JAC Advance Access originally published online on September 6, 2007
Journal of Antimicrobial Chemotherapy 2007 60(5):1151-1154; doi:10.1093/jac/dkm311
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Effect of cloned inhibitor-resistant TEM ß-lactamases on the susceptibility of Haemophilus influenzae to amoxicillin/clavulanate
School of Human Life Sciences, University of Tasmania, Launceston, Tasmania 7250, Australia
Received 4 May 2007; returned 3 July 2007; revised 12 July 2007; accepted 28 July 2007
* Corresponding author. Tel: +61-3-63-243323; Fax: +61-3-63-243658; E-mail: stephen.tristram{at}utas.edu.au
Objectives: To determine the effect of cloned inhibitor-resistant TEM ß-lactamases (IRTs) on the susceptibility of Haemophilus influenzae to amoxicillin/clavulanate.
Methods: IRT-2, -4 and -5 genes with various promoters were cloned into control strains of H. influenzae and the amoxicillin/clavulanate MICs were measured using Etests.
Results: IRT enzymes were able to raise the amoxicillin/clavulanate MICs to between 0.38/0.19 and 4.0/2.0 mg/L depending on the IRT and promoter genotype, compared with MICs of 0.19/0.09 to 0.5/0.25 mg/L for the corresponding strains with TEM-1. Strains with an IRT and altered penicillin-binding proteins had amoxicillin/clavulanate MICs as high as 8.0/4.0 mg/L.
Conclusions: Cloned IRT enzymes in H. influenzae raise the amoxicillin/clavulanate MICs to an extent comparable to naturally occurring strains with decreased amoxicillin/clavulanate susceptibility.
Keywords: H. influenzae , IRTs , susceptibility