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Genetic relatedness among Enterococcus faecalis with transposon-mediated high-level gentamicin resistance in Swedish intensive care units
Linköping University, Department of Molecular and Clinical Medicine, Clinical Microbiology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Molecular and Clinical Medicine, Clinical Microbiology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Molecular and Clinical Medicine, Clinical Microbiology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Biomedicine and Surgery. Linköping University, Faculty of Health Sciences.
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2003 (English)In: Journal of Antimicrobial Chemotherapy, ISSN 0305-7453, E-ISSN 1460-2091, Vol. 52, no 2, 162-167 p.Article in journal (Refereed) Published
Abstract [en]

We studied 45 isolates of Enterococcus faecalis with high-level gentamicin resistance (HLGR), all but one concomitantly resistant to ciprofloxacin, and 25 ciprofloxacin-resistant isolates without HLGR for genetic relatedness using pulsed-field gel electrophoresis (PFGE). E. faecalis were isolated from patients admitted to intensive care units at eight hospitals in southern Sweden from December 1996 through December 1998. Genomic analysis by PFGE resulted in three clusters of genetically related isolates (designated clusters I, II and III) and 23 unique clones. Cluster I was found predominantly in the eastern and central parts of southern Sweden and clusters II and III in south-western Sweden. Among the 45 isolates with HLGR, 69% belonged to cluster I, 20% to cluster II, and 11% had unique PFGE patterns, which suggests that the majority of isolates with HLGR are closely related. Among the 25 ciprofloxacin-resistant isolates without HLGR, 68% had unique PFGE patterns, 12% belonged to cluster I and 20% to cluster III, which suggests the ciprofloxacin-resistant isolates are not related. All isolates with HLGR contained the aac(6)Ie-aph(2)Ia gene, which was carried on a Tn5281-like transposon in all isolates except one. We conclude that HLGR in E. faecalis was mainly due to dissemination of genetically related clones during the time studied, and that HLGR in these isolates was due to the presence of the aac(6)Ie-aph(2)Ia gene.

Place, publisher, year, edition, pages
2003. Vol. 52, no 2, 162-167 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-26483DOI: 10.1093/jac/dkg315Local ID: 11035OAI: oai:DiVA.org:liu-26483DiVA: diva2:247032
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Enterococci in Swedish intensive care units: studies on epidemiology, mechanisms of antibiotic resistance and virulence factors
Open this publication in new window or tab >>Enterococci in Swedish intensive care units: studies on epidemiology, mechanisms of antibiotic resistance and virulence factors
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The purpose of this thesis was to study enterococci in Sweden, their resistance to antibiotics in general and high-level gentamicin resistance (HLGR) in particular, with a special focus on the ICU setting. Dynamics of rectal colonisation during prolonged intensive care unit (ICU) stay was assessed. In addition, enterococcal virulence factors and the ability to adhere to abiotic surfaces such as urinary catheters were studied.

We found that among prolonged-stay patients admitted to ICUs, the rectal flora was altered, with a decrease in Gram-negative rods in favour of Gram-positive bacteria, mainly Coagulase negative staphylococci and enterococci.

Among clinical enterococcal isolates from patients admitted to Swedish ICUs, although vancomycin resistant enterococci (VRE) were only sporadically found, multidrug resistance was common. This was most apparent in Enterococcus faecium, where the majority of isolates were ampicillin- and quinolone resistant. Enterococcus faecalis was still the most frequently isolated enterococcal species in clinical specimens. Among patients admitted to Swedish ICUs 1996-1998, E. faecalis with HLGR was found in higher frequency (20%) than previously reported. The majority (89%) of these isolates belonged to two dominating clusters of genetically related E. faecalis. Cluster I (69%), which was predominantly found in the eastern and central parts of southern Sweden and Cluster II (20%) in south-western Sweden.

In the County of Östergötland, the first E. faecalis with HLGR isolated from blood cultures was found in 1996. The yearly incidence of isolates with HLGR in E. faecalis bacteraemia was studied from 1996-2001, and varied between 9-22%. The majority of these isolates were genetically related and belonged to Cluster I, also found in the previous study. The first blood isolate of E. faecium with HLGR in the County of Östergötland was found in 1999. A clone of E. faecium, with HLGR and ampicillin resistance, was found to colonise 6/10 and 2/11 prolonged-stay patients admitted from November 2001 through January 2002 to the general ICU and cardio-thoracic ICU, respectively, at the University Hospital of Linköping.

All studied isolates with HLGR carried the gene aac(6')-Ie-aph(2'')-Ia encoding the bifunctional aminoglycoside modifying enzyme Aac(6')Ie-Aph(2'')Ia, which conveys resistance to all commercially available amino-glycosides except streptomycin. The location of the gene, aac(6')Ie-aph(2'')-Ia, was studied in 45 E. faecalis isolates and the gene was carried on a Tn5281-like transposon in all isolates except one. The 30 µg disc diffusion test, as recommended by the SRGA, had 100% sensitivity and specificity when compared to PCR detection of aac(6')-Ie-aph(2'')-Ia.

E. faecalis isolates with HLGR belonging to widely disseminated clusters of genetically related isolates were more likely to carry both the gene encoding enterococcal surface protein (esp) and the gene encoding aggregation substance (asa1) compared to unique isolates. Esp was the only virulence factor found among E. faecium isolates, where it was common. E. faecalis isolates adhered with higher bacterial densities to urinary tract catheters compared to E. faecium isolates. In vitro adherence to urinary tract catheters was not affected by esp.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2005. 99 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 880
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-28709 (URN)13876 (Local ID)91-737-3861-1 (ISBN)13876 (Archive number)13876 (OAI)
Public defence
2005-02-18, Berzeliussalen, Hälsouniversitetet, Campus US, Linköpings Universitet, Linköping, 13:00 (English)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-09-28Bibliographically approved
2. Characterization of clinical enterococcal isolates in Swedish hospitals: studies on genetic relatedness and high-level gentamicin resistance
Open this publication in new window or tab >>Characterization of clinical enterococcal isolates in Swedish hospitals: studies on genetic relatedness and high-level gentamicin resistance
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

During the last few decades, and in parallel with increasing resistance to multiple antibiotics, enterococci have become one of the leading pathogens that cause nosocomial infections. High-level gentamicin resistant (HLGR) enterococci have become frequent. Thus, there are compelling reasons to control the transmission of enterococci with HLGR. Many different typing methods have been used for epidemiological typing of enterococci. Pulsed-field gel electrophoresis (PFGE) has been shown to be the most discriminating typing method and is currently considered the "gold standard" for typing of enterococci. However, PFGE is an expensive method and remains time-consuming, which may be of critical importance when comparing data obtained from numerous isolates.

The aim of this thesis was to characterize clinical enterococcal isolates from patients admitted to Swedish hospitals, with special focus on HLGR strains and their genetic relatedness. Our purpose was also to develop a faster PFGE protocol for typing of enterococci, as well as to investigate if the Phene Plate (PhP) system can be used as a rapid screening method for detection of genetically related isolates of enterococci. If this could be achieved, it would be possible to minimize the number of isolates subjected to PFGE typing, which would save time and money.

In paper I, we performed a thorough investigation of eight different parameters of importance for the separation of DNA fragments by PFGE. This resulted in a modified PFGE protocol for typing of enterococci with much enhanced resolution. HLGR E. faecalis isolates obtained from patients admitted to eight Swedish ICUs during 1996 and 1998 (paper II), and isolates obtained from patients with bacteremia in the County of Östergötland during the period 1994-2001 (paper III) were characterized by our modified PFGE method. We found that the majority (69%) of isolates from ICUs in the eastern and central parts of southern Sweden, belonged to one dominating cluster, and the same cluster was also found in blood isolates from Östergötland. In nearly all cases, HLGR was due to the presence of the aac(6 ')Ie-aph(2 '')la gene situated on a Tn5281-like transposon (paper II). In the County of Östergötland, HLGR E. faecalis was first isolated from blood cultures in 1996, and the first blood isolates of HLGR E. faecium were found in 1999. During the study period, only 4 HLGR E. faecium isolates were observed, and all of them showed unique PFGE patterns.

To evaluate the efficiency of the gentamicin disk diffusion method for detection of HLGR in clinical isolates of enterococci, all enterococcal blood isolates from paper III were studied with a 30-µg gentamicin disk as recommended by SRGA, and the method was found to have 100% sensitivity and specificity when compared with PCR.

A "biochemical fingerprinting" method (PhP) was compared with PFGE for epidemiological characterization of enterococci. In earlier studies of the PhP method, enterococci were collected mainly from the environment or from normal human flora. Our study indicates that PhP may be a useful screening method for clinical E. faecalis isolates, with a relatively high concordance with PFGE, but that it is less useful for E. faecium since the concordance for E. faecium was low. To fully evaluate PhP as a tool for epidemiological characterization of enterococci from clinical settings, and to address questions regarding the validity of PFGE, further studies using additional genotyping methods, preferably newer typing systems based on DNA sequencing such as MLST, are warranted.

Place, publisher, year, edition, pages
Linköping: Linköping Universitet, 2005. 80 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 899
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-30067 (URN)15528 (Local ID)91-85299-12-X (ISBN)15528 (Archive number)15528 (OAI)
Public defence
2005-05-27, Berzeliussalen, Hälsouniversitet, Linköping, 09:00 (Swedish)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-10-02Bibliographically approved

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Hällgren, AnitaSaeedi, BaharakNilsson, MaudMonstein, Hans-JürgIsaksson, BarbroHanberger, HåkanNilsson, Lennart

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