BSAC Susceptibility Testing Residential Workshop

BSAC Userday 2018

Mandy Wootton Slides credit: Trevor Winstanley

Intrinsic & Exceptional Resistance

What is an Expert?

BSAC Userday 2018

An expert is a person who has made all the mistakes that can be made, in a narrow field.

Niels Bohr

An expert knows all the answers - if you ask the right questions. Levi Strauss

An expert is a person who makes three correct guesses consecutively. Laurence J. Peter

Someone with 5 minutes to spare and access to Google Conrad Wight

An expert is somebody who is more than 50 miles from home, has no responsibility at all for implementing the advice given, and shows slides.

Edwin Meese

Expert rules & Interpretative reading

BSAC Userday 2018

ASM News 1992; 58: 368-75

Interpretive reading of antimicrobial susceptibility testsPatrice Courvalin

EUCAST Expert Rules

BSAC Userday 2018

Comprehensive collection of rules • brought together by an expert

subcommittee

• wide consultation

Updated regularly

May be applied manually or incorporated into expert systems

EUCAST Expert Rules

BSAC Userday 2018

Stand alone systems

Part of LIMs

Part of an automated AST system

EUCAST Expert Rules

BSAC Userday 2018

Intrinsic Resistance• v 3.1 (Sept 2016)

Exceptional Resistance Phenotypes• v 3.1 (Sept 2016)

Interpretive Reading• v 2.0 (valid until Sept 2016; out to review)

Intrinsic resistance

BSAC Userday 2018

Not acquired or mutational resistance

Characteristic of all (or almost all) representatives of the species

The drug is, in effect, clinically useless

• AST is normally unnecessary

“Susceptible” results should be viewed with caution

• an error in identification or susceptibility testing?

• if S is confirmed, the drug should preferably not be used

Intrinsic resistance

BSAC Userday 2018

Table 1:Enterobacteriaceae

Table 2: Non-fermentative Gram negative bacteria

Table 3:Gram negative bacteria other than those above

Table 4:Gram positive bacteria

Intrinsic resistance

BSAC Userday 2018

C. koseri

BSAC Userday 2018

P. mirabilis

BSAC Userday 2018

Intrinsic resistance

BSAC Userday 2018

Intrinsic resistance

BSAC Userday 2018

Most labs remember some intrinsic R

• Proteus / NIT or COL

No easy way to remember them

Print & laminate tables for lab

Add notes to disc templates

Authorisers: wrong code for agent added to LIMs

Knowing intrinsic resistance

Knowing Improves quality of susceptibility testing reports

• Most common: K. pneumoniae S to AMP / AMOX

Exceptional phenotypes

BSAC Userday 2018

Not yet reported or very rare

An error in identification or susceptibility testing?

• further study or referral

Resistance may develop and increase over time

Local or national differences

• very rare in one hospital, area or country, more common in another

Exceptional phenotypes

BSAC Userday 2018

Table 5 Gram negative bacteria

Table 6 Gram positive bacteria

Table 7 Anaerobes

Exceptional phenotypes

BSAC Userday 2018

Exceptional phenotypes

BSAC Userday 2018

Confirmation of unusual resistances

BSAC Userday 2018

StaphylococciCeftaroline, ceftibiprole, daptomycin, linezolid, tedizolid, teicoplanin (not CoNS ££), tigecycline & vancomycin

EnterococciVancomycin/teicoplanin (vanA/B/C ££), tigecycline, linezolid, tedizolid, ampicillin (not E. fcm), daptomycin>2mg/L (E. fcl), >4mg/L (E. fcm)

S. pneumoniaePenicillin (>2mg/L), cefotaxime or ceftriaxone (>2mg/L), moxifloxacin

Confirmation of unusual resistances

BSAC Userday 2018

EnterobacteriaceaeCeftazidime-avibactam. Colistin (unless intrinsic not tested). Tigecycline > 2 mg/L (except for Morganella, Proteus & Providencia). Pan-aminoglycoside resistance. (ESBL; AmpC; isolates from rectal swabs or faecal screens ££).

Carbapenem R EnterobacteriaceaeRarer CPEs (IMP, GES etc) or more common (KPC, NDM, OXA-48, VIM). Do not test faecal screens/environment in CPE confirmed outbreaks –will test infection.

Carbapenem R Acinetobacter spp., Pseudomonas spp.Colistin, confirmed MBL, [Acinet: OXA ££, Pseud: ampC & porin ££]

Charge for S results so check first

Expert rules – things to appreciate

BSAC Userday 2018

• Continual need to update

• Novel / multiple resistance mechanisms

• Editing may skew resistance data e.g. iMLSB

• Mechanisms do not always indicate resistance

• Can be obviated by changes in breakpoints

• Wide range of agents may need to be tested

• Organisms need to be fully identified

• Need for stronger evidence base

• Dependent on some form of expert system for wide application

Expert rule – things to appreciate

BSAC Userday 2018

• Detect anomalous results

• Detect improbable phenotypes

• Detect weakly expressed resistances

• Highlight rare resistances

• Can deduce susceptibility to non-tested agents

• Indicate further appropriate agents to test

• Determine when to refer to AMRHAI

• Facilitate epidemiological studies

• Improve clinical interpretation, consistency and quality. Promote stewardship.