THE SELECTIVE SYNTHETIC NUTRIENT MEDIUM «ACINETOBACTER PHENYLALANINE AGAR» FOR THE ISOLATION AND IDENTIFICATION OF THE ACINETOBACTER CALCOACETICUS – ACINETOBACTER BAUMANNII COMPLEX
Infekciâ i Immunitet
The aime of the study is clinical microbiological testing of the selective nutrient medium «Acinetobacter phenylalanine agar» for the isolation and identification of bacteria of the Acinetobacter calcoaceticus - Acinetobacter baumannii complex (ACB complex). In the clinical and bacteriological laboratory of the Military Medical Academy, in 2018, 400 samples of clinical material (discharge of wounds, blood, urine, broncho-alveolar lavage) were studied in parallel both by the traditional method
... raditional method (seeding on blood agar, pure cultures isolating and identifying with biochemical tests and with analysis on microbiological analyzer Vitek 2, bioMerieux) and by seeding on plates with a nutrient medium «Acinetobacter phenylalanine agar». The selectivity of this medium is due to acinetobacters trophic selection of L-phenylalanine as the sole source of nitrogen and carbon and trimethoprim additional selection. Acinetobacters of the ACB complex were identified after 18-24 h of incubation at 37 ° C by the presence of characteristic colonies on a selective medium. Control tests for cytochrome oxidase and the oxidative/fermentation (OF)-glucose test by the peroxide-hydrogen microvolume method (for 1 h) allowed to expressly distinguish the acinetobacters of the ACB complex from other bacteria and from the group of acinetobacter non-oxidizing glucose. Then, the species of all isolated strains of acinetobacters was identified by the method of matrix-activated laser desorption / ionization with time-of-flight mass spectrometry (MALDI - TOF MS). Acinetobacters were isolated on selective medium in 26 samples (18 samples in monoculture, 8 - in association with Pseudomonas aeruginosa or Klebsiella pneumoniae subsp. pneumoniae with very small associate colonies); by the traditional method - in 20 samples (7 in monoculture, 13 - in associations with Pseudomonas aeruginosa, Klebsiella, Escherichia, Citrobacter, Providencia, Staphylococcus, Enterococcus, Candida albicans). Using the MALDI-TOF MS method, it was established that out of 26 strains of acinetobacter isolated on a selective medium, 25 belong to the ACB complex (A. baumannii - 23, A. pittii - 2). One strain (A. baylyi) did not belong to the species of the ACB complex. Therefore, the diagnostic specificity of the Acinetobacter phenylalanine agar synthetic medium for the isolation and identification of bacteria of the A. calcoaceticus - A. baumannii complex is 96.2%, and its diagnostic sensitivity exceeds the traditional method by 25%. The use of selective medium accelerates the study - the isolation and identification of the acinetobacters of ACB complex ends 18-24 h after the seeding of clinical material. The selectivity of the nutrient medium is potentially stable, since its main trophic selection factor does not depend on the acquired antibiotic resistance of bacteria. As a synthetic nutrient medium, it is suitable for standardized studies.