Faecal Carriage of Gram-Negative Multidrug-Resistant Bacteria among Patients Hospitalized in Two Centres in Ulaanbaatar, Mongolia
Faecal Carriage of Gram-Negative Multidrug- Resistant Bacteria among Patients Hospitalized in Two Centres in Ulaanbaatar, Mongolia
Bayaraa Baljin 0 1
Ganbaatar Baldan 0 1
Battogtokh Chimeddorj 0 1
Khosbayar Tulgaa 1
Batbaatar Gunchin 0 1
Tsogtsaikhan Sandag 0 1
Klaus Pfeffer 1
Colin R. MacKenzie 1
Andreas F. Wendel 1
0 Department of Microbiology and Immunology, School of Biomedicine, Mongolian National University of Medical Sciences , Ulaanbaatar , Mongolia , 2 Department of Molecular Biology and Genetics, School of Biomedicine, Mongolian National University of Medical Sciences , Ulaanbaatar , Mongolia , 3 Institute of Medical Microbiology and Hospital Hygiene, University Hospital, Heinrich-Heine-University , D uÈsseldorf , Germany
1 Editor: Patrick Butaye, Ross University School of Veterinary Medicine , SAINT KITTS AND NEVIS
Gram-negative multidrug-resistant organisms (GN-MDRO) producing β-lactamases (ESBL, plasmid-mediated AmpC β-lactamases and carbapenemases) are increasingly reported throughout Asia. The aim of this surveillance study was to determine the rate of bacterial colonization in patients from two hospitals in the Mongolian capital Ulaanbaatar. Rectal swabs were obtained from patients referred to the National Traumatology and Orthopaedics Research Centre (NTORC) or the Burn Treatment Centre (BTC) between July and September 2014, on admission and again after 14 days. Bacteria growing on selective chromogenic media (CHROMagar ESBL/KPC) were identified by MALDI-ToF MS. We performed susceptibility testing by disk diffusion and PCR (blaIMP-1, blaVIM, blaGES, blaNDM, blaKPC, blaOXA-48, blaGIM-1, blaOXA-23, blaOXA-24/40, blaOXA-51, blaOXA-58, blaOXA-143, blaOXA-235, blaCTX-M, blaSHV blaTEM and plasmid-mediated blaAmpC). Carbapenemase-producing isolates were additionally genotyped by PFGE and MLST. During the study period 985 patients in the NTORC and 65 patients in the BTC were screened on admission. The prevalence of GN-MDRO-carriage was 42.4% and 69.2% respectively (p<0.001). Due to the different medical specialities the two study populations differed significantly in age (p<0.029) and gender (p<0.001) with younger and more female patients in the burn centre (BTC). We did not observe a significant difference in colonization rate in the respective age groups in the total study population. In both centres most carriers were colonized with CTX-M-producing E. coli, followed by CTXM-producing K. pneumoniae and CTX-M-producing E. cloacae. 158 patients from the NTORC were re-screened after 14 days of whom 99 had acquired a new GN-MDRO (p<0.001). Carbapenemases were detected in both centres in four OXA-58-producing A. baumannii isolates (ST642) and six VIM-2-producing P. aeruginosa isolates (ST235). This study shows a high overall prevalence of GN-MDRO in the study population and highlights
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
Funding: This work was supported by the Medical
Faculty of the Heinrich-Heine-University,
DuÈsseldorf, Germany, in collaboration with the
ESCMID Study Group on Genomic and Molecular
Diagnostics (ESGMD), Basel, Switzerland. and by
the DAAD-PAGEL program (54448058).
Competing Interests: The authors have declared
that no competing interests exist.
the importance of routine surveillance, appropriate infection control practice and antibiotic
prescribing policies to prevent further spread especially of carbapenemases.
Antimicrobial resistance is an increasing threat to health systems worldwide leading to
treatment failure, high treatment costs and increased mortality. The rise of β-lactamase-producing
Gram-negative multidrug-resistant organisms, such as extended-spectrum β-lactamase
(ESBL)-, plasmid-mediated AmpC β-lactamases or carbapenemase-producing bacteria is of
particular concern . The main reservoirs of the different Gram-negative species are the
environment and the gut of animals and humans and these organisms may cause health-care
associated or community-acquired infections in humans. Due to the presence of co-resistance to
other antibiotic classes (especially fluoroquinolones and aminoglycosides) the antibiotic
treatment of infections caused by these organisms is a challenge [
]. The dissemination of these
βlactamase enzymes is facilitated by both horizontal transfer via mobile genetic elements
(integrons, transposons and plasmids) and bacterial clonal proliferation [
]. Globally antimicrobial
resistance surveillance data varies from country to country, ranging from no data to effective
national surveillance programs . Asia, which is known for its high prevalence of
ESBL-producing Enterobacteriaceae, metallo-β-lactamases like NDM-1 and nosocomial
multidrugresistant A. baumannii, represents one of the epicentres of antimicrobial drug resistance [
The ESBL carriage rates in the community in Asia are amongst the highest worldwide
(exceeding 50% in some studies), the lowest reported from Europe and North America [2, 4±6]. With
regards to Mongolia, the monitoring system of multidrug-resistant bacteria is less well
developed, mainly due to a limited diagnostic infrastructure. Cultures are only taken when empiric
antibiotic therapy fails and numbers of hospital-associated infections are certainly
]. There is evidence pointing to presence of ESBL- and carbapenemase-producing
bacteria in Mongolia. A previous study has shown the spread of multidrug-resistant A.
baumannii, mainly carrying blaOXA-23-like or blaOXA-58-like genes, in hospitals . Other studies
have reported the presence of CTX-M enzymes in clinical E. coli and Klebsiella isolates in
clinical samples [
]. Additionally one of the major risk-factors for the development of
resistance, the uncontrolled use and misuse of antimicrobial drugs, is widespread in Mongolia
The aim of this cross-sectional study is to determine the carriage rate of
β-lactamase-producing Gram-negative multidrug-resistant bacteria (GN-MDRO) by patients on hospital
admission and the frequency of nosocomial acquisition. Subsequently the main mechanisms
of β-lactamase drug-resistance were explored among these GN-MDRO. In this study the term
GN-MDRO is defined as non-susceptibility to at least three antimicrobial categories as defined
by Magiorakis et al. [
Materials and Methods
Setting and sampling
The study was performed at two tertiary care hospitals providing specialized care located in
Ulaanbaatar, between July and September 2014. The National Hospital of Traumatology
and Orthopaedics (NTORC) has 260 beds and is divided into seven subunits/wards (intensive
care unit, neurosurgery, spinal surgery, orthopaedics, hand surgery, paediatric surgery and
trauma surgery). The 60-bed Skin Burn Treatment Centre (BTC) is comprised of three wards
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(children, adults and intensive care). Rectal swabs (eSwab, Copan Diagnostics, Italy) were
taken from in-patients referred to both hospitals on admission (up to the 3rd day of admission)
and a second sample collection was done of those remaining in the hospital after two weeks
Strain identification and susceptibility testing
Swabs were cultured on selective chromogenic media (CHROMagar ESBL and KPC,
CHROMagar, France) and plates were incubated for 24 h at 37ÊC. Bacteria with a distinct colonial
morphology and/or colour on media were subcultured on blood agar and were further
processed for identification (MALDI-TOF MS, and, in case of ambiguous results, VITEK 2
system, bioMeÂrieux, Germany). Antibiotic susceptibility testing (AST) by disk diffusion method
(Becton Dickinson, Germany) was performed on Mueller-Hinton agar with the antibiotics:
cefotaxime, ceftazidime, cefoxitin, ertapenem, imipenem, meropenem, ciprofloxacin,
gentamicin, tobramycin, tigecycline, chloramphenicol, nitrofurantoin and
trimethoprim-sulfamethoxazole. In case of carbapenemase production we further performed a colistin Etest (bioMeÂrieux,
Marcy l'Etoile, Germany). EUCAST breakpoints were used for AST result interpretation. In
Enterobacteriaceae β-lactamase resistance genes were identified following the EUCAST
screening cut-off values for ESBL, AmpC β-lactamases and carbapenemases. Exceptions to this
were Enterobacteriaceae with known inducible chromosomal AmpC β-lactamase
(Enterobacter spp., C. freundii, M. morganii, P. stuartii, Serratia spp. or H. alvei), where EUCAST
screening cut-off values for cefoxitin were not applied . In Pseudomonas spp. molecular detection
of carbapenemases was performed if the isolate was non-susceptible to ceftazidime and at least
one carbapenem (imipenem and/or meropenem). In Acinetobacter spp. molecular detection of
carbapenemases was performed if the isolate was non-susceptible to imipenem and/or
Molecular detection of β-lactamase genes
DNA preparation was performed from one colony by heating in a volume of 100 μl tris buffer
at 95ÊC for 10 minutes followed by centrifugation at 12000 × g. Based on the AST results the
supernatant was subjected to the following conventional and real-time multiplex PCRs to
detect the ESBL-, AmpC β-lactamase- and carbapenemase-encoding genes: blaIMP-1,
blaVIM-1like, blaVIM-2-like, blaGIM-1, blaNDM, blaGES, blaKPC and blaOXA-48 [
blaCTX-M-2, blaCTX-M-9 and blaCTX-M-8/-25 groups [
]; different plasmid-mediated ampC gene
subgroups (blaACC, blaFOX, blaCMY, blaDHA, blaMOX, blaLAT, blaBIL-1, blaACT-1 and blaMIR-1)
]. If results were negative for blaCTX-M, PCRs for blaTEM and blaSHV [
] were performed.
Acinetobacter spp. were additionally tested for relevant blaOXA genes (blaOXA-23, blaOXA-24/40,
blaOXA-51, blaOXA-58, blaOXA-143 and blaOXA-235) as described previously [
]. In case of the
isolated detection of blaOXA-51 gene we further checked for ISAba1 upstream of and adjacent
to blaOXA-51-like genes as previously described [
Phenotypic detection of ESBL, AmpC β-lactamases and
In the case of inconclusive results (AST pointing to a certain resistance mechanisms, but
negative PCR) confirmatory phenotypic methods were applied as follows: for ESBL a
combineddisk test (CDT) proposed by EUCAST  or MIC test strip cefepime/cefepime + clavulanic
acid (Liofilchem, Italy); for AmpC β-lactamases a MIC test strip cefotetan/cefotetan +
cloxacillin (Liofilchem, Italy); for carbapenemases an MBL imipenem/imipenem + EDTA MIC test
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strip (Liofilchem, Italy); or a modified-Hodge-Test as recommended by CLSI with a 10 μg
meropenem disk and/or a Rapidec1 CarpaNP Test (biomeÂrieux, France).
Genotyping of carbapenemase-producing bacteria
The genetic relatedness of the carbapenemase-producing isolates was investigated using MLST
as described previously for A. baumannii [
] and Pseudomonas aeruginosa [
PFGE with SpeI was performed of the VIM-2 producing P. aeruginosa isolates. DNA
separation was performed in 1% agarose in 0.5× TBE buffer using a CHEF-DR III System (Bio-Rad,
La Jolla, CA, USA) as described previously  under the following conditions: 6 V/cm with
an angle of 120Ê for 22 h with pulse times of 5 s to 45 s. As a marker we used a (45.5 kb± 1 Mb)
Lambda ladder from Biolabs (New England Biolabs, Hitching, UK). The strain relatedness was
calculated with GelCompar II software (version 5.1) in accordance with the Tenover criteria
]. Epidemiologically non-related clinical strains were used as a reference.
Genetic characterisation of VIM-2-producing P. aeruginosa
The complete class 1 integron sequence containing the blaVIM-2 cassette was resolved with
primers targeting conserved-sequences and the blaVIM-2 gene cassette. At the 3'-end we not
only targeted the common class 1 integron 3'-end composed of the qacEΔ1 gene overlapping
with the sul1 gene, but also the tniC gene associated in rare cases with VIM-2-carrying
integrons (e.g. described in [
]). The primers used are shown in Table 1. The PCR protocol
included 5 min denaturation at 95ÊC followed by 35 cycles of 1 min 95ÊC denaturation, 1 min
60ÊC annealing and 1 min 72ÊC elongation. Sequencing was performed at the Biological and
Medical Research Centre (BMFZ) core facility of the University of DuÈsseldorf using the Sanger
technique with cycle sequencing and dye-marked terminators (BigDyes, Applied Biosystems,
Darmstadt, Germany) using a 3130 xl Genetic Analyser (Applied Biosystems). Gel plugs of
chromosomal DNA were prepared for the PFGE and S1-nuclease digestion as previously
described and in-gel hybridisation was performed using a 32P-radiolabelled blaVIM-2-probe
(product of primers VIM2S1-F1 and VIM2S1-R2 (Table 1)) .
Statistical analysis was performed with SPSS 22.0.0. The Student t test was used for continuous
normally distributed (parametric) variables, the Mann-Whitney U test for variables that did
not follow a normal distribution and the χ2 test or Fisher's exact test for categorical variables.
The McNemar test was used to compare colonization rates at admission and after 14 days. All
association tests were 2-tailed and a value of p<0.05 was considered to be statistically
significant. 95% confidence intervals for proportions were calculated based on binomial distribution.
Nucleotide sequence accession number
The blaVIM-2 integron sequence was submitted to GenBank and has been allocated the
accession number KT768111.
The study was approved by the Ethics committee of the Mongolian National University of
Medical Sciences. Written informed consent was obtained from each patient (if minor from
the parents), before swabs were taken.
Percentages are rounded to one decimal place in the presentation of the results.
During the study period, a total of 1050 patients were screened for GN-MDRO carriage. 985
patients were sampled in the trauma hospital (NTORC), 65 patients in the burn hospital
(BTC) at admission. 158 out of 985 patients from the NTORC were re-screened after 14 days.
In the BTC no second swabs were obtained. The basic patient characteristics and significance
values are displayed in Table 2. The two hospital populations differed significantly in gender,
age and sex.
Prevalence of MDRO at admission and after 14 days
The prevalence of carriage of GN-MDRO on admission was 42.4% (95% CI [39.3, 45.5]) in the
NTORC and 69.2% (95% CI [58, 80.4]) in the BTC (Table 2). The overall prevalence was
44.2% (95% CI [41.2, 47.2]). Significantly more patients in the BTC compared to the NTORC
carried more than one GN-MDRO (32.3% vs. 5.7% resp., p<0.001) (Table 2). Analysis of
colonization in different age subgroups (<6 years, 7±17 years, 18±59 years and >60 years) did not
show a significant difference in the total study population or the NTORC. In the BTC children
(< 6 years) were significantly less colonized with GN-MDRO than adults (18±60 years) (51.7%
vs. 82.8% resp.; p = 0.012).
Of the 158 patients from the NTORC from whom an additional sample was obtained at day
14, 110 were GN-MDRO-positive after 14 days. A significant number of patients (n = 99,
p<0.001) acquired a new GN-MDRO, either a GN-MDRO for the first time or a second new
strain. Additionally, on the 14th hospital day the percentage of patients that carried more than
one strain rose from 3.1% to 13.3% (p = 0.001).
Characterization of species and β-lactamase genes
A total of 478 (NTORC) and 71 (BTC) different β-lactamase-producing GN-MDRO were
collected on admission; on day 14 (NTORC) 133 different β-lactamase-producing GN-MDRO
Total (n = 1050)
40, 0.5, 90
NTORC (n = 985)
41, 2, 90
BTC (n = 65)
19, 0.5, 68
cAmpC, chromosomal AmpC β-lactamase (phenotypic result, only taken into consideration in Enterobacteriaceae)
NTORC day 14 (n = 133) No.
BTC admission (n = 71) No.
were collected. A detailed overview of the species/resistance mechanism combinations of all
three groups are depicted in Table 3.
In both centers on admission most patients were colonized with CTX-M-producing E. coli
(NTORC: 38%; BTC: 53.8%; p = 0.01), followed by CTX-M-carrying K. pneumoniae (NTORC:
2.1%; BTC: 24.6%; p<0.001) and CTX-M-carrying E. cloacae (NTORC: 1.5%; BTC: 4.6%;
p = 0.09). On day 14 CTX-M group-producing E. coli remained the most abundant coloniser
(admission: 28.5%; day 14: 53.1%; p<0.001). Compared to admission the carriage rate on day
14 of ESBL-producing K. pneumoniae and E. cloacae rose from 1.3% to 9.5% (p = 0.001) and
from 0.6% to 7.6% (p = 0.001) respectively. In all three groups carriage with CTX-M-9
groupproducing E. coli was more common than with CTX-M-1 group-producing E. coli.
Interestingly, multiple patients carried two bacteria of the same species (especially E. coli) with
different CTX-M groups. Six E. coli isolates encoded ESBLs from both CTX-M-1 and CTX-M-9
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groups, two CTX-M-9 group-producing E. coli isolates co-expressed the plasmid-mediated
AmpC β-lactamase CMY-2. In all three groups, plasmid-mediated ampC resistance genes,
blaCTX-M-2 group and blaCTX-M-8/-25 group genes were only rarely detected. No carbapenemase
genes were detected in Enterobacteriaceae. OXA-carbapenemases were detected in a total of
ten A. baumannii isolates, all of which carried the constitutive blaOXA-51 gene and four
additionally carried the acquired blaOXA-58 gene. In the six blaOXA-51-only isolates an upstream
ISAba1 was not detected. VIM-2 metallo-beta-lactamase was found in six isolates of P.
aeruginosa (Table 3).
Antibiotic susceptibility testing
Of the 666 Enterobacteriaceae isolates all except one (CTX-M-producing P. agglomerans)
displayed non-susceptibility to cefotaxime and 55.5% non-susceptibility to ceftazidime. The
highest rate of resistance among Enterobacteriaceae for non-β-lactam antibiotics was observed for
trimethoprim-sulfamethoxazole (82%), gentamicin (51.4%) and ciprofloxacin (38.7%).
Carbapenem-resistance in Enterobacteriaceae was very low, six isolates of K. pneumoniae and two
isolate of E. cloacae were resistant to ertapenem. This was likely due to a combination of ESBL/
AmpC β-lactamase and porin loss as phenotypic and molecular results were negative for
carbapenemases. All six blaOXA-51-only A. baumannii isolates displayed intermediate
susceptibility to meropenem and susceptibility to imipenem. The other four blaOXA-58-carrying A.
baumannii and the blaVIM-2-carrying P. aeruginosa isolates were resistant to imipenem and
meropenem and showed co-resistance to all the other antibiotic groups tested except for
colistin. The results of antimicrobial susceptibility testing are shown in Table 4. Confirmatory
phenotypic testing did not reveal antimicrobial resistance, possibly mediated by a β-lactamase
gene not included in the PCR panel.
Integron sequencing and genotyping of carbapenemase-producing isolates
The blaVIM-2 gene in P. aeruginosa was present on a class 1 integron with a 3'-conserved
sequence consisting of a tniC gene. The integron array was composed additionally of the two
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aminoglycoside resistance genes aacA7 and aacC5b and the dihydrofolate reductase gene
dfrB5 (gene cassette array In559 according to the INTEGRALL database). The blaVIM-2 gene
was located on the chromosome. PFGE genotyping of the six P. aeruginosa isolates revealed
four isolates that were genetically related to each other and the remaining two were classified
as singletons. All blaVIM-2-carrying P. aeruginosa isolates were confirmed to be sequence type
235. All four blaOXA-58-carrying A. baumannii isolates were confirmed to be sequence type
The main finding in this study is a high colonization rate of Gram-negative
multidrug-resistant organisms (GN-MDRO) producing β-lactamases in the study population. In Mongolia,
there is little data available regarding antimicrobial resistance and to our knowledge this is the
first surveillance study that estimates faecal carriage of GN-MDRO. The high carriage rate of
GN-MDRO on admission (42.4% in the trauma hospital and 69.2% in the burn hospital) is
mainly due to dissemination of CTX-M-producing E. coli with more than one third of all
patients admitted to the trauma hospital and every second patient to the burn hospital being
colonized. ESBL-producing Klebsiella spp., Enterobacter spp. and other Enterobacteriaceae
were found at a much lower rate; unsurprisingly as in the community setting ESBL-producing
E. coli is known to play a bigger role, both as a normal intestinal commensal in humans and a
major pathogen [
]. E. coli and K. pneumoniae, the main species identified, are worldwide the
predominant organisms harbouring ESBL genes, the CTX-M enzymes representing the major
mechanism of 3rd generation cephalosporin resistance [
]. In all Enterobacteriaceae 3rd
generation cephalosporin resistance was nearly exclusively mediated by CTX-M-9 group and (to a
lesser extent) by CTX-M-1 group enzymes. Two Mongolian studies have reported the presence
of CTX-M enzymes in E. coli and Klebsiella isolates in clinical samples [
]. And a similar
spread of theses specific resistance gene groups were reported from China in E. coli, where the
CTX-M-9 group was also the most abundant type .
On a global scale the carriage rate of ESBL-producing Enterobacteriacae in the community
differs greatly ranging from low-prevalence countries like Northern-Europe to high prevalence
regions like South-East Asia [
]. The observed high carriage rate at admission in this study is
comparable to data from neighbouring China, where an alarming high prevalence of MDRO
has been described, e.g. a 42% carriage rate of ESBL-producing Enterobacteriaceae in healthy
]. Interestingly in the bordering province Inner Mongolia 57% of
communityacquired E. coli infections were ESBL producers [
]. The main reservoirs of the different
Gram-negative species are the environment (city and hospital) and the gut of animals and
humans, which explains the possible routes of acquisition [
]. A major risk factor for resistance
development is the unregulated antibiotic consumption. Antimicrobials, despite the existing
laws in Mongolia, are commonly purchased without prescription [
]. We also collected data
about recent antibiotic therapy from a subgroup of 631 patients at admission to the trauma
centre. As the data collection was anonymous no correlations can be made to the
GN-MDROcarrier status. Nevertheless 50% had taken antibiotics within the six months prior to admission
(data not shown).
Our study also highlights the acquisition of GN-MDRO within the hospital setting. In the
patients of whom swabs were taken after two weeks a significant number of patients (62.7%)
were colonized with a new GN-MDRO and carried more than one GN-MDRO. The carriage
rate of typically hospital-acquired multidrug-resistant species like Klebsiella spp. was more
pronounced in the hospital setting. This can possibly be explained by nosocomial
transmission, probably due to a less rigorous infection control practice in the hospital. Little is known
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about hospital-associated infection rates in Mongolia and resistance in clinical isolates since a
surveillance system is not well established [
]. On the other hand, pre-hospital (asymptomatic)
colonization is often only revealed once selection pressure is exerted in the hospital setting by
prescription of antibiotics, so the high number might not reflect the true intrahospital
transmission rate. The predominant role of ESBL-producing E. coli may support this hypothesis.
From the clinical point of view, this data of a high ESBL carrier rate is alarming as many
critically ill patients in Mongolia are treated initially with 3rd generation cephalosporins. For
severe ESBL-driven infections, carbapenems are the drugs of choice. Unfortunately,
carbapenems are not widely available in Mongolia [
]. We were able to show relevant co-resistances
for Enterobacteriaceae against frequently used antibiotics such as
trimethoprim-sulfamethoxazole, gentamicin or ciprofloxacin in our isolates, further obstacles for a therapy. This
phenomenon could be explained by the widespread use or abuse of these antimicrobials, but also by
the presence of the resistance genes on common integrons and plasmids [
Carbapenemase-producing organisms, only rarely detected in our study population, are
certainly the most worrisome in the emergence of antimicrobial resistance and the prevalence
is growing in Asia [
]. Carbapenemases were detected in both hospitals in four A. baumannii
isolates (ST 642) driven by OXA-58 enzymes. The same sequence type was already described
in clinical specimens in another hospital in Ulaanbaatar (First Central hospital) in 2013 [
We were also able to detect the metallo-β-lactamase VIM-2 in six carbapenem-resistant P.
aeruginosa isolates (ST235). This is to our knowledge the first report of its presence in Mongolia.
The unusual structure of the VIM-2 integron (In559) ending with a tniC gene shows the
variability of these mobile genetic platforms and it was previously also reported from neighbouring
country Russia with a near endemic presence of VIM-2-carrying P. aeruginosa of the same
sequence type (ST235) throughout the country [
]. Both countries, Mongolia and Russia,
have strong historical connections. Another important clinical fact of the discovery of
VIM2-producing P. aeruginosa is that they were found in the burn hospital. Especially burn patients
are at risk of acquiring nonfermenters such as P. aeruginosa [
]. Despite being detected on
admission to the burn hospital theses bacteria are a probable indicator for nosocomial
transmission, as we did not find any MBL-carrying P. aeruginosa in the second hospital (NTORC)
and four of six isolates were closely related (by PFGE) to each other.
The two study sites, a trauma and a burn hospital, not only differed significantly in their
carrier rate (42.4% and 69.2% resp.), but also in gender and age. Gender and age can be
explained by the different specialisation of the two hospitals. Men are more inclined to trauma
and injuries as they pursue riskier activities at the workplace and at home (e.g. [
whereas burns are a leading cause of injuries in children in Mongolia [
]. In the BTC we
did observe a colonization rate exceeding 50% in all age groups though significantly less in
children. Other studies performed in the community in China and Germany did not observe
any major age related differences [
]. Also the significant higher colonization rate in the
burn hospital with significantly more patients being colonized with more than one
GNMDRO may be due to a different study population. This may be due to previous
hospitalisations in the burn hospital. Burn patients are prone to be (chronically) colonized by diverse
Gram-negative species in the hospital setting, especially P. aeruginosa . Alternatively swabs
were taken in an undetected outbreak situation, in which patients were colonized within the
three-day period of admission-sampling. Further studies including more patients included are
needed to clarify this aspect.
There are a few limitations of this study. Firstly, colonization with a GN-MDRO may have
occurred before the collection of the first swab (up to the third day of admission,
approximately 48 hours, which is a defined interval for the definition of hospital-acquired infections
]). Taking a swab directly at admission or even in out-patients might me more suited, but
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was not feasible in this study. Secondly the number of patients from whom a second swab was
obtained was low, as most patients were discharged within two weeks and thus there might be
a bias towards more critically-ill patients as they tend to stay longer in the hospital. To allow a
clear analysis of in-hospital transmission data concerning antimicrobial resistance in clinical
isolates from sites of infection is required. In addition, more surveillance data from the
community is required, as our data indicate a high colonization rate at admission, but are possibly
not representative for the Mongolian population, as we only performed this study at two very
In summary, antimicrobial resistance in Gram-negative bacteria mediated by the
extendedspectrum β-lactamases (CTX-M) represents a public health concern in Mongolia affecting the
hospitalized patients and the community setting. This study emphasizes the importance of
routine surveillance, appropriate infection control practice and antibiotic prescription practice
to prevent further spread of Gram-negative multidrug-resistant organisms, especially of
carbapenemases. Further studies exploring faecal carriage in healthy individuals and
hospital-associated infections as well as antibiotic prescribing policies are needed.
S1 File. Dataset of the patient characteristics and colonization status.
Special thanks go to the five graduates of School of Biomedicine (Ulaanbaatar, Mongolia)
Yundendash Dashzeveg, Munkhzul Ganbold, Enkhdemberel Radnaa, Munkhzaya Otgonbayar and
Otgonsaihan Ganbold and to Raquel Guadarrama-Gonzalez and Birgit Lamik (Institute of
Medical Microbiology and Hospital Hygiene, DuÈsseldorf, Germany) for technical assistance.
We also thank the Institute of Medical Microbiology and Hospital Hygiene DuÈsseldorf for
providing consumables and reagents. The authors also thank the PAGEL project coordinators
Thomas Bruhn, Wilfried Schwippert and Ulamnemekh Otgonbayar from the Institute of
Medical Microbiology and Hospital Hygiene, DuÈsseldorf (Germany) for their support. Positive
control stains were provided by Martin Kaase (Institute of Medical Microbiology, Ruhr
University Bochum, Germany), Michael Kresken and Barbara KoÈrber-Irrgang (Antiinfectives
Intelligence, Campus Hochschule Bonn-Rhein-Sieg, Germany) and Paul Higgins (Institute for
Medical Microbiology, Immunology and Hygiene, University of Cologne, Germany).
Conceptualization: GB CRM BG KP.
Data curation: BB AFW.
Formal analysis: BB AFW.
Funding acquisition: KP BG.
Investigation: BB AFW CRM.
Methodology: KT GB CRM AFW.
Project administration: KP BG BC GB CRM.
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Resources: KP BG.
Supervision: GB BC TS BG CRM.
Validation: BB AFW CRM.
Visualization: AFW BB.
Writing ± original draft: AFW.
Writing ± review & editing: CRM KP BB.
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15. EUCAST. EUCAST guidelines for detection of resistance mechanisms and specific resistances of
clinical and/ or epidemiological importance 2013.
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