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Staphylococci and Enterococci: Studies on activity of antimicrobial agents and detection of genes involved in biofilm formation
Linköping University, Department of Clinical and Experimental Medicine, Clinical Microbiology . Linköping University, Faculty of Health Sciences.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Gram-positive cocci, Staphylococcus aureus, coagulase negative staphylococci (CoNS), Enterococcus faecalis and Enterococcus faecium, are the bacteria most often isolated from patients with hospital acquired infections. S. aureus is one of the most important pathogens and have a variety of virulence mechanisms which help it to infect the patient and cause tissue damage. CoNS and enterococci are low virulent bacteria and predominantly cause infections in individuals with underlying illness, individuals that have undergone surgery or with suppressed immune-system. The aims of this thesis were i) to investigate the susceptibility to different antimicrobial agents among S. aureus, CoNS, E. faecium and E. faecalis isolates from primary care centres, general hospital wards and intensive care units in Denmark, Finland, Norway and Sweden and ii) to study the prevalence of the cytolysin genes and genes involved in biofilm formation among CoNS, E. faecium and E. faecalis. The results in this thesis show that the resistance rates among S. aureus and E. faecalis is still rather low in the north European countries. Among CoNS and E. faecium resistance rates are higher and comparable with rates in other European countries and US. CoNS had statistically significant differences in susceptibility rates between the ward levels with the lower susceptibility rates found at ICUs. Continued surveillance of resistance rates to antimicrobial agents among both staphylococci and enterococci are important internationally, nationally and locally. The results in this thesis also show that all multidrug resistant and 96% of the susceptible CoNS isolates carried at least one of the atlE and aap genes or the ica operon. Among E. faecalis isolates with HLGR, belonging to a cluster of genetically related isolates, both the esp and asa1 genes were carried in a high degree while the cyl operon was less frequently found. In addition, about 30% of unique E. faecalis isolates carried two or more of the virulence genes. Among E. faecium isolates the esp gene was common but asa1 and the cyl operon was not found in any of the isolates. Both CoNS and E. faecalis isolates from hospitalised patients are well equipped with genes involved in biofilm formation. These genes, when expressed and even more in combination with resistance to antimicrobial agents, might give these isolates an advantage compared to other isolates when it comes to adhesion to artificial surfaces, persistence in the hospital environment, colonisation of hospitalised patients and to cause nosocomial infections. Further studies are needed to be able to determine which isolates that causes hospital acquired infections and to evaluate the importance of the genes involved in biofilm formation as virulence factors and about how to prevent biofilm related infections from emerging

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2010. , 83 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1187
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-59523ISBN: 978-91-7393-353-7 (print)OAI: oai:DiVA.org:liu-59523DiVA: diva2:352084
Public defence
2010-09-24, Berzeliussalen, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 13:00 (Swedish)
Opponent
Supervisors
Available from: 2010-09-17 Created: 2010-09-17 Last updated: 2010-09-17Bibliographically approved
List of papers
1. Susceptibility of staphylococci and enterococci to antimicrobial agents at different ward levels in four north European countries
Open this publication in new window or tab >>Susceptibility of staphylococci and enterococci to antimicrobial agents at different ward levels in four north European countries
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2007 (English)In: Scandinavian Journal of Infectious Diseases, ISSN 0036-5548, Vol. 39, no 11-12, 1002-1012 p.Article in journal (Refereed) Published
Abstract [en]

A multicentre susceptibility study was performed on staphylococci and enterococci isolated from patients at 3 different ward levels: primary care centres (PCCs), general hospital wards (GHWs) and intensive care units (ICUs), in Denmark, Finland, Norway and Sweden. There was a markedly higher incidence of resistance among CoNS in ICUs compared to GHWs and PCCs. Resistance rates were low among S. aureus isolates and no differences were found between the ward levels. Oxacillin resistance was found among 1.6% of S. aureus and 47% of CoNS isolates. 14% of CoNS and 0.9% of S. aureus isolates were glycopeptide intermediate. The prevalence of E. faecium isolates in this study differed significantly between the ward levels with the lowest prevalence found at PCCs. High level gentamicin resistant (HLGR) enterococci occurred in 11-25% of E. faecium and 6-20% of E. faecalis isolates. The HLGR rate was significantly higher among E. faecalis from hospitalized patients (GHWs and ICUs) compared to patients at PCCs. For enterococcal isolates, no other significant differences in antimicrobial resistance were found between the ward levels. All enterococci were teicoplanin susceptible, but decreased susceptibility to vancomycin was found among 2.0% and 0.6% of the E. faecium and E. faecalis isolates, respectively.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-39203 (URN)10.1080/00365540701472064 (DOI)47229 (Local ID)47229 (Archive number)47229 (OAI)
Note
Study Group, The ScopeAvailable from: 2009-10-10 Created: 2009-10-10 Last updated: 2010-09-17
2. Antimicrobial activity of tigecycline and comparative agents against clinical isolates of staphylococci and enterococci from ICUs and general hospital wards at three Swedish university hospitals
Open this publication in new window or tab >>Antimicrobial activity of tigecycline and comparative agents against clinical isolates of staphylococci and enterococci from ICUs and general hospital wards at three Swedish university hospitals
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2009 (English)In: SCANDINAVIAN JOURNAL OF INFECTIOUS DISEASES, ISSN 0036-5548 , Vol. 41, no 3, 171-181 p.Article in journal (Refereed) Published
Abstract [en]

The activities of tigecycline and comparative agents on staphylococci and enterococci isolated from patients at general hospital wards (GHWs) and intensive care units (ICUs) at 3 university hospitals in Sweden were investigated. Oxacillin disc diffusion and minimal inhibitory concentration with E-test were used. The presence of mecA, vanA or vanB genes was determined with PCR. Statistically significant higher incidence of clindamycin, fusidic acid, rifampicin and multidrug-resistant CoNS was found at ICUs compared to GHWs. Resistance rates were low among S. aureus. Tigecycline, linezolid and vancomycin were the only agents with high activity against methicillin-resistant S. aureus and multidrug-resistant CoNS. Resistance rates were low among E. faecalis, except for high-level gentamicin-resistant (HLGR) E. faecalis. E. faecium showed high resistance rates to ampicillin, piperacillin/tazobactam and imipenem. The HLGR rates among E. faecium were lower than the rates for E. faecalis. Tigecycline and linezolid were the only drugs with high activity against all enterococci including vancomycin-resistant enterococci. No statistically significant differences in susceptibility rates were found between the ward levels for S. aureus and enterococcal isolates and no statistically significant differences were found between the hospitals.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-17132 (URN)10.1080/00365540902721368 (DOI)
Available from: 2009-03-07 Created: 2009-03-07 Last updated: 2010-09-17
3. Molecular typing and detection of the aap and atlE genes and ica operon in multi-drug resistant and susceptible coagulase negative staphylococci
Open this publication in new window or tab >>Molecular typing and detection of the aap and atlE genes and ica operon in multi-drug resistant and susceptible coagulase negative staphylococci
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The aims of the present study were to identify clinical isolates of multidrug resistant (MDR) and susceptible coagulase negative staphylococci (CoNS), (n=76) to the species level by rpoB amplicon sequencing and to detect and compare the presence of the atlE and aap genes and the ica operon between MDR (n=26) and susceptible (n=27) Staphylococcus epidermidis isolates. Detection of the atlE and aap genes and ica operon was carried out using PCR amplification. Most of the isolates were S. epidermidis, both among the MDR and susceptible CoNS. Staphylococcus haemolyticus was the only other species found in the MDR group. All MDR and 96% of the susceptible S. epidermidis isolates carried the atlE gene. The ica operon was present in about 30% of both the MDR and susceptible S. epidermidis isolates. By comparison, aap gene carriage was more common among susceptible S. epidermidis isolates (44%) than the MDR S. epidermidis isolates (27%). The atlE gene was the only gene that was found alone in the S. epidermidis genome. About 25% of the S. epidermidis isolates carried the atlE and aap genes and the ica operon simultaneously. In conclusion, rpoB gene amplicon sequencing is an easy and reliable method to identify CoNS isolates at the species and subspecies level. Both MDR and susceptible S. epidermidis isolates were found to be well equipped with adhesion and aggregation genes which might help them to adhere to artificial surfaces, colonize hospitalised patients and cause biofilm-related infections.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-59522 (URN)
Available from: 2010-09-17 Created: 2010-09-17 Last updated: 2010-09-17
4. Molecular detection of aggregation substance, enterococcal surface protein, and cytolysin genes and in vitro adhesion to urinary catheters of Enterococcus faecalis and E. faecium of clinical origin
Open this publication in new window or tab >>Molecular detection of aggregation substance, enterococcal surface protein, and cytolysin genes and in vitro adhesion to urinary catheters of Enterococcus faecalis and E. faecium of clinical origin
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2009 (English)In: International Journal of Medical Microbiology, ISSN 1438-4221, Vol. 299, no 5, 323-332 p.Article in journal (Refereed) Published
Abstract [en]

It has been hypothesized that nosocomial enterococci might have virulence factors that enhance their ability to colonise hospitalised patients. The objectives of this study were to investigate the prevalence of genes encoding 3 virulence factors: aggregation substance (asa1), enterococcal surface protein (esp), and 5 genes within the cytolysin operon (cylA, cylB, cylM, cylL(L), cylL(S)) and cytolysin production in 115 enterococcal clinical isolates (21 Enterococcus faecium and 94 E. faecalis). Adhesion to siliconized latex urinary catheters in relation to presence of esp was analysed in a subset of isolates. The isolates were previously characterised by pulsed-field gel electrophoresis (PFGE). esp was the only virulence gene found in E. faecium. It was found in 71% of the 21 E. faecium isolates. asa1, esp, and the cyl operon were found in 79%, 73% and 13% respectively, of the 94 E. faecalis isolates. There was a complete agreement between presence of the cyl operon and phenotypic cytolysin production. Isolates belonging to a cluster of genetically related isolates carried esp and asa1 more often when compared to unique isolates. No difference was found with respect to cyl genes. E. faecalis isolates adhered with higher bacterial densities than E. faecium. E. faecalis isolates within the same PFGE cluster adhered with similar bacterial densities, but there was no association between adhesion and the presence of esp when isolates within the same cluster were compared. In conclusion, E. faecalis isolates with high-level gentamicin resistance (HLGR) belonging to clusters of genetically related isolates widely distributed in Swedish hospitals, were likely to carry both esp and asa1. Adhesion was not affected by esp.   

Keyword
Enterococcus; Nosocomial infection; Aggregation substance; Enterococcal surface protein; Cytolysin; Biofilm
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-43672 (URN)10.1016/j.ijmm.2008.10.001 (DOI)74509 (Local ID)74509 (Archive number)74509 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2010-09-17

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