Molecular characterization of multi-drug resistant (MDR) and extremely drug resistant (XDR) Streptococcus pneumoniae isolates from Canadian hospitals between 2007-2013.
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Date
2014-08-08
Authors
Rosenthal, Margot
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Abstract
Streptococcus pneumoniae is a major pathogen causing pneumonia, otitis media, bacteremia,
and meningitis across all age groups in Canada. Multi-drug resistant (MDR) S. pneumoniae
represent approximately 2.8% of all S. pneumoniae isolates and are of increasing concern due
to limited treatment options. Isolates for this study were obtained from the CANWARD
surveillance study between 2007-13 and chosen based on their MDR phenotype. Antimicrobial
susceptibility testing was performed according to CLSI methods. Phenotypic and genotypic
relatedness were assessed by serotyping and pulsed-field gel electrophoresis (PFGE).
Mechanisms of macrolide resistance mef(E) and erm(B) were detected by PCR analysis and
mechanisms of penicillin resistance were assessed by PCR amplification followed by DNA
sequencing of penicillin binding protein (PBP) genes 1 A, 28 and 2X. Detection of pilus type 1
(P1) and type 2 (P2) pathogenicity islets assessed by PCR. This study characterized MDR
S.pneumoniae obtained from across Canada. MDR S. pneumoniae obtained from Canadian
hospitals are genetically related and primarily composed of serotypes 19A and 19F. Within
MDR isolates, resistance rates of >75% were associated with clarithromycin, clindamycin,
doxycycline, penicillin and trimethoprim/sulfamethoxazole, with 72.4% of isolates displaying
simultaneous resistance to all five antimibiotics. Isolates commonly carried resistance to
penicillin + 4 other chemically unrelated classes of antibiotics, a level of resistance we termed
extremely drug-resistant (XDR). All isolates tested positive for either macrolide resistance
genes mef(E) (88.5%) or erm(B) (82.0%), with many of the isolates (70.5%) testing positive for
both genes. Penicillin resistance was associated with highly similar amino acid substitutions in
PBP1 A, 28 and 2X. The majority ot isolates carried P1 (80.3%) or P2 (73.8%), with 73.8% of
isolates carrying both pili. PFGE revealed 4 clusters that were genetically related and
associated with known clones Taiwan19F-14, England14-9, Spain9V-3, Spain23F-1.
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Keywords
multi-drug resistant, extremely drug resistant (XDR), Streptococcus pneumoniae