Post on 20-Mar-2018
Antibiotic Susceptibility
Testing Methods reporting and
Emerging Resistances in
Laboratories
Dr. John Merlino
ASM ASIG National Convenor
Antimicrobial AST Methods
Outline
• What AST are used in Australia
Laboratories
• Discuss some complex issues with
phenotypic methods and how AST
Methods may vary according to the
standardised methods used especially
when reporting resistances
RCPA QAP Results
Standardised Methods Used • CLSI
• CDS Users
• EUCAST (and CLSI)
• CLSI and EUCAST
EUCAST: EUCAST www.eucast.org/ 2015
RCPA AST Performance in
2010 to 2013
Merlino, J. AST Testing Methods and Emerging
Resistances in Hospitals, Microbiology Australia,
Vol. 35 (1), March 2014.
Disc Testing Valuable in detecting Resistance
Mechanisms
Luis Martínez-Martínez - Interpretative
reading of the antibiogram
FOX
Emerging Resistance Mechanisms
CR-AB clones emerge
VRE Carbapenemases –Enterobacteria;
NDM-1 KPC, VIM/IMP
discovered
CTX-M ESBL ‘explosion’ starts
Lin-R enterococci
VRE in animals
Dap-R staphs & enterococci
1st CTX-M ESBL
MRSA
PCR Genome sequence
VISA
HVISA
Amp C
MIC Mechanism
When reporting –
more complicated
What’s more important?
Infection Control Clinical Treatment
Emerging Resistance
For Emerging Resistance–
EUCAST/CLSI
MIC Clinical/Epidemiological
• Epidemiological Cut off (ECOFF) EUCAST
• Epidemiological Cut off Variation (ECVs)
CLSI
Standardised Methods May Vary in reporting
criteria Very common mechanism of cephalosporin resistance is derepressed
chromosomal AmpC β-lactamase in these species
• CLSI report only ESC - Enterobacter, Serratia and Citrobacter
• EUCAST Enterobacter spp, Serratia spp., Citrobacter freundii, Morganella morganii, Providencia spp, Hafnia alvei
• CDS Users - ESCHAPPM (or ESCAPPM) is a mnemonic for a group of Enterobacteriaceae (Enterobactercloacae, Enterobacter aerogenes, Serratia marcescens, Citrobacter freundii, Hafnia alvei, Aeromonas hydrophila, Aeromonas caviae, Aeromonas veronii, Providencia stuartii,Providencia rettgeri and Morganella morganii)
Careful when Reporting
MICs
CLSI and EUCAST
EUCAST have Intermediate category 7. In order to simplify the EUCAST tables, the intermediate category is not listed. It is interpreted as values
between the S and the R breakpoints. For example, for MIC breakpoints listed as S ≤ 1 mg/L and R > 8
mg/L, the intermediate category is 2-8 (technically >1-8) mg/L, and for zone diameter breakpoints listed as
S ≥ 22 mm and R < 18 mm, the intermediate category is 18-21 mm.
(a)
(b)
Principle (a) and interpretation (b) of the Carba NP test recently developed
for the rapid identification of carbapenemase producers among
Enterobacteriaceae and Pseudomonas spp.