Journal
JOURNAL OF ANTIMICROBIAL CHEMOTHERAPY
Volume 69, Issue 5, Pages 1238-1242Publisher
OXFORD UNIV PRESS
DOI: 10.1093/jac/dkt511
Keywords
antimicrobial resistance; clinical epidemiology; horizontal gene transfer; phylogenetic analysis
Funding
- ALF-YF
- Alfred Osterlund
- Anna and Edwin Berger and the Greta and Johan Kock Foundation
- Swedish Medical Research Council [521-2010-4221]
- Cancer Foundation at the University Hospital in Malmo
- Physiographical Society (Forssman's Foundation)
- Skane County Council's research and development foundation
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The -lactamase genes of Haemophilus influenzae are commonly positioned on large integrative and conjugative elements, but a group of bla(TEM)-carrying small plasmids (40006000 bp) with a common structural backbone have recently been characterized. In this study we investigated the epidemiological significance and potential for transfer of this group of small plasmids. We developed a two-step PCR assay to screen for and type this group of resistance plasmids in H. influenzae. A large collection of respiratory isolates (n2845) from south Sweden, obtained from 2009 to 2011, as well as a collection of invasive Swedish H. influenzae from 1997 to 2010 (n310) was screened. The distribution of plasmid types among clinical isolates was investigated using multilocus sequence typing (MLST). In the collection, 15.8 of -lactamase-producing isolates and 1.4 of total isolates possessed a small plasmid with the signature structure. The plasmids were genetically conserved and widely spread geographically. MLST revealed that the spread of small plasmids occurred by both clonal expansion and horizontal transfer. In vitro experiments suggested that one plasmid type, pN223, can transfer ampicillin resistance to susceptible Escherichia coli. Small -lactamase-encoding plasmids constitute a significant mechanism for -lactam resistance in H. influenzae and can spread through clonal expansion of resistant clones as well as through horizontal plasmid transfer.
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