## 3 Discussion  
The goal of this work was to comprehensively characterize clinical isolates of the UPEC strains. Our studies show that these strains present characteristic features of their genus, but we also demonstrated a new characteristic phenotypic pattern for the studied collection, which should be further explored. Among the 9 genes coding for the virulence factors tested, the most frequently detected were _fimH_ (100%), _sitA_ (92.5%), _aer_ (75%), and _sfa_ (70%). Such a high distribution of the _fimH_ gene was also confirmed in studies conducted in Ethiopia, Romania, Mongolia, Iran, Mexico, and China [13; 41; 42; 43; 44; 45; 46], which may indicate a key role of this factor in the development of UTI. The percentage of other VFs (Sfa, PapC, HlyA, CNF1) that characterize the strains in the studied collection is on par with another study conducted in Poland [47], while in other countries, the share of these factors varies [13; 48; 49; 50; 51; 52]. A high percentage of sequences encoding SitA and Aer characterized the UPEC studied, and this observation is in line with the results obtained in other studies [53; 54; 55; 56; 57]. The presence of such proteins indicates that, despite the environment in the urinary tract where iron access is limited, UPEC strains are able to survive and develop UTI. Additionally, the presence of the two genes in our study was significantly correlated with each other (Figure 2). Moreover, we observed a correlation between the genes of toxins related with a pathogenicity island, namely _hlyA_ and _cuf_. The _cuf_ gene was recently shown [58] to be dependent on _hlyA_ presence, while _hlyA_ occurrence is independent of _cuf_. The invasive protein IbeA and the serum survival enhancing factor Iss were the least frequent, with similar percentages described by [PERSON] et al. [59]. The described virulence factors are crucial for triggering urinary tract infections; however, UPEC strains can differ significantly in terms of genetic background. This was confirmed by the fact that in the studied population of 120 strains, as many as 51 different viurlotypes were obtained. Pathotypes of virulent _E. coli_ strains are often associated with a particular phylogeny. We determined that the predominant group in the collection was group B2 (71.7%), followed by groups B1 (10.8%) and D (7.5%). It is noteworthy that virulent extraintestinal strains mainly belong to groups B2 and D [60]. Similar findings were obtained in other studies, in which the B2 group was predominant [45; 49; 61; 62; 63]. Different phylogenetic groups expressed different average VF counts. Group B2 had the highest score of 6.01, groups A, C, and D were intermediate, while B1 had the lowest number of VF genes. A similar relationship for groups B2 and B1 was reported recently by [PERSON] et al. [64]. A positive correlation of VFs and those phylogroups was further observed in studies from the early 2000s [65; 66]. The increasing prevalence of UTIs results in the overuse of broad-spectrum antibiotics, such as fluoroquinolones, cephalospors, and aminoglycos, which contributes to increased antibiotic resistance [10]. Resistant strains, including those not susceptible to more than one antibiotic, were also present in the population of isolates studied. The highest resistance was attributed to ampicillin (92.5%) and chemotherapy (norfloxacin, ciprofloxacin, nitrofurantoin, trimethoprim/sulfamethoxazole; 58.5%). In their study, [PERSON] et al. reported 59% of strains resistant to at least one of the antimicrobial agents tested, including the highest for ampicillin (51%) and trimethoprim-sulfamethoxazole (44%) [50]. Likewise, in an Australian study on antimicrobial use and bacterial resistance conducted in 2014-2015, the highest resistance rate for _E. coli_ was also recorded for ampicillin (53.2%), followed by trimethoprim (31.3%). It is also worth mentioning that the percentage of resistant isolates was higher in 2015 when compared to 2014 [67]. A high rate of ampicillin-resistant strains was also obtained in other studies [47; 52; 68].