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- Melin (Mernelius), Sara, et al.
(författare)
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Epidemiological typing of methicillin-resistant Staphylococcus aureus (MRSA) : spa typing versus pulsed-field gel electrophoresis
- 2009
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Ingår i: SCANDINAVIAN JOURNAL OF INFECTIOUS DISEASES. - : Informa UK Limited. - 0036-5548 .- 1651-1980. ; 41:6-7, s. 433-439
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Tidskriftsartikel (refereegranskat)abstract
- Molecular methods based on sequencing, such as spa typing, have facilitated epidemiological typing of bacterial isolates compared to the gold standard pulsed-field gel electrophoresis (PFGE), a technically more demanding method. We studied methicillin-resistant Staphylococcus aureus (MRSA) in 4 Swedish counties from 2003 through 2005, and compared spa typing and PFGE results to epidemiological data. Of 280 MRSA isolates, 91 were from sporadic cases and 189 were associated with 35 outbreaks. A total of 50 spa types and 74 PFGE patterns were detected. 60 (21%) of the MRSA isolates carried the Panton-Valentine leukocidin (PVL) genes. 12 of the PVL-positive MRSA were healthcare associated. 25 of the spa types and 31 of the PFGE patterns were associated with outbreaks. In 1 of the outbreaks we found isolates with different but closely related spa types, and in 6 of the outbreaks we observed isolates with different but related PFGE patterns. In this low-endemic setting, with outbreaks limited in time and place, we found spa typing to be a useful tool for epidemiological typing of MRSA, due to its rapidity, accessibility, ease of use, and standardized nomenclature.
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| 2. |
- Hæggman, Sara
(författare)
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Evolution of beta-lactam : resistance in Klebsiella pneumoniae
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- K. pneumoniae is recognized as a common opportunistic pathogen. Numerous reports have been published worldwide on outbreaks in different healthcare settings. K. pneumoniae is inherently resistant to penicillins, including semisynthetic broad-spectrum penicillins. The drug of choice for empirical treatment is often a cephalosporin. However, the use of cephalosporins is known to select for extended-spectrum beta-lactamase (ESBL)-producing strains. The focus of this thesis is the beta-lactamase gene in K. pneumoniae, and its relationship to beta-lactamase genes present in plasmids in gram-negative bacteria. In Paper I, the intension was to identify presumed beta-lactamase SHV-1-encoding plasmids in fecal Klebsiella isolates from neonates in Swedish special care units. No such plasmids were detected, however. Instead, a chromosomal beta-lactamase gene was identified in all K. pneumoniae, but in none of the Klebsiella oxytoca isolates. This species-specific gene was seen in 10 allelic variants; some closely related to the prototypic plasmid-borne SHV-1 gene, indicating that an allelic variant of the K. pneumoniae chromosomal betalactamase gene is the ancestor of the plasmid-borne SHV-encoding genes. In Paper II, the observed diversity of the chromosomal K. pneumoniae betalactamase gene was further investigated in order to study its evolution in relation to the three phylogenetic groups of K. pneumoniae. Three sequence groups, corresponding to the phylogenetic groups, were identified, blaSHV, blaLEN, and blaOKP. In Paper III, the genetic context of blaSHV in K. pneumoniae chromosomes and plasmids from various gram-negative bacteria was analyzed. Plasmid-borne blaSHV genes were found to be surrounded by DNA highly similar to the K. pneumoniae chromosome. IS26 elements flanked the blaSHV regions. Nine distinct junctions between IS26 and K. pneumoniae chromosomal DNA, and seven different region-lengths were identified. In contrast to a high diversity observed among chromosomal sequences, only two groups of plasmid sequences were seen. This thesis has demonstrated that only one of three ancient K. pneumoniae chromosomal beta-lactamase gene families, blaSHV, is found on plasmids. This is possibly the result from a single IS26 mediated mobilization of blaSHV and surrounding DNA from K. pneumoniae. The two groups of plasmid blaSHV regions seen today could be the result of post-mobilization evolution involving size reductions and nucleotide substitutions. We conclude that mobilization of blaSHV from K. pneumoniae chromosomes is not a driving force in the emergence of resistance in response to beta-lactam therapy. The spread is more likely a consequence of mobilization of IS26 flanked blaSHV regions between plasmids, and mobilization of plasmids between different bacteria.
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| 3. |
- Torell, Erik, et al.
(författare)
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Clonality among ampicillin-resistant Enterococcus faecium in Sweden and relation to ciprofloxacin resistance
- 2003
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Ingår i: Clinical Microbiology and Infection. - : Elsevier BV. - 1198-743X .- 1469-0691. ; 9:10, s. 1011-1019
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Tidskriftsartikel (refereegranskat)abstract
- Objective To investigate clonal relationships in a nationwide sample of human Enterococcus faecium isolates. Methods Biochemical fingerprinting (PhP (PhenePlate) typing) was used to compare 180 fecal ampicillin-resistant E. faecium (ARE) isolates with 169 matched fecal ampicillin-susceptible E. faecium (ASE) isolates from patients in 23 hospitals, collected in 1998, and to study 39 fecal ARE isolates from non-hospitalized individuals collected in 1998, and five ARE and 29 ASE isolates from the early 1990s. Representative ARE and ASE isolates were subjected to pulsed-field gel electrophoresis (PFGE) analysis of genomic DNA and sequencing of the regions encoding the fluoroquinolone targets of the enzymes GyrA and ParC. Results Both PhP and PFGE results showed a higher homogeneity among ARE than among ASE isolates (P < 0.001). One PhP type (FMSE1) comprised 73% of the hospital ARE isolates (53% of ARE isolates from non-hospitalized individuals, and four of five ARE isolates from the early 1990s), but only 1% of the ASE isolates. PFGE of the hospital E. faecium isolates revealed that 23 of the 25 ARE isolates and one of the 22 ASE isolates were of one dominating type. High-level resistance to ciprofloxacin (MIC > 16 mg/L) was present in 91% of ARE isolates, whereas only low-level resistance (MIC 4–16 mg/L; 35% of isolates) was found among ASE isolates. One mutation in parC (codon 80) and one of two mutations in gyrA (codons 83 or 87) were detected in all ARE isolates tested with high-level ciprofloxacin resistance, but were lacking in ARE and ASE isolates with low-level ciprofloxacin resistance. Conclusion Most ARE isolates in Sweden were clonally related. High-level ciprofloxacin resistance was found in ARE isolates of PhP type FMSE1 as well as in other PhP types, but never in ASE isolates.
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