**5. Control strategies to prevent CAUTI**

a polysaccharide matrix surrounds the bacteria [7, 74]. At around 12 h post infection, late IBCs are formed, when UPEC regain their rod shape and motility and flux out of the bladder cells. Fluxing aids UPEC in infecting neighboring cells [74]. The last phase of IBC formation results in UPEC filamentation which occurs 24 to 48 h post infection, where filamentation helps UPEC evade host immune responses. The filamentous bacteria can also separate to form rod-shaped daughter cells. The appearance of filamentous cells also coincides with the appearance of small

The pathogenesis of CAUTI depends on the physicochemical properties of the catheter material and its susceptibility to bacterial colonization. Bacterial binding to the bladder mucosa triggers an inflammatory response that leads to neutrophil influx and sloughing of the infected epithelial cells [78]. This helps to clear the bacteria from the mucosal surface. In the case of a catheter, besides the absence of inherent defense mechanisms, they also provide a survival advantage to the bacteria which become difficult to eradicate. The advantages include resistance from being swept away by the urine flow, resistance to phagocytosis and antimi‐ crobials [167]. In addition to the catheter providing an environment for biofilm formation, the presence of a catheter helps to weaken many normal defenses of the bladder. The catheter helps to connect the heavily colonized perineum with the sterile bladder, thus providing a route for bacterial entry into the bladder. Urine pools in the bladder or in the catheter and the resulting urinary stasis promote bacterial growth. Additionally, the catheter also damages the bladder mucosa by triggering inflammatory response and mechanical erosion [175]. Once bacteria gain entry into the urinary tract, low level bacteriuria progresses within 24 to 48 h in

**Chronic bacterial prostatitis**: The prostatic ducts and acini provide a safe environment for bacteria to multiply and induce host response. If the bacteria are not eradicated by the immune response, it leads to their persistence and formation of bacterial microcolonies. The presence of microcolonies induces persistent immunological stimulation and chronic inflammation

**Recurrent cystitis**: UPEC binds to superficial bladder epithelial cells resulting in neutrophil recruitment and influx into the bladder lumen. Neutrophil recruitment occurs due to the recognition of bacterial LPS by the toll-like receptors. Additionally, interaction between type I pili and the uroepithelium results in exfoliation of the superficial epithelial cells causing pathogen shedding into the urine [129]. When IBCs form in the epithelial cells, they persist as

**Pyelonephritis**: Once the bacteria reach the kidney, they adhere to the uroepithelium and form thin biofilms before invading the renal tissue [106]. Additionally encrustation and obstruction to the catheter flow due to formation of crystalline biofilms leads to bladder distention, urine

groups of UPEC on newly infected healthy cells [74].

*4.3.1. Pathogenesis of catheter-associated biofilm*

64 Recent Advances in the Field of Urinary Tract Infections

the absence of an antimicrobial therapy [145].

a chronic reservoir, which leads to recurrent cystitis.

**4.4. Biofilm related UTIs**

[105].

CAUTI is the most common hospital acquired infection and accounts for up to 40% of all health care associated infections in the United States [102, 156]. About 15-25% of hospitalized patients have an urethral catheter in place during some point of their stay. It is estimated that around 30 million bladder catheters are placed annually in the United States, resulting in several hundred thousand cases of CAUTI [156]. A systemic review of the proportion of health care associated infections that can be prevented revealed that CAUTI was the most preventable nosocomial infection [170]. An estimate of the number of avoidable cases ranged from 95,483 to 387,550 per year and associated lives saved ranged from 2225 to 9031 annually. This prevention could also avoid the annual cost of these illnesses which is estimated at \$1.8 million to \$115 million [170]. This underscores the need for control strategies to prevent CAUTI. Prevention of CAUTI is primarily based on reviewing the criteria for appropriate placement and early removal of catheters. The advances in our understanding of the pathogenesis and key factors that influence the onset of infection are also critical in the development of adequate and effective control strategies [137]. Several protective strategies have been suggested for CAUTI, some of which are already in place for patient care, whereas others are still in development. The control strategies include:

### **5.1. Need for and duration of catheterization**

It is estimated that about 21-50% of catheters are placed without justified need and catheters are inappropriately retained for 33-50% of total device days [73, 101]. The most effective ways for the preventing CAUTI are by reducing the duration of catheterization and its early removal [51]. Use of interventions such as nurse prompted removal suggestions and computer based reminders to the patients have resulted in a decline in catheter retention and a concomitant reduction in bacteriuria [164]. Thus, it is important to refrain from using an indwelling catheter without an appropriate indication. A study conducted in an emergency department indicated that use of pre-insertion checklists have led to an improved adherence to indications for placement resulting in the increase in the number of appropriately placed catheters from 37% to 51% [50].

### **5.2. Catheter placement and management**

Since the catheter provides a connection between the highly colonized perineum and the sterile bladder, sterility during catheter handling and placement is of greatest importance. In this regard, hand hygiene plays a vital role in the prevention of CAUTI [16]. Insertion of a catheter in the emergency room rather than an operating room has been shown to be associated with higher rates of catheter associated bacteriuria (CAB; 158). Use of an aseptic insertion technique reduces the risk of acquiring resistant organisms in the hospital [63]. A randomized study conducted by Platt and others [1983; 118] demonstrated that hospitalized patients intubated with a catheter without a pre-sealed junction were 2.7 times more likely to develop CAB than patients with pre-connected catheter drainage bags and sealed junctions. Therefore, the use of closed catheter drainage systems universally is recommended [63]. Similarly, any breach in the closed drainage system would also increase the risk for CAB. Any manipulation of the indwelling catheter should be avoided so that breaches in the closed drainage and shear trauma can be minimized [25].

**5.5. Antimicrobial coating**

planktonic cells of uropathogens [56].

*5.5.1. Nanoparticles and iontophoresis*

reduced the viable count from 109

CFU/ml to 103

from 107

*5.5.2. Antimicrobials*

Antimicrobial modification of catheters is achieved by coating, matrix loading and immersion in an antimicrobial solution. The primary objective behind the incorporation of antimicrobial on a catheter is to reduce bacterial attachment and biofilm formation. Additionally, release of antimicrobials from the catheters into the milieu is also another potential approach to control

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

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

67

Nanoparticles by virtue of their small size have the ability to penetrate bacterial cells, disrupt cell membranes and bind to the chromosomal DNA. Lelouche and others [2009; 84] demon‐ strated that glass surfaces coated with magnesium fluoride nanoparticles inhibited biofilm formation by *S. aureus* and *E. coli*, whereas magnesium fluoride solutions did not affect biofilm

The application of low intensity direct current (Ionotophoresis) *in vitro* has been shown to increase the antimicrobial activity of antibiotics on bacteria embedded in biofilms [27]. Chakravarti and others [2005; 21] used a urinary flow model to test the *in vitro* antibiofilm efficacy of iontophoretic silver wire containing silicone catheters. These catheters were challenged with *P. mirabilis* and then exposed to a steady current of 150 µA. It was observed that application of the electric field increased the time to blockage from 22 h to 156 h, and

CFU/ml to 104

intubated with catheters containing platinum electrodes showed a decline in pathogen count

A variety of antimicrobials applied on urinary catheters have been investigated for their efficacy in controlling UTIs using *in vitro* and *in vivo* models.Nitrous oxide is known to exhibit bactericidal activity [123]. Urinary catheters impregnated with gaseous nitrous oxide, a known antimicrobial, and challenged with *E. coli*resulted in the slow release of nitrous oxide into the urine for over 14 days, and decreased biofilm formation by *E. coli*. Chlorhexidine is a common antimicrobial used against oral plaques. *In vivo* studies in rabbits intubated with genidine (combination of chlorhexidine and gentian violet) coated silicone catheters showed a reduction in biofilm formation by *E. coli*, *E. faecium*, *P. aeruginosa*, *K. pneumoniae* and *Candida* in compar‐ ison to silver coated and uncoated catheters [54]. Catheter associated bacteriuria was noticed in 60% and 71% of the rabbits with uncoated catheters and silver hydrogel coated catheters, respectively, whereas CAB did not occur in any of the rabbits with genidine coated catheters. Similar to chlorhexidine, triclosan is another antibacterial ingredient in toothpastes and cleaners used in health care settings. Triclosan exerts its antibacterial effect by inhibiting bacterial fatty acid synthesis [147]. Incorporation of triclosan in the balloon of catheters resulted in its release and diffusion through latex and silicon catheter balloons. The balloon served as a reservoir and the membrane helped in controlled release of triclosan. This in turn slowed encrustation and maintained the lumen patent for 7 days as compared to 24 h in saline-filled

CFU/ml on application of a direct current of 400 µA [33].

CFU/ml. Similar *in vivo* study in sheep

formation. This highlights the size dependent effect of nanoparticles.

### **5.3. Catheter design**

Catheter design has not changed significantly since the inception of the Foley catheter in the 1930s [97]. In addition to the catheter design, biocompatibility of the material is crucial. Catheter material can also impact the rate of biofilm formation. Scanning electron microscopy imaging of latex catheters revealed that presence of more uneven surfaces on it than other silicone counterparts which can promote bacterial adhesion [150]. Additionally latex has been associated with toxic effects *in vitro* and proinflammatory reactions *in vivo* leading to polypoid cystitis on chronic exposure [49]. Moreover, silicone catheters are more popular to avoid allergic reactions associated with latex use. Besides being hypoallergenic, silicone catheters have a larger lumen and are minimally prone to encrustation by crystalline biofilms [36]. A newly engineered silicone catheter with a trefoil cross-section was shown to reduce CAB and inflammation when compared to a standard urinary catheter [153]. The trefoil conformation helps to minimize the surface area of contact between the catheter and the urethra, thereby decreasing friction and trauma and increasing drainage of urethral secretions [137].

#### **5.4. Hydrogel coated catheters**

Cross linked insoluble polymers that are hydrophilic and trap water are known as hydrogels. Use of hydrophilic coating on catheters has been shown to improve patient comfort, reduce bacterial adherence and encrustation. The presence of hydrogels also increases lubrication and decreases bacterial adhesion to the interface of the tissue and the catheter [11]. However, conflicting data exist on the ability of hydrogel coated catheters to reduce CAUTI, which could be attributed to the type of hydrogel incorporated. Tunney and Gorman [2002; 169] used *in vitro* models to demonstrate that Poly(vinyl pyrollidone)-coated polyurethane catheters had a lower rate of encrustation when compared to uncoated polyurethane and silicone catheters. Another study showed that the use of poly(ethylene oxide)-based multiblock copolymer and segmented polyurethane increased the time to encrustation and catheter blockage from 7.8 h to 20.1 h [116]. These findings collectively suggest that the type of hydrogel coating can affect the rate of encrustation and the resulting catheter blockage.

### **5.5. Antimicrobial coating**

in the emergency room rather than an operating room has been shown to be associated with higher rates of catheter associated bacteriuria (CAB; 158). Use of an aseptic insertion technique reduces the risk of acquiring resistant organisms in the hospital [63]. A randomized study conducted by Platt and others [1983; 118] demonstrated that hospitalized patients intubated with a catheter without a pre-sealed junction were 2.7 times more likely to develop CAB than patients with pre-connected catheter drainage bags and sealed junctions. Therefore, the use of closed catheter drainage systems universally is recommended [63]. Similarly, any breach in the closed drainage system would also increase the risk for CAB. Any manipulation of the indwelling catheter should be avoided so that breaches in the closed drainage and shear trauma

Catheter design has not changed significantly since the inception of the Foley catheter in the 1930s [97]. In addition to the catheter design, biocompatibility of the material is crucial. Catheter material can also impact the rate of biofilm formation. Scanning electron microscopy imaging of latex catheters revealed that presence of more uneven surfaces on it than other silicone counterparts which can promote bacterial adhesion [150]. Additionally latex has been associated with toxic effects *in vitro* and proinflammatory reactions *in vivo* leading to polypoid cystitis on chronic exposure [49]. Moreover, silicone catheters are more popular to avoid allergic reactions associated with latex use. Besides being hypoallergenic, silicone catheters have a larger lumen and are minimally prone to encrustation by crystalline biofilms [36]. A newly engineered silicone catheter with a trefoil cross-section was shown to reduce CAB and inflammation when compared to a standard urinary catheter [153]. The trefoil conformation helps to minimize the surface area of contact between the catheter and the urethra, thereby

decreasing friction and trauma and increasing drainage of urethral secretions [137].

the rate of encrustation and the resulting catheter blockage.

Cross linked insoluble polymers that are hydrophilic and trap water are known as hydrogels. Use of hydrophilic coating on catheters has been shown to improve patient comfort, reduce bacterial adherence and encrustation. The presence of hydrogels also increases lubrication and decreases bacterial adhesion to the interface of the tissue and the catheter [11]. However, conflicting data exist on the ability of hydrogel coated catheters to reduce CAUTI, which could be attributed to the type of hydrogel incorporated. Tunney and Gorman [2002; 169] used *in vitro* models to demonstrate that Poly(vinyl pyrollidone)-coated polyurethane catheters had a lower rate of encrustation when compared to uncoated polyurethane and silicone catheters. Another study showed that the use of poly(ethylene oxide)-based multiblock copolymer and segmented polyurethane increased the time to encrustation and catheter blockage from 7.8 h to 20.1 h [116]. These findings collectively suggest that the type of hydrogel coating can affect

can be minimized [25].

66 Recent Advances in the Field of Urinary Tract Infections

**5.3. Catheter design**

**5.4. Hydrogel coated catheters**

Antimicrobial modification of catheters is achieved by coating, matrix loading and immersion in an antimicrobial solution. The primary objective behind the incorporation of antimicrobial on a catheter is to reduce bacterial attachment and biofilm formation. Additionally, release of antimicrobials from the catheters into the milieu is also another potential approach to control planktonic cells of uropathogens [56].

### *5.5.1. Nanoparticles and iontophoresis*

Nanoparticles by virtue of their small size have the ability to penetrate bacterial cells, disrupt cell membranes and bind to the chromosomal DNA. Lelouche and others [2009; 84] demon‐ strated that glass surfaces coated with magnesium fluoride nanoparticles inhibited biofilm formation by *S. aureus* and *E. coli*, whereas magnesium fluoride solutions did not affect biofilm formation. This highlights the size dependent effect of nanoparticles.

The application of low intensity direct current (Ionotophoresis) *in vitro* has been shown to increase the antimicrobial activity of antibiotics on bacteria embedded in biofilms [27]. Chakravarti and others [2005; 21] used a urinary flow model to test the *in vitro* antibiofilm efficacy of iontophoretic silver wire containing silicone catheters. These catheters were challenged with *P. mirabilis* and then exposed to a steady current of 150 µA. It was observed that application of the electric field increased the time to blockage from 22 h to 156 h, and reduced the viable count from 109 CFU/ml to 104 CFU/ml. Similar *in vivo* study in sheep intubated with catheters containing platinum electrodes showed a decline in pathogen count from 107 CFU/ml to 103 CFU/ml on application of a direct current of 400 µA [33].

### *5.5.2. Antimicrobials*

A variety of antimicrobials applied on urinary catheters have been investigated for their efficacy in controlling UTIs using *in vitro* and *in vivo* models.Nitrous oxide is known to exhibit bactericidal activity [123]. Urinary catheters impregnated with gaseous nitrous oxide, a known antimicrobial, and challenged with *E. coli*resulted in the slow release of nitrous oxide into the urine for over 14 days, and decreased biofilm formation by *E. coli*. Chlorhexidine is a common antimicrobial used against oral plaques. *In vivo* studies in rabbits intubated with genidine (combination of chlorhexidine and gentian violet) coated silicone catheters showed a reduction in biofilm formation by *E. coli*, *E. faecium*, *P. aeruginosa*, *K. pneumoniae* and *Candida* in compar‐ ison to silver coated and uncoated catheters [54]. Catheter associated bacteriuria was noticed in 60% and 71% of the rabbits with uncoated catheters and silver hydrogel coated catheters, respectively, whereas CAB did not occur in any of the rabbits with genidine coated catheters. Similar to chlorhexidine, triclosan is another antibacterial ingredient in toothpastes and cleaners used in health care settings. Triclosan exerts its antibacterial effect by inhibiting bacterial fatty acid synthesis [147]. Incorporation of triclosan in the balloon of catheters resulted in its release and diffusion through latex and silicon catheter balloons. The balloon served as a reservoir and the membrane helped in controlled release of triclosan. This in turn slowed encrustation and maintained the lumen patent for 7 days as compared to 24 h in saline-filled catheters [150]. Another antibacterial shown to possess antibiofilm effect is nitrofurazone, which interferes with bacterial ribosomes, DNA and cell wall. When nitrofurazone coated catheters were compared with standard catheters, it was observed that nitrofurazone signifi‐ cantly reduced CAB [133]. Besides nitrofurazone, norfloxacin coated catheters were also shown to inhibit the growth of *E. coli*, *K. pneumoniae* and *P. vulgaris* for up to 10 days [115]. Similarly, gentamicin coated catheters were also effective in reducing CAB in rabbits [23]. Another study demonstrated that sparfloxacin coated and heparin coated catheters reduced colonization by *S. aureus*, *E. coli* and *S. epidermidis* for greater than 26 days compared to control catheters [79]. However, the use of antibiotics on catheters to control bacterial biofilms could potentially lead to the emergence of antibiotic resistant bacteria [126]. Repeated use of antibiotics for treating UTIs has been linked to the emergence of antibiotic resistant UPEC [41, 126]. Therefore, there is an increasing interest in the use of natural antimicrobials for controlling microbial infections, including UTIs.

cranberry juice can help to prevent the adhesion of UPEC to the uroepithelium and thereby help reduce the incidence of UTIs. With rising concerns of antibiotic resistance among UPEC,

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

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

69

Trans-cinnamaldehyde (TC) is a major component of the bark extract of cinnamon [1]. It is a generally recognized as safe (GRAS) molecule approved for use in foods by the Food and Drug Administration (FDA). The U. S. Flavoring Extract Manufacturers' Association reported that TC has a wide margin of safety between conservative estimates of intake and no observed adverse effect levels, from sub-chronic and chronic studies [1]. The report also indicated no genotoxic or mutagenic effects due to TC. Although, cinnamon or cinnamon oil has been used for ages in the treatment of UTIs, no scientific study was undertaken to investigate its antimi‐ crobial efficacy against uropathogens. Amalaradjou and group [2010; 4] investigated the efficacy of TC for controlling UPEC biofilm formation. They observed that TC as a catheter lock solution or as a coating significantly inactivated UPEC and prevented biofilm formation when compared to untreated catheters. In a follow up study, these researchers reported that TC decreased the attachment and invasion of UPEC in cultured urinary tract epithelial cells

Besides the use of cranberry and TC, other plant derived natural antimicrobials have also been shown to be effective against uropathogens. Sosa and Zunino [2009; 141] demonstrated that *Ibicella lutea* (Devils claw or Rams horn) extracts had an effect on bacterial growth rate and morphology of *P.mirabilis* by affecting its swarming differentiation, hemagglutination and biofilm formation on glass and polystyrene. Similarly, the use of *Coccinia grandis* (Ivy gourd) plant extracts have been reported to inhibit growth of UPEC *in vitro* [119]. Several other herbs that are used for the treatment of UTIs, but lacking scientific basis include *Agrimonia eupato‐ ria* (agrimony), *Althea officinalis* (marshmallow), *Apium graveolens* (celery seed), *Arctium lappa* (burdock), *Elymus repens* (couchgrass), *Hydrangea aborescens* (hydrangea), *Juniperus communis* (juniper), *Mentha piperita* (peppermint*), Taraxacum officinalis* leaf (dandelion), *Ulmus fulva*

Silver is a well-known antimicrobial exerting its bactericidal action by inactivating bacterial enzymes and causing cell wall damage [96]. Silver alloy and silver oxide coatings on catheters were investigated for reducing CAB, where silver alloy coating was found to be more effective [131]. In addition to reducing CAB, other studies also demonstrated the ability of silver alloy to decrease CAUTI compared to silver oxide or latex catheters [143]. However other researchers have observed conflicting results with no difference in antibiofilm effect of silver alloy and

Urease producing bacteria are known to produce crystalline biofilms and encrustation on catheters. Use of urease inhibitors such as acetohydroxamic acid and fluorofamide have been reported to reduce encrustation and thereby prevent CAB [98]. These urease inhibitors have

cranberry could serve as an effective alternative in controlling UTIs.

by down-regulating several virulence genes in the pathogen [5].

(slippery elm) and *Zea mays* (corn silk; 3).

*5.5.4. Silver coated catheters*

silver oxide [122, 143].

**5.6. Enzyme inhibitors**

### *5.5.3. Plant molecules*

Plants are capable of synthesizing a large number of molecules [47], most of which are produced as a defense mechanism against predation by microorganisms and insects. A variety of plant-derived polyphenols are active components in traditional medicines [178]. A signifi‐ cant body of literature exists on the positive effects of dietary intake of berry fruits on human health, performance and disease [134]. Cranberry products such as its juice and tablets have been used as an alternative medicine to prevent UTIs in humans for decades. Clinical and epidemiological studies support the use of cranberry in maintaining a healthy urinary tract [117]. Although several studies have tested the antimicrobial effect of cranberries against multiple uropathogens, it was found to be most effective against UPEC.

Cranberries exert anti-adhesive effects on certain uropathogens [112] and this effect is specific to certain components of cranberry [110]. Cranberries contain three different flavonoids (flavonols, anthocyanins and PAC), catechins, hydroxycinnamic and other phenolic acids and triterpenoids. The anthocyanins are absorbed in the human circulatory system and transported without any chemical change to the urine [117]. Cranberry products do not inhibit bacterial growth, but reduced bacterial adherence to uroepithelial cells, thereby decreasing the devel‐ opment of UTI. The anti-adhesive effects of p-fimbriated UPEC to uroepithelial cells are related with A-linked PAC as compared with lack of anti-adhesion activities of B-linked PAC from grape, apple juice, green tea and chocolate [67]. The A-type PAC in cranberries enhances the anti-adhesive effects *in vitro* and in urine. PAC binds to lipopolysaccharide in gram-negative bacteria. When *E. coli* was grown in the presence of cranberry components, the bacterial morphology changed to a more spherical cell-like form. These changes cause them to be repelled by the human cells [88]. Similar study by Tao and others [2011; 159] have also demonstrated that consumption of cranberry juice cocktail reduced the adhesion of UPEC to a silicon nitride probe.

Cranberry has undergone extensive evaluation in the management of UTIs. However, currently there is no evidence that cranberry can be used to treat UTIs. Hence, the focus has been on its use as a prophylactic agent in the prevention of UTIs [52]. The consumption of cranberry juice can help to prevent the adhesion of UPEC to the uroepithelium and thereby help reduce the incidence of UTIs. With rising concerns of antibiotic resistance among UPEC, cranberry could serve as an effective alternative in controlling UTIs.

Trans-cinnamaldehyde (TC) is a major component of the bark extract of cinnamon [1]. It is a generally recognized as safe (GRAS) molecule approved for use in foods by the Food and Drug Administration (FDA). The U. S. Flavoring Extract Manufacturers' Association reported that TC has a wide margin of safety between conservative estimates of intake and no observed adverse effect levels, from sub-chronic and chronic studies [1]. The report also indicated no genotoxic or mutagenic effects due to TC. Although, cinnamon or cinnamon oil has been used for ages in the treatment of UTIs, no scientific study was undertaken to investigate its antimi‐ crobial efficacy against uropathogens. Amalaradjou and group [2010; 4] investigated the efficacy of TC for controlling UPEC biofilm formation. They observed that TC as a catheter lock solution or as a coating significantly inactivated UPEC and prevented biofilm formation when compared to untreated catheters. In a follow up study, these researchers reported that TC decreased the attachment and invasion of UPEC in cultured urinary tract epithelial cells by down-regulating several virulence genes in the pathogen [5].

Besides the use of cranberry and TC, other plant derived natural antimicrobials have also been shown to be effective against uropathogens. Sosa and Zunino [2009; 141] demonstrated that *Ibicella lutea* (Devils claw or Rams horn) extracts had an effect on bacterial growth rate and morphology of *P.mirabilis* by affecting its swarming differentiation, hemagglutination and biofilm formation on glass and polystyrene. Similarly, the use of *Coccinia grandis* (Ivy gourd) plant extracts have been reported to inhibit growth of UPEC *in vitro* [119]. Several other herbs that are used for the treatment of UTIs, but lacking scientific basis include *Agrimonia eupato‐ ria* (agrimony), *Althea officinalis* (marshmallow), *Apium graveolens* (celery seed), *Arctium lappa* (burdock), *Elymus repens* (couchgrass), *Hydrangea aborescens* (hydrangea), *Juniperus communis* (juniper), *Mentha piperita* (peppermint*), Taraxacum officinalis* leaf (dandelion), *Ulmus fulva* (slippery elm) and *Zea mays* (corn silk; 3).

### *5.5.4. Silver coated catheters*

catheters [150]. Another antibacterial shown to possess antibiofilm effect is nitrofurazone, which interferes with bacterial ribosomes, DNA and cell wall. When nitrofurazone coated catheters were compared with standard catheters, it was observed that nitrofurazone signifi‐ cantly reduced CAB [133]. Besides nitrofurazone, norfloxacin coated catheters were also shown to inhibit the growth of *E. coli*, *K. pneumoniae* and *P. vulgaris* for up to 10 days [115]. Similarly, gentamicin coated catheters were also effective in reducing CAB in rabbits [23]. Another study demonstrated that sparfloxacin coated and heparin coated catheters reduced colonization by *S. aureus*, *E. coli* and *S. epidermidis* for greater than 26 days compared to control catheters [79]. However, the use of antibiotics on catheters to control bacterial biofilms could potentially lead to the emergence of antibiotic resistant bacteria [126]. Repeated use of antibiotics for treating UTIs has been linked to the emergence of antibiotic resistant UPEC [41, 126]. Therefore, there is an increasing interest in the use of natural antimicrobials for controlling microbial infections,

Plants are capable of synthesizing a large number of molecules [47], most of which are produced as a defense mechanism against predation by microorganisms and insects. A variety of plant-derived polyphenols are active components in traditional medicines [178]. A signifi‐ cant body of literature exists on the positive effects of dietary intake of berry fruits on human health, performance and disease [134]. Cranberry products such as its juice and tablets have been used as an alternative medicine to prevent UTIs in humans for decades. Clinical and epidemiological studies support the use of cranberry in maintaining a healthy urinary tract [117]. Although several studies have tested the antimicrobial effect of cranberries against

Cranberries exert anti-adhesive effects on certain uropathogens [112] and this effect is specific to certain components of cranberry [110]. Cranberries contain three different flavonoids (flavonols, anthocyanins and PAC), catechins, hydroxycinnamic and other phenolic acids and triterpenoids. The anthocyanins are absorbed in the human circulatory system and transported without any chemical change to the urine [117]. Cranberry products do not inhibit bacterial growth, but reduced bacterial adherence to uroepithelial cells, thereby decreasing the devel‐ opment of UTI. The anti-adhesive effects of p-fimbriated UPEC to uroepithelial cells are related with A-linked PAC as compared with lack of anti-adhesion activities of B-linked PAC from grape, apple juice, green tea and chocolate [67]. The A-type PAC in cranberries enhances the anti-adhesive effects *in vitro* and in urine. PAC binds to lipopolysaccharide in gram-negative bacteria. When *E. coli* was grown in the presence of cranberry components, the bacterial morphology changed to a more spherical cell-like form. These changes cause them to be repelled by the human cells [88]. Similar study by Tao and others [2011; 159] have also demonstrated that consumption of cranberry juice cocktail reduced the adhesion of UPEC to

Cranberry has undergone extensive evaluation in the management of UTIs. However, currently there is no evidence that cranberry can be used to treat UTIs. Hence, the focus has been on its use as a prophylactic agent in the prevention of UTIs [52]. The consumption of

multiple uropathogens, it was found to be most effective against UPEC.

including UTIs.

*5.5.3. Plant molecules*

68 Recent Advances in the Field of Urinary Tract Infections

a silicon nitride probe.

Silver is a well-known antimicrobial exerting its bactericidal action by inactivating bacterial enzymes and causing cell wall damage [96]. Silver alloy and silver oxide coatings on catheters were investigated for reducing CAB, where silver alloy coating was found to be more effective [131]. In addition to reducing CAB, other studies also demonstrated the ability of silver alloy to decrease CAUTI compared to silver oxide or latex catheters [143]. However other researchers have observed conflicting results with no difference in antibiofilm effect of silver alloy and silver oxide [122, 143].

### **5.6. Enzyme inhibitors**

Urease producing bacteria are known to produce crystalline biofilms and encrustation on catheters. Use of urease inhibitors such as acetohydroxamic acid and fluorofamide have been reported to reduce encrustation and thereby prevent CAB [98]. These urease inhibitors have been also shown to prevent urea break down and pH increase *in vitro* by *P. mirabilis* besides decreasing the associated encrustation. Another enzyme target is N-acetyl-D-glucosamine-1 phosphate acetyltransferase, which is essential for peptidoglycan, lipopolysaccharide and adhesion synthesis. Inhibitors of the enzyme belonging to the N-substituted maleimide family have produced antibiofilm activity against *P. aeruginosa* and *S. epidermidis* compared to silver hydrogel coated catheters [17].

route for the control of biofilms. *Delisea pulchra*, an algal species has been shown to produce furanones that interfere with autoinducer signaling and biofilm formation [92]. *In vitro* and *in vivo* sheep experiments using furanone containing catheters have been evaluated against *S. epidermidis* [35]. Similarly, use of azithromycin has been shown to inhibit the production of quorum sensing signals, swimming, swarming and twitching motilities, and biofilm formation

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

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71

Catheters containing peizo elements can generate low energy acoustic waves that can lead to the formation of a vibrating coat along the catheter and prevent bacterial attachment and biofilm formation [60]. Scanning electron microscopy studies demonstrated that application of surface acoustic waves led to reduced biofilm formation by *E. coli*, *E. faecalis*, *Candida albicans* and *P. mirabilis*. An *in vivo* study in rabbits demonstrated that peizo element containing catheters with acoustic vibration led to a delayed positive urine culture compared to control animals [60]. The acoustic waves generated resulted in bacterial vibration at the same fre‐

Catheter associated urinary tract infections are the most common nosocomial infections and a vast majority of them are caused by biofilms formed on catheters. The complica‐ tions caused by biofilms can undermine the patient's quality of life and threaten their health. The high incidence of CAUTI and the consequent complications warrants the de‐ velopment and application of effective control strategies. Prevention is predominantly based on enforcing guidelines for appropriate catheter placement and early removal. However, a comprehensive understanding of bacterial biofilm formation, pathogenesis and other key factors essential for development of UTIs would help in the development

and Kumar Venkitanarayanan2

\*Address all correspondence to: kumar.venkitanarayanan@uconn.edu

1 Department of Food Science, Purdue University, West Lafayette, IN, USA

2 Department of Animal Science, University of Connecticut, Storrs, CT, USA

quency, thereby preventing bacterial attachment and eventual biofilm formation.

*in vitro* [9].

**6. Conclusion**

**Author details**

*5.6.5. Surface vibroacoustic stimulation*

of novel and effective control strategies.

Mary Anne Roshni Amalaradjou1

### *5.6.1. Bacterial interference*

Use of nonpathogenic microorganisms to counteract pathogenic bacteria is known as bacterial interference [137]. Colonization of catheter surfaces with nonpathogenic bacteria can prevent adhesion and colonization by pathogens. The nonpathogenic *E. coli* 83972 has been extensively investigated both *in vitro* and *in vivo* in bacterial interference protocols [68]. Initially, studies with this nonpathogenic strain were done by instilling the bacteria into the bladder of patients. Colonization by *E. coli* 83972 protected these patients from symptomatic UTI. To reduce the need for instillation of bacteria into the bladder of patients, experiments were later conducted with catheters coated with the nonpathogenic strain [168]. This study also revealed that *E. coli* 83972 was effective in reducing symptomatic UTI similar to previous experiments with direct infusion of the bacteria.

### *5.6.2. Bacteriophages*

Another potential approach investigated for controlling CAUTI is the use of bacteriophages. Catheters coated with T4 bacteriophage against *E. coli* and coli-proteus bacteriophage active against Proteus were exposed to *E. coli* ATCC 11303, *P. mirabilis* or saline. It was observed that phage treatment of catheters led to approximately 90% reduction in biofilm formation compared to control catheters [19]. It was also observed that the application of phage cocktail on catheters was more effective against bacteria than the use of a single phage [19]. When hydrogel coated catheters were pretreated with a five-phage cocktail, *P. aeruginosa* biofilm formation was reduced by 99% after 48 h [45].

#### *5.6.3. Liposomes*

Liposomes are carrier or delivery vehicles that can carry both hydrophilic and hydrophobic molecules to their target site for delivery. This helps to increase the half life of the drugs besides protecting them from the environment. Liposomes containing ciprofloxacin embedded in a hydrogel coated catheter were evaluated in a rabbit model to investigate its antibiofilm effect against *E. coli* induced CAUTI [121]. The results from this study revealed that liposomal ciprofloxacin treated group had a delayed onset of positive urine cultures compared to the control group.

### *5.6.4. Quorum sensing inhibitors*

Quorum sensing between bacterial cells in a biofilm have been shown to be essential for biofilm formation and maintenance. Inhibition of quorum sensing could therefore provide a potential route for the control of biofilms. *Delisea pulchra*, an algal species has been shown to produce furanones that interfere with autoinducer signaling and biofilm formation [92]. *In vitro* and *in vivo* sheep experiments using furanone containing catheters have been evaluated against *S. epidermidis* [35]. Similarly, use of azithromycin has been shown to inhibit the production of quorum sensing signals, swimming, swarming and twitching motilities, and biofilm formation *in vitro* [9].

### *5.6.5. Surface vibroacoustic stimulation*

Catheters containing peizo elements can generate low energy acoustic waves that can lead to the formation of a vibrating coat along the catheter and prevent bacterial attachment and biofilm formation [60]. Scanning electron microscopy studies demonstrated that application of surface acoustic waves led to reduced biofilm formation by *E. coli*, *E. faecalis*, *Candida albicans* and *P. mirabilis*. An *in vivo* study in rabbits demonstrated that peizo element containing catheters with acoustic vibration led to a delayed positive urine culture compared to control animals [60]. The acoustic waves generated resulted in bacterial vibration at the same fre‐ quency, thereby preventing bacterial attachment and eventual biofilm formation.
