Theoretical framework on the uses of standardised antibiotic phenotype and pattern indexes

Abstract number: p1278

Acuner  I.C.

Objectives: 

Acuner et al. have defined standard antibiotic phenotype and pattern indexes that are suitable for phenotype and pattern cataloguing using information derivable from probability distributions in event space. Here, I explore the theoretical framework of the indexes, compare their advantages to the possible alternatives in numerical taxonomy, and discuss the potential uses, especially in antimicrobial resistance surveillance.

Methods: 

The standard antibiotic phenotype index (SAPI) has been defined as: I = c^v/p where; c = observed value of the different categorical case probabilities, v = total number of tested variables, p = specific position (location) of the tested variable in event space. {{{{\rm{ I}}}=\sum_{{i=1}}^{{v}}(c^v\div p_i)}}. The index is aimed at including and representing the information derivable from all of these defined dimensions that forms the event space, such that none of the index values obtained would match with other values. Wherever the derivable information is categorical, it has been digitized for use in the index. To define the dimensions that constructs the event space and use the index for the purposes of standardized antibiotic susceptibility phenotype (pattern) surveillance of bacteria; a. probable categorical case results; resistant, intermediate and susceptible have been digitized as 1, 2 and 3, respectively, and used as probable c values, b. total number of the tested antibiotics has been used as v, c. specific positions (locations) of the tested antibiotics have been digitized as 1, 2,..., N in order. An example of a theoretical bacterial taxon at a specific taxon level (genus, species, subspecies) has been considered to be tested against 21 different antibiotics, and the index values have been calculated. The index values obtained for each of the sequential observable pattern probabilities are digitized as standard pattern index (SPI) values in the same order as 1, 2,...., n. The numerical taxonomy alternative on the base-3 system has been compared.

Results: 

The index value for the theoretically most sensitive phenotype (i.e. susceptibility results of all tested antibiotics are sensitive) is I = 3.645358705; SPI = 1. The index value for the theoretically most resistant phenotype is I = 38131739603; SPI = n.

Conclusion: 

It has been concluded that SAPI and SPI may be useful in phenotype (including MIC) and pattern cataloguing for the purposes of resistance surveillance besides being a potential tool for the investigation of population dynamics of bacteria.