Method for identification of acinetobacter baumannii bv. tryptophandestruens and its subbiovars A and B

The aim of the study was to increase diagnostic sensitivity for identification of A. baumannii bv. tryptophandestruens bacteria and assess prevalence of this biovar and its subbiovars among A. baumannii clinical isolates. There were examined 210 primary strains of A. baumannii isolated in 2021–2022 at Bacteriological Laboratory of the Military Medical Academy named after S.M. Kirov, of which 42 strains were A. baumannii bv. tryptophandestruens. Tryptophandestruens biovar bacteria were identified by chromogenic biotransformation of sodium benzoate on a dense nutrient medium (g/l): peptone enzymatic 5.0; NaCl 5.0; FeCl₃ 6H₂O (10% aqueous solution) 0.1–1 ml; bromothymol blue (1.6% aqueous solution) 3 ml; agar 15.0; NaOH (4% solution) 2.6–3 ml; distilled water 1 l; all components were dissolved by heating and added with sodium benzoate (CAS 532-32-1) 1.0–2.0; adjusted pH 7.2±0.2; sterilized at 121°С, poured into Petri dishes. Bacteria of subbiovars A and B of biovar tryptophandestruens were identified by chromogenic biotransformation of L-tryptophan using the same nutrient medium supplemented with L-tryptophan (1.0–2.0 g/l) instead of sodium benzoate. Both nutrient media were used simultaneously. The A. baumannii cultures studied were seeded with a loop on the media sectors in the form of a plaque, incubated aerobically at 37°С for 18–24 hours, and analyzed final data as follows: the presence of a dark brown color zone of the nutrient medium around bacterial lawn on sodium benzoate- and L-tryptophan-containing medium indicated detection of subbiovar A of the tryptophandestruens biovar; in case of dark brown zone on sodium benzoate- but not L-tryptophan-containing medium around bacterial lawn identified biovar tryptophandestruens subbiovar B. The study revealed for the first time the chromogenic biotransformation of sodium benzoate (benzoic acid) and its importance as a marker for the biovar tryptophandestruens A. baumannii. Two subbiovars A and B of the tryptophandestruens biovar were found. A method was developed to identify the biovar tryptophandestruens A. baumannii and its subbiovars A and B by chromogenic biotransformation of sodium benzoate and L-tryptophan, which enhances diagnostic sensitivity by detecting the subbiovar B. The frequency of tryptophandestruens biovar distribution among primary clinical isolates of A. baumannii in 2021–2022 was determined: out of 210 strains of A. baumannii were 42 (20.0±3.5%) strains of bv. tryptophandestruens including subbiovar A — 27 (12.9±2.3%), subbiovar B — 15 (7.1±1.7%).