Investigation of Biofilm Formation and Phylogenetic Typing of Escherichia Coli Strains Isolated from Milk of Cows with Mastitis / Ispitivanje Formiranja Biofilma I Filogenetska Tipizacija Sojeva Escherichia Coli Izolovanih Iz Mleka Krava Sa Mastitisom

Escherichia coli is an opportunistic pathogen affecting bovine mammary gland causing mainly transient infections; however, some recent reports indicated that some strains are able to adhere to and internalize into the epithelial cells, which can result in the persistence of the pathogen in the tissue and development of recurrent mastitis. The mechanism of adaptation of E. coli to the mammary gland relies on structures that are distinctive components of its extracellular matrix - curli fimbriae (proteinaceous component) and cellulose (polysaccharide). Expression of these components varies among the isolates. In this study, we investigated the capacity of expression of curli fimbriae and cellulose (via colony morphotype on Congo Red agar) and ability of biofilm formation (microtiter plate test) in 25 strains of E. coli isolated from milk of cows with clinical mastitis. Phylogenetic grouping of the isolates was performed using PCR method based on detection of chuA, yjaA and TspE4-C2 amplicons. Antimicrobial susceptibility was examined using standard disk diffusion test. Production of both extracellular matrix components was established in 56%, and expression of curli fimbriae in 64% E. coli isolates. All isolates that produced curli fimbriae, demonstrated this ability at a temperature of 37°C, indicating the potential role of these adhesive structures in the pathogenesis of mastitis. The results of phylogenetic typing confirmed that E. coli strains isolated from milk of cows with mastitis are typical commensals mainly belonging to phylogenetic groups A and B1. All curli and curli/cellulose producing isolates formed biofilm under in vitro conditions. The biofilm potentially plays an important role in the development of persistent infections as well as recurrent clinical symptoms after antibiotic therapy in spite of quite good in vitro antimicrobial susceptibility of the agent.