This article presents data on the frequency of synthesis of the enzyme pyrrolidonylpeptidase by enterobacteria isolated from food and animal feed, thereby establishing its importance for the identification of enterobacteria. In microbiology, many rapid tests are used to differentiate and identify enterobacteria (Api-test, Enter-test, etc.). They include reagents, which determine the presence of the enzyme L-pyrrolidonyl peptidase. Most of the laboratories in Ukraine, these test systems are almost not used, because of their expensive cost, as their composition includes many tests that are not provided for in GOST and ISO. But when interpreting the results of studies, there are often doubts, since salmonella are similar to other representatives of the Enterobacterialae family, such as Citrobacter spp., and without the help of ELISA, ELFA, PCR and other analyzers it is difficult to ensure the correct result. Analyzers and consumables for them are not always available in conventional laboratories. In veterinary bacteriology of Ukraine detection the enzyme L-pyrrolidinyl peptidase is not widespread since the identification of enterobacteria is carried out in accordance with the requirements of ISO, EN, DSTU, GOST and methodological developments, in which the definition of this enzyme is not described.

Enterobacteria were isolated from 886 specimens, of which 659 were food products and 227 samples for animal feed. For comparison of field crops, reference strains of enterobacteria were used, which were provided to us from the State Scientific Control Institute of Biotechnology and Microorganisms and the Institute of Microorganisms L. Gromashevsky: Salmonella typhimurium 144, Salmonella adobraco 1, Escherichia coli АТСС 25922, Shigella flexneri GІСК 266а, Klebsiella  pneumonia NCTC 5055, Serratia marcescens НДА-1, Enterobacter aerogenes GІСК 2531, Proteus vulgaris GІСК 160209. Since the bacteria evolve adapting to the environmental conditions during their existence, therefore, for the solution of the problem, we artificially contaminated food roducts (pork, beef and chicken meat, raw dumplings, cold-smoked fish) and animal feeds with strains of microorganisms (1 ml 10⁴ per 50 g) which were kept in a thermostat at a temperature of 30 °C for 20–24 hours.

Identification of the enzyme pyrrolidonyl peptidase was carried out using a PYR test (from Erba Lachema, Czech Republic). To this end, a suspension of the daily agar culture was applied to a strip moistened with distilled water impregnated with reagent № 1 – pyrolidonyl. The strips with cultures were placed in sterile Petri dishes and incubated at 37 °C for 10 min. Further, the reagent № 2 of a color developer (dimethylaminocinnamalaldehyde solution) was applied and the color change was observed at room temperature after 1–2 minutes. Under the action of the bacterial peptidase enzyme, pyrolidonyl-b-naphthylamide is cleaved to b-naphthylamide, and after application of the solution with dimethylamino-cinnamalaldehyde, the color of the strip changes to red or red-orange.

But the results of our experimental studies indicate that the detection of the pyrrolidonyl peptidase enzyme is of great importance for identification in Enterobacteriaceae, namely Salmonella and Citrobacter. Studies have shown that Citrobacter possess L-pyrrolidinylpeptidase in 100 % of cases, regardless of the type of material: food or feed. In contrast, the Salmonella does not completely produce it. Also obtained data on the frequency of synthesis of pyrrolidonyl peptidase from other representatives of enterobacteria: Klebsiella spp. аnd Serratia spp. рroduce in 100 % of cases, (11,5 %), Hafnia spp., E. coli, Proteus spp. аnd Shigella spp. do not have pyrrolidonyl peptidase activity.

Therefore, we propose to test for the enzyme L-pyrrolidonyl peptidase (in the absence of analyzers for the detection of Salmonella) as a supplement to DSTU EN 12824, DSTU ISO 6579 and DSTU IDF 93A and other standards for the detection and identification of Salmonella spp. and Citrobacter spp., which are similar to each other with biochemical properties and antigenic structure.

Key words: significance, identification, pyrrolidonilpeptidase, feed, Salmonella, Citrobacter, food.