© Wydawnictwo Aluna 78 Wiadomości Lekarskie 2020, tom LXXIII, nr 1 INTRODUCTION The human’s colon maintains a microbial density ap- proaching 10 12  organisms per gram of feces, representing a perfectly balanced ecosystem. e commensal microbiota, derived from the Latin commensal and meant sharing a table, consists of more than 400 species and lives in perfect harmony with the human intestine [1,2]. Escherichia coli is a commensal inhabitant of the intes- tinal tracts of healthy humans and many animal species, but it can also cause a wide range of diseases, ranging from diarrhea to extraintestinal infections [2, 3]. But E. coli is more than just a laboratory workhorse or harmless intestinal inhabitant; it can also be a highly versatile, and frequently deadly, pathogen. Extraintestinal pathogenic Escherichia coli (ExPEC), the specialized strains of E. coli that cause most extraintestinal E. coli infections, represents a major but little-appreciated health threat. Although the reasons for their evolution remain mysterious, by virtue of their numerous virulence traits ExPEC clearly possess a unique ability to cause disease outside the host intestinal tract. Broader appreciation of the existence and importance of ExPEC and better understandings of their distinctive vir- ulence mechanisms, reservoirs, and transmission pathways may lead to effective preventive interventions against the morbid and costly infections ExPEC cause [4,5]. Escherichia coli is one of the most common isolates in clinical microbiology laboratories and classified into three major groups: commensal strains, intestinal pathogenic strains, and extraintestinal pathogenic strains, according to their biological significance to humans [5, 6, 7]. Pu- rulent peritonitis in modern conditions differs from the bacteriological point of view of a combined flora with ever-increasing pathogenic properties. At the same time, Escherichia coli retains the dominant role in the microbial etiology of peritonitis [8]. As pathogenic factors we define adaptive mechanisms of infectious diseases. First of all you should decide on such a fundamental property of bacteria as pathogenic. e presence of microbial pathogenicity factors is im- portant for assessing the etiological significance. For E. coli, pathogenicity is not a species sign and is not related to a specific serogroup. ey are able to realize their pathogenic potential and cause disorders in the human body, limited only by those genetic determinants that have a specific strain of E. coli. THE AIM To study the biological properties of museum and clinical strains of E. coli isolated from patients with peritonitis. STUDY OF PATHOGENIC FACTORS OF E.COLI ISOLATED FROM PATIENTS WITH PERITONITIS DOI: 10.36740/WLek202001114 Olha Yu. Kosilova 1 , Oleksandra O. Vovk 1 , Nataliia M. Katelevska 1 , Tetiana P. Osolodchenko 2 , Svitlana V. Ponomarenko 2 , Viacheslav Yu.Vdovichenko 1 1 KHARKIV NATIONAL MEDICAL UNIVERSITY, KHARKIV, UKRAINE 2 STATE INSTITUTION «I. MECHNIKOV INSTITUTE OF MICROBIOLOGY AND IMMUNOLOGY NATIONAL ACADEMY OF MEDICAL SCIENCES OF UKRAINE», KHARKIV, UKRAINE ABSTRACT The aim: To study the biological properties of museum and clinical strains of E.coli isolated from patients with peritonitis. Materials and methods: It was used 94 strains (clinical, museum and reference). The ability of E. coli to adhere was investigated by hemadhezive method to formal human erythrocytes of 0 (I) Rh-positive blood group. The study measured the ability of microorganisms to produce gelatinaze, caseinase, fibrinolysin, hemolysin. To control of the enzyme activity the positive and negative control with reference strains were used. Synchronisation of cultures activity before experiments was achieved by one-time effect of low temperature (+4 С) during 30 minutes. Results: To investigate the pathogenic factors of E. coli we carried out determining of proteolytic, gelatinous, caseinous, fibrinolytic, haemolytic and adhesion properties. Conclusions: In our investigation pathogen icspecies of Esherihies are virtually indistinguishable from representatives of normal microflora on its morphological, biochemical and cultural properties. During investigation of serological properties of selected of E. coli strains (n = 94) 65.8% of pathogenic serotypes were revealed. Moreover, all marked E. coli isolated from the abdominal cavity of children and adults, as well as museum strains related to enteropathogenic E. coli (O127: K63, O33: K-) and 1 – to enteroinvazive Escherichia coli (O144: K-). KEY WORDS: E.coli, peritonitis, biological properties Wiad Lek. 2020;73(1):78-82 ORIGINAL ARTICLE PRACA ORYGINALNA