Open Journal of Gastroenterology, 2013, 3, 42-48 OJGas Published Online February 2013 (
A methachromatic-based experimental model for
identification of bowel a s the focus of an acute
Sravya Sowdamini Nakka1, Jessica Johansson2, Faisal Shahzad1, Anders Hanning3, Fariba Nayeri1,4#
1R & D Department, Institution for Protein Environmental Affinity Surveys, PEAS Institut, Linköping, Sweden
2Department of Clinical Medicine, School of Health and Medical Sciences, Örebro University, Örebro, Sweden
3Episentec AB, Fjällvägen 6B, Sollentuna, Sweden
4Division of Infectious Diseases, Department of Clinical and Experimental Medicine, Linköping University Hospital, Linköping, Sweden
Received 27 December 2012; revised 25 January 2013; accepted 2 February 2013
Diarrhea is the most common symptom of acute in-
flammation in gastrointestinal tract and the patients
are isolated in order to inhibit transmission and to
conduct investigations. Yet there is no standard test to
distinguish gastrointestinal infection from more gen-
eralized diseases at admittance which might cause
delay in therapy. Hepatocyte growth factor (HGF) is
produced upon injury by mesenchymal cells. On the
contrary to chronic inflammation, HGF produced in
the course of acute inflammation is biologically active
and shows binding affinity to heparan sulphate pro-
teoglycan (HSPG) and dextran sulphate (DS). Based
on this phenomenon, an agarose gel containing DS
was prepared and immobilized on loo ps to investigate
the feces samples for the presence or absence of
growth factors such as HGF with affinity to DS. The
study is conducted as a clinical evaluation of an ex-
perimental model to distinguish acute infectious gas-
troenteritis from other causes of diarrhea. 656 fecal
samples gathered consequently from patients seeking
for bowel disturbances and healthy were tested by the
test and the medical reports were investigated. Upon
interaction with DS, methylene blue changes color to
pink. This phenomenon was inhibited by HGF and
converted by addition of anti-HGF antibodies to the
samples. The test distinguished acute infectious gas-
troenteritis with high sensitivity and specificity (96%
and 92% respectively) from other causes of diarrhea.
We introduce a metachromatic experimental model
that might distinguish acute inflammation in alimen-
tary tract from other causes of diarrhea. This model
might be used in developing rapid diagnostic tests.
Keywords: Gastroenteritis; Hepatocyte Growth Factor;
HSPG; Metachromasy; Rapid Test
Besides to acute infectiou s gastroenteritis, diarrhea is the
symptom of several other serious systemic infections as
well as inflammatory diseases that need immediate in-
tervention. Because the therapeutic strategies differ sig-
nificantly between different diseases it is of great value
to establish the right diagnosis as soon as possible. The
most available procedures that are undertaken to estab-
lish diagnosis in patients with diarrhea by examination of
stool are direct microscopy, cultures, parasitological ex-
aminations, PCR and Elisa tests to identify virus, deter-
mination of hemoglobulin, calprotectin and toxins. How-
ever, with respect to antibiotic consumptions and/or low
antigen burden the tests have a limited sensitivity [1,2].
Studied widely since 20 years ago hepatocyte growth
factor (HGF) has shown to be highly involved in bio-
logical procedures relating to development and regenera-
tion [3,4]. Thus changes in presence, structure and con-
figuration of this growth factor might have consequences
in lack of healing or disease development [3]. Biosensor
technology, such as surface plasmon resonance (SPR), is
a reproducible method for real-time evaluation of bind-
ing affinity to ligands and receptors [5]. Biologically
active HGF shows binding affinity to HSPG in SPR sys-
tem and the affinity is decreased after addition of sul-
phated oligo saccharides such as DS to the samples [6,7].
Biosensor coated with DS was recently introduced for
detection of HGF in cellular medium [8]. HGF as a po-
tential therapeutic strategy in treatment of chronic in-
flammatory bowel diseases has been discussed in recent
*There is a pending patent regarding the gel preparation.
The project was funded by ALF Grants County Council Östergötland
and PEAS Institut.
The study was approved by the Ethical Committee in Linköping
S. S. Nakka et al. / Open Journal of Gastroenterology 3 (2013) 42-48 43
studies [9-11]. However it might be of importance to
further study the presence and quality of HGF during
different inflammatory processes since high amounts of
HGF is produced during acute inflammation in bowel [12].
Metachromasy is a characteristic color change that
certain aniline dyes exhibit when bound to chromotrope
substances [13]. This phenomenon has been widely used
in study of tissue sections. Methylene blue (O-Toluidine)
is considered an excellent metachromatic dye, which
upon binding to high molecular weight polysaccharides,
such as DS, changes the color of the indicator solution
from blue to pink [13].
Taking advantage of previous studies and ob servations,
an experimental model has been established and pre-
sented using agarose membrane containing DS sodium
salt that changes color to pink in contact with methylene
blue [7,8]. Incubation of this membrane in feces in 10
seconds might distinguish samples containing active
HGF that binds to DS and inhibits metachromasy.
DS sodium salt from Leuconostoc spp. with molecular
weight 6500- > 500,000, high resolution agarose, Tolu-
idine Blue O (trade name for Methylene Blue indicator
solution), Fetal bovine serum (FBS), Proclin 300, D-(+)-
Glucose were all obtained from Sigma Aldrich, Sweden.
Mannitol (150 mg/mL) was from Fresenius Kabi AB,
Sweden, Phosphate Buffer Solution (pH 7.4) from Apo-
teket, Linköping, Sweden, Recombinant HGF from R &
D systems Inc., Minneapolis, USA and Styrene plastic
loop 1 µl and micro-tubes Safe Seal 1.5 mL were ob-
tained from Sarstedt AB, Linköping, Sweden.
2.1. Preparation of Gel and Immobilisation on
Loops (the Test)
DS MW 100,000 (0.9 mg), Agarose high resolution (9
mg), Glucose (4 mg), 300 µl PBS in 700 µl distilled wa-
ter and Mannitol (50 µl), were mixed and heated until a
clear solution. Plastic loops were dipped once in the so-
lution, approximately 5 mm above the loop, and were
next placed with the loop pointing upwards to dry at
room temperature (60 min). PBS (pH 7.4), distilled water,
0.5% serum albumin solution or 0.5% FBS were used as
negative controls. Recombinant HGF (R & D) diluted in
0.5% FBS (125 - 8000 pg/ml) was used as positive con-
2.2. Preparation of Indicator and Feces Diluent
A 1% methylene blue (100 mg in 10 ml distilled water)
stock solution diluted to 0.003% (1 mL in 300 ml
distilled water) was used as indicator solution. Proclin
300 (50 µl in 10 ml) was added to FBS which was used
as feces dilution solution.
2.3. Participants
2.3.1. Retrospect i ve
Feces samples that were gathered in 2003 during a pre-
vious study of HGF in blood and feces of patients with
IBD and infectious gastroenteritis (n = 146) were re-
thawed once and examined by the test. This material is
consisted of healthy volunteers and patients with defined
diagnosis (Infla mmatory Bowe l Disease; IBD n = 58, 19
- 80 years old and 32 women, Infectious gastroen teritis n
= 70, 9 - 90 years old and 37 women and healthy n = 6 in
3 consecutive occasions, 19 - 35 years old, 3 women).
2.3.2. Prospec ti ve
This material (1 - 100 years old) was collected at the
Department of Infectious Diseases (n = 63 January
2010-June 2011) or from samples sent by other wards to
the Departments of Biochemistry (n = 106, 18th May-
1st June 2011) and Microbiology (n = 313, 1st -30th June
2011). The samples were coded at once and unidentified.
The project leader studied the patient-journals and the
result of the test and the medical history were docu-
mented directly. The files were updated daily and the
results of routine tests, x-rays, endoscope procedures and
final diagnosis before patient was dismissed were docu-
mented consequently. Total 482 feces samples from pa-
tients that searched the health care centers (n = 122) or
were admitted to the University Hospital in Linköping,
County hospitals in Norrkoping and Motala (n = 360)
were analyzed consecutively with the test within 48
hours after collection before the culture or PCR results
were available. Further 27 culture negative feces samples
from healthy volunteers without diarrhea (9 - 73, Median
53 years, 17 women) were included. The physician in
charge in each ward conducted the diagnosis procedure
and treatment. Therefore the reference tests were per-
formed accordingly on patients and it was not known to
the physicians which patients were going to be included
in the study.
2.4. Assay Accomplishment and Interpretation
of Results
Feces samples stored in room temperature for 15 minutes
prior to performing the test. The loop was first immersed
in feces for 10 sec, the excess feces was gently wiped off
and the loop was next placed in micro tubes containing
70 µl indicator solution for 10 sec and twisted gently by
rolling the loop between thumb and index finger for 1
sec. The loop was removed and the color observed. A
blue color (positive test) indicates presence of active
HGF in feces, and a pink color (negative test) indicates
no presence or presence of HGF with no affinity to DS.
In the case of a negative result 15 µl feces was diluted in
80 µL dilution solution and the above process was re-
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S. S. Nakka et al. / Open Journal of Gastroenterology 3 (2013) 42-48
peated. This procedure was undertaken to avoid false
negative results relating to hook or prozone effect (too
high level of binding growth factor in the sample) [14].
In the present work all of the fresh samples were tested
originally and after dilu tion. Positive test both in original
and diluted feces indicated a high DS affinity in feces
HGF. Positive test in original feces with diarrhea and
negative in diluted one indicated a low affinity of HGF
to immobilized DS. When the results were negative in
original feces, but turned to positive after dilution, pres-
ence of HGF with high affinity to DS is suspected (posi-
tive). When the results are negative in both original and
diluted feces it might show that no HGF with affinity to
DS is present in feces. The CMYK system was used for
interpretation of colors as follows: 701500, 502500,
453000 are ranges of positiv e result and 354000, 254000
as negative results [15].
2.5. Test Reproducibility
In order to analyze all the feces samples collected during
study period it was necessary to prepare different batches
of loops to supply the study with test material. Approxi-
mately 500 loops could be prepared from 1 ml DS gel
from each batch prepared. In order to control method
variability in preparation, 5 - 10 samples were analyzed
with; the old and the new batch of loops. In case the re-
sult of sample analysis differed completely in more than
two samples, the complete loop batch was discarded and
a new batch was prepared. Twenty loops from each batch
were also tested with negative controls (PBS, Albumin,
FBS, distilled water) and positive control (125 pg/ml
recombinant HGF). Positive and negative controls were
also used prior to analysis of samples daily. Feces sam-
ples were analyzed in duplicates.
2.6. Inhibition of Interaction
Feces sample from 2 patients with diarrhea caused by
Salmonella enteritis (27 ng/ml HGF) and Clostridium
difficile (7.9 ng/ml HGF) were diluted in distilled water,
stirred and centrifuged for 20 minutes at 3000 g. The
supernatant was dilu ted in distilled water 1:10 and sterile
filtered. Anti-human HGF antibody 0.1 mg/ml (Sigma
Aldrich) was add ed 1:5 to the samples and incub ated in 1
h 37˚C. Distilled water was added 1:5 to the control sam-
ple. Forty loops (10 loops for each sample with and
without antibody) were tested.
2.7. Reference Tests
Stool examinations by means of a combination of mi-
croscopic, virolog y (Calicivirus with PCR, Rotavirus and
Adenovirus antigen detection with ELISA) and bacterial
culture methods as well as serological and toxin-identi-
fication techniques (Clostridium difficile toxin), method
for detection of semi-quantitative calprotectin and fecal
hemoglobulin were performed as routine tests at the Uni-
versity Hospital in Linköping. A variety of X-ray and
endoscopic techniques were utilized as indicated.
Regression analysis was performed for correlations using
Graphpad prism version 5. Specificity (number of true
negative/number of true negative + number of false posi-
tive), Sensitivity (number of true positive/number of true
positive + number of false negative), Positive Predictive
Value (PPV = True positive/true positive + false positiv e),
Negative Predictive Value (NPV = True negative/true
negative + false negative) and Accuracy (True positive +
true negative/true positive + true negative + false posi-
tive + false negative) of the test results were calculated.
The Regression analysis was performed to calculate the
correlation between parameters (Graphpad prisma ver-
sion 5).
3.1. Gel Preparation
The first observation showing that addition of HGF to
DS solution could inhibit the interaction and thereby
changing of color of methylene blue, motivated the test-
ing of HSPG and DS with different molecular weights
and concentration with different diluents and composi-
tions. DS MW 100,000 in the composition mentioned in
Material & Method gave the most reliable results.
3.2. The Diagnostic Procedures
The feces cultures (n = 195), diagnostic virology tests (n
= 58), toxin (n = 318), parasitological tests (n = 44),
semi-quantitative calprotectin (n = 111) and feces hemo-
globulin (n = 61) were performed on feces samples (n =
482) at admittance. These tests were performed on the
same feces samples used in this study. However the re-
sults of the test were observed and documented before
the results of reference tests were available.
3.3. Infectious Gastroenteritis
After the results of routine tests were available it was
shown that 137 cases (8 - 100 year s, Median 70 years old,
61 women, loose feces n = 131) the stool examinations
revealed positive cultures (Salmonella n = 6, Campylo-
bacter n = 10), Clostridium difficile toxin (n = 89), viral
diagnosis (n = 24, Calicivirus n = 7, Rotavirus n = 16,
Adenovirus n = 1) parasites (n = 8, Giardia intestinalis n
= 5, Schistosomia mansoni n = 1 and Blastocystis homo-
nis n = 2). Double infection was observed in 2 cases.
Together 207 feces samples (2003 and 2011) had verified
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S. S. Nakka et al. / Open Journal of Gastroenterology 3 (2013) 42-48
Copyright © 2013 SciRes.
infection (Figure 1). The test was negative in 2 cases
without diarr he a and 5 cases with diarrhea. tion of colitis.
Fifty-eight samples from 2003 with defined IBD di-
agnosis were included in this group and in total 82 sam-
ples with IBD the test was positive in 14 cases (Table 1).
3.4. Non-Infectious Diarrhea
In 143 cases (3 - 96, median 55 years, 64 women, loose
feces n = 95) bowel as focus of infection was ruled out.
However in one patient with diarrhea Blastocystis hominis
cyst was found in feces but the performed X-ray and
endoscopy showed terminal ileitis. In this group the test
was positive in six cases (Table 1).
3.6. Sepsis
Diarrhea during the course of sepsis with multiple organ
dysfunctions was observed in 22 samples from 19 pa-
tients (32 - 92, median 69 years, 15 women). The test
was positive in 18 cases (Table 2). The blood cultures
yielded growth of Staphylococcus aureus in 3 cases,
Klebsiella pneumoniae in 2 cases, Klebsiella pneumoniae
+ Bacteroides fragilis in one case, Streptococcus pneu-
moniae in one case, Streptococcus Oralis in one case,
Streptococcus agalactiae (GBS) + Candida albicans in
one case, Proteus mirabilis in 1 case, Cand ida albicans in
one case, Staphylococcus aureus + Bacteroides fragilis in
one case, E. coli in 2 cases, Enterococcus gallinarum in
one case and aerococcus spp. in one case. The blood cul-
tures were negative in 3 cases with sepsis and multiple
organ failure.
3.5. Inflammatory Bowel Diseases (IBD)
The patients with bowel disturbances in which infection
could not be verified by stool examinations and debut or
exacerbation of IBD was suspected, were classified un-
der this sub-group. Total 24 samples from 21 patients (14 -
83, median 59.5 years, 14 women, loose feces n = 20,
ulcerous colitis n = 15, crohn disease n = 4, micro-
scopic colitis n = 4, celiac disease n = 1) were collected.
The diagnosis was verified by a recent endoscopy in 14
cases. Out of 15 samples of patients diagnosed as exac-
erbation of ulcerous colitis, the test was positive in both
original and diluted samples in 4 patients (Tab le 2 ). En-
doscopic examination (n = 4) revealed acute or exacerba-
This group is excluded from statistical analysis be-
cause the patients had generalized inflammation and or-
gan dysfunction.
Figure 1. The study population presented in a flow chart.
S. S. Nakka et al. / Open Journal of Gastroenterology 3 (2013) 42-48
Table 1. Validation of the diagnostic test.
Non-infectious cases Total
Diagnostic test result Verified infectious diarrhoeaOther causeshealthy IBD
Positive 200 6 0 14 220
Negative 7 136 45 68 256
Total 207 142 45 82 476
Sensitivity and s p eci ficity of the test we r e calculated as 96.6% and 92.5% respectively while Positive Predictive Value (PPV)
and Negati ve P redi cti ve Value are calculated as 9 0. 9% and 97 .2%. Validati on of diag nos tic tes t r esult s ar e fou nd to b e 94.3%
Table 2. The index test result in feces samples and subgroups collected in 2011.
Subgroups Positive (positive)Positive (negative)Negative (positive)Negative (negative)
Sepsis 13 4 1 4
Verified infection 102 13 17 5
Non-infectious diarrhea 3 3 0 136
Suspected Infection 71 8 15 6
IBD 4 5 0 15
Positive/negative = test positive in undiluted form, Negative/Positive = test positive after dilution (hook effect). Nega-
tive/negative result is considered as negative test. Results mentioned in brackets represent the result obtained upon dilution
of faeces samples in 1:5 ration of FBS-Proclain 300 solution.
3.7. Suspected Infection
In 100 patients (4 - 93, median 64 years, 61 women loose
feces n = 95) reference tests did not reveal infection but
infectious gastroenteritis was highly suspected because
of medical history and/or previous cultures. The test was
positive in 94 cases (Table 2). This group is not included
in statistical analysis because the diagnosis was not ob-
jectively verified.
3.8. Unclear Cases
The medical history and/or the diagnostic procedure
were incomplete or classed as high secret and therefore it
was not possible to find out the cause of diarrhea in 58
patients (29 women) which were excluded from statisti-
cal calculations (Figure 1).
3.9. Estimates
1) Inhibition of HGF
Incubation of diluted feces with anti HGF antibodies
resulted in inhibition of HGF and a negative result in
80% (16 out of 20 loops).
2) Reliability of test
Sensitivity, specificity, positive predictive value and
negative predictive value as well as accuracy were cal-
culated in two groups; verified infectious gastroenteritis
(n = 207) and non-infectious gastroenteritis which in turn
included patients with IBD, patient with other systemic
diseases and healthy (n = 268). As shown in Table 1, the
test could distinguish acute infectious gastroenteritis with
a sensitivity of 96.6% and specificity 92.4% and a posi-
tive predictive value of 90.9% and negative predictive
value of 97.2%. The accuracy of test was 94.3%.
The results of the test did not correlate to fecal calpro-
tectin (R = 0.015, R2 = 0.02) or fecal hemoglobulin (R =
0.29, R2 = 0.08) but correlated positively to loose feces
(R = 0.59, R2 = 0.35 p < 0.001). Fecal calprotectin had
no correlation to feces consistence (R = 0.09, R2 = 0.008)
but correlated to fecal hemoglobulin (R = 0.47, R2 = 0.22,
p = 0.001).
In the present work an experimental model for evaluation
of HGF in faeces samples and determination of bowel as
the focus of acute inflammation is introduced. The chro-
motropic character of HSPG and DS in inducing meta-
chromatic colour ch ange in methylene blue and toluidine
blue has been used in development of test. We have
shown that the results can discriminate an acute inflam-
mation in bowel from a chronic one with high test
predictive values.
Our observations regarding discrepancy between con-
centration of HGF (ELISA) and its binding affinity to
ligands (SPR) together with decreased biological activity
in vitro during chronic inflammation was the basis of
development of a method to discriminate chronic injuries
in which treatment with biologic active HGF might be
beneficial [16-18]. Using the underlying theory a DS
membrane (the test) was prepared to determine the bind-
ing affinity of HGF to DS in feces [19,20]. During
preparation of the membrane it was shown that the mo-
lecular weight of DS was crucial in reaction and stability
Copyright © 2013 SciRes. OPEN ACCESS
S. S. Nakka et al. / Open Journal of Gastroenterology 3 (2013) 42-48 47
of the membrane. DS, 100,000 MW was used and this
was in agreement to results reported by Berger et al., [8]
Preparation of membrane was also dependent on volume,
pH and temperature of solutions [13].
Diarrhea is the major symptom of food borne illnesses
which in turn can be divided to bacterial, viral, chemical
and parasitic categories. A large portion of the outbreak s
are of unknown etiolog ies (45.1%) [21] and th erefore the
limited tests used at the laboratory could not possibly
rule out infection in all patients with gastroenteritis. In
order to evaluate the sensitivity of routine diagnostic
tests to determine the etiology of gastroenteritis in our
ward we studied journal of patients that were admitted to
the Department of Infectious Diseases in Linköping and
were dismissed under diagnosis acute infectious gastro-
enteritis (n = 181, January to December 2011). Feces
cultures (at least once in all of the cases), viral diagno stic
tests (n = 123), direct microscopy and parasitological
tests (n = 51) were performed accordingly which could
verify infection in 59% of cases (submitted manuscript).
The test recognized acute inflammation caused by in-
fection with a high sensitivity in patients with diarrhea.
When diarrhea was not the presenting symptom the test
was negative in spite of positive cultures. It might indi-
cate that the test is sensitive to the grade of in flammation
not presence of an infectious agent such as in carriers. In
the patients with sepsis and multiple organ failure and
diarrhea, positive test might indicate a generalized in-
flammatory process and a higher risk for bacteremia.
Calprotectin (semi-quantitative and quantitative) tests
are recently been used as a routine to rule out a chronic
inflammatory process in bowel [22]. There was no sig-
nificant correlation between the test and calprotectin re-
sults in our observation. However in cases with negative
calprotectin and positive test viral and parasitic infec-
tions might b e suspected. On the oth er hand positiv e cal-
protectin together with negativ e test might have values in
detection of IBD (data not show n).
We conclude that Dextran-activity test is a simple ex-
perimental model for evaluation of HGF in feces. The
results are in agreement with our previous observations
and the model might be used to develop rapid and cost-
effective tests for distinguishing cases in which bowel is
the focus of acute inflammation such as in food borne
outbreaks in need of isolation. Special attention should
be paid to cases of gastroenteritis with negative test
which need complementary examinations to rule out
more serious conditions in need of appropriate therapeu-
tic strategies without delay.
We are grateful to Tayeb Nayeri, Prof. Fredrik Winqvist and Per Stal-
handske for their valuable suggestions in the development of method.
We are also grateful to Clinical and Laboratory staff of Linköping
University hospital in helping us with collection of samples.
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