JAC Advance Access originally published online on February 21, 2006
Journal of Antimicrobial Chemotherapy 2006 57(4):747-749; doi:10.1093/jac/dkl039
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Combination of altered PBPs and expression of cloned extended-spectrum ß-lactamases confers cefotaxime resistance in Haemophilus influenzae
1 Mikrobiyoloji ve Klinik Mikrobiyoloji, Adnan Menderes Üniversitesi Hastanesi, Aydin, Turkey; 2 School of Human Life Sciences, University of Tasmania, Launceston, Tasmania, Australia; 3 Department of Pathology, Hershey Medical Centre, Hershey, PA, USA
Received 15 November 2005; returned 19 January 2006; revised and accepted 19 January 2006
* Corresponding author. Tel: +90-256-214-80-41; Fax: +90-256-212-31-69; E-mail: bbozdogan{at}adu.edu.tr
Background: Resistance to ß-lactams in Haemophilus influenzae is mostly due to the presence of TEM ß-lactamases. ß-Lactamase-negative ampicillin resistance (BLNAR) also occurs as a result of PBP3 modifications. BLNAR strains are particularly common in Japan and France, and strains with combined mechanisms of altered PBP3 and ß-lactamase (BLPACR) are emerging. Although the prevalence of ß-lactamase-positive strains is high, TEM-derived extended-spectrum ß-lactamase (ESBL)-mediated cephalosporin resistance, which is common in Enterobacteriaceae, has not been reported in H. influenzae. In this study, the ability of ESBLs TEM-3, -4 and -5 to confer ß-lactam resistance in H. influenzae strains with or without modified PBP3 was tested.
Methods: The genes encoding TEM-1, -3, -4 and -5 were cloned into plasmid pLS88 and were used to transform H. influenzae Rd and BLNAR H. influenzae Rd strains with PBP3 modifications. MICs were determined using CLSI macrobroth dilution. The ability of amoxicillin/clavulanate pre-diffusion disc tests to discriminate between ESBL-producing strains and other strains was also tested.
Results: The presence of ESBLs in BLNAR strains conferred cefotaxime resistance, but H. influenzae Rd strains expressing ESBLs and BLNAR strains expressing TEM-1 remained cefotaxime susceptible. The amoxicillin/clavulanate pre-diffusion tests were able to discriminate the ESBL-producing strains from the other strains.
Conclusions: The presence of altered PBP3 increases the effect of ESBLs in recombinant H. influenzae strains to produce cefotaxime resistance. Amoxicillin/clavulanate pre-diffusion disc tests can discriminate ESBL-producing strains from other strains.
Keywords: H. influenzae , ESBLs , ß-lactams , penicillin binding proteins
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