Cc. Sanders et al., Ability of the VITEK 2 advanced expert system to identify beta-lactam phenotypes in isolates of Enterobacteriaceae and Pseudomonas aeruginosa, J CLIN MICR, 38(2), 2000, pp. 570-574
The Advanced Expert System (AES) was used in conjunction with the VITEK 2 a
utomated antimicrobial susceptibility test system to ascertain the p-lactam
phenotypes of 196 isolates of the family Enterobacteriaeae and the species
Pseudomonas aeruginosa. These isolates represented a panel of strains that
had been collected from laboratories worldwide and whose beta-lactam pheno
types had been characterized by biochemical and molecular techniques. The a
ntimicrobial susceptibility of each isolate tvas determined with the VITEK
2 instrument, and the results were analyzed with the AES to ascertain the b
eta-lactam phenotype. The results were then compared to the beta-lactam res
istance mechanism determined by biochemical and molecular techniques. Overa
ll, the AES was able to ascertain a beta-lactam phenotype for 183 of the 19
6 (93.4%) isolates tested. For 111 of these 183 (60.7%) isolates, the corre
ct beta-lactam phenotype was identified definitively in a single choice by
the AES, while for an additional 46 isolates (25.1%), the AES identified th
e correct beta-lactam phenotype provisionally within two or more choices. F
or the remaining 26 isolates (14.2%), the beta-lactam phenotype identified
by the AES was incorrect. However, for a number of these isolates, the erro
r nas due to remediable problems. These results suggest that the AES is cap
able of accurate identification of the beta-lactam phenotypes of gram-negat
ive isolates and that certain modifications can improve its performance eve
n further.