## 1 Introduction
Biofilms are increasingly recognized as major contributors to pathogenicity, recurrence, chronicity, and recalcitrance-to-treatment of UTIs, as well as many other diseases. Biofilm is defined as a structured formation of bacterial cells adhering to a surface, surrounded by a polymeric matrix that they have produced [22]. Biofilm formation can be considered to be another virulence factor for UPEC strains, which promotes their survival in the urinary tract by protecting against the cleansing effects of hydrodynamic forces, host defense mechanisms, and antibiotics [23]. Currently, the ability to form a biofilm is not well understood, and several factors are generally considered to be involved in its formation, including adhesins and specific proteins such as antigen 43 [24]. Thus, the problem of frequent UTI recurrences and the tendency for UTIs to develop into a chronic form has been associated with biofilm formation during infection [25]. There is a general consensus in the research that the so-called stringent response is involved in the control of the pathogenicity of various bacterial species as a mechanism of bacterial adaptation towards changing environmental conditions through the modulation of gene expression. It is involved in processes related to growth, stress, starvation, and survival, and for many bacterial species, the stringent response is required for efficient expression of the virulence factors [26; 27; 28]. In the broadest terms, the stringent response is the global response of a cell to stress conditions resulting in inhibition of most processes requiring energy consumption [26]. The key molecules in the stringent response are the small-nucleotide alarmones, ppGpp, and ppGpp (guanosine tetra- and pentaphosphates) collectively referred to as (p)ppGpp. These alarmones are synthesized in _E. coli_ by two enzymes. One is ReIA, which responds to amino acid starvation, and the other is the SpoT enzyme, which is responsible for the synthesis of (p)ppGpp during other types of stresses and deprivation, but additionally is involved in the hydrolysis of (p)ppGpp [26; 29]. However, the importance of (p)ppGpp in the exponential growth rate control has also been presented [30]. The (p)ppGpp signaling controls global metabolic changes in response to environmental fluctuations and regulates such processes as biofilm formation, quorum sensing, adaptive processes, or bacterial virulence [31]. The entrance of cells into the stationary phase of growth is correlated with increased accumulation of intracellular (p)ppGpp [26]. This is caused by environmental constraints on growth, such as the depletion of nutrients or excess intermediate metabolites secreted into the environment, and it activates the effector proteins RelA and SpoT to synthesize the alarmones. This leads to changes in the expression of a number of metabolism-related genes, as well as the activation of the regulator FimB, which controls the phase variation of type 1 fimbiae in _E. coli_[32; 33]. Type I fimbiae mediate the adhesion and invasion of UPEC and also are an important factor at the initial stages of biofilm formation [9; 34; 35]. Due to the prevalence of UTIs and their potential for recurrence and subsequent medical complications, UPEC infections are a serious health problem worldwide. The main aim of this study was to examine the genetic diversity of UPEC isolates from UTI patients from northern Poland. Furthermore, we conducted a phylogenetic clustering based on [PERSON]'s classification, as well as testing evaluating susceptibility to basic antibiotics. In our thorough approach, we also investigated the UPEC strains' biofilm-forming ability (assessed by differentiation on Congo red agar), and evaluated their metabolic phenotypes by measuring the stringent response alarmones' basal levels, as well as assessing the growth rates of selected strains. Then, strains showing specific phenotypes were subjected to virulence analysis in a surrogate infection model of _Galeria mellonella_.