 and
54?)
Heating (10, 20, 30 min)
TSA
Incubated at 37? for 48 h
Counting Colony
21Table 3. D-values of control, acid-adapted, and
acid-shocked cells of E. coli O157H7 cells in
TSB(pH7.2), apple cider(AC1, AC2), and orange
juice(OJ1, OJ2) at 52 and 54?
22Conclusions
- 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