Interpretative reading of the

antibiogram

Luis Martínez-MartínezService of Microbiology

University Hospital Marqués de ValdecillaSantander, Spain

ANTIMICROBIAL AGENT

MICRO-ORGANISM PATIENT

RESISTANCE

SUSCEPTIBIL

ITY

VIRULENCEMECHANISMS OF DEFENSE

TOXICITY

PK/PD

ANTIBIO

GRAM

1920 1930 1940 1950 1960 1970 1980 1990 2000

Discovery of antimicrobial agents

Introduction into clinical practice

Susceptibility testing standardization

Interpretative criteria

Description of mechanisms of resistance

Relationship between resistance and

therapeutic failure

Interpretative reading

Automation and expert systems

Antibiogram Reading

Ø Inh. zone (mm)

MIC (mg/L)

S-I-R

Clinical Categories

•CLSI (NCCLS): Clinical and Laboratory Standards Institute•EUCAST: European Committee on Antimicrobial Susceptibility Testing

• SFM: Société Française de Microbiologie

• BSAC: British Society for Antimicrobial Chemotherapy

• MENSURA: Mesa Española de Normalización de la Sensibilidad y Resistencia a los Antimicrobianos•...

Patrice Courvalin.Interpretative reading of antimicrobial susceptibility test.

ASM News 1992, 58:368-375.

ANTIBIOGRAM

“Interpreative reading of the antibiogram”

Phenotype - Resistance

Susceptibility testing results for a concrete microorganism considering a GROUP of antimicrobial agents (usually of the same family)

ANTIBIOGRAM

“Interpreative reading of the antibiogram”

1.- Define Phenotype of susceptibility and Resistance

2.- Deduce the possible mechanism of resistence

3.- Adequate Clinical Categories to the inferred mechanism of resistance, and change phenotype if necessary

S-I-R Microbiological Knowldge

CLINCAL REPORT OF RESULTS

ANTIBIOGRAM

“Interpreative reading of the antibiogram”

AES

S-I-R SOFTWARE

(Expert system)

CLINCAL REPORT OF RESULTS

INTERPRETATION

[Not available in English!]

[Not available in English!]

• Identification of the microorganism (To species level))

• Analysis of susceptibility/resistance Phenotype- Groups (families) of antimicrobial agents - Antimicrobial indicators of resistance

• Define Phenotype- Common Phenotypes- Unusual Phenotypes- “Impossible”Phenotypes

• Deduce biochemical mechanism of resistance• Clinical Relevance of the inferred resistance• Re-define Clinical Categories

Interpreative reading

Requirements of Interpretative reading of the antibiogram

• Identification of the microorganism

• Analysis of S/I/R phenotype

• Use of indicator agents

• Study antibiotic-inhibitor combinations

• Quantitative study of susceptibility

• Use of high inocula (in some occasions)

• Local epidemiology information

• Availability of reference methods

R. Cantón. Enferm Infecc Microbiol Clin 2002; 20: 176-186

MicroorganismIdentification

+antibiogram

REPORT

Antibiogram

Interpretation

Deduce Phenotype of Resistance

Deduce Biochemical Mechanism of Resistance

Clinical Relevance of the mechanism of

resistance

Re-Define Clinical Categories, if necessary

Deduce susceptibility/resistance to non tested antimicrobial agents

Livermore D et al JAC 12001, 48 Suppl 1, 87-102

Livermore D et al JAC 12001, 48 Suppl 1, 87-102

Livermore D et al JAC 12001, 48 Suppl 1, 87-102

Livermore D et al JAC 12001, 48 Suppl 1, 87-102

Livermore D et al JAC 12001, 48 Suppl 1, 87-102

Livermore D et al JAC 12001, 48 Suppl 1, 87-102

Livermore D et al JAC 12001, 48 Suppl 1, 87-102

K. pneumoniae K. pneumoniaeESBL (+)

AMP AMP

IMPIMP

CTX

CTX

CPMCPM

CAZCAZ

Enterobacter cloacae

SHV-12 IN Enterobacter

Klebsiella pneumoniaeCMY-2

Mueller- Hinton Mueller-Hinton Cloxacillin 250 mg/L

MβL

Staphylococcus aureus

OX AK

CN

E

P

PBP2a

ß-lactamR

APH(2”)-AAC(6´)

AminoglicosydeR

erm Macrolides-14R

-15R

-16?

E

S. aureus

ermInducible methylase

ermconstitutive methylase

msrA-BActive efflux

EE

EDA DADA

112414Isolates number

EDCBAREP-PCR pattern

NoneNot doneNoneNotdone

Ser80Ile (2)

Not done (12)Mutations in parC

NoneSer83PheNoneNoneSer83Ile (14)

Asp87Asn (1)Mutations in gyrA

1.5 (I)3 (R)2-4 (I/R)0.38 (S)>32 (R) MIC ciprofloxacin (mg/L)

32 (R)>256 (R)8-16 (S)8 (S)>256 (R)MIC nalidixic acid (mg/L)

REP-PCR

qnrS-PRODUCING Enterobacter cloacae

Cano ME et al, submitted

Enterobacteriaceae COLISTIN RESISTANCE

Calvo J et al unpublished results

Limitations to interpretative reading of the antibiogram

• High complexity of resistance mechanisms

• Limited informatioN about some mechanisms of resistance

• Low level resistance

• Multifactorial multiresistance

• Oversimplification of “interrpetative reading”

• Mistakes when deducing mechanisms of resistance

Modified from: R. Cantón. Enferm Infecc Microbiol Clin 2002; 20:176-186

Benefits of the interpretative reading of theantibiogram

• Adequacy of antimicrobial therapy

• Detection of new mechanisms of resistence

• Analysis of epidmeiology of resistance

• Antimicrobial policy

• Improved quality in laboratory testing

Modified from: R. Cantón. Enferm Infecc Microbiol Clin 2002; 20:176-186