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Published on: January 17, 2014
Characterization of extended-spectrum beta-lactamase-producing isolates of Haemophilus parainfluenzae
Stephen G Tristram1, Marthinus J Pitout, Karen Forward
1School of Human Life Sciences, University of Tasmania, Launceston, Tasmania 7250, Australia. stephen.tristram@utas.edu.au
Objectives:
To characterize the beta-lactam resistance mechanisms of two clinical isolates of cefotaxime-resistant Haemophilus parainfluenzae recovered from patients in South Africa.
Methods:
The relatedness of isolates and plasmids was assessed using PFGE and restriction enzyme analysis, respectively. Plasmid-mediated and chromosomally integrated bla(TEM) genes and ftsI genes were sequenced, and the plasmid-mediated bla(TEM-15) was used to transform a range of control organisms.
Results:
The two isolates were found to be unique according to PFGE, but had an identical 3.7 kb plasmid encoding a TEM-15 beta-lactamase. Both isolates also had substitutions in penicillin binding protein 3 (PBP3) consistent with substitutions known to exist in beta-lactamase-negative ampicillin-resistant (BLNAR) strains of Haemophilus influenzae. The cefotaxime MICs for control strains of H. influenzae, H. parainfluenzae and BLNAR H. influenzae transformed with the plasmid-mediated bla(TEM-15) were 1.0, 1.0 and 4.0 mg/L, respectively, compared with 16.0 and 8.0 mg/L, respectively, for the two parent H. parainfluenzae.
Conclusions:
The high-level cefotaxime resistance in the H. parainfluenzae isolates was due to a combination of a plasmid-mediated TEM-15 extended-spectrum beta-lactamase with altered PBP3 probably contributing. Other contributing resistance mechanisms could not be excluded.
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