Thesis
Investigating the genetic factor(s) responsible for daptomycin resistance in Staphylococcus aureus isolated in Australia
Masters by Research, Murdoch University
2022
Abstract
Staphylococcus aureus is an opportunistic gram-positive bacterium associated with invasive community and nosocomial infections. For the treatment of multidrug resistant S. aureus infections, daptomycin is considered a last-line antimicrobial. Although rare, an increasing number of daptomycin non-susceptible S. aureus (DNSSA) infections have been reported worldwide. The most prevalent mechanism associated with daptomycin non-susceptibility involves an increase in the net positive cell surface charge conferred by mutations in the multiple peptide resistance factor (MprF), encoded by mprF.
In this study, we compared the S. aureus daptomycin MIC of isolates previously reported daptomycin non-susceptible by VITEK® 2 against the ETEST® and broth microdilution (BMD) methods. To identify genetic factors associated with daptomycin non-susceptibility, whole genome sequencing was performed.
Of the 70 isolates sequenced, all had a daptomycin MIC >1 mg/L by the ETEST®, whilst only 81.4% (n=57) had a daptomycin MIC >1 mg/L by BMD. The isolates were polyclonal, with 13 clonal complexes (CCs) containing 24 unique sequence types (STs), including two novel STs. ST22 and ST1 were the predominant STs whilst CC1 was the predominant CC. A total of 31.4% of the isolates were multidrug resistant. Daptomycin non-susceptibility was primarily due to MprF mutations. Nine different MprF amino acid mutations known to confer daptomycin non-susceptibility were identified in 70% (n=49) isolates. Novel mprF point mutations resulting in amino acid substitutions were also identified. Furthermore, 96 non-MprF mutations were identified in candidate daptomycin non-susceptibility genes, including 36 previously reported mutations and 60 novel mutations. In vitro mutational studies of the identified mutations will allow better understanding of their role in conferring daptomycin non-susceptibility. The findings provide epidemiological insights of the DNSSA population in Australia, crucial for infection control and management measures.
Details
- Title
- Investigating the genetic factor(s) responsible for daptomycin resistance in Staphylococcus aureus isolated in Australia
- Authors/Creators
- Wan C Lim
- Contributors
- Geoffrey Coombs (Supervisor) - Murdoch University, Centre for Biosecurity and One HealthShakeel Mowlaboccus (Supervisor) - Murdoch University, Centre for Biosecurity and One HealthChristopher Mullally (Supervisor)
- Awarding Institution
- Murdoch University; Masters by Research
- Identifiers
- 991005556069307891
- Murdoch Affiliation
- Centre for Biosecurity and One Health
- Resource Type
- Thesis
- Note
- Accelerated Masters with Training of Murdoch University
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