JAC Advance Access originally published online on January 16, 2004
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Journal of Antimicrobial Chemotherapy (2004) 53, 371-374
© 2004 The British Society for Antimicrobial Chemotherapy
BRO ß-lactamase alleles, antibiotic resistance and a test of the BRO-1 selective replacement hypothesis in Moraxella catarrhalis
Departments of 1 Biological Sciences, Box 70703 and 2 Internal Medicine, Box 70622, East Tennessee State University, Johnson City, TN 37614; 3 James H. Quillen Veterans Affairs Medical Center (11C), Mountain Home, TN 37684, USA
Received 18 July 2003; returned 9 October 2003; revised 7 November 2003; accepted 10 November 2003
Objectives: The hypothesis that BRO-1 selectively replaced the BRO-2 isoform of the Moraxella catarrhalis BRO ß-lactamase was tested by examining the temporal distribution, antibiotic resistance and epidemiological characteristics of isolates from a long-term collection at a single locale.
Methods: A rapid, one-step PCR assay conducted on 354 isolates spanning 1984–1994 distinguished bro alleles in over 97% of the ß-lactamase-producing isolates. Probes of dot blots were used to distinguish PCR failure from non-ß-lactamase-mediated penicillin resistance.
Results: BRO-2 isolates comprised 0–10% of the population per year with no evidence of a decline over time. All ß-lactamase producers exceeded the clinical threshold for penicillin resistance. Bimodality of penicillin MICs for ß-lactamase producers was caused by variation within BRO-1 rather than differences between BRO-1 and BRO-2. Non-ß-lactamase factors also confer resistance to penicillin and may contribute to the BRO-1 bimodality. The 13 BRO-2 isolates were associated with diverse genotypes within which there was evidence of epidemiologically linked clusters. The exclusive association of BRO-2 with four unrelated genotypes suggested maintenance of BRO-2 by recurrent mutation or horizontal exchange.
Conclusions: The relative rarity of BRO-2 throughout the study, the absence of a declining temporal trend, and genetic diversity within BRO-2 all failed to support the hypothesis that BRO-2 was more common in the past and has been selectively replaced by BRO-1.
Keywords: disease transmission, molecular epidemiology, selection
* Corresponding author. Tel: +1-423-439-6926; Fax: +1-423-439-5958; E-mail: levyf{at}etsu.edu
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