**1. Introduction**

Urinary tract infections (UTI's) can be defined as bacteriuria (>105 CFU/mL in adults; >104 CFU/ mL in children) of an uropathogen with associated clinical signs that include dysuria and urgency [18]. According to the United States Centers for Disease Control and Prevention (CDC), a symptomatic urinary tract infection must meet at least one of the following criteria:


UTI is considered to be the most common bacterial infection [107]. It is the second most common infection of any organ and is one of the most common infections in humans [157]. UTIs account for nearly 8 million physician visits and 1.5 million visits to emergency rooms annually in the United States [44, 87, 144]. Although every individual is susceptible to UTIs, certain specific subpopulations are more predisposed to the risk of UTIs. This includes infants, pregnant women, elderly, patients with spinal cord injuries and/or catheters, patients with diabetes, multiple sclerosis, or acquired immunodeficiency virus, and patients with underly‐ ing urologic abnormalities [13, 31, 43, 127, 130]. UTIs are usually localized to the bladder, kidneys or prostate. The etiology of UTIs has been regarded as well-established and consistent.

properly cited.

*Escherichia coli* is the predominant uropathogen responsible for almost 80% of all cases, followed by *Staphylococcus*, *Klebsiella*, *Enterobacter*, *Proteus* and *Enterococci* species [128]. The financial implications of UTIs are enormous due to high incidence. UTIs account for a total annual cost of more than \$ 3.5 billion in the United States [87].

formation is an ancient and integral characteristic of prokaryotes. It is likely that biofilms provided homeostasis during the harsh and fluctuating conditions of the primitive earth such as extreme temperatures, pH and exposure to UV light, thus enabling complex interactions between individual cells. It is, however, generally accepted that planktonic cells existed before the development of biofilm communities. The concomitant development of both planktonic and sessile bacteria in biofilm communities could be attributed to the conditions offered by life on surfaces [151]. The ability of bacteria to adhere to surfaces and form biofilms in different environments is due to the selective advantage that surface association offers the bacteria.

Role of Bacterial Biofilms in Catheter-Associated Urinary Tract Infections…

http://dx.doi.org/10.5772/55200

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The definition of biofilm has evolved over the years. Marshal in 1976 [94] observed the presence of fine extracellular polymer fibrils that anchored bacteria to the surface. Costerton and coworkers [1978; 28] defined biofilms as communities of attached bacteria that were found to be encased in a glycocalyx matrix of polysaccharide that mediates adhesion [28]. They also stated that biofilms consist of single cells and microcolonies which are embedded in the matrix [26]. This definition was later modified to include the ability of biofilms to adhere to surfaces and to each other forming microbial aggregates and floccules [29]. The adhesion to a surface also triggers the expression of genes controlling production of bacterial components required for biofilm formation, thus including the role of gene modulation in the definition [29]. Consequently, a definition of biofilm must include the ability of cells to attach to a surface, extrapolymeric encasing, presence of noncellular and abiotic components in the matrix, physiological attributes of these organisms and the differential gene expression in biofilm cells versus planktonic cells. Taking all this into account, biofilms can be defined as a microbially derived sessile community consisting of cells that are attached to an interface or to each other, are embedded in an extracellular polymeric matrix that they have produced and demonstrate altered phenotype associated with differential gene expression [38]. This definition also applies to biofilm cells that have broken off from a biofilm on a colonized medical device and circulate

Biofilms can form on abiotic surfaces such as minerals, air-water interfaces, and biotic surfaces such as plants, other microbes and animals. In the human body, bacteria reside as biofilms on skin, oropharynx and nose, intestine and indwelling medical devices. To form a biofilm, bacteria are attracted to the surface by environmental signals. On reaching the surface, the bacteria attach to it as single cells or as clusters. When single cells attach to a surface they form a monolayer biofilm. A monolayer biofilm can be defined as one in which the bacteria attach only to the surface [75]. When bacteria attach to a surface as a cluster, they form a multilayer biofilm. Multilayer biofilms can be defined as a microbial community, where the bacteria are attached both to the surface and the neighboring bacterial cells [75]. The type of biofilm formed depends on the environmental conditions and surfaces that favor their development, the genes

that are activated, the architecture of the biofilm and the matrix composition [75].

in the body fluids with the ability to establish itself in another niche.

**3.2. Biofilm formation and structure**

**3.1. Definition**
