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Prevalence and genotypic characteristics of β-lactamase-negative ampicillin-resistant Haemophilus influenzae in Australia

journal contribution
posted on 2023-05-17, 06:10 authored by Witherden, EA, Montgomery, J, Henderson, B, Stephen TristramStephen Tristram

Objectives: To determine the prevalence of β-lactamase-negative ampicillin-resistant (BLNAR) Haemophilus influenzae in Australia and characterize the associated amino acid substitutions in penicillin-binding protein 3.

Methods: Two hundred consecutive non-repeat clinical isolates of H. influenzae were collected and β-lactamase-negative isolates were screened for reduced ampicillin susceptibility using an ampicillin 2 μg disc (breakpoint <17 mm) and Etest (breakpoint ≥0.25 mg/L). All screen-positive isolates had their ampicillin MICs determined by reference broth microdilution and their ftsI genes were sequenced.

Results: No BLNAR strains (MIC ≥4 mg/L) were found, but 5 (2.5%) low BLNAR (L-BLNAR) strains (MIC ≥2 mg/L) and 36 (18%) genetic BLNAR (gBLNAR) strains (R517H or N526K) were found. Of the gBLNAR strains, four had the R517H substitution and the remainder had N526K, while no strains had combined N526K and M377I/S385T/L389F substitutions. A number of strains with neither R517H nor N526K substitutions that did not meet the gBLNAR definition had other BLNAR-associated substitutions.

Conclusions: BLNAR and L-BLNAR strains are uncommon in Australia, while gBLNAR strains are more common than previously recognized.

History

Publication title

Journal of Antimicrobial Chemotherapy

Volume

66

Issue

5

Pagination

1013-1015

ISSN

0305-7453

Department/School

School of Health Sciences

Publisher

Oxford Univ Press

Place of publication

Great Clarendon St, Oxford, England, Ox2 6Dp

Rights statement

The definitive publisher-authenticated version is available online at: http://www.oxfordjournals.org/

Repository Status

  • Restricted

Socio-economic Objectives

Clinical health not elsewhere classified

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