This method constitutes a tool for specialists in clinical
microbiology, general microbiology, marine microbiology, in all laboratories
where antimicrobial susceptibility testing is an important part of the
service provided.
The NRI method can determine interpretive limits for antimicrobial
susceptibility and can thereby calibrate the AST in the individual laboratory.
Such results are therefore comparable with data from other laboratories.
Also, the standard deviation is a quality marker of the test performance
in the laboratory.
NRI to set interpretive breakpoints
NRI for quality assessment of AST
NRI to calibrate AST for international
comparisons
AST = Antimicrobial susceptibility test
Göran Kronvall, born in 1938 MD, PhD, Inventor of NRI.
Also invented the co-agglutination test method.
Also invented SRA, Single Strain Regression Analysis
Also invented acid acridine orange staining of specimens.
Also discovered Ig binding to grp A, C, and G strep.
Also discovered albumin binding to bacteria.
Also produced the original ADBact LIS.
Aggregated measurements from antimicrobial
susceptibility tests, MIC or disc diffusion tests, are close to Gaussian
distributions for individual bacterial species and antibiotics, slightly
peaked and skewed towards higher zone values.
Close collaboration with professor Peter Smith,
Galway, Ireland, marine microbiologist, has contributed in several important
ways to NRI testing.
NRI can calculate the optimal Gaussian distribution
for test results and a susceptibility limit can therefore be set as a defined
value for the standard deviation. This means that susceptibility results
can be calibrated and therefore compared with other results internationally
and world wide.
Important: Instructions and comments
have been added below for both NRI-MIC and NRI-Disk test results.
By downloading and using these Excel programmes, you agree to acknowledge:
"The automatic excel programmes were made available through courtesy
P.Smith, W.Finnegan, and G.Kronvall." The reference is: Smith
P, Finnegan W, Ngo T, Kronvall G. Influence of incubation temperature
and time on the precision of MIC and disc diffusion antimicrobial susceptibility
test data. Aquaculture 2018; 490:19-24.
References:
a/ original references to the
NRI principles and to the analysis of inhibition zone diameter distributions:
1. Kronvall G,
Kahlmeter G, Myhre E, Galas MF. A new method for normalized interpretation of
antimicrobial resistance from disk test results for comparative purposes. Clin
Microbiol Infect 2003; 9(2):120-132.
2. Kronvall G.
Determination of the real standard distribution of susceptible strains in zone
histograms. Int J Antimicrob Agents 2003; 22:7-13.
b/ when analyzing MIC distributions:
3. Kronvall G,
Karlsson I, Walder M, Sörberg M, Nilsson LE. Epidemiological MIC cut-off
values for tigecycline calculated from Etest MIC values using normalized resistance
interpretation. Journal of Antimicrobial Chemotherapy 2006; 57:498-505.
4. Kronvall G.
Normalised Resistance Interpretation, NRI, as a tool for establishing epidemiological
MIC susceptibility breakpoints. J Clin Microbiol 2010; 48(12):4445-4452.
