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influenzae isolates harbouring the TEM-1 β-lactamase (with the same replicon and promoter types commonly reported in H. The prevalence and mechanisms of β-lactam resistance were identified to be similar for both bacterial species, with 13.1% of H. influenzae isolates, collected during the GROMIT study using a well defined patient population. As a result, Chapter 4 examined the phenotypic and genotypic characteristics of β-lactam resistance mechanisms in a large collection of H. haemolyticus, a respiratory commensal commonly mis-identified as H. Little was known about the β-lactam resistance profile of H. A search of ftsI gene sequences available on GenBank revealed that the AAT to AAG or AAA codon changes occurred with equal prevalence in N526K-positive BLNAR isolates, suggesting that the prevalence of BLNAR isolates would go under-reported when these PCR algorithms were used for BLNAR detection. As the PCR primers investigated were designed for detection of the N526K substitution encoded by the AAG SNP only, they failed to detect N526K encoded by AAA. The poor performance of these PCR primers was attributed to the fact that the N526K substitution can be encoded by an AAT-AAG codon change at base pair (bp) position 1576-1578 of ftsI, as well as the recently described AAT-AAA codon change.
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(2009) primers for detecting the N526K substitution in BLNAR isolates by amplification (sensitivity 96% specificity 26%). Similar findings were reported for the sensitivity and specificity of the Nakamura et al. Isolates were taken from 1) the University of Tasmania (UTAS) culture collection (n=44), isolates was unreliable (sensitivity 84% specificity 26%). influenzae.Ī working strain collection comprising a total of 393 Haemophilus isolates was established and used for all the subsequent studies conducted in this thesis. influenzae, which further complicates the role of the diagnostic laboratory in guiding antibiotic therapy for infections involving H. haemolyticus isolates are frequently mis-identified as H. influenzae, in diagnostic specimens from the respiratory tract, has compounded the issue. Furthermore, the recent recognition of Haemophilus haemolyticus, a close non-pathogenic relative of H.
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As a result genotypic testing methods are being increasingly adopted for BLNAR detection. This type of resistance, termed β-lactamase-negative ampicillin-resistance (BLNAR), is difficult to detect in the diagnostic laboratory, as many BLNAR isolates do not actually show an ampicillin resistant phenotype using standard susceptibility testing methods. However, the efficacy of these antibiotics is currently threatened by the increasing prevalence of β-lactam resistance mediated by specific mutations in the ftsI gene that produce an N526K substitution in the encoded penicillin-binding protein 3 (PBP3), a protein that is the target of these antibiotics. These infections frequently require antibiotic therapy for management, with antibiotics of the β-lactam class such as amoxicillin, cefaclor, and amoxicillin-clavulanate historically used as first line therapies. Haemophilus influenzae is a significant opportunistic pathogen that causes a range of respiratory infections, including community-acquired pneumonia (CAP), acute exacerbations of chronic obstructive pulmonary disease (COPD) and acute otitis media (AOM). | Document not available for request/download (Complete thesis including published material) (Complete thesis excluding published material)Īvailable under University of Tasmania Standard License.