Characterization of extended-spectrum beta-lactamase-producing isolates of Haemophilus parainfluenzae.
OBJECTIVE
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.
Tristram
Stephen G
SG
School of Human Life Sciences, University of Tasmania, Launceston, Tasmania 7250, Australia. stephen.tristram@utas.edu.au
Pitout
Marthinus J
MJ
Forward
Karen
K
Campbell
Sarah
S
Nichols
Scott
S
Davidson
Ross J
RJ
D001483:Base Sequence; D002439:Cefotaxime / Q000627:therapeutic use; D002648:Child; D024881:Drug Resistance, Bacterial / Q000235:genetics; D005260:Female; D006192:Haemophilus Infections / Q000188:drug therapy / Q000201:enzymology / Q000235:genetics; D044135:Haemophilus parainfluenzae / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification*; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D008875:Middle Aged; D008969:Molecular Sequence Data; D001618:beta-Lactamases / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification*
D001618:beta-Lactamases; D002439:Cefotaxime