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.

AST Methods Used 2014

AST Methods Used 2014

AST Methods Used 2014

AST Methods Used 2014

Phenotypic Methods MIC Used

Yeast MIC Susceptibility Testing Sensititre

Automated AST Methods

Resistance Mechanisms

Disc Testing Valuable in detecting Resistance

Mechanisms

Luis Martínez-Martínez - Interpretative

reading of the antibiogram

FOX

S. aureus BORSA

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 Determination can be difficult

MIC Mechanism

When reporting –

more complicated

What’s more important?

Infection Control Clinical Treatment

Emerging Resistance

CLSI ad EUCAST

Adapted John Turnidge ASM 2010 Annual meeting in Sydney

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)

CDS Users Group

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.

Resistance Rates CLSI and EUCAST

Enterobacteriaceae

(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.

Concluding

Remarks

Susceptibility testing requires a

Thinking concept:

Luis Martínez-Martínez - Interpretative reading of the

antibiogram