# Biofilm Lifestyle in Recurrent Urinary Tract Infections
## 1 Introduction  
Urinary tract infections (UTIs) are one of the most common bacterial infections in humans, and account for 40% of all nosocomial infections [1, 2, 3, 4]. The incidence of UTIs among the population has increased by 60% between the years 1990 and 2019, confirming that UTIs represent a common public health problem that is far from being eradicated [5]. Typical symptoms include bacteriuria accompanied by urinary frequency, urgency, dysuria and suprapublic discomfort [6]. UTIs can be classified into complicated and uncomplicated urinary tract infections. Uncomplicated UTIs, commonly calledystitis, are a lower urinary tract infection, which only involves the bladder. Such infections are simple and easily resolved with antibiotic treatments. On the other hand, a complicated urinary tract infection is a simple infection that has progressed to the upper urinary tract and is usually associated with other risk factors. Complicated UTIs usually require longer antibiotic courses and areassociated with high rates of treatment failure, recurrent infection, sepsis, and significant morbidity and mortality [6; 7; 8]. Uncomplicated UTIs are common in females, affecting 40-60% of females at least once in their lifetime, while all urinary tract infections in males are considered complicated [6; 8]. Recurrent UTIs are defined as at least two acute episodes of UTIs occurring within a 6-month period or three episodes in a 12-month period, with much higher incidence in females than males [9; 10]. The infection can be community-acquired, hospital-acquired or self-infected [10; 11; 12]. Most community-acquired infections result from poor personal hygiene, low sanitary precautions, or multiple sexual partners. Self-infection usually arises in immunocompromised individuals or high-risk cases, usually caused by commensal inhabitants from the perine urethral, vaginal or rectal flora [13; 14].  
Biofilm formation represents the cornerstone in the pathogenesis of UTIs, since bacterial biofilms play a pivotal role in catheter-associated UTIs (CAUTIs), which account for 40% of all nosocomial infections [15; 16; 17]. Furthermore, biofilm formation is considered one of the most important mechanisms behind the high rates of recurrence and antimicrobial resistance that are often associated with UTIs [15; 17; 18; 19]. Bacterial pathogens, both Gram-negative and Gram-positive, are the most common suspects behind UTIs [9; 19; 20]. _Escherichia coli_, _Proteus mirabilis_, _Klebsiella pneumoniae_, _Staphylococcus epidermidis_, _Staphylococcus saprophyticus_, _Staphylococcus aureus_ and _Enterococcus faecalis_ are among the most frequent bacterial pathogens that are common in uncomplicated UTIs and complicated UTIs, as well as in CAUTIs [5; 6; 14; 21; 22; 23]. This is not to mention the increasing role of _Pseudomonas aeruginosa_ and _Acinetobacter baumaniii_ in complicated nosocomial UTIs [24; 25]. However, some fungi, such as _Candidia_ spp., are also associated with high incidence of UTIs. Although using different pathogenic pathways, _Candidia_ spp. share bacterial pathogen with their ability to form persistent biofilms that contribute to chronic recurrent UTIs [26; 27; 28; 11]. The current work aims to review UTIs' pathogenesis, shedding light on the most frequent UTI pathogens, with special focus on biofilm lifestyle and its impact on pathogenesis of UTIs. Furthermore, the present review summons some of the more traditional approaches to eradicating biofilms in addition to the latest ones.