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Applied and Environmental Microbiology, January 2003, p. 711-714, Vol. 69, No. 1
0099-2240/03/$08.00+0 DOI: 10.1128/AEM.69.1.711-714.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Survival and Resuscitation of Ten Strains of Campylobacter jejuni and Campylobacter coli under Acid Conditions
P. Chaveerach,1,2* A. A. H. M. ter Huurne,3 L. J. A. Lipman,1 and F. van Knapen1
Department of Public Health and Food Safety, Faculty of Veterinary Medicine, Utrecht University, Utrecht,1
DLO-Institute for Animal Science and Health, Lelystad, The Netherlands,3
Department of Veterinary Public Health, Faculty of Veterinary Medicine, Khon Kaen University, Khon Kaen, Thailand2
Received 26 July 2002/
Accepted 23 October 2002

ABSTRACT
The culturability of 10 strains of
Campylobacter jejuni and
Campylobacter coli was studied after the bacteria were exposed
to acid conditions for various periods of time.
Campylobacter cells could not survive 2 h under acid conditions (formic acid
at pH 4). The 10
Campylobacter strains could not be recovered,
even when enrichment media were used. Viable cells, however,
could be detected by a double-staining (5-cyano-2,3-ditolyl
tetrazolium chloride [CTC]-4',6'-diamidino-2-phenylindole [DAPI])
technique, demonstrating that the treated bacteria changed into
a viable but nonculturable (VBNC) form; the number of VBNC forms
decreased over time. Moreover, some VBNC forms of
Campylobacter could be successfully resuscitated in specific-free-pathogen
fertilized eggs via two routes, amniotic and yolk sac injecting.

INTRODUCTION
In recent years, the frequency of human enteritis caused by
Campylobacter jejuni and
Campylobacter coli has increased in
many developed countries. The potential source of the infection
has been identified as the consumption of undercooked poultry
products or water contaminated with
Campylobacter species (
2,
28). Hence, poultry contaminated with
Campylobacter is a source
of human
Campylobacter infection. At broiler farms, drinking
water is the prime suspect as the vehicle that spreads
Campylobacter throughout the flock (
23). Therefore, decontamination of the
water is needed. The use of acidified water (using organic acids
to control pathogenic agents) is a convenient and safe decontamination
method.
Several studies have shown that strong acids, such as formic, acetic, ascorbic, and lactic acids, rapidly inhibit the growth of Campylobacter species (9, 11, 12, 15, 34). Organic acids have also been used (5, 11, 13, 33) to reduce the amount of infection with Campylobacter and Salmonella on carcasses or to prevent broilers from becoming infected. Acidified water is intensively used in food industries and animal husbandry. However, it is still not known whether Campylobacter bacteria were just below the detection limit and had changed into dormant cells or whether the bacteria had died after exposure to the acid conditions. The survival of Campylobacter depends on many factors, such as aerobiosis, presence of nutrients, temperature, and pH levels (17, 21, 24). In unfriendly environments, Campylobacter may be able to enter a nonculturable stage. The viability of these cells cannot be detected by a routine culture method. This phenomenon, the viable but nonculturable (VBNC) stage, was first described by Rollins and Colwell (26). The VBNC stage has been considered to play a role in human health. In recent years, several studies have explored the recovery of VBNC forms of Campylobacter cells. However, the recovery of VBNC forms of Campylobacter cells is still controversial (3, 6, 8, 19, 20, 22, 27, 29, 30, 33).
The aim of this study was to better understand the survival of Campylobacter in acidified Mueller-Hinton broth over time. Hence, experiments were conducted to determine the recovery of 10 Campylobacter strains after exposure to acidity; four experiments checking survival, resuscitation in enrichment media, formation of VBNC forms, and recovery of VBNC forms were performed. The potential resuscitation of the treated bacteria was checked by injecting VBNC Campylobacter in 9-day-old specific-free-pathogen (SPF) embryonated chicken eggs.

Campylobacter strains.
Ten
C.
jejuni and
C.
coli strains isolated from chickens were
used (
9). They were kept at -70°C in glycerol (20% [vol/vol]).
A 100-µl sample of each strain was thawed and then inoculated
in 10 ml of brucella broth (BBL; Becton Dickinson, Sparks, Md.).
Subsequently, the inoculated broth tubes were incubated at 37°C
for 48 h under microaerophilic conditions (5% O
2, 10% CO
2, and
85% N
2) generated by using a Gas Pak Plus envelope (BBL; Becton
Dickinson) in anaerobic jars. Thereafter, all strains were subcultured
onto Columbia agar with 5% (vol/vol) defibrinated horse blood
(Bio Trading Benelux BV, Mijdrecht, The Netherlands) and were
kept under microaerophilic conditions at 37°C for 48 h.
Then, one typical
Campylobacter colony was transferred to Mueller-Hinton
(MH) broth (Oxoid, Hampshire, United Kingdom) and incubated
under microaerophilic conditions at 37°C for 48 h. These
10 strains were the active
Campylobacter stock solutions used
in this study.

Campylobacter under acid conditions.
For each of the 10
Campylobacter strains, 1 ml of the active
stock solution was transferred to 4 ml of MH broth, with an
adjusted pH of 4 by using formic acid (analytical grade) (Merck
KgaA, Darmstadt, Germany). The acid condition was used throughout
the experiments. The cultures were kept at 37°C under anaerobic
conditions by using a Gas Pak Plus envelope with palladium catalyst
(BBL; Becton Dickinson) to prevent exposure of the
Campylobacter to the excess oxygen atmosphere in the jars. As a general method,
1 ml of each treated culture was taken and diluted 10-fold,
by putting the 1-ml culture sample in 9 ml of buffer peptone
water (BPW) (10 g of peptone, 5 g of NaCl, 4.5 g of Na
2HPO
4 · 2H
2O, and 1.5 g of KH
2PO
4 [all amounts given per liter]),
after which 0.1 ml of each diluted suspension was placed onto
Colombia agar plate supplemented with horse blood for 0, 0.5,
1, 2, and 4 h, respectively. All plates were incubated at 37°C
for 72 h under microaerophilic conditions. Typical colonies
of
Campylobacter were counted and expressed as log
10 CFU milliliter
-1.
This experiment was performed in triplicate.

Resuscitation in liquid medium.
The resuscitation experiment was performed to check the potential
recovery of injured or culturable
Campylobacter cells after
exposure to acid conditions. For each
Campylobacter strain,
1 ml of active stock solution was transferred to 4 ml of acidified
MH broth. All treated cultures were kept under microaerobic
conditions at 37°C for 2 h. The cultures were then centrifuged
in a Centrifuge 5415C (Merck, Darmstadt, Germany) at 10,000
rpm for 10 min. The pellets were retained and resuspended with
1 ml of phosphate-buffered saline; 0.5 ml of each resuspended
culture was then transferred to 9 ml of a modified selective
enrichment medium, charcoal-cefoperazone-deoxycholate broth
(CCDB), which contains the same ingredients as the CCDA plates
(
4) but without the addition of antibiotics. All resuspended
cultures in CCDB were microaerophilically incubated at 37 or
43°C for 2 days. After incubation, 1 ml of the resuspended
culture in CCDB was taken and put into 9 ml of BPW, thereby
diluting it 10-fold. Samples (0.1 ml) of the diluted and undiluted
suspension were plated on CCD blood agar plates. The plates
were microaerophilically incubated at 37 or 43°C for another
2 days. Typical colonies of the bacteria were examined and counted.
This experiment was done in duplicate.

Direct culturable, total, and viable cell counts.
Campylobacter strains C350, C4602, and C144 were randomly selected
to study and compare the numbers of culturable, total, and viable
cells after exposure to acid conditions. One milliliter of each
active culture strain was transferred to 4 ml of the acidified
MH broth.
Campylobacter samples were taken at 0, 1, 2, and 4
h, and the samples were processed as described below for culturable,
active or viable, and total cell counts. For culturable cell
counts, 1 ml of each
Campylobacter strain in the acid solution
was put into 9 ml of BPW, thereby diluting it 10-fold, and 0.1
ml of the diluted solution was placed on Columbia blood agar
plates. The plates were microaerophilically incubated at 37°C
for 3 days. Colonies were counted and compared to the original
concentration; counts are in log CFU milliliter
-1. The remaining
solution (4 ml) was centrifuged at 10,000 rpm for 10 min. The
pellets were collected to determine total and viable cell counts
by using a double-staining (5-cyano-2,3-ditolyl tetrazolium
chloride [CTC]-4',6'-diamidino-2-phenylindole [DAPI]) technique
described by Cappelier et al. (
7). Results were expressed as
the number of corresponding bacteria per milliliter of the original
sample. This experiment was performed in triplicate.

Resuscitation via SPF embryonated chicken eggs.
For each of the 10
Campylobacter strains, 1 ml of active stock
solution was transferred to 4 ml of the acidified MH broth.
Three 9-day-old SPF embryonated eggs were aseptically injected
with 0.5 ml of each treated
Campylobacter strain. All inoculated
eggs were kept at 37°C on shaking trays for 3 days. Thereafter,
the eggshell was gently peeled off. Yolk sac and amniotic fluid
were carefully separated immediately. Fifty microliters of the
yolk sac fluid was then taken and streaked onto Columbia blood
agar plates with a sterilized swab, while 50 µl of amniotic
fluid was spread onto Columbia blood agar plates. The plates
were incubated at 37°C under microaerophilic atmosphere
for 5 days. The positive-control group was inoculated with
Campylobacter solution without acid treatment, and the negative-control group
was inoculated with 0.5 ml of formic acid without
Campylobacter.
Typical colonies of each
Campylobacter strain were counted per
plate. The identification of
Campylobacter was done with a phase-contrast
microscope when necessary.

Survival of Campylobacter in acidified MH broth.
The culturability of each of the 10
Campylobacter strains rapidly
decreased during 1 h of incubation with formic acid at pH 4.
After a 2-h incubation period, the bacteria could not be cultured.
These results were similar to those of our previous study, in
which formic acid was in a mixture of organic acids and feed
(
9). It has been confirmed that formic acid at pH 4 inhibits
Campylobacter growth. The use of acidified water (organic acids)
as a decontamination method is widespread in food industries
and animal husbandry in an effort to control pathogenic agents.
However, the failure of acidified water to prevent growth of
pathogenic agents has also been reported (
1,
5,
25). The lack
of effectiveness of acidified water may be influenced by the
short exposure time, trace amounts of the remaining acid, or
cell survival traits.

Recovery of Campylobacter by CCD broth.
Injured cells may recover under appropriate conditions, such
as enrichment media and a microaerophilic atmosphere. All undiluted
(original) and diluted suspensions of each treated strain in
CCDB were spread onto the CCD agar plates supplemented with
blood, and no growth was observed on these plates for all 10
Campylobacter strains at different temperatures.

Total, culturable, and viable cell count results.
Fig.
1a, b, and c show the total, culturable, and viable cell
counts for strains C4602, C144, and C350, respectively. The
total cell counts of these three
Campylobacter strains were
constant throughout the 4-h incubation time. At the beginning,
the culturable cells of C4602, C144, and C350 were at 7.08 ±
0.05, 5.47 ± 1.65, and 6.18 ± 0.81 log
10 CFU ml
-1,
respectively. The culturability of C144 cells could not be observed
on the spread blood agar plate after 1 h under acid conditions,
while the culturability of C4602 and C350 dramatically decreased
by 3.97 and 3.15 log
10 CFU ml
-1, respectively. After incubation
for 2 h, the culturability of these strains could not be observed.
It has been demonstrated that microcosm water can induce
Campylobacter to change to the VBNC form (
7,
14,
21,
30,
31). To demonstrate
the formation of the VBNC form of
Campylobacter under acid conditions,
the double staining (CTC-DAPI) technique was used (
7). The results
demonstrated that
Campylobacter cells could enter the VBNC stage
under acid conditions, while no colony growth was observed.
The numbers of viable cells of the three strains decreased slightly
over time (Fig.
1). After 2 h of incubation, the numbers of
viable cells of strains C4602 and C350 were 4.18 ± 0.24
and 3.76 ± 0.20 log
10 CFU ml
-1, respectively, whereas
the number of viable C144 cells was 2.76 ± 0.07 log
10 CFU ml
-1. At the end of the experiment, the numbers of viable
cells of C4602, C144, and C350 remained at 3.96 ± 0.00,
1.76 ± 0.00, and 3.22 ± 0.01 log
10 CFU ml
-1, respectively.
Each
Campylobacter strain responded to the acid differently.
Nevertheless, the number of
Campylobacter (viable cells) after
exposure to acid in our experiment was less than those in other
studies (e.g., number after starvation) (
6-
8,
14,
21,
26). Probably,
in our experiment, the undissociated acid form of formic acid
could diffuse into the cells and destroy DNA synthesis (
10)
and/or could cause loss of outer cell membrane (
9), which would
yield a reduced number of VBNC.

Recovery of Campylobacter via SPF embryonated eggs.
The recovery experiment demonstrated that after exposure to
acidity for 2 h, 4 of the 10
Campylobacter strains were resuscitated
via embryonated eggs successfully. In the positive-control group,
8 of the 10
Campylobacter strains could be found in the yolk
sac in higher numbers than in the amniotic fluid (Table
1).
It is extremely difficult to be 100% sure that no culturable
cells were inoculated into the eggs, but the recovery experiment
of treated
Campylobacter cells, after 2 h of incubation, in
the enrichment liquid media demonstrated that no culturable
cells remained in the acid solution. Our experiment is the first
to demonstrate that
Campylobacter under acid conditions, where
the cells were probably in the VBNC stage, can resuscitate in
embryonated eggs. Comparing the results from the three strains,
a higher number of VBNC cells may give more probability of recovery.
This explains the unsuccessful resuscitation when the number
of VBNC cells was low (
8). The recovery may depend on the animal
model and the strain used. Studies have shown that some researchers
have been successful in recovering VBNC form (
6,
19,
27,
29)
while some have had no success (
3,
20,
22,
32). Our results
revealed the successful resuscitation of VBNC cells via both
the allantoic and yolk sac routes of embryonated eggs. The yolk
sac, containing sufficient nutrients and growth factors, yielded
more colonies of
Campylobacter than the allantoic sac, where
biological defensive lysozymes and a high pH are present (
16,
18). These results are in agreement with the experimental results
of Cappelier et al. (
8), in which passage in embryonated eggs
is the preferable model for recovery of the VBNC stage of
Campylobacter.
In conclusion, our findings indicate that
Campylobacter can
enter into a nonculturable (VBNC) stage under acid conditions.
Moreover, the VBNC stage can be resuscitated after passage through
embryonated eggs. These results could help to explain the failure
of the use of acidified water (using organic acids) to control
Campylobacter at the farm level or in the slaughter process.
From the epidemiological point of view, these findings demonstrate
that the spread of
Campylobacter through acidified drinking
water can still be the source of recontamination in commercial
chicken-rearing houses.
View this table:
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TABLE 1. Colonization of 10 strains of Campylobacter cells treated with formic acid at pH 4 via two injection routes of SPF embryonated chicken eggs
|

ACKNOWLEDGMENTS
We greatly appreciate the excellent technical assistance of
Thaweesak Songserm and Dirk van Roozelaar.
This study was funded in part by financial support from the Royal Thai government (to P.C.).

FOOTNOTES
* Corresponding author. Mailing address: Department of Public Health and Food Safety, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 2, P.O. Box 80 175, 3508 TD Utrecht, The Netherlands. Phone: 31-30-2533379. Fax: 31-30-2532365. E-mail:
Chaveerach{at}vvdo.vet.uu.nl.


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Applied and Environmental Microbiology, January 2003, p. 711-714, Vol. 69, No. 1
0099-2240/03/$08.00+0 DOI: 10.1128/AEM.69.1.711-714.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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