Carriage of ESBL/AmpC-producing or ciprofloxacin non-susceptible Escherichia coli and Klebsiella spp. in healthy people in Norway
Ulstad et al. Antimicrobial Resistance and Infection Control
Carriage of ESBL/AmpC-producing or ciprofloxacin non-susceptible Escherichia coli and Klebsiella spp. in healthy people in Norway
Charlotte R. Ulstad 0
Margrete Solheim 0
Sophie Berg 0
Morten Lindbaek 1
Ulf R. Dahle 0
Astrid L. Wester 0
0 Domain for Infection Control and Environmental Health, Norwegian Institute of Public Health , Oslo , Norway
1 Institute of Health and Society, University of Oslo , Oslo , Norway
Background: Asymptomatic carriage has been recognised as an important risk factor for infection caused by antibiotic resistant bacteria. A 14% global prevalence of Extended-Spectrum Beta-lactamase (ESBL) carriage was recently reported, but large intra-and interregional variations were observed. We investigated the faecal carriage rates of ESBL-, AmpC-producing and ciprofloxacin non-susceptible Escherichia coli and Klebsiella spp. in healthy Norwegians. Methods: Rectal samples were obtained from 284 volunteers, together with demographic data and information on recent travel history. The rectal samples were screened by selective plating and E. coli and Klebsiella spp. identified using MALDI-TOF. Phenotypic and molecular characterization of resistant isolates was also performed. Results: ESBL- or AmpC-producing E. coli and Klebsiella spp. were isolated from 4.9% and 3.2% of the study population, respectively. Carriage of ciprofloxacin non-susceptible isolates was detected in 9.9% of the volunteers. Molecular typing of ESBL/plasmid-mediated AmpC (pAmpC)-producing isolates suggested an allodemic situation rather than the dissemination of a specific clone in the Norwegian community. In concurrence with previous findings, travel to South-East Asia was associated with increased risk of carrying resistant E. coli or Klebsiella spp., highlighting the contribution of factors such as increased global mobility in erasing the boundaries between healthcare and community settings when it comes to spread of resistant bacteria. Conclusions: Overall, our study recognised Norway as a low-incidence country for faecal carriage of resistant bacteria among healthy individuals. Furthermore, our work denoted the importance of healthy humans as a reservoir for transmission of antibiotic resistant E. coli and Klebsiella spp.
Faecal carriage; ESBL; Ciprofloxacin; Norway; Escherichia coli; Klebsiella
The prevalence of antimicrobial resistance (AMR) is
increasing worldwide, and represents a serious threat to the
global health [1, 2]. Enterobacteriaceae is one of the most
common causes of both nosocomial and community
acquired bacterial infections . Traditionally, betalactam
antibiotics and fluoroquinolones have been the treatment of
choice for infections originating from Gram negative bacilli
[2, 4]. However, the emergence of extended-spectrum
betalactamases (ESBL and plasmid-mediated AmpC; pAmpC)
and different mechanisms of ciprofloxacin resistance have
rendered such infections notoriously challenging to treat
and cure [4, 5].
Faecal carriage of ESBL probably represents the most
important reservoir for infections with ESBL-producing
Enterobacteriaceae [6, 7]. However, differences in the
prevalence of gut colonization with ESBL-producing
bacteria are observed both between and within regions,
and the rates of colonization with ESBL-producing
bacteria are generally increasing [8, 9]. Overall, an annual
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worldwide increase of 5.38% has been suggested .
CTX-M is the dominating ESBL-variant in communities
worldwide . Among clinical isolates found in
Scandinavia, the predominant genotype is blaCTX-M-15 [10–12].
Data on community carriage of pAmpC is more limited,
but it represents an important mechanism of resistance
to extended-spectrum cephalosporins , although less
common than ESBLs .
Reports on faecal colonization of ciprofloxacin-resistant
Enterobacteriaceae are often based on the proportions
of quinolone resistance in ESBL screening isolates,
rather than screening for ciprofloxacin resistance in the
first place. These observations may therefore be biased
due to a significant association between ESBL production
and ciprofloxacin resistance . Prevalence studies in
which ciprofloxacin resistance has been the primary
criterion for selection are less frequent. The most recent data
available corresponds to pre-travel colonization rates from
studies reporting on travel-associated acquisition of
resistant bacteria [16, 17].
Traditionally, Scandinavia is regarded as a low incidence
area for antibiotic resistance . Previous reports on
faecal carriage in Sweden and Denmark confirm a favourable
situation compared to most of Europe, including carriage
among healthy volunteers [19–21]. In Norway, data on
ESBL prevalence in clinical isolates is available through
the Norwegian antibiotic resistance surveillance system
(NORM). Two Norwegian studies report on faecal
carriage rates of AMR bacteria. Rettedal et al. found that
2.9% and 0.3% of healthy pregnant women were colonised
by ESBL-producing or AmpC-producing E. coli,
respectively , whereas Jørgensen et al. observed an overall
ESBL carriage rate of 15.8% in patients with diarrhoea,
ranging from 10.3% in patients with no recent travel
history to 56.3% in patients with a history of recent travel to
The primary objectives of this study were to
determine the prevalence of ESBL/AmpC-producing and
ciprofloxacin-resistant E. coli and Klebsiella spp. in
healthy people in Norway. The data obtained may be used
as an initial measurement in a time series evaluation of
the prevalence of carriage among healthy humans in
our country. In addition, we wanted to phenotypically
characterise resistant isolates, and to determine the
ESBL/pAmpC genotypes of the isolates identified.
Participants and collection of faecal samples
Healthy Norwegians volunteered to participate in the
study from October 2014 to March 2016. They were
recruited by general practitioners located in different parts
of Norway, at health-related universities and other health
institutions. Exclusion criteria were as follows: 1) recent
acute gastroenteritis, 2) chronical illness which implies
immunosuppression, 3) repeated hospitalisations, and 4)
use of antibiotics within the past year. In a written
questionnaire, each participant provided information on age,
gender, county of residence, and travel abroad during the
past 3 and 12 months. They also provided a faecal sample
from their rectum using FecalSwab™ (Copan Italy, Brescia,
Italy), and delivered it by mail together with the
questionnaire to the National reference laboratory of
enteropathogenic bacteria at the Norwegian Institute of Public Health
(NIPH). Samples and questionnaires were identified by
study-ID numbers only. The samples were analysed upon
arrival, or stored at -70 degrees until analysed. All
participants provided informed consent.
Isolation of resistant E.coli and Klebsiella spp.
From each participant’s sample, the rectal swab was
removed and 100 μl of Cary-Blair medium were spread onto
MacConkey agar plates, supplemented with cefotaxime
(1 mg/L; Duchefa Biochemie, Haarlem, the Netherlands),
ceftazidime (2 mg/L; Sigma Aldrich, St. Louis, US),
ciprofloxacin (0,125 and 0,25 mg/L; Fluka Chemicals, Buchs,
Switzerland), and one control plate without
supplementation. In addition, 200 μl and 400 μl of Cary-Blair medium
were added into two separate tubes with MacConkey broth
supplemented with 1 mg/L cefotaxime. Agar plates and
broths were incubated overnight at 35 °C. The following
day, the broths were spread to MacConkey agar plates with
cefotaxime (1 mg/L), and incubated overnight at 35 °C.
Single colonies of E.coli or Klebsiella spp. were selected
from the different plates. If multiple morphologies were
observed, all unique morphotypes were selected. Species
identification was performed using MALDI-TOF MS
(Bruker Daltonik GmbH, Bremen, Germany). Samples
that yielded no, or sparse growth on the MacConkey
control plate, were excluded from the study.
Antibiotic susceptibility testing and ESBL identification
Antibiotic susceptibility testing (AST) against ciprofloxacin
was performed using MIC (minimal inhibitory
concentration) strip test (Liofilchem, Abruzzi, Italy), according
to EUCAST guidelines and interpreted according to
NORDICAST Clinical Breakpoints . AST against a
broad range of other antibiotics (ampicillin,
amoxicillinclavulanic acid, azetronam, cefotaxime, cefoxitin,
cefuroxime, ceftazidime, gentamicin, imipenem, meropenem,
mecillinam, nalidixic acid, piperacillin-tazobactam, and
temocillin) was performed using the disc diffusion (BD
Sensi-Disc, Becton-Dickinson, Sparks, USA) according to
EUCAST guidelines (EUCAST disk diffusion method, v.
5.0, January 2015), and interpreted according to
NORDICAST Clinical Breakpoints (or EUCAST
epidemiological cut-offs (ECOFFs), if clinical breakpoint were not
available). For meropenem, isolates with a zone diameter
narrower than the NORDICAST screening breakpoint
(<27 mm) were submitted to the Norwegian National
Advisory Unit on Detection of Antimicrobial Resistance
(K-res) for further characterization. Phenotypic
confirmation of ESBL or AmpC was performed using the
Total ESBL + AmpC Confirm kit (Rosco Diagnostica,
Denmark). This kit utilises tablets containing cefotaxime
or ceftazidime in combination with β-lactamase inhibitors
(i.e. clavulanate and/or cloxacillin) to detect ESBL and
AmpC production phenotypically. Results were interpreted
according to manufacturer's instructions, by comparing
the inhibition zones of the different tablets and thereby
identifying synergy effects. E.coli ATCC25922 and two
strains of K. pneumoniae (CTX-M 15) and Providencia
stuartii (CMY-2), obtained from K-res, were used as
controls. Isolates either resistant or intermediately sensitive
to ciprofloxacin were categorised as ciprofloxacin
nonsusceptible, whereas isolates non-susceptible to three or
more groups of antibiotics were categorised as multi-drug
resistant (MDR; ).
Differentiation of multiple isolates obtained from the
An in house MLVA scheme was used together with
phenotypic resistance profiles to differentiate multiple ESBL/
AmpC-producing isolates from the same faecal sample.
Bacterial DNA was prepared by boiling lysis (100 °C for
15 min, followed by 3 min. centrifugation at 14000 × g).
MLVA was performed by targeting 10 tandem repeats
(CVN001, CVN002, CVN003, CVN004, CVN007,
CVN014, CVN015, CCR002, CVN016, CVN017), as
previously described .
Molecular characterization of ESBL and pAmpC types
E. coli and Klebsiella spp. displaying an ESBL or AmpC
phenotype were screened for ESBL-and pAmpC
encoding genes by multiplex PCR. The primers used for PCR
are listed in Additional file 1: Table S1. PCR was carried
out as previously described . PCR products were
separated and visualised using the Bioanalyzer DNA
1000 system (Agilent Technologies, Santa Clara, US)
according to the manufacturer’s protocol.
Isolates with positive PCR results were selected for
whole-genome sequencing (WGS) to further
characterise the mechanism of resistance. Cells were grown over
night in Luria Broth (Sigma Aldrich, St. Louis, US) with
shaking at 35 °C, and DNA was extracted from 1 ml
culture using the Wizard Genomic DNA Kit (Promega,
Madison, US) according to the manufacturer's
instructions. Quantification of total DNA was performed using a
Qubit fluorometer (Life Technologies, Waltham, US), with
broad range or high specificity reagents as appropriate.
The sequencing libraries were prepared with the Nextera
XT DNA Sample Prep Kit (Illumina, Eindhoven, the
Netherlands) and sequencing was performed using a
MiSeq sequencer (Illumina) in a 2 × 150-bp paired-end
run. AMR genes were identified from WGS data using
ResFinder  and Arg-annot .
Statistical analyses were performed using SPSS (SPSS Inc.,
Chicago, Illinois). Chi squared test and Fisher’s exact test
were used, as appropriate. A p-value of <0.05 was
considered statistically significant. Odds Ratios (OR) with 95%
confidence intervals (95% CI) were computed manually.
For calculations of OR, the group “Not travelled/Travelled
within Scandinavia” was treated as a reference.
Rectal samples were obtained from 308 healthy
individuals, of whom 296/308 (96.1%) returned the
questionnaire (Fig. 1). Samples from an additional 12/308 (3.9%)
volunteers showed no growth on control media, and
were therefore excluded from the study, leaving the
remaining 284/308 (92.8%) eligible for further analyses.
174/284 (61.3%) were female and 102/284 (35.9%) were
male (Table 2). Eight participants did not provide gender
information. Fifty-three subjects (18.7%) belonged to the
age category 18-29 years, whereas 108 (38.0%), 76 (26.8%)
and 44 (15.5%) belonged to the age categories 30-49 years
50-64 years 65-84 years, respectively (Table 2). Three
subjects (1.0%) did not provide information about age. The
volunteers resided in fourteen of 19 different Norwegian
counties (results not shown).
Prevalence and characterization of ESBL
ESBL-producing strains were isolated from 14/284 healthy
volunteers (4.9%). From the fourteen positive samples, 16
different ESBL-producing isolate were obtained, i.e. two
individuals carried more than one ESBL-producing isolate.
Overall, 15/16 isolates were identified as E.coli (93.8%)
and 1/16 (6.2%) as K. pneumoniae. One of the two carriers
of more than one isolate was colonised with both E.coli
and K. pneumoniae.
The β-lactamase genes of all ESBL-producing isolates
were further characterised by PCR and sequencing. For
one ESBL-producing isolate, SHV was detected by PCR,
but WGS yielded no known ESBL-gene, and this isolate
will therefore be further investigated. Among the
remaining isolates, CTX-M accounted for 13/16 (86.7%)
of the ESBL production, with CTX-M1 and CTX-M9 as
the dominant CTX-M groups (Table 1). blaCTX-M-15 was
the dominant genotype (6/16; 37.5%). One isolate showed
co-occurrence of blaCTX-M-1 and blaTEM-210, and in an
additional 4/16 (25%) isolates a variant of blaCTX-M was
detected in combination with blaTEM-1B. The E.coli and K.
pneumoniae isolates originating from the same volunteer
harboured blaCTX-M-15 and blaSHV-12, respectively.
Fig. 1 Study protocol for ESBL- and AmpC prevalence. Study protocol for investigating prevalence of extended-spectrum beta-lactamase (ESBL
and AmpC)-producing E.coli and K. pneumoniae among healthy Norwegians, in travellers and non-travellers. One volunteer was carrier of both
ESBL- and AmpC-producing isolates
ESBL-producing E. coli and K. pneumonia isolates
displayed resistance to multiple other classes of antimicrobial
agents as well (Fig. 2 and Additional file 1: Table S2), and
all of them (16/16; 100%) were by definition MDR. One
isolate displayed resistance against 8 antimicrobial drug
groups, and 10 antimicrobial agents (Fig. 3a).
Prevalence and characterisation of pAmpC
Furthermore, 9/284 (3.2%) of the volunteers were
colonised by AmpC-producing E.coli. The methodology used
Table 1 The dominating ESBL-genotypes isolated from E.coli and
Klebsiella pneumoniae from healthy people in Norway. For one of
the isolates obtained, the genotype could not be determined
ESBL gene identified
blaCTX-M1 + blaTEM-210
for phenotypic characterisation does not distinguish
between chromosomally encoded and pAmpC resistance
and only 2/9 of the isolates were confirmed as pAmpC
by PCR and WGS. Isolates from which negative PCRs
were obtained were considered hyperproducers of
chromosomally encoded AmpC. The two pAmpC-producing
isolates were obtained from two different individuals,
resulting in a carriage rate of 0.7% (2/284) for pAmpC.
Of the two pAmpC-producing isolates, one was found
to harbour blaDHA-1 and the other blaCMY-2 in
combination with blaTEM1-C (Table 1). No co-producers of ESBL
and pAmpC were recovered; however, one volunteer
carried both an ESBL (blaCTX-M-15) - and a
pAmpCproducing isolate (blaDHA-1). The nine AmpC-producing
isolates displayed resistance to additional classes of
antibiotics (Fig. 4 and Additional file 1: Table S3). 4/9 (44.4%) of
the isolates were MDR (Fig. 3b). The isolates that
harboured blaDHA-1 and blaCMY-2+TEM-1C were resistant to
5 and 7 antimicrobial drug groups, respectively.
Prevalence and characterization of isolates
non-susceptible to ciprofloxacin
A total of 28/284 (9.9%) volunteers carried E.coli or
Klebsiella spp. isolates that had MIC-values indicating
non-susceptibility to ciprofloxacin; of which half (14/
28) carried isolates displaying intermediate resistance
Fig. 2 Antibiotic susceptibility among ESBL-producing isolates. Antibiotic susceptibility of faecal ESBL-producing E.coli and K. pneumoniae isolated
from healthy Norwegians. Resistant (black); intermediate (grey), susceptible (white)
to ciprofloxacin (MIC 0.5-1 mg/L; Fig. 5 and Additional
file 1: Table S4). From the 28 subjects, 33 isolates were
recovered; of which 5/33 (15.2%) were ESBL positive and
4/33 (12.1%) were AmpC positive. Of the remaining, 4/24
(16.7%) were K. pneumoniae and 20/24 (83.3%) were E.coli.
The susceptibility of the ciprofloxacin non-susceptible
isolates to several other classes of antibiotics was also tested
(Fig. 5 and Additional file 1: Table S4) and 12/24 (50.0%)
were categorised as MDR, including all the K. pneumoniae
isolates (Fig. 3c). Meropenem zone diameters just below
the NORDICAST screening breakpoint were observed
for two non-ESBL/AmpC-producing ciprofloxacin
nonsusceptible isolates (Fig. 3c, 5 and Additional file 1:
Table S4), and these isolates were thus submitted to
Kres for further characterisation. However, none of the
isolates were found to be carbapenemase-producing.
The ECOFF values for ciprofloxacin are set
considerably lower than the clinical breakpoint for both E.coli
and Klebsiella spp. If ECOFFs had been applied to
categorise susceptibility in the present study, 66 ciprofloxacin
non-susceptible isolates were obtained from 56/284
The associations between faecal carriage of ESBL/
AmpC-producing- and/or ciprofloxacin non-susceptible
E. coli and Klebsiella spp. and various individual factors
were assessed (Table 2). There were no significant
associations between colonisation with resistant bacteria,
and gender, age or county of resident (not shown)
among the healthy volunteers.
Univariate analysis of travel information recognised
travel to South-East Asia during the last 3 months as a
risk factor of faecal carriage of ESBL/AmpC-producing
E. coli or Klebsiella spp. (OR 61.67; 95% CI 5.82-653.13),
whereas travel to South-East Asia during the last
12 months was associated with increased risk of faecal
carriage of ESBL/AmpC-producing ciprofloxacin
nonsusceptible E. coli or Klebsiella spp. (OR 100; 95% CI 3.34
to 2997.88). ESBL/AmpC-producing isolates were
recovered from 75% (3/4) of travellers to South-East Asia
compared to 3.9% (11/280) for those with no recent travel
history or those who had travelled to other regions during
the last 3 months (Table 2). Of note, all three carriers of
more than one ESBL/AmpC-producing isolate had been
visiting South-East Asia. Furthermore, travel to multiple
WHO regions during the last 3 months (OR 6.24; 95% CI
1.45-26.86) was significantly associated with faecal
carriage of ciprofloxacin non-susceptible E. coli or Klebsiella
spp. The prevalence of ciprofloxacin non-susceptible
isolates among travellers to multiple WHO regions
(Additional file 1: Figure S2) during last 3 months was
27.3% (3/11) compared to 7.0% (19/273) for those who
did not travel or travelled to one region only (Table 2).
Fig. 3 (See legend on next page.)
(See figure on previous page.)
Fig. 3 Antibiotic resistance profiles for resistant isolates. The number of isolates that displayed each unique resistance profile among the a)
ESBLproducing, b) AmpC-producing, and c) ciprofloxacin non-susceptible E.coli and K. pneumoniae isolates obtained from healthy Norwegians. The
numbers on the x-axis denote the number of isolates with that exact resistance profile. Both resistant and intermediate phenotypes are included.
Klebsiella spp. are intrinsically resistant to ampicillin, and profiles recovered from isolates identified as Klebsiella spp. are marked with an asterisk (*)
The present study was undertaken to assess community
carriage rates of antibiotic resistant E. coli and
Klebsiella spp. in Norway. From 284 volunteers, we found
that 4.9% were colonised with ESBL- and 3.2% with
AmpC-producing E. coli or Klebsiella spp. Of the latter,
the proportion of plasmid-mediated resistance
corresponded to a carriage rate of pAmpC-producing E. coli or
Klebsiella spp. of 0.7%. Our results were thus consistent
with an ESBL colonisation rate of 3-6% in Europe . In
Scandinavia, the ESBL carriage rate has traditionally been
lower than that in other parts of Europe; however,
numbers are rising here as well. A recent report from
Sweden documented that the faecal carriage among
elderly subjects varied from 8.7% to 11%, depending on the
living situation . Our findings thus indicate a lower
carriage rate among healthy individuals in Norway than in
Sweden. Still, an increase in cephalosporin resistance rates
has been observed among clinical isolates in Norway from
the turn of the century , and it is likely that the
colonisation level of healthy individuals in the country is
following the same trend.
In accordance with epidemiology worldwide , the
majority of ESBL-positive isolates in the present study were
E.coli and the predominant ESBL allele was blaCTX-M-15.
However, the diversity of genotypes detected suggests
simultaneous community spread of various ESBL genotypes,
as opposed to spread of this particular ESBL gene. An
overlap in the distribution of genotypes between
community and clinical settings is observed for both ESBL and
pAmpC, indicating that resistant microbial populations
are shared between hospitals and community .
However, the ratio between ESBL/AmpC-producing Klebsiella
spp. and E.coli is considerably lower than the ratio
observed in healthcare settings , indicating a difference
in transmission dynamics between E. coli and Klebsiella
Fig. 4 Antibiotic susceptibility among AmpC-producing isolates. Antibiotic susceptibility of faecal AmpC-positive E.coli isolated from healthy
Norwegians. Resistant (black); intermediate (grey), susceptible (white)
Fig. 5 Antibiotic susceptibility among ciprofloxacin non-susceptible isolates. Antibiotic susceptibility of faecal ciprofloxacin non-susceptible E.coli
and K. pneumoniae isolated from healthy Norwegians. Resistant (black); intermediate (grey), susceptible (white)
spp. This is in line with previous findings, and suggests
that ESBL/AmpC-producing E.coli is more likely to spread
in the community [30, 31].
Ciprofloxacin non-susceptible isolates were recovered
from 28/284 (9.3%) volunteers. A positive correlation has
been reported between total usage of fluoroquinolones
and the prevalence of fluoroquinolone non-susceptibility
among clinical isolates in Norway , mirroring the
internationally observed situation . There is a notable
lack of recent data on community carriage of ciprofloxacin
resistant isolates in Europe, and our study thus adds new
and significant information on the situation. Increased
knowledge on prevalence and trends in resistance
development can, together with information on antibiotic use,
assist in the evaluation of any measures taken to control
NORDICAST clinical breakpoints rather than ECOFFs
were primarily applied to categorise susceptibility herein.
For ciprofloxacin, the application of ECOFFs, in addition
to clinical breakpoints, enabled us to differentiates between
‘percentage clinical resistant’ and ‘percentage decreased
susceptible’ isolates. Indeed, considerable differences
were observed between the two populations: ~15% of
participants can be suspected to carry isolates with an
acquired or mutational mechanism of ciprofloxacin
resistance of unknown clinical relevance. Decreased
susceptibility to fluoroquinolones is associated with
decreased clinical responses to fluoroquinolones in
Salmonella infections . The marked differences in
prevalence obtained by the application of clinical
breakpoints compared to ECOFF values demonstrate
the relevance of applying both cut-offs in studies like
the present, as application of only clinical breakpoints
can mask important shifts in MICs.
In our study, we found that all ESBL/pAmpC-producing
and > 50% of the ciprofloxacin non-susceptible isolates,
including all ciprofloxacin non-susceptible Klebsiella isolates
were MDR. High rates of community faecal carriage of
MDR isolates contribute to an increase in colonisation
pressure and highlight the need for appropriate infection
Several reports identify travel as a risk factor of
acquiring EBSL-producing isolates, with India and South-East
Asia as high risk travel destinations [8, 34–36]. This is in
agreement with our findings. A Dutch study found that
travel to Asia is also a risk factor of being colonised with
Table 2 Characteristics of the participants and associations with faecal carriage of resistant bacteria
Participants Isolates with ESBL/AmpC
(% of total) production alone
Isolates with ciprofloxacin-non Isolates with both ESBL/AmpC
susceptibility alone and ciprofloxacin non-susceptibility
Geographic regions# visited
last 3 months
Geographic regions# visited
last 12 months
127 (95.5) .051
Europe (outside Scandinavia)
Europe (outside Scandinavia)
127 (95.5) .089
163 (93.6) .746
163 (93.6) .375
EAP = ESBL-or AmpC-producing, CNS = ciprofloxacin non-susceptible. Significant p-values are given in bold. Carriers of multiple isolates are represented one time
per isolate if the isolates belong to different resistance groups, and percentage in the table may thus deviate from percentage presented in the text. E.g. both
ciprofloxacin non-susceptible isolates and AmpC-producing ciprofloxacin non-susceptible isolates were recovered from two subjects, whereas both an
ESBL-producing isolate and an AmpC-producing ciprofloxacin non-susceptible isolate were obtained from a third subject. Consequently, the first two subjects are represented
both in the CNS and the EAP + CNS columns, while the third subject is represented both in the EAP and the EAP + CNS columns
*Significantly different from the Not travelled/travelled within Scandinavia group, which was treated as a reference (p < 0.05)
**Significantly different from the Not traveled/travelled within Scandinavia group, which was treated as a reference (p < 0.005)
ciprofloxacin-resistant isolates . The data presented
herein recognise travel to multiple WHO regions within
the same time frame, as a risk factor for being colonised
with ciprofloxacin non-susceptible E. coli and
Klebsiella spp. The majority of the visitors to multiple WHO
regions reported South-East Asia or Western Pacific as
one of the regions visited (Additional file 1: Figure S1).
This is in line with the findings of Reuland et al. .
A potential limitation of our study was that the
participants were not representative for the Norwegian population
according to gender and county of residence. Most of the
participants were female and live in the eastern part of
Norway. However, only minor geographical differences in
the prevalence of ESBL have been observed among clinical
isolates in Norway , and it is likely that this observation
can be extrapolated into community settings as well.
Moreover, many of the volunteers were recruited via general
practitioners and medical teaching institutions, where it is
possible that augmented exposure to resistant bacteria can
contribute to an overestimation of prevalence. Rigid
exclusion criteria were therefore applied to reduce biases related
to skewed individual recruitments. The employment of
stringent exclusion criteria confounds recruitment of
participants to the study, but adds validity to the associated
findings. However, conclusions based on results from regions
with small numbers of travellers should be made with
caution. Furthermore, the sensitivity may have been decreased,
because of insufficient self-sampling, storage conditions and
by the sending of samples by regular mail. However, a
sampling kit optimised for transport and preservation of faecal
samples were chosen to minimise this effect.
The frequency of AMR in clinical isolates in Norway is
well-documented through NORM, and although
increasing, it continues to be low when compared to other parts
of Europe. An ambitious national strategy against
antibiotic resistance, together with the low prevalence of
antibiotic resistance in Norway, offers a unique opportunity to
gain knowledge on how to effectively prevent faecal
colonisation with resistant Enterobacteriaceae in the
community. As stated in the WHO Global action plan on AMR
, surveillance is one of the main strategic objectives
for preventing further spread and development of AMR
worldwide. In order to strengthen our knowledge base, it
is pivotal to monitor AMR trends consistently over time.
Community carriage rates constitute an important
source for information regarding the AMR situation in
different populations, and AMR surveillance systems
should thus be expanded to cover community carriers
as well, e.g. by implementing a sampling campaign as
part of the European Antibiotic Awareness Day.
In conclusion, our study recognises Norway as a country
with low prevalence of AMR carriage in the intestinal
flora in healthy individuals. ESBL- producers were
obtained from 4.9% of the study population, whereas
AmpC-producers were obtained from 3.2%. Of the latter,
the proportion of pAmpC corresponded to an overall
carriage rate of 0.7%. In comparison, the carriage rate of
ciprofloxacin non-susceptible isolates was 9.9%. A high
proportion of intermediately ciprofloxacin resistant
isolates may represent a shift in the ciprofloxacin MIC away
from fully susceptible wild-type populations. Overall, our
study denotes the importance of healthy humans as a
reservoir for transmission of antibiotic resistant E. coli and
Klebsiella spp., even in low incidence countries.
Additional file 1: Supplemental material. (DOCX 32 kb)
AMR: antimicrobial resistance; AST: antibiotic susceptibility testing;
ECOFF: epidemiological cut-off; ESBL: extended-spectrum betalactamases;
EUCAST: European committee on antimicrobial susceptibility testing;
K-RES: Norwegian National Advisory Unit on Detection of Antimicrobial
Resistance; MDR: multidrug resistant; MIC: minimal inhibitory concentration;
NIPH: Norwegian Institute of Public Health; NORM: Norwegian surveillance
system for antimicrobial resistance (Norsk overvåkingssystem for
antibiotikaresistens hos mikrober); UTI: urinary tract infection; WHO: World
We are grateful to all volunteers and to the general practitioners who
contributed in recruitment of volunteers. We thank the personnel at the
National reference laboratory of enteropathogenic bacteria at NIPH for
excellent technical assistance, with a special thanks to Liselotte Buarø,
Marianne Sunde and Irene Rauk. We also thank the Norwegian National
Advisory Unit on Detection of Antimicrobial Resistance (K-res), Tromsø,
Norway, for kindly providing two of the control strains used in the study.
Conceived and designed the study: ML URD ALW. Performed the
experiments: CRU MS SB. Analysed the data: CRU MS SB. Contributed
reagents/materials/analysis tools: ML URD ALW. Drafted the manuscript:
CRU MS. Revision of manuscript: SB ML URD ALW. All authors have read
and accepted the final manuscript.
The authors declare that they have no competing interests.
Consent for publication
Ethics approval and consent to participate
The study was approved by Regional committees for medical and health
research ethics, Norway (2014/419/REK sør-øst D). All participants provided
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