Back to Search Start Over

A Combined Phenotypic-Genotypic Predictive Algorithm for In Vitro Detection of Bicarbonate: β-Lactam Sensitization among Methicillin-Resistant Staphylococcus aureus (MRSA)

Authors :
Selvi C. Ersoy
Warren E. Rose
Robin Patel
Richard A. Proctor
Henry F. Chambers
Ewan M. Harrison
Youngju Pak
Arnold S. Bayer
Source :
Antibiotics, Vol 10, Iss 9, p 1089 (2021)
Publication Year :
2021
Publisher :
MDPI AG, 2021.

Abstract

Antimicrobial susceptibility testing (AST) is routinely used to establish predictive antibiotic resistance metrics to guide the treatment of bacterial pathogens. Recently, a novel phenotype termed “bicarbonate (NaHCO3)-responsiveness” was identified in a relatively high frequency of clinical MRSA strains, wherein isolates demonstrate in vitro “susceptibility” to standard β-lactams (oxacillin [OXA]; cefazolin [CFZ]) in the presence of NaHCO3, and in vivo susceptibility to these β-lactams in experimental endocarditis models. We investigated whether a targeted phenotypic-genotypic screening of MRSA could rule in or rule out NaHCO3 susceptibility upfront. We studied 30 well-characterized clinical MRSA bloodstream isolates, including 15 MIC-susceptible to CFZ and OXA in NaHCO3-supplemented Mueller–Hinton Broth (MHB); and 15 MIC-resistant to both β-lactams in this media. Using a two-tiered strategy, isolates were first screened by standard disk diffusion for susceptibility to a combination of amoxicillin-clavulanate [AMC]. Isolates then underwent genomic sequence typing: MLST (clonal complex [CC]); agr; SCCmec; and mecA promoter and coding region. The combination of AMC disk susceptibility testing plus mecA and spa genotyping was able to predict MRSA strains that were more or less likely to be NaHCO3-responsive in vitro, with a high degree of sensitivity and specificity. Validation of this screening algorithm was performed in six strains from the overall cohort using an ex vivo model of endocarditis. This ex vivo model recapitulated the in vitro predictions of NaHCO3-responsiveness vs. nonresponsiveness above in five of the six strains.

Details

Language :
English
ISSN :
20796382
Volume :
10
Issue :
9
Database :
Directory of Open Access Journals
Journal :
Antibiotics
Publication Type :
Academic Journal
Accession number :
edsdoj.9cbc9a6770de490e872e6b7f70073558
Document Type :
article
Full Text :
https://doi.org/10.3390/antibiotics10091089